Applied Catalysis A, General (v.393, #1-2)
Editorial Board (CO2).
Catalyzed ring opening of epoxides: Application to bioplasticizers synthesis by Gabriella Fogassy; Pan Ke; François Figueras; Philippe Cassagnau; Sophie Rouzeau; Valérie Courault; Georges Gelbard; Catherine Pinel (1-8).
Display Omitted▶ Hydrotalcites are efficient reusable catalysts for ring opening of epoxide. ▶ Influence of Brönsted/Lewis characters of solid has been established. ▶ Potential bioplasticizers of PVC are synthetized from vegetable oils.The ring opening of mono, di or tri-substituted epoxides by acetic anhydride to corresponding diacetates is catalyzed by weak bases such as hydrotalcite in the carbonated form. This reaction is performed at 423 K without solvent and the solid catalyst is reused after simple regeneration for 4 runs with constant conversion. Ring-opening of methyl oleate epoxide leads to the formation of useful diacetate methyl oleate.Starting from vegetable oils, polyacetate derivatives are prepared in three catalytic steps (methanolysis, epoxidation then ring opening). Plastisol was prepared by mixing these products with PVC and their rheological properties were evaluated. The recorded data show that they can act as bioplasticizer with similar behaviour as phthalate reference.
Keywords: Hydrotalcite; Epoxide; Solvent free reaction; Bioplasticizer; PVC;
Co,Ba,K/ZrO2 coated onto metallic foam (AISI 314) as a structured catalyst for soot combustion: Catalytic activity and stability by E.D. Banús; M.A. Ulla; E.E. Miró; V.G. Milt (9-16).
Display Omitted▶ Co,Ba,K/ZrO2/AISI 314 foam is active and stable for diesel soot combustion. ▶ After TPO runs, Co and K migration improves oxidizing properties. ▶ The performance of the catalyst was maintained during 120 h of time-on-stream.This work presents results on the catalytic activity and stability in the diesel soot combustion of a structured catalyst composed of a Co,Ba,K/ZrO2 layer coated onto a metallic foam (AISI 314). The washcoated ZrO2 layer, mainly of tetragonal structure, adopted the form of mosaics (flakes) with interconnected surface cracks. After the impregnation of the active components, the fresh catalyst was constituted by a complex mixture of phases originated in the chemical compositions of both the metallic foam and the active ingredients, the main crystalline phases detected being Cr2O3, FeCr2O4, Mn1.5Cr1.5O4, ZrO2, BaCO3, K2CrO4 and BaCrO4. The performance of the structured catalyst was maintained within a wide range of soot:catalyst ratios, which is an important factor to be considered for practical applications due to the variable soot amounts that are released by the engine during its operation under different conditions. The stability of the catalyst was evaluated under loose contact conditions during 120 h of time-on-stream, showing that the catalytic activity remained practically constant. The characterization of the fresh and used catalysts indicated the migration of both Co and K towards more exposed positions after TPO runs, which could be a positive factor given the oxidizing properties of Co oxides and the improvement of the soot-to-catalyst contact given by K species. However, a longer duration or severe ageing temperatures might lead to sintering and loss of soot oxidation ability.
Keywords: Structured catalyst; Soot combustion; Metallic foam; Co,Ba,K/ZrO2 coating; Catalyst stability;
Fischer–Tropsch synthesis: Metal–support interfacial contact governs oxygenates selectivity over CeO2 supported Pt–Co catalysts by Muthu Kumaran Gnanamani; Mauro C. Ribeiro; Wenping Ma; Wilson D. Shafer; Gary Jacobs; Uschi M. Graham; Burtron H. Davis (17-23).
Display Omitted▶ Pt–Co/CeO2 catalysts are active towards forming oxygenates during FTS. ▶ A proposed pathway for alcohol formation is based on the Co–CeO2 interface. ▶ Selectivity to oxygenates decreased with an increase of cobalt metal loading. ▶ Selectivity depends on the surface fugacity of ceria OH groups in contact with Co0.The catalytic performance during Fischer–Tropsch synthesis (FTS) of Pt promoted Co/CeO2 catalysts at two different cobalt metal loadings was investigated using a slurry-phase reactor. CeO2 supported Pt–Co catalysts exhibit higher selectivities to oxygenates and especially linear alcohols (14.8%) at lower cobalt loadings. A plausible pathway for the formation of alcohols was proposed based on Co–CeO2 interfacial catalysis, in which termination of chain growth occurs at the metal-oxide junction and involves bridging OH groups on partially reduced ceria. As cobalt content increases, the selectivity to oxygenates decreases. The resulting increase in cobalt metal particle size accelerates the mechanism involving normal FT termination, since the on-top surface area of cobalt increase at the expense of the interfacial area at the junction with ceria. Compared to γ-Al2O3, CeO2 supported Pt–Co catalysts exhibit significantly higher oxygenates at similar CO conversions. Selectivity control is thus achieved by controlling the surface fugacity of bridging OH groups (i.e., located on ceria) in contact with cobalt sites on a per Co surface atom basis.
Keywords: Fischer–Tropsch synthesis; Alcohol synthesis; Cobalt catalyst; Oxygenates; Ceria; Noble metal;
Application of well-defined ruthenium alkylidenes to the ROMP of norbornene derivatives: Methoxyphenyl-substituted polynorbornene dicarboximides by Sevil Çetinkaya; Taner Özker; Rifat Bayram (24-28).
Display Omitted▶ Well-defined ruthenium initiators are effective metathesis catalysts for the syntheses of PMeOPhONDI and PMeOPhNDI. ▶ Methoxy group decreases the chain mobility and increases the rotational barrier of the polymer chains. ▶ Ruthenium alkylidene catalysts produced polymers with trans configuration of the double bonds.The applicability of ruthenium alkylidenes as initiators in the ring opening metathesis polymerization (ROMP) of methoxyphenyl group containing norbornene derivatives has been investigated. The synthesis and polymerization of exo-N-4-methoxyphenyl-oxanorbornene-5,6-dicarboximide (MeOPhONDI) and exo-N-4-methoxyphenyl-norbornene-5,6-dicarboximide (MeOPhNDI) are reported. Polynorbornene derivatives were obtained via ROMP using first- and second-generation ruthenium alkylidene initiators. The structural properties of the polynorbornene derivatives were analyzed by NMR, DSC and GPC. Analyses of the polymer microstructures indicate that polymers contain trans stereoconfiguration of the double bonds (55–86% trans-content). The glass transition temperatures of the polymers obtained from exo-monomers are higher than 211 °C.
Keywords: Metathesis; Polynorbornene dicarboximide; ROMP; Ruthenium alkylidene; Homogeneous catalysis;
Cleavage of the C–O–C bond on size-selected subnanometer cobalt catalysts and on ALD-cobalt coated nanoporous membranes by Weiling Deng; Sungsik Lee; Joseph A. Libera; Jeffrey W. Elam; Stefan Vajda; Christopher L. Marshall (29-35).
Display Omitted▶ A new route to breakdown cellulosic materials by catalytic oxidative hydrolysis. ▶ Co sub-nanometer are much active than nanometer cobalt oxide for the C–O–C cleavage. ▶ Co clusters position vs. gas flow direction dictates the selectivity of the products.The cleavage of the C–O–C bond was studied under oxidizing conditions on nanostructured membrane supported cobalt-based catalysts using a cellulose model surrogate, 1-methoxy-2-methyl-2-propanol. The cobalt catalysts were found to break the C–O–C bond, producing alcohols and/or ketones by further oxidation. The size-selected sub-nanometer size cobalt clusters exhibited a per metal activity of up to 5 orders of magnitude higher than the with atomic layer deposition uniformly coated membranes. The large difference in activity is attributed to the high fraction of the surface atoms of the subnanometer clusters. The positioning of the clusters at the entrance vs. exit of the catalytic membrane allows for a control of the contact time and consequently of the selectivity of the catalyst.
Keywords: Oxidative decomposition; Cellulose; C–O–C bond cleavage; Size-selected clusters; Cobalt; Anodized aluminum oxide; Atomic layer deposition;
Quintinite as a bifunctional heterogeneous catalyst for biodiesel synthesis by Narasimharao Kondamudi; Susanta K. Mohapatra; Mano Misra (36-43).
Display Omitted▶ Quintinite-3T as a catalyst for conversion of triglycerides into biodiesel. ▶ Quintinite-3T as a catalyst for conversion of t free fatty acids into biodiesel. ▶ Lewis basic and BrØnsted acidic sites for transesterification and esterification. ▶ Beneficial catalyst for high free fatty acid containing feedstocks. ▶ Suitable candidate for multi-feedstock applications.Biodiesel synthesis from waste vegetable oils, restaurant grease and poultry fat gained industrial importance compared to the high priced, food based vegetable oils. The major drawback of waste streams is the free fatty acid (FFA) content, which is difficult to convert into biodiesel. This paper describes synthesis, characterization and catalytic activity of Quntinite-3T, a bifunctional heterogeneous catalyst that converts FFA and triglycerides (TGs) simultaneously into biodiesel. The catalyst is prepared by sol–gel process and is characterized by XRD, SEM, and HR-TEM. The catalyst is tested for soy, canola, coffee and waste vegetable oils with variable amounts of FFAs (0–30 wt%). 1H NMR, HPLC, GC–MS were used for analyzing the reaction products. The catalyst successfully converted both FFA and TGs in a single step batch reactor.
Keywords: Heterogeneous catalysis; Quintinite; Biodiesel; Transesterification; Vegetable oils;
The effects of oxide supports on the low temperature hydrogenation activity of acetone over Pt/Ni bimetallic catalysts on SiO2, γ-Al2O3 and TiO2 by Suitao Qi; Beth A. Cheney; Renyang Zheng; William W. Lonergan; Weiting Yu; Jingguang G. Chen (44-49).
Display Omitted▶ Oxide supports significantly affect the activity of Pt/Ni bimetallic catalysts. ▶ The hydrogenation activity on the support leads the trend of SiO2 > r-Al2O3 > TiO2.Low temperature (308 K) hydrogenation of acetone was used as a probe reaction to investigate the support effect on the hydrogenation activity of Pt/Ni bimetallic catalysts supported on TiO2, SiO2 and γ-Al2O3. The oxide supports significantly affected the catalytic properties of Pt/Ni catalysts, in which Pt/Ni/SiO2 bimetallic catalysts exhibited significantly higher activity than the other two bimetallic catalysts. TEM measurements revealed that the three supported Pt/Ni bimetallic catalysts have similar particle size distribution, while CO chemisorption measurements showed very different chemisorption capacity. Extended X-Ray absorption fine structure (EXAFS) measurements of the Pt LIII-edge indicated that Pt atoms were fully reduced and the Pt–Ni bimetallic bonds were formed on all three catalysts. The extent of Pt–Ni bond formation followed the trend of SiO2 > γ-Al2O3 > TiO2, which correlated very well with the hydrogenation activity.
Keywords: Support effect; Pt/Ni bimetallic catalysts; Hydrogenation; Acetone; EXAFS;
Influence of porous characteristics of the carbon support on alkali-modified trimetallic Co–Rh–Mo sulfided catalysts for higher alcohols synthesis from synthesis gas by Venkateswara Rao Surisetty; Ajay Kumar Dalai; Janusz Kozinski (50-58).
Display Omitted▶ The blocking extent was high on the microporous activated carbon supported catalysts. ▶ Dispersion of metal species is higher on the surface of mesoporous activated carbon. ▶ The pore size of the support has direct influence on higher alcohols synthesis.Alkali-modified trimetallic Co–Rh–Mo sulfided catalysts supported on commercial activated carbons with different textural characteristics were tested for the synthesis of higher alcohols from synthesis gas and compared with a similar catalyst supported on multi-walled carbon nanotubes (MWCNTs). Addition of metals (Co, Rh, and Mo) to the microporous and mesoporous activated carbons, and the MWCNT supports increased the mean pore diameter and % mesoporosity of the catalysts. The N2 adsorption–desorption isotherms of the MWCNTs support and the MWCNT-supported alkali-modified trimetallic C–Rh–Mo catalyst revealed that the mesoporous structural integrity of the catalyst was unchanged from the support after impregnation of the catalyst species. The formation of large particles took place due to the agglomeration of metal species on the microporous activated carbon supports. The metal dispersion of the sulfided catalysts on different supports is: MWCNTs < AC-CGP Super < AC-Fluid Coke < AC-RX3 Extra < AC-Darco. The total alcohols STY and selectivity of 0.296 g/(g of cat./h) and 35.6%, respectively were found to be on the MWCNTs-supported alkali-modified trimetallic C–Rh–Mo catalyst compared to similar catalysts supported on activated carbon. The % CO conversion as well as alcohols space time yield are not related to the BET surface area and pore volume of the support, whereas, textural properties of the support such as pore size and mesoporosity has direct influence on the synthesis of mixed alcohols from synthesis gas. Little or no sintering of metal species was observed on the spent catalyst supported on MWCNTs, whereas, the agglomeration of catalytic species is high on the microporous activated carbon support compared to that of the mesoporous activated carbon supported catalysts.
Keywords: Higher alcohols synthesis; Alkali-promoted molybdenum catalyst; Multi-walled carbon nanotubes; Rh promotion; Co promotion; Trimetallic catalyst; Mesoporous activated carbon;
Transformations of alkyl aromatics over delaminated MCM-22 zeolites and their composites with mesoporous MCM-41 silicate by Márton Kollár; Iliyan Kolev; Magdolna R. Mihályi; Vesselina Mavrodinova (59-70).
.Display Omitted▶ The crystallite size of zeolite MCM-22 precursor is crucial for the effectiveness of its delamination and insertion in a composite with MCM-41. ▶ The lamellae structuring defines the acidity and catalytic performance of the delaminated and composite materials. ▶ Delamination and preparation of composites consisting of zeolite MCM-22 and MCM-41 silicate are beneficial for catalytic transformations of more basic and bulkier alkylaromatic reactants.Small (S)- and large (L)-crystalline zeolite MCM-22 precursors with the same Si/AlF ratio of 17, were synthesized and either converted to zeolites MCM-22(S/L) or delaminated. From the delaminated zeolite MCM-22 precursors delaminated zeolites MCM-22 (dl-MCM-22(S/L)) were prepared. Delaminated zeolite precursors were admixed to the synthesis mixture of mesoporous silica MCM-41 to obtain the respective dl-MCM-22/MCM-41(S/L) composite materials. The preparations were characterized by XRD, N2 adsorption measurements, scanning electron microscopy. FT-IR spectroscopic studies of pyridine (Py) and 2,4-dimethylquinoline (2,4-DMQ) adsorption were used for determination of total (Brønsted and Lewis acidity) and external Brønsted acidity, respectively. It was found that the crystallite size of the MCM-22 precursors strongly influenced the structural, acidic and catalytic properties of the delaminated and composite materials. The effectiveness of the delamination procedure for the zeolite MCM-22(S) precursor having smaller and thinner particles is higher. At same synthesis gel compositions, the amount of mesoporous fraction in the composite materials was different. In dl-MCM-22/MCM-41(S) composite the formation of the mesoporous component was suppressed. Moreover, delamination resulted, for both delaminated and composite materials, in a similar decrease in the Brønsted acidity.The reduction in toluene disproportionation activity confirmed the above structural and acidity changes. 2,4-DMQ adsorption results proved that both the dl-MCM-22 samples and the composites possess higher amount of external Brønsted acid sites than zeolite MCM-22. The enhanced external acidity and accessibility of the active sites of these preparations appeared favorable when more basic and bulkier reactant, such as 1,2,4-trimethylbenzene was transformed.
Keywords: Small- and large-crystalline MCM-22; Delaminated MCM-22; MCM-22/Si-MCM-41 composite; Toluene disproportionation; 1,2,4-Trimethylbenzene transformation;
Asymmetric ceramic hollow fibres: New micro-supports for gas-phase catalytic reactions by F.R. García-García; M.A. Rahman; B.F.K. Kingsbury; K. Li (71-77).
Display Omitted▶ A novel catalytic hollow fibre micro-reactor (CHFMR) is developed. ▶ The catalytic activity of the CHFMR is tested using water-gas shift (WGS) reaction. ▶ The CHFMR improves the heat and mass transfer, and the mixing of gases during the reaction.Al2O3 hollow fibres fabricated by phase-inversion, followed by sintering at different temperatures (1350, 1400 and 1450 °C) have been employed for the further development of a novel catalytic hollow fibre micro-reactor (CHFMR). After depositing with a 10%CuO/CeO2 catalyst, the catalytic activity of the CHFMR has been compared with that of a conventional fixed-bed reactor using water gas shift (WGS) as a sample reaction. The deposition of catalyst into the finger-like voids was carried out using the sol–gel Pechini method. The Al2O3 hollow fibres were characterized before and after catalyst deposition by BET surface area analysis, Hg porosimetry and SEM–EDS. The catalytic activity tests were performed at P = 1 atm and between T = 200 and 400 °C. It has been observed that the dispersion of the 10%CuO/CeO2 catalyst within the Al2O3 hollow fibres is strongly dependent on the physical and chemical properties of the fibre surface, which are determined by the sintering temperature. Finally, an increase of 20% in the CO conversion of the WGS reaction was observed for the CHFMR when compared with a conventional fixed-bed reactor, since the finger like structure of Al2O3 hollow fibres (D p = 10 μm) acts as a micro-reactor and improves the heat and mass transfer, and the mixing of gases during the reaction.
Keywords: Al2O3 hollow fibres; Catalytic hollow fibre micro-reactor; Sol–gel Pechini method; The WGS reaction;
Influence of the chemical activation of carbon nanofibers on their use as catalyst support by Antonio Nieto-Márquez; Vicente Jiménez; Antonio Manuel Raboso; Sonia Gil; Amaya Romero; José Luis Valverde (78-87).
Display Omitted▶ Chemical activation by RbOH and KOH impacted on CNF porosity, acidity and crystallinity. ▶ CNF chemical activation impacted on size and morphology of deposited Ni particles. ▶ Ni particles deposited on activated CNFs promoted butyronitrile hydrogenation to lower extent. ▶ Selectivity to amines was not sensitive to metal particle size, but it was to catalyst acidity.Three nickel catalysts supported on carbon nanofibers (CNFs) have been prepared by deposition–precipitation (ca. 3%, w/w). The CNFs were prepared by catalytic chemical vapour decomposition of ethylene over a Ni/SiO2 catalyst, and chemically activated with RbOH (CNFRbOH) and KOH (CNFKOH). The materials were characterized by transmission electron microscopy (TEM), N2 adsorption–desorption, temperature-programmed oxidation, X-ray diffraction (XRD), acid–base titrations and temperature-programmed decomposition in helium. KOH was the most effective activating agent, developing carbon porosity, decreasing the crystalline character and increasing surface acidity to a higher extent. After nickel introduction, the catalysts were characterized by temperature-programmed reduction, XRD, TEM, N2 adsorption–desorption and acid–base titrations. Surface-area weighted mean Ni particle diameters (post reduction at 400 °C) followed the sequence: Ni/CNFKOH (4.9 nm) < Ni/CNFRbOH (8.6 nm) < Ni/CNF (25.5 nm), where a further activation of the support led to smaller/better dispersed nickel particles. The surface acidity of the catalysts followed the sequence: Ni/CNFRbOH < Ni/CNF < Ni/CNFKOH. The gas phase hydrogenation of butyronitrile was used as a surface characterization test, where bigger nickel particles consistently developed higher catalytic activity. Selectivity, however, was not sensitive to metal particle size, but increased towards condensation products with increasing catalyst acidity.
Keywords: Chemical activation; Carbon nanofibers; Nickel; Butyronitrile hydrogenation;
Enhanced performance of HY zeolites by acid wash for glycerol etherification with isobutene by Ling Xiao; Jingbo Mao; Jinxia Zhou; Xinwen Guo; Shuguang Zhang (88-95).
Display Omitted▶ Glycerol etherification performance improved on acid-treated HY zeolite. ▶ Acid strength increased after acid treatment. ▶ Acid treatment generated mesopores. ▶ Pore size of the zeolite is likely a key factor for the improved performance.The etherification of glycerol with isobutene to synthesize di-tert-butyl glycerol ethers (DTBG) and tri-tert-butyl glycerol ether (TTBG) was studied on acid-treated HY zeolites. Compared to the parent commercial HY, both activity and selectivities to the desired ethers were doubled after optimal acid treatments. At 70 °C with 1 wt% catalyst loading, the glycerol conversion and the selectivities to DTBG and TTBG after 7 h were 85% and 58%, respectively on a citric acid washed HY. The catalyst showed higher selectivity than an acidic resin (SAC-13) and was reusable. Similar performance was also achieved using nitric acid solutions. Although the acid wash resulted in fewer acid sites due to dealumination, the zeolite crystalinity was retained. Besides increased acid strength, enlarged surface area and pore volume from the generation of mesopores were observed, which were likely to be the key factors for the improved catalytic performance by facilitating mass transfer.
Keywords: Glycerol; Isobutene; Etherification; Zeolite; Acid treatment; Mesopore;
Parametric study of dealkylation–transalkylation reactions over mordenite-based bi-functional catalysts by S.A. Ali; M.A. Ali; K. Al-Nawad; C. Ercan; Y. Wang (96-108).
Display Omitted▶ Influence of Mo, Re and mordenite on conversion of heavy reformate was studied. ▶ Catalyst with 3 wt.% Mo enhanced methylethylbenzene (MEB) dealkylation and trimethylbenzene (TMB) transalkylation. ▶ 0.5 wt.% Re exhibited higher activity than 1 wt.% Mo but also formed more methane. ▶ General trend of conversion was PBz ≫ 1M2EB > 1M4EB > 1M3EB ≫ 123TMB > 124TMB ≫ 135TMB. ▶ Linear correlation between MEB conversion and xylene yield was observed.Transalkylation of heavy reformate (96% A9 and 4% A10) without addition of toluene was conducted over four bifunctional mordenite-based catalysts at various process conditions using a flow reactor. The effects of (i) molybdenum content (3 vs. 1 wt.%); mordenite content (80 vs. 67 wt.%); and (iii) metal type (Re vs. Mo) were assessed. The composition of products and their trends was scrutinized to determine the influence of the aforesaid parameters on dealkylation–transalkylation reactions. Higher molybdenum content enhanced the methylethylbenzene (MEB) dealkylation as well as trimethylbenzene (TMB) transalkylation, resulting in increased toluene and xylene formation. Higher mordenite content had little effect on either MEB or TMB conversion. Compared to molybdenum-containing catalysts, rhenium-containing catalyst not only exhibited higher MEB dealkylation and TMB transalkylation, but also resulted in higher hydrogen consumption and methane formation. A reaction scheme for the transalkylation of heavy reformate without the addition of toluene is proposed. Among several reactions that occur during this type of a process, de-ethylation of MEBs is kinetically controlled and probable rate-determining step in the overall reaction scheme. A linear correlation between MEB conversion and xylene yield was observed, which also supports the above rationale.
Keywords: Transalkylation; Mordenite; Molybdenum; Xylenes; Heavy reformate;
Effect of water on the space-time yield of different supported cobalt catalysts during Fischer–Tropsch synthesis by Sara Lögdberg; Magali Boutonnet; John C. Walmsley; Sven Järås; Anders Holmen; Edd A. Blekkan (109-121).
Display Omitted▶ Positive kinetic effect of added water demonstrated for Co supported on TiO2 and Al2O3. ▶ Rapid and extensive deactivation of cobalt supported on narrow-pore alumina. ▶ Methane formation follows a rate expression different from the higher hydrocarbons.The effect of partial pressure of water on the Fischer–Tropsch (FT) rate of six cobalt-based catalysts supported on three different carrier materials (γ-Al2O3, α-Al2O3, TiO2) with varying Co particle sizes was investigated in a fixed-bed reactor by changing space velocity and by external water vapour addition. A typical catalyst pellet size (<100 μm) for industrial slurry-bed FT reactors was used. Water was found to have a positive kinetic effect, at least up to moderate amounts, on the FT rate of all catalysts in the present study, including the γ-Al2O3-supported catalyst with pores smaller than ∼10 nm. The reason for the apparent negative effect on the space-time yield at a direct exposure of Co supported on narrow-pore γ-Al2O3 to high partial pressures of water is due to a rapid and extensive deactivation. This could be ascribed to formation of hard-to-reduce oxidized cobalt species. The choice of support material was found to have a major effect on the response to changes in partial pressure of water, both with respect to deactivation behaviour and kinetics. However, there is a minor Co-particle size effect on the magnitude of the kinetic effect of water, larger Co particles showing a more positive response. Different extents of mass transfer limitations and/or differences in fugacities of H2, CO and water among the six catalysts could be ruled out as causes for the observed differences.
Keywords: Fischer–Tropsch; Cobalt; Water; Deactivation; Particle size; Microemulsion;
Nano ZnO synthesis by modified sol gel method and its application in heterogeneous photocatalytic removal of phenol from water by Khizar Hayat; M.A. Gondal; Mazen M. Khaled; Shakeel Ahmed; Ahsan M. Shemsi (122-129).
Display Omitted▶ Nano ZnO was synthesized by modified sol gel and precipitation methods. ▶ The average particle size is 15 nm synthesized by sol gel and 47 nm prepared by precipitation. ▶ The nano-structured ZnO particles were characterized by XRD, FESEM, EDXS and TEM. ▶ The nano-ZnO shows higher photocatalytic activity than commercial ZnO for phenol degradation. ▶ The operational parameters significantly influence the degradation of phenol.Zinc oxide nanoparticles were synthesized by precipitation and modified sol gel methods. The influence of calcination temperature on morphology and crystallite size of ZnO was studied by varying temperature from 400 to 700 °C. The nano-structured ZnO particles were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDXS) and tranmission electron microscopy (TEM). The photo catalytic activity of as-prepared ZnO was evaluated by degradation of phenol under UV laser irradiation. The Photocatalytic degradation (PCD) efficiency of ZnO was found to decrease with the increase in calcination temperature due to agglomeration of particles and the increase in particle size. In addition to the effect of calcination temperature, the influence of various other parameters such as photocatalyst concentration, initial pH and the initial phenol concentration was also investigated to achieve the maximum PCD of phenol. The operational parameters show the expected influence regarding the efficiency of the photocatalytic degradation process. The results follow the pseudo-first order rate kinetics.
Keywords: Nano zinc oxide; Calcination temperature; Heterogeneous photocatalysis; Phenol degradation; Laser applications;
Deutero-1-pentene tracer studies for iron and cobalt Fischer–Tropsch synthesis by Muthu Kumaran Gnanamani; Robert A. Keogh; Wilson D. Shafer; Burtron H. Davis (130-137).
Display Omitted▶ D5-1-pentene initiates chain growth without any H/D scrambling for both Fe and Co FT synthesis. ▶ Hydrogenation and isomerization of the added D5-1-pentene are dominating reactions. ▶ D5-labeled FT products show a characteristic lower chain growth probability.The addition of D5-1-pentene[4,4,5,5,5] to the synthesis gas fed to cobalt and iron catalysts under Fischer–Tropsch synthesis conditions show that H/D exchange does not occur to a measurable extent. The added D5-1-pentene[4,4,5,5,5] underwent hydrogenation, isomerization to interval alkenes and initiated chain growth to a greater extent with the cobalt than the iron catalyst. The data show similar results for both catalysts with the readsorbed alkene initiating chain growth, but not in an amount to significantly impact the product distribution. For cobalt, but not for iron, the added alkene may also be involved in the hydroformylation reaction. The data clearly show that vapor pressure and product accumulation effects must be accounted for in mechanism studies using isotopic tracers. The added D5-1-pentene[4,4,5,5,5] was found to initiate a growing hydrocarbon chain as the CD3CD2CH2CH2CH2 unit without measurable scrambling of the isotope label in contrast to earlier work with deuterated ethanol using a cobalt catalysts.
Keywords: Isotopic tracer; Fischer–Tropsch synthesis; Reaction mechanism; Alkene reincorporation; Iron catalysts; Cobalt catalysts;
Effect of H2O on sulfur poisoning and catalytic activity of Ni–YSZ catalysts by Nandita Lakshminarayanan; Umit S. Ozkan (138-145).
Effect of H2S and H2O in steady-state methane oxidation over Ni–YSZ.Display Omitted▶ Ni sites for methane oxidation and decomposition have different sulfur poisoning characteristics. ▶ Effect of H2S on catalytic activity of Ni–YSZ is more severe in the presence of water. ▶ S interactions with YSZ substrate were observed. ▶ XAFS analysis showed oxidation of Ni sites with exposure to H2S.Solid oxide fuel cells (SOFCs) are the most desirable fuel cells for stationary power generation and are used as auxiliary power sources in transportation applications. The fuel flexibility and higher efficiency of an SOFC make it a favorable choice. The Ni-based catalysts that are currently used have coking and sulfur tolerance issues. The current work focuses on studying the effect of H2S on the catalytic activity of Ni–YSZ catalysts, for various methane conversion reactions. Steady-state reaction experiments are complemented by temperature programmed desorption (TPD) studies and post-reaction characterization using TEM and X-ray absorption fine structure (XAFS) spectroscopy. It is found that oxidation sites are less susceptible to sulfur poisoning, and that the presence of water in the feed increases deactivation due to sulfur. Interactions between sulfur and the YSZ support are also observed. These results provide further insight into the deactivation process due to sulfur over Ni–YSZ catalysts, and hold relevance in determining operating conditions of internally reforming fuel cells for sulfur-contaminated hydrocarbon fuels.
Keywords: Ni–YSZ; Sulfur poisoning; Catalyst deactivation; Coking;
Effect of the second metal of Anderson type heteropolycompounds on hydrogenation and hydrodesulphurization properties of XMo6(S)/Al2O3 and Ni3-XMo6(S)/Al2O3 catalysts by P.A. Nikulshin; N.N. Tomina; A.A. Pimerzin; A.Yu. Stakheev; I.S. Mashkovsky; V.M. Kogan (146-152).
.Display Omitted▶ The nature of a heteroatom of heteropolycompounds effects catalytic activity. ▶ Heteropolycompounds are effective precursors of a multilayered active phase. ▶ Heteroatom X optimizes electron density on the Mo atom. ▶ So it promotes productivities of the active sites in HDS and HYD reactions.The catalysts of the XMo6(S)/Al2O3 and Ni3-XMo6(S)/Al2O3 structures were prepared from heteropolycompounds (HPCs) of Anderson type (where X = Co, Ni, Cr, Mn, Fe, Cu, Zn, Ga). The precursors and synthesized catalysts were characterized by FTIR, XRD, EXAFS, HRTEM techniques. The prepared catalysts were examined in model reactions of thiophene HDS and benzene HYD and in hydrotreating (HDT) of diesel fraction. The correlations between the catalytic activities in HDS and HYD and the heats of thiophene adsorption depending on the nature of the heteroatom prove that it plays an important role in the formation and behavior of the HYD and HDS active sites. It was found that heteropolycompounds are effective precursors of a multilayered active phase of hydrotreating catalysts.
Keywords: Hydrotreatment; Catalysis; Heteropolycompounds; Diesel; Activity; Benzene; Thiophene;
New mesoporous perovskite ZnTiO3 and its excellent catalytic activity in liquid phase organic transformations by Nabanita Pal; Manidipa Paul; Asim Bhaumik (153-160).
Display Omitted▶ First report on mesoporous perovskite ZnTiO3. ▶ Pluronic P123 templated synthesis for cubic pore wall structure. ▶ High catalytic activity in Friedel-Crafts benzylation. ▶ High catalytic activity in Fischer esterification of different long chain carboxylic acids.A new mesoporous perovskite ZnTiO3 material has been synthesized by the evaporation-induced self-assembly (EISA) method using non-ionic surfactant Pluronic P123 as template. After calcination of the dried gel of equimolar concentrations of Zn(II) and Ti(IV) at 673 K, a new perovskite mesophase of ZnTiO3 (MZT-11) formed, having highly crystalline cubic ZnTiO3 pore wall. Interestingly, in the absence of P123 but otherwise identical synthesis conditions showed no cubic structure and a mixed phase consisting of ZnO and TiO2 phases (ZT-11). The BET surface area of the mesoporous perovskite materials (MZT-11) was 136 m2 g−1 and the average dimension of the pores was ca. 5.1 nm. The material was thoroughly characterized by different analytical methods including small and wide angle powder XRD, FE SEM, TEM, FT IR, UV–visible, photoluminescence (PL) and X-ray fluorescence (XRF) analysis. This new mesoporous perovskite material showed excellent catalytic activity in the Friedel-Crafts (FC) benzylation of aromatics and in the Fischer esterification of different long chain carboxylic acids in the presence of methanol under solvent-free conditions.
Keywords: Liquid phase catalysis; Mesoporous materials; Perovskite; ZnTiO3;
Coking behavior of a submicron MFI catalyst during ethanol dehydration to ethylene in a pilot-scale fixed-bed reactor by Fei Wang; Man Luo; Wende Xiao; Xiaowei Cheng; Yingcai Long (161-170).
Display Omitted▶ Submicron MFI catalyst possessed high activity, stability and regenerability. ▶ Coke deposits change from intermediates to alkyl aromatics along the tube length. ▶ Loss of acidity rather than pore volume should be responsible for deactivation.Coking behavior of a submicron MFI catalyst for ethanol to ethylene was studied in a pilot scale tubular reactor. The experimental results showed that the submicron MFI catalysts possessed high activity and stability. Ethanol conversion and ethylene selectivity over the fresh/regenerated catalyst were around 97.9%/96.2% and 99.1%/98.9%, respectively. The fresh catalyst illustrated an active duration of 1606 h while the regenerated of 2008 h, which implied the regeneration can enhance the stability. In the reactor, the coke mainly consisted of adsorbed substances at the forepart and of alkyl aromatics at the end, and the coke contents presented an approximate U-shape trend along the tube length. Further tests revealed that the loss of acidity rather than the pore volume should be responsible for the catalyst deactivation.
Keywords: Ethanol dehydration; Submicron MFI zeolite; Coke deposition; Pilot plant;
Towards understanding sodium effect on USY zeolite by Luis-Ernesto Sandoval-Díaz; Liliam-Alexandra Palomeque-Forero; Carlos Alexander Trujillo (171-177).
Display Omitted▶ Sodium destroys USY zeolite but does not increase dealumination rate. ▶ Sodium affects activity but not selectivity in n-butane cracking. ▶ Exchange, if exist, is not selective to a particular kind of Brønsted acid site. ▶ At low sodium loads accessibility of probe molecules increase but at higher loads destruction overcomes this initial effect. ▶n-Butane activation may occur in spatially constrained environments exposed by sodium action on Y zeolite.Samples of a commercial USY zeolite were exchanged with NaCl solution and then thermally treated under dry atmosphere. Resulting samples were evaluated by n-butane cracking, isopropylamine (i-pam) decomposition, TG–DSC, nitrogen adsorption, and powder XRD. Activation barriers for n-butane reactions were determined as a function of sodium load in the samples. The addition of sodium chloride has a marked negative effect upon material crystallinity, but dealumination rate does not seem to be affected, which suggests framework destruction mediated by sodium does not involve aluminum atoms. As sodium was loaded, samples were less able to retain water because of loss in crystallinity as shown by XRD and volume of micropore measurements. Activity to n-butane cracking decreases monotonically with sodium load, but selectivity to cracking, dehydrogenation, and hydride transfer products remained unaltered; that shows sodium chloride effect is not selective to a particular kind of acid site. The Brønsted acid site (BAS) density measured by i-pam decomposition exhibits a volcano-like profile with sodium load; at low sodium contents there is a gain in i-pam accessibility due to structural collapse but at higher loads BAS disappearance overcomes accessibility and density of acid sites decreases. The average pore size increases with sodium load. After thermal treatment in presence of sodium chloride, gates are opened in zeolite structure, allowing n-butane and isopropylamine to reach formerly inaccessible sites; hydrocarbon conversion can occur in spatially constrained environments where stabilization effects lead to low-energy/low-entropy activated complexes and apparent activation energy shows a minimum with sodium chloride load. Sodium chloride has an effect on Y zeolite even in dry conditions at temperatures similar to those predominant in FCC regenerator.
Keywords: USY zeolite; Sodium contamination; n-butane cracking; Apparent activation energy; Accessibility; Isopropylamine decomposition; Cracking selectivity;
Inverse kinetic isotope effects and deuterium enrichment as a function of carbon number during formation of C–C bonds in cobalt catalyzed Fischer–Tropsch synthesis by Buchang Shi; Chunfen Jin (178-183).
▪.▶ Confirmed the inverse isotope effect during Fischer–Tropsch synthesis (FTS). ▶ Deuterium enrichment in alkanes was observed during Co/SiO2 catalyzed FTS. ▶ A modified alkylidene mechanism is proposed to account for the IKIE and D-enrichment. ▶ IKIE and D-enrichment were explained by combining alkylidene mechanism with ASF kinetics.How the deuterium is enriched in hydrocarbons produced by Fischer–Tropsch (FT) synthesis is of broad scientific interest, particularly to those studying the mechanism of the FT reaction and the formation of hydrocarbons in the Earth's crust or in the nebula. In order to determine whether there is an inverse isotope effect and whether there exists the deuterium enrichment in hydrocarbons during the FT reaction, we performed the H2/D2 switching experiments in cobalt catalyzed FT reactions and found that the values of α H/α D are in a range of 0.93–0.98 under five different reaction conditions, a clear indication of the inverse kinetic isotope effect. We also conducted the H2/D2 competition experiments using an equal molar ratio of D2 and H2 as the reagents and found that the H/D ratios in alkanes from C6 to C24 obtained are less than 1 and decrease with increasing molecular size. To account for these results, we proposed a modified alkylidene mechanism for the FT reaction. By combining the modified alkylidene mechanism with the Anderson–Schulz–Flory equation, the results obtained in this study can be quantitatively explained and the isotope fractionation patterns and deuterium enrichment observed in abiogenic hydrocarbons produced by the FT-type reactions can be predicted.
Keywords: Inverse kinetic isotope effect; Deuterium enrichment; C–C coupling; Fischer–Tropsch synthesis;
Ba,K,Co/CeO2 catalysts for NO x traps: Effect of preparation procedure by María Ariela Peralta; Bárbara S. Sánchez; María Alicia Ulla; Carlos A. Querini (184-188).
Display Omitted▶ BaCoK/CeO2 catalysts have capacity for NO x adsorption. ▶ The preparation procedure has a major impact on the adsorption capacity. ▶ Catalyst obtained by successive impregnations using Co(NO3)2 induces the formation of a BaCoO3 perovskite. ▶ The nitrogenated compounds formed on this perovskite are more unstable.Ba,K,Co/CeO2 catalysts for diesel soot and NO x abatement were studied. Different preparation procedures were analyzed, varying the cobalt precursor and the order of their impregnation. The catalyst interaction with NO + O2 was studied using a microbalance and testing in both NO + O2 and He atmospheres. Fourier Transformed Infrared Spectroscopy (FTIR) and X-Ray Diffraction (XRD) were used to characterize the catalysts. The behavior of these catalysts as NO x traps was different. It was found that when cobalt nitrate was added to the Ba,K/CeO2 catalyst, a high NO x adsorption capacity was obtained and, what is even more interesting, that the decomposition of the nitrated species occurred at lower temperature. The identification by XRD of a perovskite BaCoO3 formed upon this preparation procedure was considered to be responsible for the different behavior observed in this particular catalyst.
Keywords: NO x traps; Barium; Cobalt; Potassium; Perovskite;
On the influence of pore geometry and acidity on the activity of parent and modified zeolites in the synthesis of methylenedianiline by Michael Salzinger; Matthias B. Fichtl; Johannes A. Lercher (189-194).
Display Omitted▶ Pore size and geometry have an pronounced impact on catalyst activity. ▶ MFI and MWW type materials are inactive. ▶ BEA and FAU type materials are active, but the reaction is limited by pore diffusion. ▶ Mesoporous materials offer increased activity by avoiding mass transport limitation. ▶ MCM-36 and dealuminated FAU type materials display the highest TOFs.Methylenedianiline synthesis from formaldehyde and aniline is catalyzed by solid acid catalysts, such as zeolites, which offer strong acidity and high acid site density. Critical parameters for catalyst activity were explored using materials with MFI, BEA, MOR and FAU structure. While materials with MOR and MFI structure hardly show activity, BEA and FAU type zeolites are active and selective. The higher activity for the latter materials is related to their larger pore structure. Nevertheless, the reaction is limited by pore diffusion over parent BEA- and FAU-type zeolites. Mesoporous materials, such as dealuminated FAU, offer significantly higher activity as pore diffusion limitation can be overcome. Therefore, we synthesized and tested other mesoporous aluminosilicates such as desilicated BEA and the delaminated MWW materials ITQ-2 and MCM-36. It was shown that desilication increases the activity of parent BEA type zeolites for MDA formation, yet not to the same extend as dealumination in case of FAU. ITQ-2 shows promising results, but MCM-36 surpasses ITQ-2 in terms of activity by a factor of two displaying activities similar to the dealuminated FAU materials.
Keywords: Methylenedianiline; Zeolites; ITQ-2; MCM-36; Alkaline leaching;
The Heck arylation of mono- and disubstituted olefins catalyzed by palladium supported on alumina-based oxides by Ewa Mieczyńska; Andrzej Gniewek; Iweta Pryjomska-Ray; Anna M. Trzeciak; Hanna Grabowska; Mirosław Zawadzki (195-205).
Display Omitted▶ Palladium supported on alumina-based oxide is highly active in Heck reactions. ▶ Support has an improving influence on the catalytic activity of palladium. ▶ During Heck reaction supported Pd(II) forms Pd(0) nanoparticles. ▶ The diameter of Pd(0) nanoparticles is not changed during Heck reaction.Palladium catalysts containing Pd(0) or Pd(II) supported on alumina-based mixed oxides prepared by alkoxide sol–gel method (Al2O3, Al2O3–ZrO2, Al2O3–ZrO2–Eu2O3, Al2O3–MgO, Al2O3–CeO2, Al2O3–Fe2O3) are very effective in the Heck coupling of bromobenzene with butyl acrylate in DMF solvent. In the presence of an excess of bromobenzene, butyl cinnamate (1) was formed as the main product after 4 h. With the same catalysts, good results, up to 97% yield of ethyl β-phenylcinnamate (3), were also obtained in the coupling of bromobenzene with ethyl cinnamate. The three most active catalysts, Pd(0)/Al2O3, Pd(II)/Al2O3, and Pd(II)/Al2O3–Fe2O3, were applied in the Heck cross-coupling of cinnamates with different bromobenzene and iodobenzene derivatives, leading to β-arylcinnamate products. The highest yield was observed when iodoanisole and cinnamic aldehyde were used as substrates. The formation of Pd(0) nanoparticles in the Heck reaction carried out with supported Pd(II) catalyst precursors was confirmed by TEM measurements.
Keywords: Heck reaction; Nanostructured alumina-based oxides; Palladium nanoparticles; Supported palladium; β-Arylcinnamate;
Benzylation of benzene with benzyl alcohol on zeolite catalysts by N. Candu; M. Florea; S.M. Coman; V.I. Parvulescu (206-214).
Display Omitted▶ Diphenylmethane (DPM) is mostly used in the fragrance industry and agrochemicals. ▶ Benzylation is carried out in “green” advantageous conditions with S DPM of 88.9%. ▶ Used catalysts are cheap and the experimental set-up is simple and practical. ▶ The purification of the final product is easily done.The catalytic liquid phase benzylation of benzene to diphenylmethane (DPM) with benzyl alcohol (BnOH) was investigated over various zeolite catalysts (HSZ 600 mordenite, CBV 20A mordenite, H-beta zeolites with Si/Al of 10.8 and 35.8, respectively) at 353–423 K and under atmospheric pressure, using three reaction methodologies: (A) by adding all benzyl alcohol at the beginning of the reaction, (B) by dropwise addition of benzyl alcohol (1–2 drops/min for 4 h) and (C) under continuous flow conditions. Nafion-embedded silica and AlCl3/MCM-41 were also tested for comparison. The conversion and product distribution largely depended on the experimental conditions and the zeolite nature. Under optimal conditions using the Beta zeolite (Si/Al molar ratio of 10.8) and the (C) methodology, selectivity to DPM of 88.9% for a conversion of BnOH of 99.2% were achieved. Recycling tests showed that the catalyst preserved its activity and selectivity to DPM after several cycles.
Keywords: Benzylation; Diphenylmethane; Benzyl alcohol; Zeolites;
Catalytic properties of Cu/SBA-3 in oxidative dehydrogenation of methanol—The effect of the support composition by Justyna Florek-Milewska; Piotr Decyk; Maria Ziolek (215-224).
Display Omitted▶ Chemical composition of SBA-3 supports determines copper species loaded. ▶ NbSBA-3 favours isolated Cu2+ which chemisorb methoxy species from methanol. ▶ Nucleophilic oxygen adsorbs on anionic vacancies and abstract hydrogen from –OCH3. ▶ Cu–Nb interaction decreases strength of LAS and increases formaldehyde selectivity.Silicate, niobosilicate and aluminosilicate mesoporous sieves of SBA-3 type with hexagonal arrangement of pores were synthesised and modified by the wetness impregnation with copper (1 wt% loading). The physicochemical properties of the samples were investigated by XRD, N2 adsorption–desorption, XRF, ICP, H2-TPR, ESR, UV–vis, XPS techniques and in acid-basic test reactions—acetonyloacetone cyclisation, 2-propanol reaction as well as by pyridine adsorption combined with FTIR measurements. The oxidative/dehydrogenation catalytic activity of prepared catalysts was examined in the methanol oxidation reaction. Depending on the chemical composition of the SBA-3 support, various copper species were found to be formed and a range of catalytic activities could be achieved. On SBA-3, AlSBA-3 and NbSBA-3 the following copper species were found dominant: bulk CuO, oligonuclear [Cu δ+⋯O δ−⋯Cu δ+] n clusters and isolated copper cationic species, respectively. Migration of niobium species from the inert part of walls onto the surface after copper loading was observed. The Si/Nb ratio in the support was established to determine the activity and selectivity of Cu modified samples. By the proper combination of the content of Nb and Cu on the surface of SBA-3 materials it can be possible to obtain the catalysts selective to the desired products in oxidation of methanol. The highest production of formaldehyde from methanol was obtained on Cu/NbSBA-3-64 (Si/Nb = 57 in bulk and 43 on the surface, Nb/Cu = 0.8 on the surface).
Keywords: SBA-3; AlSBA-3; NbSBA-3; Modification with Cu; Oxidation of methanol;
Efficient allylic oxidation of cyclohexene catalyzed by trimetallic hybrid nano-mixed oxide (Ru/Co/Ce) by Mehran Ghiaci; Behzad Aghabarari; A.M. Botelho do Rego; A.M. Ferraria; Saeed Habibollahi (225-230).
Display Omitted▶ The RuO2/Co3O4/CeO2 nanoparticles (THNO) were synthesized and characterized. ▶ This nano-catalyst was used for oxidation of cyclohexene. ▶ Cyclohexene was oxidized over THNO to the corresponding α,β-unsaturated ketone as the major product.The paper deals with the reactivity of RuO2/Co3O4/CeO2 nanoparticles prepared by a reverse micelle approach, which was precipitated by alkali-hydrolysis of RuCl3, Co(NO3)2 and Ce(NO3)2 and transformed into RuO2/Co3O4/CeO2 catalyst by calcinations in air at 400 °C. The catalysts were investigated with XRD, TEM, XPS, and BET techniques and were tested for oxidation of cyclohexene. The nano-catalyst exhibited high catalytic activities for the oxidation of cyclohexene to the corresponding α,β-unsaturated ketone under heterogeneous condition. In order to obtain maximum conversion of cyclohexene, the reaction parameters, like reaction temperature and time, were optimized. Under the optimized conditions, a maximum of 97.7% cyclohexene conversion and 95% selectivity, was achieved with RuO2/Co3O4/CeO2 mixed oxide nano-catalyst.
Keywords: Reverse micelle; Heterogeneous catalyst; Cyclohexene oxidation; Trimetallic nanoparticles;
Pd nanosized particles supported on chitosan and 6-deoxy-6-amino chitosan as recyclable catalysts for Suzuki–Miyaura and Heck cross-coupling reactions by Banothile C.E. Makhubela; Anwar Jardine; Gregory S. Smith (231-241).
Display Omitted▶ Chitosan-supported Pd(II) catalysts were synthesized in good yield. ▶ The Pd(II) catalysts were characterized using various analytical techniques. ▶ High catalytic activity was exhibited in Suzuki–Miyaura and Heck coupling reactions. ▶ No Pd leaching was detected in the products as determined by ICP-MS. ▶ The catalysts could be recycled and reused up to five times with consistent activity.Several chitosan and 6-deoxy-6-amino chitosan-Schiff base ligands (1–4) were prepared by condensation of either 2-pyridinecarboxaldehyde or 2-(diphenylphosphino)benzaldehyde with the amino group(s) on chitosan and its derivative (6-deoxy-6-amino chitosan). The supported ligands were reacted with [PdCl2(COD)] to form chitosan-supported PdII catalysts (5–8). All the supported catalysts were air- and moisture-stable and have been characterized using elemental analysis, ICP-MS, UV–vis, FT-IR, PXRD, TGA, 31P solid state NMR and TEM. As models for the heterogenized catalysts (5 and 6), mononuclear PdII complexes (9 and 10) were also prepared via the Schiff-base condensation reaction of 1,3,4,6-tetra-O-acetyl-β-d-glucosamine hydrochloride to form 1,3,4,6-tetra-O-acetyl-β-d-glucos-2-pyridylimine and 1,3,4,6-tetra-O-acetyl-β-d-glucos-2-(diphenylphosphino)imine which were subsequently reacted with [PdCl2(COD)]. Complexes (9 and 10) and their precursors were characterized by 1H and 31P NMR, UV–vis, FT-IR spectroscopy and elemental analysis.Catalytic Suzuki–Miyaura and Heck carbon–carbon cross-coupling reactions were carried out using the supported Pd catalysts and their mononuclear analogues. The immobilized and homogeneous catalysts showed high activity for both the Suzuki–Miyaura and Heck cross-coupling reactions in organic and aqueous media. Homogeneous catalysts (9 and 10) decomposed during the first run, while the supported catalysts could be recycled and reused up to five times.
Keywords: Chitosan; Suzuki–Miyaura; Heck; Heterogeneous PdII catalysis; Schiff-base;
Modified crosslinked polyacrylamide anchored Schiff base–cobalt complex: A novel nano-sized heterogeneous catalyst for selective oxidation of olefins and alkyl halides with hydrogen peroxide in aqueous media by Bahman Tamami; Soheila Ghasemi (242-250).
A new nano-sized polymer-supported Schiff base–cobalt complex catalyst based on crosslinked polyacrylamide was synthesized and characterized. The polymeric catalyst showed high efficiency and selectivity in the oxidation of various olefins with environmentally friendly H2O2 as a sole oxidant in aqueous media. The catalyst can be recycled several times with no significant loss in its activity or degradation of polymer matrix.Display Omitted▶ Synthesis and characterization of a supported metal catalyst. ▶ Oxidation of olefins and alkyl halides using this catalyst. ▶ Oxidation carried out in green aqueous media with high degree of selectivity. ▶ The catalyst recycled several times. ▶ The catalyst showed nanosized fiber-like image.A new nano-sized polymer-supported Schiff base–cobalt complex catalyst based on crosslinked polyacrylamide was synthesized and characterized. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) of the catalyst show nanosize fiber-like image of the polymeric catalyst. The catalyst activity was studied in the oxidation of various olefins including non-activated terminal olefin in water with hydrogen peroxide as an oxygen source. The catalyst showed high degree of selectivity. The effects of reaction parameters such as solvent, oxidant, temperature, molar ratio of catalyst and catalyst structure on the oxidation of styrene were investigated. The oxidation of benzyl halides to their corresponding carbonyl compounds in the presence of this heterogeneous catalyst was studied as well. The catalyst can be recycled several times without significant loss in its activity.
Keywords: Polyacrylamide supported catalyst; Heterogeneous catalysis; Schiff base–cobalt complex; Olefin oxidation;
Vapor phase oxidation of dimethyl sulfide with ozone over ion-exchanged zeolites by Chien-Liang Hwang; Nyan-Hwa Tai (251-256).
Display Omitted▶ Ag-Mn/ZSM-5 oxidizes DMS in the presence of ozone. ▶ The Mn2+ in Ag-Mn/ZSM-5 enhances the oxidizing activity of the catalyst for DMS. ▶ The two metals contained in Ag-Mn/ZSM-5 are cooperative in the oxidization of SO2. ▶ Ag-Mn/ZSM-5 converts SO2 into H2SO3 and oxidizes SO2 to H2SO4 in gas phase.This work studied the catalyst activity and stability of ion-exchanged zeolites during the oxidation of dimethyl sulfide (DMS) in the presence of ozone. Ozone was used as an oxidant to assess the oxidation capability of Ag/ZSM-5, Mn/ZSM-5 and Ag-Mn/ZSM-5 of DMS at both room temperature and 130 °C. Ion-exchange with silver ions (Ag+) strengthened the adsorption of DMS, resulting in an increased oxidation capacity for DMS. Furthermore, the introduction of manganese ions (Mn2+) strengthened the oxidation capability of DMS, thus enhancing the selectivity of SO2 obtained from the oxidation and reducing the degradation of activity because the pores of the catalyst were blocked by the oxidation products, such as dimethyl sulfoxide (DMSO) and dimethyl sulfone (DMSO2). Ag-Mn/ZSM-5 demonstrated a 100% conversion of DMS; not only SO2 but also H2SO3 and H2SO4 were detected at a high GHSV (90,000 h−1) and low reaction temperature (130 °C). The SO2 adsorption curve and temperature-programmed desorption (TPD) showed that the single metal ion-exchanged zeolite had a weak adsorption capability for SO2 at room temperature, whereas the bi-metal ion-exchanged zeolite had an excellent adsorption capability towards SO2; it could convert SO2 into H2SO3 and could convert oxidized SO2 into H2SO4 in gas phase at room temperature.
Keywords: Dimethyl sulfide; Ion-exchanged zeolite; Desulfurization; Oxidation; Adsorption;
Structure-reactivity relationship for aromatics transalkylation and isomerization process with TNU-9, MCM-22 and ZSM-5 zeolites, and their industrial implications by M. Teresa Portilla; Francisco J. Llopis; Cristina Martínez; Susana Valencia; Avelino Corma (257-268).
Display Omitted▶ TNU-9 for aromatic alkylation. ▶ Industrial possibilities of TNU-9 as alkylation catalyst. ▶ Ethylbenzene formation with medium pore zeolites.TNU-9 is a medium pore zeolite with a complex tridimensional channel system. Its catalytic properties have been studied in some reactions that involve the BTX fraction, such as benzene and toluene alkylation with methanol, ethanol or isopropanol. These reactions use in practice medium pore zeolites such as ZSM-5 (MFI) or MCM-22 (MWW), and the selectivities obtained with TNU-9 are compared and analyzed from the point of view of the zeolite structure and pore topology, as well as from its possible industrial application. For benzene alkylation to give ethylbenzene (EB), TNU-9 is an active and selective catalyst with selectivities to EB much higher than ZSM-5 and close to those of the industrially relevant MCM-22. However, olefin oligomerization within the pores of TNU-9 occurs in a larger extension than with MCM-22, leading not only to some lower selectivity, but also to a faster catalyst deactivation. In the case of cumene formation, again the selectivity of TNU-9 to the desired product is higher than ZSM-5 but lower than MCM-22, owing to the formation of larger amounts of n-propylbenzene in the former as a result of its pore topology. Nevertheless, TNU-9 may be worth to be studied further for the disproportionation of toluene to give xylenes. In this case, its comparison with ZSM-5 appears of interest.By studying the alkylation of toluene with alcohols of different chain length, i.e. methanol, ethanol and isopropanol, it has been found that TNU-9 has an antagonistic behaviour, closer to ZSM-5 or MCM-22 depending on the activity or selectivity parameters considered that could be explained by its complex topology, formed by 10-ring tortuous channels with crosses as in ZSM-5, and large cavities as in MCM-22.
Keywords: BTX aromatics; TNU-9 zeolite; Benzene alkylation; Toluene alkylation;
Aqueous phenol oxidation catalysed by molybdenum and tungsten carbonyl complexes by Zhe Wang; Choon Wee Kee; Shenyu Li; T.S. Andy Hor; Jin Zhao (269-274).
Display Omitted▶ Cp′M(CO)3X/H2O2 system has been used for the catalytic phenol oxidation in aqueous solution. ▶ The main oxidation products in solution are oxalic acid and catechol.The catalytic activities of the complexes, Cp′M(CO)3X (Cp′ = Cp (η5-C5H5), Cp* (η5-C5Me5); M = Mo, W; X = Cl, CH3) and Mo(CO)6 have been examined for the oxidation of phenol (37.6 g/L) using H2O2 as oxidant in aqueous solution. Among them, CpMo(CO)3Cl and CpMo(CO)3(CH3) showed the highest catalytic activity. Conversion of phenol at 55 °C is more than 80% after 24 h when water is used as solvent and the ratio of catalyst:phenol:H2O2 is 1:50:200. The main oxidation products observed in solution are oxalic acid and catechol, together with trace amount of p-benzoquinone and maleic acid. Under similar conditions, binary Mo(CO)6 catalyses phenol oxidation giving hydroquinone and p-benzoquinone as main products.
Keywords: Molybdenum; Tungsten; Phenol; Oxidation; Carbonyl; Wastewater;
A comparative study for gas-phase dehydration of glycerol over H-zeolites by Yong Tae Kim; Kwang-Deog Jung; Eun Duck Park (275-287).
Display Omitted▶ H-ferrierite (55) showed the highest selectivity to acrolein. ▶ The glycerol conversion was strongly dependent on the external surface area. ▶ Most of the micropores were filled with carbon sources initially. ▶ The acrolein selectivity increased with water content in the feed.The gas-phase dehydration of glycerol was conducted over various H-zeolites, viz. H-ferrierite, H-β, H-ZSM-5, H-Y and H-mordenite with various SiO2/Al2O3 ratios. For comparison, γ-Al2O3 and silica-alumina were also examined. Several characterization techniques: X-ray diffraction (XRD), the temperature-programmed desorption of ammonia (NH3-TPD), the temperature-programmed desorption of water (H2O-TPD), temperature-programmed oxidation (TPO) with mass spectroscopy and CHNS analysis were employed to characterize the catalysts. The initial glycerol conversion at 315 °C decreased in the following order: silica-alumina > H-β (25) > H-β (27) > γ-Al2O3 > H-mordenite (20) > H-ferrierite (55) > H-ferrierite (20) > H-ZSM-5 (23) ∼ H-β (350) > H-β (38) ∼ H-Y (5.1). H-ferrierite (55) showed the highest selectivity to acrolein at 315 °C among the tested catalysts. The glycerol conversion over the solid acid catalysts was strongly dependent on their external surface area. In the case of the H-zeolites, most of the micropores were filled with carbon sources at the initial stage of this reaction. As long as the molar ratio between water and glycerol was in the range from 2 to 11, there was only a small change in the glycerol conversion, while the acrolein selectivity increased noticeably with increasing water content in the feed. The glycerol conversion and acrolein selectivity increased with increasing reaction temperature from 290 °C to 340 °C over H-ferrierite (55). The glycerol conversion and acrolein selectivity also increased with increasing contact time (W/F glycerol) which is defined as the ratio between the catalyst's weight (W) and the molar flow rate of glycerol (F glycerol).
Keywords: Dehydration; Glycerol; Acrolein; H-zeolites; Acidity;
Supported rhenium sulfide catalysts in thiophene and 4,6-dimethyldibenzothiophene hydrodesulfurization: Effect of acidity of the support over activities by C. Sepulveda; V. Bellière; D. Laurenti; N. Escalona; R. García; C. Geantet; M. Vrinat (288-293).
Display Omitted▶ Use of zeolites to prepare ReS2 supported catalysts. ▶ Support effect for ReS2 catalysts has been evaluated in thiophene and 4,6-DMDBT HDS. ▶ Zeolites acidity induced isomerization during 4,6-DMDBT HDS. ▶ Silica-supported catalyst was found very performant in HDS reaction.Three different zeolites, γ-alumina and silica supports were used to prepare ReS2 catalysts by incipient wetness impregnation of ammonium perrhenate (NH4ReO4). The catalysts were characterized and tested in the hydrodesulfurization (HDS) of thiophene in an atmospheric fixed bed reactor, and of the 4,6-dimethyldibenzothiophene (4,6-DMDBT) HDS in a high pressure stirred tank reactor. The results showed that the acidity of the zeolites has a detrimental influence over hydrodesulfurization activity of the Re sulfide, contrarily to the enhancement observed previously with zeolite-supported Mo sulfide catalysts. The catalyst prepared over a non-acidic zeolite (HSZ-390) was found very efficient in thiophene HDS and comparable to silica for 4,6-DMDBT.
Keywords: Rhenium sulfide; Hydrodesulfurization; Zeolites; Acidity; Support effect;
Continuous homogeneous hydroformylation with bulky rhodium catalyst complexes retained by nano-filtration membranes by Jing Fang; Ranjan Jana; Jon A. Tunge; Bala Subramaniam (294-301).
Display Omitted▶ Soluble Rh complexes formed with polymer bound phosphite ligands (MWav ∼ 7000). ▶ Rh complexes retained in solution by nanofiltration membranes (Rh leakage <100 ppb). ▶ Steady hydroformylation activity shown in CSTR fitted with nanofiltration membrane.▶ Rh in reactor effluent steady at ∼20 ppb and exceeds economic viability criterion.By employing polymer bound bulky phosphite ligands (synthesized in house) in conjunction with polyimide membranes with appropriate molecular weight cutoff (MWCO), homogeneous Rh complexes were effectively retained in solution. Batch filtration of toluene-based solutions of various phosphorus ligands at constant pressure revealed that Rh complexed with polymer bound bidendate ligands (average molecular weight from 7000 to 10,000) were most effectively retained in solution with Rh leakage in the permeate being on the order of tens of ppb. Continuous filtration of toluene-based solutions containing dissolved polymer bound phosphite ligand at constant pressure and cell hold-up revealed that the Rh and P concentrations in the permeate were steady after several hours at less than 100 ppb. The higher initial concentrations of Rh and P in the permeate suggests the removal of perhaps unbound Rh and P from the initial mixture and also from the fraction of the polymers that are smaller than the MWCO of the membrane. Continuous 1-olefin hydroformylation with Rh complexed with polymer bound bidentate ligand (JanaPhos) was demonstrated at 50 °C in a stirred reactor fitted with a nanofiltration membrane. The catalyst complex was dissolved in a toluene-based reaction mixture and the feed solution (containing the substrate) and syngas were added continuously to maintain a constant flow rate and reactor pressure (3.0 MPa). At optimized conditions, the continuous run reached a steady state characterized by nearly 50% 1-olefin conversion, >98% aldehydes selectivity and a n/i ratio of 3.5, all of which remained constant even after 22 h. The Rh concentrations in the effluent were steady at approximately 20 ppb even after 22 h. The makeup Rh cost required to offset this loss during continuous processing ($0.004/lb aldehyde) exceeds the economic viability criterion ($0.013/lb aldehyde).
Keywords: Rhodium catalyzed hydroformylation; Soluble polymer bound ligands; Membrane nanofiltration;
Hydrogen production via auto-thermal reforming of bio-ethanol: The role of iron in layered double hydroxide-derived Ni0.35Mg2.65AlO4.5±δ catalysts by Lihong Huang; Qi Liu; Rongrong Chen; Andrew T. Hsu (302-308).
Ni-based LDH-derived catalysts.Display Omitted▶ Iron improves the surface area and the reducibility of Ni, and constrains acidity. ▶ Iron improves the H2 yield and relieves the coke deposition. ▶ Stability obtained in the 30-h ATR test with iron.Ni-based layered double hydroxide (LDH)-derived catalysts with Ni–Mg–Al–Fe–O were prepared via co-precipitation, and were tested in auto-thermal reforming (ATR) of ethanol for hydrogen production. The Ni0.35Mg2.65AlO4.5±δ catalyst showed poor stability and a low H2 yield, near 2.51 mol H2/mol EtOH. The tetra-component catalyst of Ni0.35Mg2.65Al0.50Fe0.50O4.5±δ, in which the trivalent component consists of both aluminum and iron, showed a promising performance in ATR of ethanol: not only did the H2 yield remain stable near 3.7 mol H2/mol EtOH during the 30-h test, but the CH4 reforming activity also improved and C2H4 disappeared in product gases. These improvements can be attributed to the synergic effect by both iron and nickel on the structural and electronic properties: the BET surface area was increased, the reducibility of the Ni metal and its resistance to oxidation in ATR were improved, and the acidity was constrained as well.
Keywords: Hydrogen production; Auto-thermal reforming of ethanol; Layered double hydroxide; Iron promoter;
Electrocatalysts for electrooxidation of methyl formate by Duck Hyun Youn; Ganghong Bae; Dong Jin Ham; Jae Sung Lee (309-316).
Display Omitted▶ Acid catalyzed hydrolysis of methyl formate to formic acid and methanol occurred in half cell and single cell conditions. ▶ The dominant reaction is the oxidation of formic acid at low potentials below 0.4 V. ▶ At higher potentials, methanol joins the oxidation process of methyl formate. ▶ Direct methyl formate fuel cell operation conducted for the first time.Carbon-supported PtSn, PtPd, and PtRuPd catalysts are prepared by chemical reduction with hydrothermal treatment, and their electrochemical properties for methyl formate electrooxidation are investigated by cyclic voltammetry, chronoamperometry, and CO stripping voltammetry in comparison with commercial Pt/C and PtRu/C catalysts. At low potentials below 0.4 V, the dominant reaction is the oxidation of formic acid produced by acid-catalyzed hydrolysis of methyl formate, and PtPd/C exhibits the highest activity. At higher potentials, methanol joins the oxidation process of methyl formate and PtRu/C, PtSn/C, and PtRuPd/C show the high activity. In single cell, direct methyl formate fuel cell operation, PtRuPd/C containing both active component for formic acid oxidation (Pd) and CO-tolerant component (Ru) shows the highest performance for electrooxidation of methyl formate.
Keywords: Direct methyl formate fuel cell; Formic acid; Methanol; Electrocatalysts;
Laser-induced fabrication of platinum nanoshells having enhanced catalytic and Raman properties by Mee Rahn Kim; Jong-Yeob Kim; Seol Ji Kim; Du-Jeon Jang (317-322).
Display Omitted▶ Platinum nanoshells have been fabricated via laser irradiation. ▶ Nanoshell thickness has been tuned. ▶ Platinum nanoshells have high catalytic performances. ▶ Platinum nanoshells show highly active surface-enhanced Raman scattering.Platinum nanoclusters topped on silica nanospheres, prepared by a seeded-growth method, have been transformed into platinum nanoshells having uniform shell thickness of 6 nm via irradiation of nanosecond laser pulses. The thickness of platinum nanoshells can be tuned readily by adjusting the concentration of H2PtCl6 for the growth of platinum nanoparticles on silica nanospheres. Compared with Pt nanoclusters-topped silica nanospheres, platinum nanoshells coated on silica nanospheres have been found to catalyze the degradation of rhodamine B very rapidly in the presence of KBH4, and they show highly active surface-enhanced Raman scattering.
Keywords: Catalysis; Laser irradiation; Nanocomposite; Nanoparticle; SERS; Silica;
Synthesis, characterization and catalytic activities of vanadium–cryptomelane manganese oxides in low-temperature NO reduction with NH3 by Liang Sun; Qingqing Cao; Bingqing Hu; Junhua Li; Jiming Hao; Guohua Jing; Xingfu Tang (323-330).
Display Omitted▶ Lewis acid and surface redox property governed NH3-SCR activity of catalyst. ▶ Doping V in cryptomelane resulted in generation of Lewis acid sites. ▶ Surface redox ability of cryptomelane could be maintained with marginal V doping. ▶ Vanadium–cryptomelane with molar ratio of V/Mn = 2% showed best NH3-SCR activity.Vanadium doped cryptomelane-type manganese oxides (V-OMS-2) with V/Mn molar ratios of 0–10% were synthesized and investigated for low-temperature selective catalytic reduction of NO by NH3 (NH3-SCR). The characterization results of XRD patterns and Raman spectra demonstrated that V5+ isomorphously substituted for framework Mn4+ of the V-OMS-2. The adsorption and desorption of NH3 and H2-TPR results revealed that both surface defect sites (Lewis acid) and redox abilities were efficiently controlled by amounts of vanadium doping, and more vanadium dopings resulted in more Lewis acid sites and weaker bulk redox abilities. The results of catalytic tests revealed that the 2%V-OMS-2 catalyst showed the highest catalytic activities among the V-OMS-2 catalysts. In fact, the desired doping amount of V5+ can not only provide more Lewis acid sites for adsorption of NH3 but also maintain excellent surface redox abilities for activation of NH3, which resulted in higher catalytic activities in the low-temperature NH3-SCR reactions.
Keywords: NH3-SCR; Cryptomelane-type manganese oxides; Vanadium doping; Lewis acid; Surface redox abilities;
Influence of alkaline metal on performance of supported silicotungstic acid catalysts in glycerol dehydration towards acrolein by Hanan Atia; Udo Armbruster; Andreas Martin (331-339).
Display Omitted▶ Glycerol reacts towards acrolein with high yield over supported silicotungstic acid. ▶ Catalyst performance is linked to acidic properties and phase behaviour. ▶ Alkaline metals (Li, K, Cs) modify catalyst acidity and dehydration performance. ▶ Catalyst preparation sequence has a strong impact on activity and selectivity.A series of supported silicotungstic acid (H4SiW12O40·xH2O) catalysts was prepared from selected silica and alumosilicate carriers. Alkaline metals lithium, potassium and caesium were added to modify catalyst Brønsted acidity. Physico-chemical characterisation of the catalysts was carried out with nitrogen adsorption (BET), X-ray diffraction (XRD), and infrared (IR) and Raman spectroscopy and revealed that the nature of the alkaline metal is significant for (i) specific surface area which rises with metal ion radii and (ii) dispersion of active compound formed from alkaline metal and silicotungstic acid on the support surface. Interestingly, acidic properties rather do not depend on nature of alkaline metal. The catalysts were catalytically evaluated at standardised reaction conditions in a continuous flow lab scale set-up (10 wt.% of glycerol in water, 225–300 °C, modified contact time 0.15 kg h mol−1). Among the tested supported catalysts, lithium exchanged H4SiW12O40·xH2O showed highest activity and maximum selectivity of 70% for acrolein at complete conversion. Main effect of alkaline metal addition can be seen in improved selectivity and activity, in particular with silica supported catalysts.
Keywords: Silicotungstic acid; Alkaline metals; Glycerol dehydration; Acrolein; Acidic properties;
Selectivity control of benzene conversion to phenol using dissolved salts in a membrane contactor by Raffaele Molinari; Teresa Poerio (340-347).
Display Omitted▶ Dissolved salts increased the amount of phenol extracted in the organic phase. ▶ Dissolved salts decreased selectivity, yield and productivity. ▶ The sulphate anion increased phenol degradation increasing tar formation. ▶ Fe(0) catalyst increased the ratio phenol productivity/amount of black solid.Effect of salts, pH, type of acids and anion sulphate in the synthesis and separation of phenol through the hydroxylation of benzene by using a Fenton reaction in a biphasic membrane contactor has been investigated. The results indicated that sodium sulphate (1 M) increased phenol extraction in the organic phase (76.3%) but also increased reaction kinetics promoting over-oxidation products and a black solid (tar) formation. The acids delayed and in some tests avoided the tar appearance as precipitate but also gave a reduction of phenol selectivity. The sulphate absence, obtained by using iron(0), did not avoid the precipitate formation but only caused its decrease favouring a significant increase of the ratio productivity/amount of black solid from 4.6 to 62.4.
Keywords: Liquid phase benzene oxidation to phenol; Catalytic membrane contactor; Selective oxidation; Tar formation from benzene; Salts and phenol extraction (from aqueous to organic);
The effect of zeolite particle size on the activity of Mo/HZSM-5 in non-oxidative methane dehydroaromatization by Yanbin Cui; Yuebing Xu; Jiangyin Lu; Yoshizo Suzuki; Zhan-Guo Zhang (348-358).
Display Omitted▶ On-line sampling and storing of the reacted effluent at desired timed intervals. ▶ Off-line analysis of stored samples to measure variations in concentrations. ▶ Dynamic catalytic behaviors of Mo/HZSM-5 at various operating conditions. ▶ Application of the approach for studying the reaction kinetics over Mo/HZSM-5.The effect of the particle size of HZSM-5 on the activity of Mo/HZSM-5 in the non-oxidative CH4 dehydroaromatization was studied. For the purpose five 5 wt%Mo/HZSM-5 catalysts based on one highly crystalline parent HZSM-5 of an average particle size of 4 μm and four ball-milled samples with their average particle sizes being 1.9, 1.0, 0.5 and 0.2 μm, respectively, were prepared using conventional impregnation method, characterized using XRD, BET, 27Al MAS NMR, NH3-TPD, H2-TPD, TPO and TG techniques, and tested at 1073 K and a wide range of space velocities from 5000 to 20,000 ml/h/g. XRD and NH3-TPD measurements revealed that both crystallinity and Brønsted acidity of the ball-milled sample became lower and lower as the average particle size decreased in the range of <1.9 μm. For this reason the catalysts based on the milled samples with the average particle sizes of 1.0, 0.5 and 0.2 μm, respectively, all showed lower Mo dispersions and fewer free acid sites than the parent zeolite-based catalyst, predicting their lower activities in CH4 dehydroaromatization. Activity evaluation tests, however, demonstrated that the maximum benzene formation activities of the catalysts based on the milled samples having the average particle sizes of 1.0 and 0.5 μm, respectively, were higher than that observed over the parent zeolite-based catalyst at 1073 K and 10,000 ml/h/g, and the differences in the maximum benzene formation activity between the former two catalysts and latter one enlarged with increasing space velocity to 20,000 ml/h/g. Simultaneously, NH3-TPD measurements also revealed that little reduction in population and strength of Brønsted acid sites occurred for the zeolite sample softly milled and having the relatively large size of 1.9 μm. Consequently, the catalyst prepared with this sample came to be fully comparable to that based on the parent zeolite in both Brønsted acidity and Mo dispersion. While this certainly suggests comparability of the activities of these two catalysts, activity evaluation tests showed again that there existed large differences between their activities, and the maximum benzene formation activity of the former catalyst based on the milled zeolite sample always kept higher than that of the latter based on the parent zeolite. All these indicate that use of the zeolites of small particle sizes with less resistance towards diffusion of formed benzene out of their short channels is certainly effective in making Mo/HZSM-5 catalyst to show its intrinsic maximum benzene formation activity. Hence, detailed discussions were made on an assumption that channel diffusion limitation existed at the tested conditions and all observations were reasonably explained.
Keywords: Methane dehydroaromatization; Mo/HZSM-5; Benzene; Diffusion resistance;
Ti-containing mesoporous silica for methylene blue photodegradation by Juan Matos; Andreína García; Sang-Eon Park (359-366).
Display Omitted▶ Ti-containing mesoporous silica prepared by microwave-assisted irradiation. ▶ Photodegradation of methylene blue on Ti-containing TUD-1 materials. ▶ Photo-active Ti-TUD-1 material in the visible range. ▶ Silica photo-assist the Ti in the photodegradation of methylene blue.Photodegradation of methylene blue (MB) on Ti-containing mesoporous silica prepared by microwave-assisted irradiation as a function of Si/Ti molar ratio was studied. The materials were characterized by N2 adsorption, XRD, UV–vis/DR, and TEM. All solids showed mesoporous textures with high surface areas, relatively small pore size diameters and large pore volume. XRD showed that framework of solids consists of amorphous silica. It was found that the lower the Si/Ti ratio the higher the photocatalytic activity. Under irradiation with a lamp with more photons from visible light the sample with a Si/Ti ratio equal to 10 showed a higher photoactivity than that of a commercial TiO2 photocatalyst. This result was in agreement with the UV–vis/DR spectra which showed that material with a Si/Ti = 10 has slightly higher energy band gap than that of commercial TiO2 suggesting that these materials behave as a photoactive semiconductor.
Keywords: TUD-1; Titanium; Photocatalysis; Methylene blue;