Applied Catalysis A, General (v.450, #C)
Editorial Board (CO2).
Continuous precipitation of Cu/ZnO/Al2O3 catalysts for methanol synthesis in microstructured reactors with alternative precipitating agents by Georg Simson; Eko Prasetyo; Stefanie Reiner; Olaf Hinrichsen (1-12).
.Display Omitted► Continuous preparation method of Cu catalysts using different micromixers presented. ► Systematic study includes variation of the precipitation conditions. ► Systematic study includes the use of different precipitating agents. ► Detailed characterization study of the precipitated Cu-based catalysts presented. ► High methanol synthesis activity of the catalysts synthesized in the micromixers.Ternary Cu/ZnO/Al2O3 catalyst systems were systematically prepared by innovative synthesis routes in microstructured synthesis setups, allowing to study different types of micromixers. The coprecipitation in the slit plate and valve-assisted mixers was operated continuously under exact control of pH, temperature, concentration and ageing time. Due to the enhanced surface to volume ratio in microstructured reactors, a precise temperature control and efficient mixing of the reactants are enabled. The precipitation was performed with sodium, ammonium and potassium carbonate as well as sodium hydroxide. To evaluate the potential of the novel synthesis routes, reference samples in a conventional batch process were prepared. The catalysts were synthesized according to the constant pH method with a molar ratio of 60:30:10 for copper, zinc and aluminum. The synthesis routes applied have a significant influence on the structures of hydroxycarbonate precursors and on the catalytic activity in methanol synthesis. XRD patterns of hydroxycarbonate precursors from the synthesis in micromixers, especially using ammonium carbonate as precipitating agent, display high crystallinity and sharp reflections of malachite and rosasite. Cu/ZnO/Al2O3 catalysts prepared in continuously operated micromixers in general show higher specific copper surface areas than catalysts prepared in conventional batch processes. The highest methanol productivity of all prepared catalyst systems was observed with the catalyst precipitated in the slit plate mixer with ammonium carbonate.
Keywords: Continuous precipitation; Microstructured mixers; Hydroxycarbonate precursors; Cu/ZnO/Al2O3 catalysts; Methanol synthesis;
Palladium supported on natural phosphate: Catalyst for Suzuki coupling reactions in water by Ayoub Hassine; Saïd Sebti; Abderrahim Solhy; Mohamed Zahouily; Christophe Len; Mohamed Nejib Hedhili; Aziz Fihri (13-18).
Display Omitted► The natural phosphate-supported palladium can provide a suitable catalyst for Suzuki coupling reactions. ► This heterogeneous catalyst displayed high catalytic activity for Suzuki coupling reactions. ► This catalyst can be simply recovered and reused without any significant loss of catalytic activity. ► No leaching was observed of the catalyst. ► The novelty of the system lies in its low cost and availability of the solid support.The Suzuki–Miyaura coupling reaction is one of the most important synthetic catalytic reactions developed in the 20th century. However, the use of toxic organic solvents for this reaction still poses a scientific challenge and is an aspect of economical and ecological relevance. The use of water as a reaction medium overcomes this issue. In the present work, we described efficient Suzuki coupling reactions in water, without any phase transfer reagents and it is possible to couple challenging substrates like aryl chlorides. Notably, this protocol also works with ultra-low loading of catalyst with high turnover numbers.
Keywords: Natural phosphate; Palladium; Supported catalysts; Suzuki coupling reactions;
Preparation and characterization of mesoporous Cs2HPW12O40 salt, active in transformation of m-xylene by L. Matachowski; A. Drelinkiewicz; R. Rachwalik; M. Zimowska; D. Mucha; M. Ruggiero-Mikołajczyk (19-27).
Display Omitted► Reagent used for Cs2HPW12O40 precipitation influences its textural properties. ► Strong increase of specific surface area of Cs2HPW12O40 salt after HBr addition. ► Higher activity of Cs2HPW12O40 prepared with CsBr and CsI than Cs2.5H0.5PW12O40 salt.The samples of Cs2HPW12O40 salt were precipitated with CsCl, CsBr or CsI reagent as well as with commonly used Cs2CO3. The use of cesium halides resulted in the Cs2HPW12O40 samples of mesoporous structure composed of relatively loosely aggregated primary particles. It was observed that the type of halogen ion influenced textural properties of the Cs2HPW12O40 samples. As the atomic size of halogen ion increased (from Cl to I), the specific surface area and microporosity decreased. The so-obtained samples exhibited textural and morphological features similar to those of Cs2.5H0.5PW12O40 salt. In the transformation of m-xylene, the pore-size sensitive reaction, the catalytic activity of the Cs2HPW12O40 samples prepared with CsBr and CsI reagents was about two-fold higher than that of Cs2.5H0.5PW12O40 salt. All these samples exhibited similar strength of acid sites. Therefore, high catalytic activity of the samples prepared with CsBr and CsI could be ascribed to their open pore structure, which allowed the accessibility of almost all active sites for m-xylene molecules.
Keywords: Cesium heteropolysalts; Cesium halides; Mesoporous structure; Catalytic activity; m-Xylene transformation;
Simultaneous production of aromatic aldehydes and dihydrogen by photocatalytic dehydrogenation of liquid alcohols over metal-loaded titanium(IV) oxide under oxidant- and solvent-free conditions by Kazuya Imamura; Hikaru Tsukahara; Kenta Hamamichi; Naoko Seto; Keiji Hashimoto; Hiroshi Kominami (28-33).
Display Omitted► Photocatalytic conversion of aromatic alcohols in CH3CN suspensions of Pt–TiO2 was examined. ► Benzyl alcohol (BnOH) was quantitatively converted to benzaldehyde (PhCHO) and H2. ► Apparent quantum efficiency of the conversion reached 38% at 366 nm. ► An oxygen-free condition was important for quantitative conversion of BnOH to PhCHO. ► Photocatalytic dehydrogenation of BnOH occurred even in a solvent-free condition.Photocatalytic conversion of aromatic alcohols in acetonitrile (CH3CN) suspensions of metal-loaded titanium(IV) oxide under various conditions was examined. Benzaldehyde (PhCHO) and hydrogen (H2) were simultaneously produced with a molar ratio of 1:1 from benzyl alcohol (BnOH) in CH3CN suspensions of platinum-loaded titanium(IV) oxide (Pt–TiO2) under deaerated conditions and BnOH was converted quantitatively with high apparent quantum efficiency of 38% at 366 nm. The yield of PhCHO in dehydrogenation under deaerated conditions (>99%) was much higher than that (53%) obtained by dehydrogenation of BnOH in the presence of oxygen accompanying the formation of water instead of H2. When a small amount of water was intentionally added to the CH3CN suspension of Pt–TiO2, reaction rates of hydrogenation drastically decreased. Control experiments carried out under air and in the presence of water indicated that an oxygen-free condition was important for quantitative conversion of BnOH to PhCHO in two points, i.e., the reaction under oxygen-free conditions yields no water and active oxygen, that caused drastic decrease in the reaction rate and undesired oxidation of BnOH and PhCHO, respectively. Photocatalytic dehydrogenation of BnOH to PhCHO occurred even in a solvent-free condition in which Pt–TiO2 particles were suspended in BnOH. Photocatalytic hydrogenation under deaerated conditions was applied for conversions of various aromatic alcohols to corresponding aldehydes.
Keywords: Photocatalyst; Titanium(IV) oxide; Dehydrogenation; Hydrogen production; Benzaldehydes; Benzyl alcohols;
Sulfonic acid functionalized MCM-41 as solid acid catalyst for tert-butylation of hydroquinone enhanced by microwave heating by Eng-Poh Ng; Siti Norbayu Mohd Subari; Olivier Marie; Rino R. Mukti; Joon-Ching Juan (34-41).
Display Omitted► SO3H-MCM-41 was prepared via sultone ring opening approach. ► SO3H-MCM-41 exhibited ordered mesoporous straight channels with SBET of 475 m2 g−1. ► The catalyst gave 88% conversion in tert-butylation reaction within 8 min under microwave irradiation. ► The catalyst gave 93% product selectivity to 2-tert-butyl hydroquinone.Covalently linked sulfonic acid (―SO3H) modified MCM-41 mesoporous catalysts was prepared, characterized and its catalytic activity under microwave irradiation was evaluated. The NH2-MCM-41 was first prepared by anchoring (3-aminopropyl)triethoxysilane (APTES) on Si-MCM-41 and further reacted with 1,4-butane-sultone to yield the desired acid catalyst. The mesophase and porosity of samples were determined by XRD, TEM and N2 sorption isotherm analyses. The presence of sulfonic acid moiety was confirmed by FT-IR, TG/DTA, sulfur elemental analysis and in situ IR study of pyridine and ammonia adsorptions. The catalyst showed high catalytic activity and high selectivity in tert-butylation of hydroquinone under microwave irradiation. No leaching problem was observed after several runs, while the catalyst can be recovered and reused without loss of reactivity under the described reaction conditions.
Keywords: Mesoporous material; Sulfonation; Sulfonic acid; tert-Butylation; Microwave synthesis;
Porous Co3O4 nanowires and nanorods: Highly active catalysts for the combustion of toluene by Guangmei Bai; Hongxing Dai; Jiguang Deng; Yuxi Liu; Fang Wang; Zhenxuan Zhao; Wenge Qiu; Chak Tong Au (42-49).
Display Omitted► Porous Co3O4 nanowires and nanorods are prepared by hydrothermal or microemulsion method. ► Porous Co3O4 nanowires and nanorods are higher in Oads content and better in reducibility. ► Porous Co3O4 nanowires and nanorods exhibit high catalytic performance for toluene combustion. ► Catalytic activity is governed by surface area, Oads content, and reducibility.Porous Co3O4 nanowires and nanorods (Co3O4-HT, Co3O4-HT-PEG, Co3O4-HT-CTAB, and Co3O4-ME-CTAB, respectively) have been fabricated via the hydrothermal or microemulsion route in the absence and presence of polyethylene glycol (PEG) or cetyltrimethylammonium bromide (CTAB), respectively. Physicochemical properties of the materials were characterized by means of numerous techniques, and their catalytic activities for toluene combustion were evaluated. It is shown that Co3O4-HT-PEG and Co3O4-HT-CTAB displayed a porous nanowire-like morphology, whereas Co3O4-ME-CTAB exhibited a porous nanorod-like shape. The porous Co3O4 samples (surface area = 47–52 m2/g) possessed much higher surface oxygen adspecies concentrations and much better low-temperature reducibility than the nonporous counterpart. The Co3O4-HT-CTAB sample showed the highest catalytic performance (T 50% = 195 and T 90% = 215 °C at a space velocity of 20,000 mL/(g h)). It is concluded that the excellent catalytic performance of Co3O4-HT-CTAB was associated with its higher surface area and surface oxygen species concentration, and better low-temperature reducibility.
Keywords: Porous Co3O4; One-dimensional material; Hydrothermal synthesis method; Microemulsion synthesis method; Toluene combustion;
Gas-phase S-alkylation of benzenethiol with aliphatic alcohols, ethers, esters, alkyl halides and olefins over halide cluster catalysts of Groups 5 and 6 transition metals by Sayoko Nagashima; Kentaro Kudo; Hitomi Yamazaki; Satoshi Kamiguchi; Teiji Chihara (50-56).
.Display Omitted► Halide clusters are versatile catalysts for the S-alkylation of benzenethiol. ► The gas-phase catalysis proceeds above 200 °C without any solvents or additives. ► Alcohols, ethers and esters are preferable for the cases of shorter alkyl chains. ► Olefins and alkyl halides are preferable for the cases of longer alkyl chains.Benzenethiol was reacted with methanol under a hydrogen stream over [(Nb6Cl12)Cl2(H2O)4]·6H2O supported on silica gel. Catalytic activity of the cluster commenced above 250 °C, yielding methyl phenyl sulfide. The selectivity was 98% at 400 °C. Molybdenum, tantalum and tungsten halide clusters with the same octahedral metal framework also catalyzed the reaction. Primary alcohols with shorter alkyl chains were effective reagents for the S-alkylation. Aliphatic ethers, dialkyl carbonates, orthoesters and alkyl halides were effective reagents for the S-alkylation. When 1-hexene was applied to the reaction, spontaneous and catalytic S-alkylation proceeded simultaneously above 200 °C, yielding n-hexyl phenyl sulfide. When alkyl acetates were subjected to this reaction, the niobium cluster afforded S-phenyl thioacetate, and the other clusters afforded alkyl phenyl sulfides selectively. A Brønsted acid site attributable to a hydroxo ligand, which is formed on the cluster complex by thermal activation, is proposed as the active site of the catalysts.
Keywords: S-Alkylation; Benzenethiol; Sulfide; Thioacetate; Halide cluster;
A highly active clay-based catalyst for the synthesis of fatty acid methyl ester from waste cooking palm oil by M.A. Olutoye; B.H. Hameed (57-62).
Display Omitted► Heterogeneous catalytic reaction with clay and waste cooking palm oil was applied to synthesis methyl esters. ► A thermally treated clay catalyst showed high activity to methyl esters. ► Simple preparation, characterization, and reusability of clay heterogeneous catalyst. ► Catalytic transesterification employed converted waste resources to useful product. ► The recovered catalyst was used in successive reactions with nearly stable conversions.Local clay was prepared, characterized and used as catalyst for the synthesis of fatty acid methyl esters from waste cooking palm oil. Calcined raw clay at various temperatures was investigated and showed good activity for transesterification reaction when samples were treated at 830 °C for 4 h. The effects of parameters affecting the catalytic reaction, methanol to oil ratio, catalyst loading and reaction temperature in the range of 150–170 °C were investigated at fixed reaction time of 5 h. The obtained data showed that at methanol/oil ratio of 15:1, catalyst loading of 3.5 wt% and reaction temperature of 150 °C, the FAME content from the process was 96%. The catalyst is easily prepared and handled, avoiding the use of expensive rare earth metals in biodiesel production, easily separated from the reaction medium and could be reused up to three cycles.
Keywords: Clay catalyst; Heterogeneous reaction; Waste cooking palm oil; Transesterification;
Improved activity and coke resistance by promoters of nanosized trimetallic catalysts for autothermal carbon dioxide reforming of methane by Annabathini Geetha Bhavani; Won Yong Kim; Jae Yul Kim; Jae Sung Lee (63-72).
Display Omitted► Highly active and stable trimetallic catalysts with promoters for autothermal CO2 reforming. ► The Ce-promoted NiCoMn/ZrO2 catalyst displayed the highest activity and stability. ► Nano-sized active metals and increased basic sites by promoters suppressed coking.Autothermal carbon dioxide reforming of methane was studied over trimetallic NiCoMn/ZrO2 catalyst promoted with different promoters (Ce, La, Ca, K) aiming to improve the performance of the catalyst and increase their resistance to coking. The promoted catalysts prepared by a coprecitation method showed metal sizes less than 10 nm and were studied with a CH4:CO2:O2 mole ratio of 1:0.8:0.2 at 800 °C under atmospheric pressure. The addition of promoters to NiCoMn/ZrO2 catalyst markedly improved CH4 and CO2 conversions as well as selectivities to H2 and CO relative to the unprompted catalyst. Rare earths Ce and La were more effective promoters than alkaline earth (Ca) and alkali metal (K), showing high and stable CO2 conversions of 95.5% and 89.9%, respectively. The promoted catalysts exhibited higher activity and improved stability with no severe coke deposition and the Ce-promoted NiCoMn/ZrO2 catalyst displayed the highest activity with no apparent activity loss. The roles of the promoters were discussed based on the results of various physicochemical characterization techniques.
Keywords: Trimetallic catalysts; Promoters; Autothermal reforming; Carbon dioxide; Coke resistance;
Simultaneous production of hydrogen and carbon nanostructured materials from ethanol over LaNiO3 and LaFeO3 perovskites as catalyst precursors by Jaime Gallego; Fanor Mondragon; Catherine Batiot-Dupeyrat (73-79).
.Display Omitted► LaFeO3 is reduced in situ under ethanol at 900 °C. ► With LaNiO3 as catalyst precursor, multiwalled carbon nanotubes are produced. ► With LaNiO3 higher yields are obtained at 700 °C compared to 900 °C. ► Twisted nanofibers are produced at 900 °C with LaFeO3.The simultaneous production of hydrogen and carbon materials from ethanol was studied using the perovskites LaNiO3 and LaFeO3 as catalyst precursors. The reaction was performed at temperatures between 700 °C and 900 °C with ethanol concentration of 50 vol%. Using LaNiO3, the yield of carbon materials is maximum at low temperature due to the presence of dense carbon like nanofibers while at higher temperatures, multiwalled carbon nanotubes are produced. A reaction temperature of 900 °C is necessary to obtain hydrogen and carbon materials with LaFeO3. The hydrogen yield reaches 16.2 L per hour and per gram of catalyst, hydrogen representing 70% in volume of the products in gas phase while methane is only 3.6%. We show that the perovskite LaFeO3 is reduced in situ under ethanol leading to the formation of Fe0 and Fe3C responsible for the carbon growth. A scheme is proposed for the growth of carbon material from the species obtained by LaFeO3 reduction. The morphology of carbon materials depends on the nature of the catalyst, MWCNTs are produced from LaNiO3 as catalyst precursor while twisted nanofibers are obtained from LaFeO3 at 900 °C.
Keywords: Perovskite; Hydrogen production; Carbon nanostructured materials; Ethanol decomposition;
Activity and deactivation nature of Ru/MnCO3 catalysts for Fischer–Tropsch reaction by Isao Takahara; Kazuhisa Murata; Kazuhito Sato; Yasutomo Miura; Megumu Inaba; Yanyong Liu (80-87).
Display Omitted► Chloride-free Ru/MnCO3 was synthesized as catalysts for Fischer–Tropsch synthesis (FTS). ► Ru/MnCO3 shows high activity under low pressure conditions below 1 MPa. ►Metallic Ru particle sizes remained constant after 120 h-FTS reaction. ► The origin of catalyst deactivation was explained in terms of the extent of hydrocarbon deposition.The catalytic activities and different behaviors for catalyst deactivation by forming surface hydrocarbon deposits were investigated on the Cl-free Ru/MnCO3 Fischer–Tropsch synthesis (FTS) catalysts in a low pressure fixed-bed reactor. Catalytic activity of LT-Ru(NO) was found to be a little higher than that of Ru(NO). The differences seem to stem mainly from ruthenium particle sizes and reduction behavior of adsorbed CO on the catalysts, which would be consistent with the results of CH4 formation from temperature-programmed reduction (TPR) of pre-adsorbed CO, as well as Ru particle sizes, as ascertained by H2 and CO adsorptions and TEM measurements. The Ru particle sizes of used catalysts obtained after 120 h-reaction were approximately close to those of fresh catalysts and no ruthenium aggregation occurred. The origin of catalyst deactivation was investigated in terms of the extent of hydrocarbon deposition. The adsorbed atomic carbon at the peak temperature around 250–350 °C was eliminated by H2 treatment, but the more heavy hydrocarbons at peak temperature over 400 °C such as polymeric and graphitic carbons were not removed by any treatment. The nature of hydrocarbon deposition would be suggested by measuring the deposited carbon with the help of the characterizations, such as thermo-gravimetric analysis, temperature-programmed reduction and diffuse reflectance infrared Fourier transform (FT-IR) measurements.
Keywords: Fischer–Tropsch synthesis; Deactivation; Ruthenium; Manganese carbonate support;
Effects of surface modification with zirconium phosphate on Ru/Co/SiO2 Fischer–Tropsch catalysts analyzed by XPS and TEM analyses by In Hyeok Jang; Soong Ho Um; Byungkwon Lim; Min Hee Woo; Ki-Won Jun; Jong-Bae Lee; Jong Wook Bae (88-95).
Display Omitted► The zirconium phosphate modification on Ru/Co/SiO2 FTS catalysts were investigated by XPS and TEM. ► The catalyst deactivation is attributed to the aggregation of cobalt clusters. ► The zirconium phosphate-modified SiO2 enhances catalytic stability by spatial confinement of cobalt clusters.The effects of surface modification with zirconium phosphate on cobalt-based Fischer–Tropch synthesis (FTS) catalyst to the enhanced catalytic stabilities were explained with the help of the surface sensitive X-ray photoelectron spectroscopy (XPS) and transmission electron spectroscopy (TEM) on the reacted catalysts at three different periods of reaction duration such as 10, 30 and 70 h on stream. The catalyst deactivation was significantly attributed to the aggregation of cobalt clusters at the very beginning of reaction, and the modification of SiO2 surface with the proper amount of zirconium phosphate largely suppressed cobalt aggregation during the reaction period of 70 h. The enhanced catalytic stability is attributed to the homogeneous distribution of cobalt clusters with a low mobility by being confined in the thermally stable zirconium phosphate matrices on SiO2 surface. The roles of zirconium phosphate on catalytic stability are mainly explained by analyzing the relative dispersion of zirconium phosphate as well as cobalt clusters on SiO2 surface with time on stream.
Keywords: Fischer–Tropsch synthesis; Cobalt; Zirconium phosphate; Aggregation; SiO2; Catalytic stability;
Degradation of Acid Blue 29 in visible light radiation using iron modified mesoporous silica as heterogeneous Photo-Fenton catalyst by Ai Ni Soon; B.H. Hameed (96-105).
Display Omitted► Effective mesoporous solid Fe-SiO2 catalyst was developed using sodium silicate as silica support. ► Fe3+ occluded in the alternative silicate support serves as active center for degradation recalcitrant Acid Blue 29. ► Visible light photocatalytic activity of the heterogeneous catalyst is more cost-efficient with high performance. ► The catalyst is reusable over four consecutive cycles and minimal leaching of iron ions.The evaluation of heterogeneous Fenton degradation on dye pollutant, Acid Blue 29 (AB29), has been investigated. The solid catalyst prepared by both sol–gel and incipient wetness impregnation methods was developed by occlusion of Fe3+ ions on synthesized mesoporous silica from sodium silicate. The prepared catalysts were characterized for their textural and surface morphology. High concentration of soluble metal precursor with 8.0 wt% Fe3+ can be easily deposited on silica. The results showed that the Fe-SiO2 catalyst demonstrated good performance in the degradation of 50 ppm Acid Blue 29 (AB29) which was nearly completed in 100 min under visible light irradiation with optimum operating conditions at 0.4 g Fe-SiO2/L, pH 3.0 and 10 mM H2O2. A possible mechanism on visible light irradiated Fenton process was proposed. The catalyst is reusable over four consecutive cycles and minimal leaching of iron ions (<0.5 ppm) was observed.
Keywords: Heterogeneous Photo-Fenton; Degradation; Fe-SiO2; Sodium silicate;
Highly reactive magnetite covered with islands of carbon: Oxidation of N and S-containing compounds in a biphasic system by Iara R. Guimarães; Amanda S. Giroto; Wladmir F. de Souza; Mário C. Guerreiro (106-113).
Display Omitted► Heterogeneous oxidation of N and S organic compounds using amphiphilic catalyst. ► Magnetite covered with islands of carbon: an amphiphilic catalyst as a promising strategy. ► Amphiphilic catalyst presented high catalytic activity for oxidation of quinoline and DBT.In this work a series of magnetite were prepared by impregnating of natural goethite (limonite) with glycerol before thermal treatment under N2 flow at 300, 400 and 500 °C. The formation of carbon spots (island) over magnetite was found. The magnetite was found to be the main phase after treatment at 400 and 500 °C with high content of Fe2+, which is the active specie in a Fenton like system. Furthermore, iron oxide particles with magnetic and amphiphilic properties were formed, which are interesting for using as a catalyst in refineries. All materials presented high catalytic activities for oxidation of quinoline and dibenzothiophene in a biphasic reaction system (water/toluene).
Keywords: Limonite; Glycerol; Amphiphilic catalyst; Oxidative process;
Investigation of biodiesel production by HUSY and Ce/HUSY zeolites: Influence of structural and acidity parameters by Luciana D. Borges; Nayara N. Moura; Andréia A. Costa; Patrícia R.S. Braga; José A. Dias; Sílvia C.L. Dias; Julio L. de Macedo; Grace F. Ghesti (114-119).
Display Omitted► HUSY and Ce/USY zeolites were active catalysts for biodiesel production. ► Impregnation with cerium leads to an acid and structural stability. ► Biodiesel production for Ce/HUSY was kept above 99% during three reaction cycles. ► A distinct biodiesel profile was produced by the zeolites due to side reactions. ► The biofuel showed high ester content and no change in its calorific power.In this work, activities of HUSY and Ce/HUSY zeolites were studied in transesterification cycles of soybean oil and ethanol to produce biodiesel. The characterization of the materials was performed by FT-IR, XRD, BET method and pyridine adsorption followed by thermal analyses. TG/DTG results indicated a decrease of acid sites for both samples after each reaction cycle. However, Ce/HUSY zeolite showed a superior stabilization of acidic sites after three catalytic cycles and intermediary activation procedures. Biodiesel production exhibited high conversion levels (>96%) for both zeolites in all transesterification cycles. Surface area and pore volume measurements evidenced that cerium incorporation reduced the number of acid sites by interacting with OH groups in the micropore and external area of the zeolitic surface. This interaction resulted in an acid and structural stability, which provided a better activity (99%) than HUSY (96%). The higher conversion values obtained by zeolites showed a final product with a different distribution when compared with the traditional transesterification process. The identification of free fatty acids, diethyl and glycerol ethers in the final products and the reduction of unsaturated compounds indicated that parallel reactions also occurred in the studied systems. Nonetheless, the biofuel produced showed high ester content and did not present changes in its calorific power.
Keywords: Biodiesel; Transesterification; USY zeolite; Cerium; Catalytic cycles;
VO x /c-Al2O3 catalyst for oxidative dehydrogenation of ethane to ethylene: Desorption kinetics and catalytic activity by S. Al-Ghamdi; M. Volpe; M.M. Hossain; H. de Lasa (120-130).
Display Omitted► We developed a 10 wt.% VO x supported on c-Al2O3 fluidizable catalyst. ► We studied ODH in a fluidized bed in an O2-free atmosphere at 500–600 °C. ► Reactivity tests gave 6.5–27.6% ethane conversion and 57.6–84.5% ethylene selectivity. ► We used TPR and TPO to show catalyst stability over repeated reduction–oxidation cycles. ► We employed ammonia TPD to assess VO x –support interaction.This study reports ethane oxidative dehydrogenation (ODH) using lattice oxygen. Ethane ODH is studied under an oxygen-free atmosphere employing a 10 wt.% VO x supported on c-Al2O3. TPR and TPO show that the prepared 10 wt.% VO x supported on c-alumina catalyst is a stable catalyst over repeated reduction and oxidation cycles. XRD shows the absence of V2O5 bulk surface species and a high dispersion of VO x on the support surface. Experiments are carried out in the CREC Fluidized Bed Riser Simulator at 550–600 °C and pressures close to atmospheric conditions. Reactivity tests show that the prepared ODH catalyst displays 6.5–27.6% ethane conversion and 57.6–84.5% ethylene selectivity in the 550–600 °C range. Metal–support interaction is assessed using ammonia TPD. This provides the desorption energy for both the bare c-Al2O3 support and for the VO x /c-Al2O3 catalyst. A slightly increased desorption energy is found when using the V-loaded catalyst. This shows low metal–support interactions and as a result, a well dispersed VO x catalyst phase with high availability of lattice oxygen for ODH. These findings are confirmed with XRD, showing no changes with respect to the XRD for the c-Al2O3 alumina support. This proves that there are no other species formed due to the interaction between the VO x surface species and the Al2O3 support.
Keywords: NH3-TPD kinetics; Oxidative dehydrogenation; Ethylene; Vanadium oxide; Lattice oxygen; Riser simulator;
Synthesis of CeO2 and CeZrO2 mixed oxide nanostructured catalysts for the iso-syntheses reaction by Raimundo Crisostomo Rabelo Neto; Martin Schmal (131-142).
Display Omitted► Selective conversion of synthesis gas on metal oxides producing isobutene/ane. ► Preparation methods of nanosized structure of CeO2 and mixed oxide CeZrO2. ► Mixed oxide presented the strongest basic sites and the highest selectivity to iso-C4. ► Ceria and ceria doped with zirconia promoted different Brönsted and Lewis sites. ► Significant is the influence of Lewis acid sites on the selectivity of isobutene and isobutane.The different CeO2 oxides and mixed oxide CeZrO2 showed nanosized structures and morphologies in particular distinct structural and surface properties. These catalysts were effective in the iso-synthesis reaction. The flowerlike CeO2 (F) and the mixed oxide (CeZrO2) showed the highest selectivity toward isobutene and isobutene and low methane formation. The turnover frequency (TOF) related to the total basicity and total acid sites are equal for all catalysts within a factor less than 2 and did not change with the oxygen lattice capacity (OSC), which confirms that the reaction is structure insensitive. The selectivity of total hydrocarbon and of CO2 are independent of the basic sites. However, the selectivity of total iso-C4 exhibits a linear relationship with the basic sites. The mixed oxide (CeZrO2) presented the strongest basic sites and thus the highest selectivity to iso-C4. Significant is the influence of Lewis acid sites on the selectivity of isobutene increasing and isobutane decreasing both linearly with Lewis acid sites. The ratio isobutene/isobutane presented a linear relationship with the Lewis acid sites which are directly related to OSC capacity of reducible oxides.
Keywords: Iso-synthesis; Cerium oxide; Mixed oxide CeZrO2; Isobutene/ane;
Catalytic oxidation of 1,2-dichlorobenzene over CaCO3/α-Fe2O3 nanocomposite catalysts by Xiaodong Ma; Quan Sun; Xi Feng; Xuan He; Jie Guo; Hongwen Sun; Huiqin Cao (143-151).
Display Omitted► Low-cost and environmentally friendly CaCO3/α-Fe2O3 nanocomposites were synthesized. ► Catalytic oxidation of 1,2-dichlorobenzene was carried out as a model reaction. ► Nanocomposite with 9.5 mol% Ca showed the highest catalytic activity. ► In situ FTIR studies were performed simulating the conditions of reactivity test. ► A two-step redox mechanism of decomposition of 1,2-dichlorobenzene was proposed.CaCO3/α-Fe2O3 nanocomposites were synthesized by one-pot method to develop a low-cost and environmentally friendly technology for the catalytic oxidation of 1,2-dichlorobenzene (o-DCB), a model of chlorinated volatile organic compounds. The nanocomposites were characterized by FAAS, XRD, N2 adsorption/desorption, TEM and XPS. Activity measurements were conducted in the range of 200–500 °C, in both the presence and absence of water. Among the tested catalysts, the nanocomposite with 9.5 mol% Ca showed the highest catalytic activity, which could be attributed to the promoting effect of CaCO3 on α-Fe2O3 with smaller crystallite size. Experimental results in the presence of water indicated that, due to the competitive adsorption of water on the active sites, there was a local minimum of catalytic activity at 350 °C. In situ FTIR experimental results revealed the presence of phenolate, catecholate, o-benzoquinone, carboxylate and anhydride type species on the surfaces of the catalysts during the oxidation of o-DCB. Spectral evidence discovered that the formate species were more prone to being formed on the surface of nanocomposite with 9.5 mol% Ca and then were further oxidized to CO, which directly lead to high activity of the catalyst. A mechanism involving dissociative adsorption of o-DCB on the surface of catalyst was proposed.
Keywords: Chlorinated volatile organic compounds; 1,2-Dichlorobenzene; Catalytic oxidation; CaCO3; Fe2O3;
Micro-mesoporous composite molecular sieves H-ZSM-5/MCM-41 for methanol dehydration to dimethyl ether: Effect of SiO2/Al2O3 ratio in H-ZSM-5 by Hansheng Li; Shichao He; Ke Ma; Qin Wu; Qingze Jiao; Kening Sun (152-159).
Display Omitted► We prepare H-ZSM-5/MCM-41 by hydrothermal method with alkali-treated ZSM-5 as source. ► H-ZSM-5/MCM-41 has ordered micropores and mesopores. ► Acid sites and amount distribution of H-ZSM-5/MCM-41 can be controlled by SiO2/Al2O3 ratio. ► H-ZSM-5/MCM-41 presents high activity and high DME selectivity.Micro-mesoporous composite molecular sieves H-ZSM-5/MCM-41 were prepared by the hydrothermal technique with alkali-treated H-ZSM-5 zeolite as source and characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, X-ray diffraction, N2 adsorption and desorption measurement, and NH3 temperature-programmed desorption. The effect of SiO2/Al2O3 ratio in H-ZSM-5 on the structure, surface acidity and catalytic performances of H-ZSM-5/MCM-41 for methanol dehydration to dimethyl ether were investigated. H-ZSM-5/MCM-41 prepared with H-ZSM-5 of different SiO2/Al2O3 ratios as source in which H-ZSM-5 nanoparticles were uniformly dispersed in MCM-41 matrix, had well-ordered micropores and mesopores. The acid amount and strength of moderate acid sites (T P1) of H-ZSM-5/MCM-41 can be controlled by the SiO2/Al2O3 ratio in H-ZSM-5 during the range from 25 to 50. Among these catalysts, H-ZSM-5/MCM-41 presented a comparable catalytic activity to the corresponding pure H-ZSM-5 and 100% dimethyl ether selectivity in a wider temperature range than the corresponding pure H-ZSM-5. The excellent catalytic performances were due to the highly active and uniform strong acid sites and the hierarchical porosity in the micro-mesoporous composite molecular sieves. The catalytic mechanism of H-ZSM-5/MCM-41 for the methanol dehydration to dimethyl ether was also discussed.
Keywords: Hierarchical porosity; H-ZSM-5; Composite molecular sieve; Methanol dehydration; Dimethyl ether;
Effect of (Zn(OH)2)3(ZnSO4)(H2O)5 on the performance of Ru–Zn catalyst for benzene selective hydrogenation to cyclohexene by Hai-jie Sun; Hong-xia Wang; Hou-bing Jiang; Shuai-hui Li; Shou-chang Liu; Zhong-yi Liu; Xue-min Yuan; Ke-jian Yang (160-168).
Display Omitted► The Zn in Ru–Zn catalyst existed as ZnO that was rich on the catalyst surface. ► The ZnO on the surface could react with ZnSO4 to form a (Zn(OH)2)3(ZnSO4)(H2O)5 salt. ► The salt chemisorbed improved the selectivity to cyclohexene of Ru–Zn catalyst. ► The pretreated Ru–Zn(8.6%) catalyst gave a cyclohexene yield of 58.9% and had a excellent stability.A series of Ru–Zn catalysts with different Zn contents were prepared by co-precipitation. The catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) – Ar+ sputter, transmission electron micrographs (TEM)–energy dispersion scanning (EDS) and temperature-programmed reduction (TPR). The performances of the catalysts for benzene selective hydrogenation to cyclohexene were investigated in the presence of 0.6 mol/L of ZnSO4. The results showed that the Ru and Zn in Ru–Zn catalyst were in metallic Ru and ZnO respectively and the ZnO was rich on the surface. The ZnO alone could not improve the selectivity to cyclohexene of Ru–Zn catalyst. However, the ZnO on the surface could react with ZnSO4 to form a (Zn(OH)2)3(ZnSO4)(H2O)5 salt. The (Zn(OH)2)3(ZnSO4)(H2O)5 salt chemisorbed played a key role in improving the selectivity to cyclohexene of Ru–Zn catalysts. After Ru–Zn(8.6%) catalyst was pretreated 22 h in ZnSO4 solution at 140 °C and 5 MPa H2, a cyclohexene selectivity of 81.4% at a benzene conversion of 54.0% was achieved at 10 min and a maximum cyclohexene yield of 58.9% was reached. Moreover, the activity was stable above 50% and the cyclohexene selectivity and yield were steadily above 76% and 40% on this catalyst in the first six recycles, respectively.
Keywords: Benzene; Selective hydrogenation; Cyclohexene; Ruthenium; Zinc;
Total oxidation of naphthalene using bulk manganese oxide catalysts by Tomas Garcia; David Sellick; Francisco Varela; Isabel Vázquez; Ana Dejoz; Said Agouram; Stuart H. Taylor; Benjamin Solsona (169-177).
Display Omitted► Manganese oxide prepared by nanocasting is highly active for Naphthalene oxidation. ► The reducibility in Mn2O3 catalysts increases when the surface area increases. ► Catalytic activity is linked to the reducibility and mobility of lattice oxygen. ► Mn2O3 presents a higher intrinsic activity for naphthalene oxidation than MnO2.Several Mn2O3 catalysts have been synthesized using different preparation methods and tested for the total oxidation of naphthalene, a model polycyclic aromatic compound. The catalysts have been characterized by several physico-chemical techniques such as XRD, TPR, XPS, EDX and TEM. The surface area of the catalyst seems to be of paramount importance, since the mass normalized activity of catalysts increases as the surface area of the Mn2O3 catalysts increases. Consequently, a high surface area ordered mesoporous Mn2O3 catalyst, obtained through a nanocasting route using mesoporous KIT-6 silica as a hard template, was the most efficient catalyst for the deep oxidation of naphthalene. In addition, this catalyst also exerts the highest surface area normalized catalytic activity, which can be related to the highest reducibility and mobility of its lattice oxygen. It was also observed that the Mn2O3 crystalline phase presents a higher intrinsic activity than MnO2.
Keywords: Naphthalene; Polycyclic aromatic compound; PAH; Manganese oxide; Total oxidation; Nanocasting;
Establishing the role of Brønsted acidity and porosity for the catalytic etherification of glycerol with tert-butanol by modifying zeolites by María Dolores González; Yolanda Cesteros; Pilar Salagre (178-188).
Display Omitted► Beta catalysts were more active than ZSM-5 and mordenite catalysts. ► The introduction of fluorine in zeolites led to higher amounts of stronger acid sites. ► The amount and strength of Brønsted acid sites mainly affected glycerol conversion. ► Fluorinated beta allowed the formation of glycerol triether in low amounts.The role of Brønsted acidity and porosity for the etherification of glycerol with tert-butanol was studied by modifying the surface and acidic characteristics of three commercial Na-zeolites (mordenite, beta and ZSM-5) by protonation, dealumination, desilication-protonation, lanthanum-exchange and fluorination. Catalytic results can be related to the amount and strength of Brønsted acid sites together with the accessibility of the reactants to the acid sites. Modifications made on ZSM-5 did not affect considerably its surface and acidic properties, and consequently its catalytic behaviour, leading moderate conversion values and low/null selectivity to di- and tri-tertiary butyl ethers of glycerol (h-GTBE). Mordenite catalysts showed low conversion and moderate/low selectivity to h-GTBE due to the lower amount of acid centres, lower external surface area, more hydrophilic character and lower dimensionality of the mordenite structure when compared with the other two zeolites. Beta catalysts exhibited the best catalytic results. The introduction of fluorine in the beta zeolite framework generated higher amounts of stronger acid sites, which were able to transform glycerol until the glycerol triether. Thus, fluorinated beta yielded the best conversion (75%) and selectivity to h-GTBE (37%) with the formation of glycerol triether in low amounts. These values were comparable to those obtained at the same reaction conditions with an Amberlyst-15, an acid catalyst traditionally used for this reaction.
Keywords: Glycerol etherification; Zeolite; Fluorination; Desilication; Dealumination; Tert-butanol; Brønsted acid sites; Porosity;
Catalytic oxidation of crude glycerol using catalysts based on Au supported on carbonaceous materials by Sonia Gil; Miriam Marchena; Carmen María Fernández; Luz Sánchez-Silva; Amaya Romero; José Luís Valverde (189-203).
Display Omitted► Au/G catalyst showed higher catalytic activity than Au/CNF-R catalyst. ► CNS-based catalyst was the most active due to the presence of many open edges in the CNS. ► The liquid phase oxidation of glycerol catalyzed by carbon-supported Au is structure sensitive. ► Catalytic activity decreased with crude glycerol in reason of the presence of impurities. ► Catalytic activity with neutralized glycerol is comparable to that with commercial glycerol.Au catalysts supported on different carbon materials, such as graphite (G, 10 m2 g−1), ribbon-type carbon nanofibers (CNF-R, 109 m2 g−1), and carbon nanospheres (CNS, 3 m2 g−1), were prepared by the sol–gold method using tetrahydroxymethyl phosphonium chloride as the reducing agent. Different techniques were employed to characterize both the supports and the final Au catalysts: atomic absorption spectrometry, transmission electron microscopy, thermogravimetric analysis, X-ray diffraction, elemental analyses, N2 adsorption–desorption analysis, temperature-programmed reduction, and temperature-programmed decomposition. Au catalysts were tested in the liquid phase by selective oxidation of both commercial and crude glycerol, the latter obtained from the manufacture of biodiesel. Catalytic results obtained with commercial glycerol showed that the product distribution was dependent on the nature of the support and consequently on the Au particle size. The highest catalyst activity was achieved using highly crystalline carbon supports, supporting small-size (highly dispersed) Au particles. Accordingly the graphite-based catalyst exhibited higher catalytic activity than the CNF-R-based one. Catalytic results similar to those obtained with commercial glycerol were obtained when testing the stream resulting from a low cost neutralization procedure of the crude glycerol.
Keywords: Carbonaceous materials; Gold supported catalysts; Liquid-phase oxidation of glycerol; Crude glycerol; Purification;
Hybrid composites octyl-silica-methacrylate agglomerates as enzyme supports by Oscar Fernández; Isabel Díaz; Carlos F. Torres; Montserrat Tobajas; Víctor Tejedor; Rosa M. Blanco (204-210).
Display Omitted► Agglomeration of octyl silica particles led to obtain larger and handy beads. ► Enzyme loading capacity of agglomerates is very close to isolated particles. ► Catalytic activities of isolated and agglomerated biocatalysts are also very close. ► Diffusional restrictions do not increase in the larger size beads. ► Agglomeration keeps advantages of silica beads and improves applicability.The use of immobilized enzymes as catalysts may be limited by particle size which must be larger than the mesh that retains them in the reactor. Octyl-silica (OS) beads of 70 μm average size were agglomerated to obtain hybrid organic–inorganic composites with particle sizes between 100 and 200 μm. The agglomeration process has been achieved by polymerization of methacrylate from glycidyl methacrylate and ethylene dimethacrylate in the presence of silica beads and further functionalization of the composite with octyl groups.Methacrylate content of the composite (20%) is high enough to stick OS beads, and low enough to preserve the advantages of these particles as supports. The properties of the octyl silica particles for lipase immobilization have been very closely reproduced with the octyl-silica-methacrylate (OSM) composite. Enzyme loading of 210 mg lipase per gram of support has been achieved on OSM vs 230 mg/g on OS. Also catalytic activity values are close for both catalysts, OSM-lipase remaining fully active and stable after 15 cycles in acetonitrile.
Keywords: Enzyme immobilization; Particle agglomeration; Hydrophobic supports; Diffusional limitations; Hybrid composites;
Carbon nanofiber supports for the preparation of Pt-based metal nanoparticles with high tolerance to sintering by Sakae Takenaka; Atsuro Iga; Kayoung Park; Eishi Tanabe; Hideki Matsune; Masahiro Kishida (211-221).
Display Omitted► Carbon nanofiber (CNF) formed by methane decomposition over Ni catalyst. ► Formation of pore structures in CNF by the treatment with concentrated HNO3. ► The pore structures of CNF support prevent the sintering of Pt metal particles. ► Effective CNF supports for the formation of Pt-based alloy nanoparticles.Fishbone-typed carbon nanofibers (CNFs) that were formed by methane decomposition over silica-supported Ni catalysts were used as catalytic supports for Pt or Pt–Co alloy nanoparticles. The treatment of CNFs with concentrated HNO3 led to the formation of porous structures as well as to the introduction of oxygen-containing functional groups. Pt metal particles of a few nanometers in diameter could be stabilized on the CNFs treated with HNO3 and showed a high tolerance to sintering at high temperatures, whereas Pt metal particles supported on the CNFs without any treatment were seriously aggregated at high temperatures. The porous structures and functional groups in the CNFs worked as anchoring sites for Pt metal nanoparticles. Thus, Pt–Co alloy particles of a few nanometers in diameter could be prepared by using the CNF support since the CNFs inhibited the sintering of the alloy particles during the treatment at high temperatures to allow for alloy formation.
Keywords: Carbon nanofibers; Pt metal nanoparticles; Pt–Co alloy nanoparticles; Pore structures; Resistance to sintering;
Application of TiO2-containing mesoporous spherical activated carbon in a fluidized bed photoreactor—Adsorption and photocatalytic activity by Mi-Hwa Baek; Ji-Won Yoon; Ji-Sook Hong; Jeong-Kwon Suh (222-229).
Display Omitted► The meso-TiO2/SAC was prepared by ion-exchange method and heat-treatment process. ► Nano-sized TiO2 was dispersed on the spherical activated carbon. ► They exhibited high adsorption and photocatalytic activity on the removal of humic acid. ► The meso-TiO2/SAC showed good photocatalytic stability and durability.A TiO2-containing mesoporous spherical activated carbon (meso-TiO2/SAC) with high adsorption capacity and photocatalytic activity was prepared using ion-exchange method and heat-treatment process. The prepared meso-TiO2/SAC was characterized by SEM, TEM, EDS, XRD, and BET analysis. Results obtained showed that meso-TiO2/SAC had a smooth spherical shape (0.30–0.45 mm) and TiO2 with crystalline size of 10–30 nm was well dispersed on the spherical activated carbon. XRD study confirmed that TiO2 existed in a mixture of anatase (83%) and rutile (17%) phase. The meso-TiO2/SAC presented a high specific surface area of 1649 m2/g. The meso-TiO2/SAC was used for the removal of humic acid (HA) in a fluidized bed photoreactor, the rate of adsorption reaction of HA by meso-TiO2/SAC followed the pseudo second-order kinetic, the adsorption isotherm fitted well to the Freundlich and Langmuir isotherm models. The maximum adsorption capacity of meso-TiO2/SAC determined from Langmuir isotherm was 2.92 mg/g. The effect of the photocatalysis of HA by meso-TiO2/SAC under UV irradiation was investigated under various conditions of varying catalyst dosage, initial HA concentration, and coexisting anion. HA was mineralized up to 80.3% under optimal experimental conditions for a catalyst dosage of 9 g/L and at an initial HA concentration of 20 mg/L. In the presence of coexisting anions, the degradation efficiency of HA was reduced to 72.1% and 72.8% for SO4 2− and NO3 −, respectively. In the cyclic reuse experiment, over 85% of the initial TOC and COD were removed after the eighth cycles, indicating the relatively high photocatalytic stability of meso-TiO2/SAC. TiO2 was not released from the spherical activated carbon during the photocatalytic reaction. The meso-TiO2/SAC developed, therefore has potentials for practical applications in water treatment.
Keywords: Adsorption; Photocatalysis; Spherical activated carbon; Titanium dioxide; Humic acid;
Synthesis, characterization and evaluation of unsupported porous NiS2 sub-micrometer spheres as a potential hydrodesulfurization catalyst by Debajyoti Mondal; Gilles Villemure; Guangchun Li; Chaojie Song; Jiujun Zhang; Rob Hui; Jinwen Chen; Craig Fairbridge (230-236).
Display Omitted► Ultrasonic spray pyrolysis method was used to prepare nanostructured NiS2. ► Pure phase cubic NiS2 submicrometer porous spheres were synthesized. ► High surface area of 300 m2 g−1 was observed for the NiS2 spheres. ► Hydrodesulfurization catalytic activity was tested using dibenzothiophene (DBT). ► A first order rate reaction rate constant of 1.51 × 10−4 s−1g cata−1 at 320 °C was observed.Nanostructured NiS2 has attracted interest due to its wide applications and special properties. Synthesis of a pure phase NiS2 in a single step has been a challenge. In this work, a new method for direct synthesis of uniform NiS2/SiO2 sub microspheres has been developed by ultrasonic spray pyrolysis. Colloidal silica was used as a sacrificial template to create the porous structure. After silica removal, hollow, porous NiS2 nano spheres were obtained. The product was characterized by using scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction (XRD), transmission electron microscopy and N2 adsorption/desorption isotherm. XRD confirmed the formation of single phase pyrite NiS2. It was found that the porous spherical NiS2 has a surface area of ca. 300 m2 g−1. The HDS catalytic activity of NiS2 was evaluated using a model compound, dibenzothiophene (DBT). It showed a first order reaction rate constant of 1.51 × 10−4 s−1 g cata−1 at 320 °C for HDS of DBT, which is significantly promising for further exploration.
Keywords: Nickel disulfide; Ultrasonic spray pyrolysis; Hydrodesulfurization; Dibenzothiophene;
Kinetics of monosaccharide conversion in the presence of homogeneous Bronsted acids by Basak Cinlar; Tianfu Wang; Brent H. Shanks (237-242).
Display Omitted► Different mineral and organic acids were tested for their activities for monosaccharide degradation. ► Glucose underwent degradation with different activation energies for weak acids at pH of 1.5 rather than 3.6. ► A common framework was established for comparing catalytic activities.For the utilization of biomass in the fuel and polymer industry, a wide variety of catalysts have been studied for their activity either on the dehydration reaction in particular or on the monosaccharide degradations in general. Yet, systematic data outlining the effects of acidic features is not available and a common framework for catalytic activity comparison is missing that is needed for rational catalyst design. The current work aimed to provide insight about the effect of the nature of the acid and initial acidity on degradation kinetics of C5 and C6 carbohydrates and thereby built a platform allowing activity comparison. Mineral and organic acids ranging in acidic strength, hydrochloric, sulfuric, phosphoric, maleic, and propane sulfonic acid, were tested for their activity in the degradation of xylose, fructose and glucose at two different pH values; 1.5 and 3.6. In the presence of weak homogeneous acids, glucose undergoes degradation with drastically different activation energies at pH of 1.5 than at pH 3.6. Such a difference does not occur in the presence of strong homogenous acids. On the other hand, xylose and fructose undergo degradation with similar activation energies of approximately 140 kJ/mol regardless of the pH or nature of the homogeneous acid. A common framework that compiles the catalytic activities and outlines the differences potentially related to underlying mechanism changes provides the basis required for rational heterogeneous catalyst design.
Keywords: Glucose; Carbohydrates; Dehydration; Acid catalysis; Sugar degradation;
The kinetics of decalin ring opening over a Ir/H-Beta catalyst by Ali H. Alzaid; Kevin J. Smith (243-252).
Display Omitted► Ring opening of decalin over Pd/H-Y-30, Ir/H-Beta-300 and Ir/H-Beta-25 is reported. ► Ir/H-Beta-25 (SiO2/Al2O3 = 25) had the highest activity and ring opening yield. ► Kinetic data described by Langmuir–Hinshelwood model with catalyst deactivation. ► Decalin isomerization and isomer ring opening had the lowest activation energies.The selective ring opening of decalin over Pd/H-Y-30, Ir/H-Beta-300 and Ir/H-Beta-25 catalysts, measured in a stirred, batch reactor at 350 °C and 3 MPa H2, showed that Ir/H-Beta-25 (SiO2/Al2O3 = 25) had the highest activity and yield of ring-opened products. The effect of temperature (275–350 °C) and pressure (3–6 MPa) on the activity and product selectivity was further investigated over the Ir/H-Beta-25 catalyst. The highest ring-opened product yield (53 mol%) was obtained at a decalin conversion of 90 mol% at 325 °C and 6 MPa H2. A Langmuir–Hinshelwood kinetic model, that assumed a bifunctional catalytic process in which hydrogenation and dehydrogenation reactions occurred on metal sites and isomerization, ring-opening and cracking occurred on acid sites, was successfully applied to the data. The model included the effect of catalyst deactivation associated with the catalyst acid sites. Activation energies estimated from the model parameters showed that the ring opening of isomers had the lowest activation energy (141 kJ/mol), whereas cracking had the highest (159 kJ/mol).
Keywords: Catalyst; Ring opening; Bifunctional; Acidity; Kinetics; Deactivation; Iridium;
N2O catalytic decomposition over nano-sized particles of Co-substituted Fe3O4 substrates by Rachid Amrousse; Akimasa Tsutsumi; Ahmed Bachar; Driss Lahcene (253-260).
Display Omitted► Preparation of nano-sized Co-substituted Fe3O4 was performed successively. ► Significant amelioration on the N2O catalytic decomposition. ► Co2+ partial incorporation into magnetite presents high active sites. ► N2O decomposition temperatures were increased after O2 addition.A novel total decomposition of N2O was performed on the nano-sized particles of substituted Co x Fe3−x O4 magnetite (with x = 0–1). The given results showed that the partial incorporation of Fe2+ by Co2+ into Fe3O4 spinel substrate led to a significant amelioration in the catalytic activity for the N2O catalytic reaction. Furthermore, the catalytic activity of prepared substances depended on the Fe2+ substitution amount by Co2+ cation. The N2O conversion achieved 100% over the nano-sized Co0.6Fe2.4O4 catalyst at 255, 285 and 291 °C for pure N2O, N2O with the presence of oxygen and N2O in the presence of water steam, respectively. A relative increasing of decomposition temperatures was observed after O2 addition. Moreover, the characterization of all samples showed that the catalyst surfaces contain nano-size particles accompanied by well distribution.
Keywords: N2O; Catalytic decomposition; Nano-sized particles; Substituted magnetite;
Ni–Fe catalysts derived from hydrotalcite-like precursors for hydrogen production by ethanol steam reforming by Sònia Abelló; Evgeniy Bolshak; Daniel Montané (261-274).
Display Omitted► Nickel–iron mixed oxides from hydrotalcite were tested in ESR for H2 production. ► Study of the influence of Fe content and calcination temperature. ► Iron improves nickel dispersion and alleviates carbon deposition. ► Higher surface area and small Ni crystallite size at low calcination temperature. ► Higher Fe content and lower calcination temperature induce superior performance.Nickel–iron mixed oxides derived from reevesite, a hydrotalcite-type compound, were tested in steam reforming of ethanol for hydrogen production. The influence of iron content (Ni/Fe ranging from 3 to 1) and the calcination temperature of the catalyst precursor (773 and 1073 K) on the catalytic performance were investigated. Both parameters were essential to optimize the reforming performance. Increasing the amount of iron in the reevesite precursors affected both the chemical and activity properties of the derived mixed oxide catalysts. Iron displays a positive role in nickel-based catalysts due to the enhancement of catalytic activity and hydrogen selectivity induced by the improved dispersion of nickel and the alleviation in carbon deposition. The calcination temperature led to variations in phase composition consisting of Ni(Fe)O x solid solution and NiFe2O4, which affected the final size and dispersion of nickel species formed during the reaction. The best catalyst, with a Ni/Fe ratio of 1 and calcined at 773 K, rendered high and stable hydrogen and carbon dioxide selectivity of up to ca. 60% and 40%, respectively, low methane content, and consisted of a Ni(Fe)O x + NiFe2O4 mixture with high surface area and small Ni0 crystallites. A higher percentage of crystalline NiFe2O4 attained at high calcination temperature (1073 K) associated with a lower carbon deposition resistance and probably Ni0 sintering brings about lower activity and fast deactivation. The improved performance over catalysts calcined at lower temperature and with lower Ni/Fe ratio is motivated by the effect of iron on the structural and electronic properties of the mixed oxides, thus inducing a slow formation of metallic nickel particles and coke deposits. Features like high surface area, higher iron content, lower reducibility of nickel species and small nickel crystallite size well dispersed on the surface of the catalyst with high iron content lead to a higher activity in ethanol dehydrogenation, acetaldehyde decarbonylation and reforming, and WGS.
Keywords: Ethanol steam reforming; Layered double hydroxide; Nickel; Iron; Hydrogen;