Applied Catalysis A, General (v.415-416, #C)
Editorial Board (CO2).
Gold-catalyzed aerobic epoxidation of trans-stilbene in methylcyclohexane. Part I: Design of a reference catalyst by Kevin Guillois; Laurence Burel; Alain Tuel; Valérie Caps (1-9).
Display Omitted► AuPPh3Cl is successfully used as a precursor to prepare gold nanoparticles on hydrophobic silica. ► The reproducible, straight-forward, one-pot method of preparation can be scaled-up. ► Au/SiO2-Aerosil R972 is the first reference catalyst for gold-catalyzed aerobic oxidations of alkenes in the liquid phase.The kinetics of the heterogeneous gold-catalyzed aerobic epoxidation of stilbene in the liquid phase has been shown to be hindered by diffusion limitations, due to the use of supports which are unsuitable to apolar reaction media. The choice of these supports is generally dictated by the ability of standard methods of preparation to stabilize highly dispersed gold nanoparticles on them. Hence, new methods need to be designed in order to produce catalytically active gold nanoparticles on hydrophobic supports in general and on passivated silicas in particular. By investigating Tsukuda's method to produce colloidal solutions of gold nanoparticles upon reduction of the triphenylphosphine gold chloride complex in solution, we found that direct reduction of AuPPh3Cl in the presence of a commercially available silica support functionalized with dimethylsiloxane, Aerosil R972, leads, in a highly reproducible and potentially scalable way, to the best catalyst ever reported for this reaction.
Keywords: Gold; Hydrophobic; Reference catalyst; Aerobic oxidation; Alkene;
Oxidation of phenol to dihydroxybenzenes by nitrous oxide by D.P. Ivanov; L.V. Pirutko; G.I. Panov (10-16).
Display Omitted► Phenol oxidation with N2O was studied in detail using full on-line GC analysis. ► High catalytic efficiency of FeZSM-5 zeolite was shown. ► The title reaction opens a new promising way for dihydroxybenzene (DHB) preparation. ► Coke deposition provides strong effect on o-, m-, and p-distribution of DHB.Gas phase oxidation of phenol by nitrous oxide for preparation of dihydroxybenzenes (DHB) is of significant interest. However, due to experimental difficulties caused by the high boiling points of DHB (240–285 °C), no detailed investigation of this reaction has been conducted until now. In the present work, the reaction was studied for the first time using a catalytic setup specially designed for operation with high-boiling compounds.FeZSM-5 zeolites were shown to be efficient catalysts for the title reaction. An unusual isomeric distribution of DHB depending on reaction conditions was found. Formation of resorcinol, in addition to hydroquinone and catechol, is a particular feature of the reaction. Although the fraction of resorcinol averaged over 12 h time-on-stream is not high (6–9 mol.%), in the initial period of reaction it may comprise over 70% of the total amount of DHB.A comparison with the current liquid-phase processes of phenol oxidation by H2O2 shows that the oxidation by N2O may open a new promising way for alternative production of DHB in the gas phase.
Keywords: Dihydroxybenzenes; Phenol oxidation; Phenol hydroxylation; N2O; FeZSM-5; Hydroquinone; Resorcinol; Catechol;
Selective synthesis of benzophenone over two-dimensional mesostructured CrSBA-15 by M. Selvaraj; D.W. Park; S. Kawi; I. Kim (17-21).
Display Omitted► Well ordered 2D mesostructured CrSBA-15 synthesized by different hydrothermal methods. ► Liquid phase oxidation of diphenylmethane with TBHP over CrSBA-15. ► Catalytic oxidation of diphenylmethane with different solvents over CrSBA-15. ► Highly selective synthesis of benzophenone.Well hexagonally ordered CrSBA-15 catalysts synthesized by different hydrothermal methods were used, for the first time, for the selective synthesis of benzophenone (BP＝O) by liquid-phase oxidation of diphenylmethane (DPM) under various reaction conditions. To investigate the leaching of chromium species on the surface of silica networks, the results of original and reusable Cr-containing mesoporous silica catalysts were correlated and compared, and the catalytic activity of washed CrSBA-15(8) was also demonstrated. Based on the all catalytic results for this reaction, CrSBA-15(8) was found to be a highly active and an environmentally friendly solid catalyst and has superior catalytic activity than other Cr-containing mesoporous catalysts.
Keywords: CrSBA-15; Liquid-phase oxidation; Catalytic activity; DPM conversion; BP＝O selectivity;
The effect of TEMPO in the hydroxylation of benzene to phenol on the [(CH3)4N]4PMo11VO40/ascorbic acid/TEMPO/O2 catalytic system: Formation of ascorbic acid radicals through hydrogen exchange of ascorbic acid and TEMPO by Hua Yang; Jia-Qi Chen; Jun Li; Ying Lv; Shuang Gao (22-28).
Display Omitted► Oxidative dissociation of ascorbic acid decreased its efficiency for the reaction. ► The interaction between TEMPO and ascorbic acid increase the hydroxylation rate. ► Oxidative dissociation of the ascorbic acid did not happen in aqueous acetic acid. ► 18.9% yield of phenol was achieved with TEMPO in aqueous acetic acid.Hydroxylation of benzene to phenol in the [(CH3)4N]4PMo11VO40/ascorbic acid/TEMPO/O2 catalytic system was carefully investigated. UV–vis, ESR and 1H NMR studies showed ascorbic acid radicals were formed through the hydrogen exchange of ascorbic acid with TEMPO (2,2,6,6-tetramethyl-1-piperidine-N-oxyl radicals) during the reaction. In acetonitrile, the ascorbic acid would be partly oxidized to 2-hydroxy-2-buten-4-olide (α-tetronic acid, isotetronic acid, compound 1) without TEMPO. The interaction of TEMPO and ascorbic acid restrained the oxidative dissociation of ascorbic acid and promoted the rate of the hydroxylation. Aqueous acetic acid solvent can also restrain the oxidative dissociation of ascorbic acid. In aqueous acetic acid, the yield of phenol could reach 18.9% in the [(CH3)4N]4PMo11VO40/ascorbic acid/TEMPO/O2 catalytic system with sufficient ascorbic acid after 400 min.
Keywords: TEMPO; Ascorbic acid; Oxygen; Benzene; Phenol;
Effect of preparation method on nature and distribution of vanadium species in vanadium-based hexagonal mesoporous silica catalysts: Impact on catalytic behavior in propane ODH by Roman Bulánek; Pavel Čičmanec; Hsu Sheng-Yang; Petr Knotek; Libor Čapek; Michal Setnička (29-39).
Display Omitted► Dispersion and redox properties of VO x complexes in HMS studied by different methods. ► Simple one-pot synthesis of vanadosilicate HMS with high vanadium loading. ► Both mono- and oligomeric VO x species with T d coordination are active and selective. ► Direct synthesis of VO x -HMS leads to catalyst with superior propene productivity. ► Active VO x species are characterized by the distinct reduction peak in TPR pattern.This work reports comparative study of catalytic performance of VO x -HMS catalysts prepared by ethanolic impregnation method and direct synthesis. In order to detailed investigation of vanadium speciation depending on vanadium content and its impact on catalytic behavior in C3–ODH, number of samples in wide range of vanadium content (1–16 wt.%) was prepared by both types of preparation. Prepared catalysts were tested in the oxidative dehydrogenation of propane at 540 °C under different contact times and catalytic results were correlated with physicochemical characteristics of the catalysts examined by XRD, XRF, SEM, N2 adsorption/desorption isotherms, H2-TPR and DR-UV–visible spectroscopy. Study led to conclusion, that (i) both monomeric VO x complexes and oligomeric VO x complexes with tetrahedral coordination containing V―O―V bonds are active and selective catalytic sites for C3–ODH, (ii) active VO x species are characterized by distinct reduction peak in H2-TPR pattern centered at 570–590 °C, (iii) VO x -HMS vanadosilicates can be directly synthesized under ambient conditions without need for autoclave in wide range of vanadia loading with preservation of good catalytic performance and (iv) the catalytic results in C3-ODH were significantly better for synthesized catalysts compared to impregnated catalysts resulting in three times higher propene productivity of the best synthesized catalyst compared to the best impregnated one under the same reaction conditions. The higher is vanadium loading the more distinct is the difference in catalytic performance of both types of catalysts.
Keywords: Vanadium; ODH; Propane; Propene; Mesoporous silica; TPR; UV–vis; HMS;
Manganese(III) complexes of novel chiral unsymmetrical BINOL-Salen ligands: Synthesis, characterization, and application in asymmetric epoxidation of olefins by Longhai Chen; Feixiang Cheng; Lei Jia; Lei Wang; Jian Wei; Jinfeng Zhang; Lihui Yao; Ning Tang; Jincai Wu (40-46).
Display Omitted► A series of Mn(III)-BINOL-Salen complexes have been designed and synthesized. ► The catalysts have been investigated for asymmetric epoxidation of alkenes. ► The positive experimental results showed these complexes are excellent catalysts. ► High or excellent enantioselectivity with good yield has been gotten by catalyst.Several chiral unsymmetrical and C2-symmetric Mn(III)-BINOL-Salen complexes have been designed, synthesized and applied to the asymmetric epoxidation of non-functionalized alkenes. Experimental results show these complexes are effective in the catalytic asymmetric epoxidation of alkenes. The catalyst 4c exhibited better enantioselectivity and reactivity than the catalysts 4b and 4a due to the steric effect of the ligands. To understand the synergistic effect of the two different chiral centers in the catalyst, the catalyst 6a has been investigated. By comparison of the enantioselectivity obtained by using 4c and 6a, respectively, the positive experimental results have proved that the chiral stereogenic centers in the diaminocyclohexane-derived catalysts played an important role in the current enantioselective epoxidation. Besides, the comparison of enantioselectivity displayed by 4c and 7a further demonstrates the significant influence through the cooperation of steric factors and chiral centers in catalyst.
Keywords: Chiral manganese(III) complex; Unsymmetrical BINOL-Salen; Asymmetric catalysis; Epoxidation; Olefins;
Solvent-free selective aerobic oxidation of toluene by ultra fine nano-palladium catalyst by Baosong Fu; Xiaowen Zhu; Guomin Xiao (47-52).
Display Omitted► Nano-size ultrafine Pd catalyst was synthesized in a size controlled way. ► Pd catalysts catalyzed solvent-free aerobic toluene oxidation. ► Pd synthesized by immobilizing method has better performance in reusability.High activity ultrafine Pd catalyst was synthesized by both functional polymer encapsulated and impregnation methods. Catalysts were characterized and used to catalyze solvent-free aerobic toluene oxidation. Reaction temperature, time, catalyst mass, air pressure and catalyst reusability were investigated. Catalyst synthesized by encapsulating and immobilizing Pd inside titanium oxide is more active and has a better reusability.
Keywords: Nano-palladium catalyst; Solvent-free; Toluene aerobic oxidation; Heterogeneous catalysis;
Effect of varying reflux durations on the physico-chemical and catalytic performance of vanadium phosphate catalysts synthesized via vanadyl hydrogen phosphate sesquihydrate by L.K. Leong; K.S. Chin; Y.H. Taufiq-Yap (53-58).
Display Omitted► Specific surface area is directly proportional to precursor reflux duration. ► Lower reflux duration induced higher selectivity but lower activity on the catalysts. ► More lattice oxygen can be removed for the shortest precursor reflux duration.A series of vanadyl pyrophosphate, (VO)2P2O7, catalysts prepared via vanadyl hydrogen phosphate sesquihydrate precursors (VOHPO4·1.5H2O) was calcined in a reaction flow of 0.75% n-butane in air mixture at 733 K for 18 h. The precursors have been synthesized by refluxing vanadyl phosphate dihydrate (VOPO4·2H2O) with 1-butanol for different lengths of time, i.e. 8, 15 and 24 h, and the produced catalysts were denoted as VPOs-R8, VPOs-R15 and VPOs-R24, respectively. X-ray diffraction (XRD) patterns of the three catalysts showed similar diffraction pattern, comprised of a well-crystallized (VO)2P2O7 phase. Brunauer–Emmett–Teller (BET) surface area measurements showed that VPOs-R24 has the highest specific surface area, i.e. 31 m2 g−1 followed by 27 m2 g−1 and 19 m2 g−1 for VPOs-R15 and VPOs-R8, respectively. Inductively coupled plasma (ICP) analyses indicated that the P/V atomic ratios of these catalysts were in the optimum range in producing (VO)2P2O7 phase. A small increment in the average oxidation number of the vanadium was observed as the precursor reflux duration increased. Scanning electron microscope showed the secondary structures of the catalysts with plate-like crystals in different sizes, which were agglomerated into rosette-shape clusters. The total amount of oxygen desorbed from the catalysts increased as the precursor reflux duration increased. Temperature-programmed reduction (TPR) in H2 profiles of all the catalysts gave three reduction peaks. VPOs-R8 gave the highest total amount of oxygen removed from V5+/V4+ phase followed by VPOs-R15 and VPOs-R24. Catalytic tests revealed that the catalyst with lower precursor reflux duration exhibited higher selectivity but lower activity and vice versa.
Keywords: Vanadyl hydrogen phosphate sesquihydrate precursor; Vanadyl pyrophosphate; Selective oxidation; Maleic anhydride;
Effect of catalyst pre-reduction temperature on the reaction of 1,2-dichloroethane and H2 catalyzed by SiO2-supported PtCu bimetallics by Lindney N. Akonwie; D.V. Kazachkin; D.R. Luebke; Julie L. d’Itri (59-69).
Display Omitted► Pt and Cu chlorides impregnated on silica. ► Hydrogen treatment at low temperature yields PtCu particles with Cu-rich surfaces. ► High temperature treatment yields particles with higher surface concentrations of Pt. ► Cu-rich surfaces catalyze ethylene from 1,2-dichloroethane and hydrogen. ► Pt-rich surfaces catalyze ethane from 1,2-dichoroethane and hydrogen.A combination of reaction kinetics experiments, temperature-programmed investigations and FTIR CO adsorption studies were used to understand the effect of catalyst pretreatment on the reaction of 1,2-dichloroethane and H2 catalyzed by SiO2 supported PtCu bimetallics prepared from metal chloride precursors. Higher initial and steady-state selectivities towards ethylene were obtained for catalysts with a Cu to Pt atomic ratio of 1, 2, and 3 after pre-reduction at 220 °C than after pre-reduction at 500 °C. For catalysts with a Cu to Pt atomic ratio of 4 and 5, the initial ethylene selectivity was higher after the 220 °C pre-reduction, but the steady-state ethylene selectivities were essentially the same. Based on the catalyst characterization results, the low temperature pre-reduction yields supported particles with Pt-rich cores covered with Cu-rich layers that are still well-chlorinated, whereas the high temperature pre-reduction yields particles both more metallic and with surfaces richer in Pt. The factors governing the evolution of the catalysts during the two different pretreatments are discussed as well as the impact catalyst pretreatment has on the macroscopic performance behavior.
Keywords: Bimetallics; PtCu bimetallics; Adsorbate-induced surface enrichment; Dual site mechanism; 1,2-Dichloroethane dechlorination; Catalyst pretreatment;
Reactivity characteristics of Pt-encapsulated zeolite catalysts for hydrogenation and hydrodesulfurization by Song Chen; Jinwen Chen; Rafal Gieleciak; Craig Fairbridge (70-79).
Display Omitted► The Pt-encapsulated catalyst behaved differently from what is normally expected. ► The Pt-encapsulated catalyst gave similar naphthalene conversion as the Mo-Ni catalyst. ► Both the Pt and Mo-Ni catalysts yielded tetralin instead of decalin. ► The Pt catalyst favors direct desulfurization pathway instead of hydrogenation pathway.Noble metal catalysts are commonly used in hydrogenation processes. They are more effective than base metal catalysts such as Mo, Ni, or Co catalysts. However, noble metal catalysts are generally used in environments with sulfur concentrations below 10 ppm since they are susceptible to sulfur poisoning. This paper presents a noble metal catalyst specially prepared by using a Pt-encapsulated zeolite material. A set of pilot plant tests were conducted with naphthalene as a model hydrogenation compound and dibenzothiophene as a model sulfur compound. Based on catalyst evaluation with the noble metal catalyst and a base catalyst using novel 2-dimensional GC × GC analysis, it was observed that the Pt-encapsulated noble metal catalyst behaved differently from what is normally expected. When exposed to a high sulfur concentration of ∼600 ppm, the Pt-encapsulated catalyst gave almost the same naphthalene conversion as the Mo-Ni catalyst at 360 °C. Furthermore, both the Pt and Mo-Ni catalysts yielded a primary hydrogenation product tetralin instead of the secondary hydrogenation product decalin. The Pt-encapsulated catalyst also showed selectivity toward the direct desulfurization pathway instead of the hydrogenation–desulfurization pathway that is expected for desulfurization with noble metal catalysts.
Keywords: Pt-encapsulated zeolite; Naphthalene; Dibenzothiophene; Hydrogenation; Hydrodesulfurization;
Supported Pt-Rh bimetallic catalysts as efficient systems for methylcyclohexane ring opening by P. Samoila; M. Boutzeloit; I. Salem; D. Uzio; G. Mabilon; F. Epron; P. Marécot; C. Especel (80-88).
Display Omitted► Supported Pt-Rh catalysts were prepared by refilling or coimpregnation method. ► Pt-Rh catalyst can be selective in MCH ring-opening (RO). ► The Pt-Rh particle size is a determining parameter modulating the RO selectivity. ► Chlorinated alumina brings the acidity sufficient for the isomerization step. ► Synergetic performances observed for Pt-Rh catalysts depending on particle size.A series of supported Pt-Rh bimetallic systems was prepared either (i) by the refilling method (a surface redox reaction), or (ii) by the classical coimpregnation or (ii) by mechanical mixture of supported monometallic Pt and Rh catalysts and acidic support (chlorinated alumina). Two oxide supports were used for these preparations, i.e. alumina and silica. All these systems, largely characterized in a previous work dedicated to methylcyclopentane (MCP) hydrogenolysis, were studied for the methylcyclohexane (MCH) ring opening (RO) performed under high pressure (39.5 bar). During MCH transformation, synergetic performances were observed with some supported Pt-Rh bimetallic catalysts, since better performances in terms of activity and RO selectivity were obtained compared to those of monometallic Pt and Rh systems. The metallic particle size acts as a determining parameter modulating the catalytic properties, since the best RO performances were obtained on bimetallic catalysts presenting the largest particle sizes, for which a Pt surface enrichment and the presence of a Pt-Rh alloy were previously detected. On these bimetallic catalysts, the ring opening occurs mainly according to a bifunctional mechanism, the chlorinated alumina support bringing the required acidic function for the first isomerization step of C6 ring to alkylcyclopentanes further opened on the metallic function. The acidic function and the metal sites should not be necessarily in close vicinity since the mechanical mixture of non-acidic Pt-Rh/SiO2 catalyst with chlorinated alumina leads also to high RO selectivities. Finally, as for MCP ring opening, the refilling method allows synthesizing supported bimetallic Pt-Rh catalysts particularly efficient in terms of activity and RO selectivity.
Keywords: Bimetallic catalysts; Ring opening; Methylcyclohexane; Platinum; Rhodium;
Effect of the acidity of the HZSM-5 zeolite catalyst on the cracking of high density polyethylene in a conical spouted bed reactor by G. Elordi; M. Olazar; M. Artetxe; P. Castaño; J. Bilbao (89-95).
Display Omitted► The SiO2/Al2O3 ratio of the HZSM-5 zeolite is a key factor in the cracking of HDPE. ► With a ratio of SiO2/Al2O3 = 80, the yield of C2–C4 olefins accounts for 59.8 wt%. ► Propylene is the main individual product, with a yield of 29.6 wt% (SiO2/Al2O3 = 80). ► The gasoline fraction yield (C5–C11) accounts for 32.1 wt% (SiO2/Al2O3 = 80). ► Catalyst slowly deactivated by exterior/interior coke deposition on zeolite.The catalytic cracking of high density polyethylene (HDPE) has been carried out at 500 °C in a conical spouted bed reactor with two catalysts prepared with HZSM-5 zeolites with SiO2/Al2O3 ratios of 30 and 80. The polyethylene has been fed continuously (1 g min−1) over 10 h to a 30 g catalyst bed. The results show the good performance of the conical spouted bed reactor in minimising the limitations of the physical steps of the process. The deactivation of the catalysts is very low and it is demonstrated that the moderation of the acidity is useful in modifying the product distribution. The SiO2/Al2O3 ratio increment involves a decrease in the total acidity and in the acid strength, resulting in a higher yield of C2–C4 olefins and that of the non-aromatic C5–C11 fraction, and a decrease in the yields of aromatic components and C1–C4 paraffins. The yield of the C2–C4 olefins obtained with the HZSM-5 zeolite catalyst with a ratio of Si/Al2O3 = 80 is 59.8 wt% (that of propylene is 29.6 wt%) and the yield of the gasoline fraction (C5–C11) accounts for 32.1 wt%. The coke deposited on the catalyst has a heterogeneous nature and is constituted by two types of coke, which are deposited on the exterior and the interior of the crystalline channels of the HZSM-5 zeolite. The evolution of the coke is attenuated as the SiO2/Al2O3 ratio of the zeolite is increased.
Keywords: Spouted bed; Acidity; Catalytic pyrolysis; Waste plastic; HZSM-5 zeolite;
Mg and Al mixed oxides and the synthesis of n-butanol from ethanol by Débora L. Carvalho; Roberto R. de Avillez; Michelly T. Rodrigues; Luiz E.P. Borges; Lucia G. Appel (96-100).
Display Omitted► The n-butanol one-step synthesis requires adjacent acid and medium basic sites. ► These pairs are generated by Al in the MgO lattice and also Mg in the γ-Al2O3. ► The C4 synthesis from ethanol does not require strong basic sites. ► High Mg concentration promotes the hydrogenation of C4 compounds to n-butanol. n-Butanol is used in a wide range of applications, especially for the production of paint, solvents and plasticizers. Recently, some companies have proposed the use of n-butanol as a fuel, which can be employed pure or blended with gasoline or diesel. At present, there is great interest in developing a one-step process that generates n-butanol from ethanol. Some works showed that Mg–Al mixed oxides are very promising catalysts for this matter. Analyzing the physical–chemical properties of these catalysts, this work aims at further studying this reaction. The Mg–Al mixed oxides were obtained by thermal decomposition of hydrotalcites employing two Mg/Al different ratios. Magnesium oxide (MgO) and alumina (Al2O3) were also prepared following the same synthetic route used for the Mg–Al mixed oxides. The synthesized samples were characterized by the following techniques: XRD, NMR, BET and XRF. The acid and basic properties of the samples were also analyzed employing probe molecules. The catalytic tests were performed using a fixed bed reactor at atmospheric pressure. It was verified that the Mg and Al mixed oxides are able to promote the synthesis of C4 compounds from ethanol. Adjacent acid and medium basic sites are needed in order to generate the intermediate compounds. These pairs of acid and medium basic sites are obtained by the insertion of Al in the MgO lattice or in consequence of the presence of Mg in the γ-Al2O3 lattice. It was observed that the higher the concentration of Mg is, the higher the hydrogenation capacity of the catalyst, since a greater selectivity to n-butanol was observed. Strong basic sites and a specific superficial atomic arrangement seem not to be essential for the synthesis of C4 from ethanol.
Keywords: Hydrotalcites; Mg–Al mixed oxides; Ethanol; n-Butanol;
Long-term WGS stability of Fe/Ce and Fe/Ce/Cr catalysts at high and low steam to CO ratios—XPS and Mössbauer spectroscopic study by Gunugunuri K. Reddy; Seok Jhin Kim; Junhang Dong; Panagiotis G. Smirniotis; Jacek B. Jasinski (101-110).
Display Omitted► Long term stability of Fe/Ce/Cr investigated for high temperature WGS reaction. ► At S/CO = 1.5 Ce do not stabilize Fe3+/Fe2+ redox couple during the WGS reaction. ► Addition of Cr to the Fe/Ce catalyst improves the WGS activity at S/CO = 1.5. ► XPS indicate that Cr and Ce stabilizes the magnetite during WGS reaction. ► XRD and Mössbauer results suggest that Cr enters at M-modified octahedral sites.Long term time on stream stability of Fe/Ce and Fe/Ce/Cr catalysts has been investigated for high temperature water gas shift (WGS) reaction. Excellent WGS stability was observed for the Fe/Ce catalyst at steam to CO ratio of 3.5 and temperature of 500 °C for 30 days. The Fe/Ce catalyst also exhibited remarkable stability in presence of sulfur since no deactivation was observed in the presence of 400 ppm of sulfur. However, at steam to CO ratio 1.5, Fe/Ce deactivated continuously with time due to continuous formation of carbon and methane. X-ray diffraction measurements reveal that all the catalysts are stable in terms of composition during the WGS reaction irrespective of the steam to CO ratio. However, sintering of the magnetite phase is rapid in the experiment at steam to CO ratio of 1.5. XPS and Mössbauer spectroscopic measurements show that surface and local structural rearrangement of iron ions are taking place in the experiment at steam to CO ratio 1.5. XPS measurements also indicate the carbonate formation during the activation of Fe/Ce catalyst. The present study shows that Ce is a good stabilizer for iron oxide for high temperature WGS reaction only for higher steam to CO ratio applications. At low steam to CO ratio, Ce does not stabilize the Fe3+/Fe2+ redox couple during the WGS reaction. Addition of Cr to the Fe/Ce catalyst improves the WGS long term stability of Fe/Ce catalyst at steam to CO ratio 1.5. Remarkably, no deactivation was observed for the Fe/Ce/Cr catalyst at steam to CO ratio 1.5 and in presence of 400 ppm of sulfur. Structural and surface characterization measurements suggest that both Ce and Cr prevent the magnetite phase from sintering of and local structural rearrangement of iron ions during the WGS reaction at steam to CO ratio 1.5.
Keywords: High temperature water gas shift reaction; Mössbauer spectroscopy; XPS; CeO2; Magnetite;
Hydrothermally synthesized nanocrystalline tin disulphide as visible light-active photocatalyst: Spectral response and stability by Raquel Lucena; Fernando Fresno; José C. Conesa (111-117).
Display Omitted► SnS2 nanoparticles are synthesized using a low-temperature hydrothermal method. ► SnS2 shows high activity to degrade formic acid under visible light irradiation. ► The photoactivity wavelength dependence is tested: even >600 nm photons are active. ► The synthesized SnS2 has higher resistance to photocorrosion than CdS.A simple hydrothermal method is implemented for the synthesis of SnS2 nanoparticles, using non expensive SnCl4·5H2O and thiourea as reactants. The photocatalytic properties of the synthesized material under visible light irradiation are evaluated examining the degradation of formic acid in an aqueous solution containing the solid in suspension, using eventually band-pass filters to verify the dependence of photoactivity on light wavelength. The results demonstrate that the material has high visible light photocatalytic activity with an action spectrum covering the full spectral range absorbed by the solid (up to ca. 600 nm), and that the latter is also more photoactive and resistant to photocorrosion than the more toxic but frequently used CdS. Tin disulphide, containing only abundant and nontoxic elements, is thus suggested as advantageous alternative for solar light use.
Keywords: SnS2; Photocatalysis; Visible light; Spectral response; Stability;
Effect of promoter SiO2, TiO2 or SiO2-TiO2 on the performance of CuO-ZnO-Al2O3 catalyst for methanol synthesis from CO2 hydrogenation by Luxiang Zhang; Yongchun Zhang; Shaoyun Chen (118-123).
Display Omitted► Promoter SiO2-TiO2 showed a higher performance than SiO2, TiO2 or without promoter. ► The CO2 conversion (40.70%) over the SiO2-TiO2 promoted catalyst is very high. ► SiO2-TiO2 was hardly used in the catalyst as a promoter.The influences of SiO2, TiO2 or SiO2-TiO2 promoters on the catalytic performance of CuO-ZnO-Al2O3 catalyst in the methanol synthesis from CO2 hydrogenation were studied. The catalysts were prepared by co-precipitation method, SiO2 and TiO2 were loaded by hydrolyzation of tetraethyl orthosilicate (TEOS) and hydrolyzation of tetra-n-butyl titanate (C16H36O4Ti), respectively. The catalytic performances of the prepared catalysts were investigated under conditions of T = 533 K, P = 2.6 MPa, H2:CO2 = 3:1 (volume ratio) and SV = 3600 h−1. The experimental results showed that the promoted catalysts showed a higher performance than CuO-ZnO-Al2O3. Especially, the one promoted with SiO2-TiO2 maximized both activity and methanol selectivity with 40.70% in CO2 conversion and 41.17% in methanol selectivity as compared to the one without promoter (15.81% in CO2 conversion and 23.31% in methanol selectivity). Characterizations of XRD, H2-TPR, H2-TPD, NH3-TPD, CO2-TPD and SEM revealed that all the promoters improved the CuO dispersion in the catalyst body and improved the adsorption/activation of H2 on the catalyst. Especially SiO2-TiO2 exhibited higher performance as compared to SiO2 or TiO2.
Keywords: Promoter; TiO2; SiO2; CO2; Hydrogenation; Methanol;
Hydroformylation of propene heterogeneously catalyzed by HRh(CO)(PPh3)3 encapsulated in to hexagonal mesoporous silica—Parametric variation and mass transfer study by N. Sudheesh; Jaydeep N. Parmar; Ram S. Shukla (124-131).
Display Omitted► Rh-complex encapsulated HMS, a heterogeneous catalyst for propene hydroformylation. ► Reaction parametric effects on conversion, selectivity and rates were investigated. ► Catalyst was effectively recycled for six times. ► Investigations on mass transfer effects were conducted.An in situ encapsulated HRh(CO)(PPh3)3 in to the pores of hexagonal mesoporous silica (HMS) acting as nanophase reactors, was investigated for the catalytic hydroformylation of propene. The encapsulated catalyst (Rh–HMS) was synthesized and characterized by PXRD, FT-IR, surface area measurements and TEM. The catalyst was effectively active with 99% conversion of propene and 100% selectivity to aldehydes. The effects of reaction parameters: temperature, partial pressure of CO and H2, amount of catalyst and HRh(CO)(PPh3)3 to TEOS ratio on conversion, selectivity and rates were investigated in detail. The rates determined in term of the formation of aldehydes were found to be first order with respect to hydrogen pressure. Catalyst showed first order dependence towards its lower amount. CO pressure variation showed positive order towards lower pressure and inhibition at higher pressures. The investigated mass transfer effects on the kinetics indicated that the reaction runs with negligible mass transfer limitations. The heterogenized Rh–HMS catalyst was effectively recycled for six times.
Keywords: Hydroformylation; Heterogeneous catalyst; Propene; Kinetics; Mass transfer;
Ammoxidation of ethylene over low and over-exchanged Cr–ZSM-5 catalysts by F. Ayari; M. Mhamdi; J. Álvarez-Rodríguez; A.R. Guerrero Ruiz; G. Delahay; A. Ghorbel (132-140).
Display Omitted► Cr–ZSM-5 solids were tested in the ammoxidation of ethylene into acetonitrile. ► Cr(VI) ions and Cr(III) oxide species coexist. ► Solid-state exchange is favorable for Cr2O3 formation. ► Aqueous exchange catalysts showed better catalytic performances. ► Cr(VI) species are actives in the ammoxidation, while Cr2O3 oxide should be avoided.Catalytic performances of Cr–ZSM-5 catalysts (5 wt.% of Cr, Si/Al = 26), prepared by solid-state reaction and aqueous exchange, from Cr nitrate and Cr acetate precursors, were evaluated in the selective ammoxidation of ethylene into acetonitrile in the temperature range 425–500 °C. Catalysts were characterized by chemical and thermal analysis, XRD, N2 physisorption, 27Al MAS NMR, TEM, UV–vis DRS, Raman, DRIFTS and H2-TPR. Characterization results shown that solid-state exchange was favorable for Cr2O3 formation, while exchanging chromium in aqueous phase led, essentially, to Cr(VI) species. Catalysts were actives and selectives in the studied reaction, and among them, those, prepared from aqueous exchange, exhibited the highest acetonitrile yields (23 ± 0.5%, at 500 °C). Improved catalytic properties can be correlated with the chromium species nature. In fact, mono/di-chromates and/or polychromate species, sited in the charge compensation positions, were definitively shown, as being, the active sites. Furthermore, during solid-state reaction, the agglomeration of Cr2O3 oxide should be avoided since these species inhibit the catalyst activity.
Keywords: Cr–ZSM-5; Ammoxidation; Acetonitrile; Solid-state exchange; Aqueous exchange;
Hydrogenation of succinic acid to tetrahydrofuran (THF) over rhenium catalyst supported on H2SO4-treated mesoporous carbon by Ung Gi Hong; Hai Woong Park; Joongwon Lee; Sunhwan Hwang; Jongheop Yi; In Kyu Song (141-148).
Display Omitted► Re catalysts supported on H2SO4-treated mesoporous carbons (Re/MC-X) were prepared. ► Re/MC-X catalysts were applied to the hydrogenation of succinic acid to THF. ► Yield for THF increased with decreasing Re particle size of Re/MC-X catalysts. ► Re/MC-X served as a reusable catalyst for hydrogenation of succinic acid to THF.Mesoporous carbon (MC) prepared by a surfactant-templating method was treated with different H2SO4 concentration (X = 0, 0.2, 0.4, 0.6, 0.8, and 1.0 M) for use as a support (MC-X) for rhenium catalyst. Rhenium catalysts supported on H2SO4-treated mesoporous carbons (Re/MC-X) were then prepared by an incipient wetness impregnation method, and they were applied to the liquid-phase hydrogenation of succinic acid to tetrahydrofuran (THF). The effect of H2SO4 treatment on the physicochemical properties and catalytic activity of Re/MC-X catalysts (X = 0, 0.2, 0.4, 0.6, 0.8, and 1.0) was investigated. It was observed that MC-X supports showed different pore characteristics depending on H2SO4 concentration. As a result, Re/MC-X catalysts showed different rhenium particle size. In the liquid-phase hydrogenation of succinic acid to tetrahydrofuran (THF), conversion of succinic acid and yield for THF showed volcano-shaped curves with respect to H2SO4 concentration. Thus, an optimal H2SO4 concentration was required to achieve maximum catalytic performance of Re/MC-X. Yield for THF in the hydrogenation of succinic acid increased with decreasing rhenium particle size of Re/MC-X catalysts. Among the catalysts tested, Re/MC-0.4 with the smallest rhenium particle size showed the highest yield for THF.
Keywords: Hydrogenation; Succinic acid; Mesoporous carbon; Rhenium; Tetrahydrofuran;