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Applied Catalysis A, General (v.327, #1)
Chromium–saponite clay catalysts: Preparation, characterization and catalytic performance in propene oxidation by G. Mata; R. Trujillano; M.A. Vicente; C. Belver; M. Fernández-García; S.A. Korili; A. Gil (pp. 1-12).
Chromium–saponite catalysts have been prepared by two synthesis procedures. The first method consisted in the intercalation of the saponite with solutions containing aluminium and chromium oligomers with various molar ratios, while the second one consisted in the incipient wetness impregnation of alumina-pillared saponite with several chromium salts, ammonium chromate, Cr(II) acetate and Cr(III) nitrate. Several techniques, X-ray diffraction, nitrogen physisorption at −196°C, thermogravimetric and differential thermal analysis, infrared and DR-UV–vis spectroscopies, temperature-programmed reduction and electron paramagnetic resonance spectroscopy at −196°C, have been used to characterize and to compare the properties of the materials synthesized. The results show that the solids obtained combine the layered structure of the clay and the thermal stability given by the alumina pillars. The catalysts have been tested in the oxidation of propene, showing a catalytic behaviour according to the Mars–van Krevelen mechanism, the performance not depending on the method in which chromium was incorporated to the clay.Chromium–saponite catalysts have been prepared by intercalation of saponite with Al–Cr oligomer solutions, and by impregnation of alumina-pillared saponite with chromium salts. Solids have been widely characterized, and their performance for oxidation of propene has been tested. The catalytic behavior agrees to the Mars–van Krevelen mechanism, the performance not depending on the method of incorporation of chromium to the clay. ▪
Keywords: Alumina-pillared clays; Chromia–alumina-pillared clays; Chromium catalysts; Propene oxidation
Influence of magnesium and chromium oxides on the physicochemical properties of γ-alumina by M. Riad (pp. 13-21).
Boehmite, magnesium–aluminum and chromium–aluminum hydroxides prepared from the corresponding chloride solutions using ammonia solution at pH∼9. The precipitated hydroxides subjected to thermal treatment at 450°C to produce γ-alumina and magnesium–aluminum mixed oxide and at 600°C to produce chromium–aluminum mixed oxide materials. The materials characterized by Fourier transformer infrared (FT-IR), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and BET surface analyses. The catalytic activity of these materials toward cyclohexane dehydrogenation reaction was performed in a pulse micro-catalytic reactor operated under atmospheric pressure at reaction temperature ranged from 250 to 550°C. The results indicated that, chromium–aluminum oxide material which possess crystallite size, 27.0nm and surface area 89.0m2/g, is the most active material toward benzene formation (23.7%) at reaction temperature 500°C. Meanwhile, magnesium–aluminum oxide is the most selective one toward benzene formation (crystallite size, 3.0nm and surface area, 209.7m2/g) as compared with the other prepared materials.▪Boehmite, magnesium–aluminum and chromium–aluminum hydroxides prepared from the corresponding chloride solutions of aluminum, magnesium and chromium, respectively, using ammonia solution at pH∼9. The precipitated hydroxides subjected to thermal treatment at 450°C to produce γ-alumina and magnesium–aluminum mixed oxide and at 600°C to produce chromium–aluminum mixed oxide materials. The materials characterized using Fourier transformer infrared spectroscopy, X-ray diffraction pattern, differential scanning calorimetry and BET surface analyses. The catalytic activity of these materials toward cyclohexane dehydrogenation reaction was performed in a pulse micro-catalytic reactor operated under atmospheric pressure at reaction temperature ranged from 250 to 550°C. The results indicated that, chromium–aluminum oxide material which possess crystallite size, 27.0nm and surface area 89.0m2/g, is the most active material toward benzene formation (23.7%) at reaction temperature 500°C. Meanwhile, magnesium–aluminum oxide is the most selective one toward benzene formation (crystallite size, 3.0nm and surface area, 209.7m2/g) as compared with the other prepared materials.
Keywords: Boehmite; Alumina; Magnesium; Chromium; Mixed oxide materials; Cyclohexane; Dehydrogenation; Benzene
Highly selective synthesis of methyl ethyl ketone oxime through ammoximation over Ti-MWW by Fen Song; Yueming Liu; Lingling Wang; Haijiao Zhang; Mingyuan He; Peng Wu (pp. 22-31).
Methyl ethyl ketone oxime is produced effectively through the liquid-phase ammoximation of methyl ethyl ketone with H2O2 and ammonia over Ti-MWW catalysts. In comparison to conventional TS-1, Ti-MWW in particular is capable of suppressing the deep oxidation of oxime.▪The liquid-phase ammoximation of methyl ethyl ketone (MEK) with ammonia and hydrogen peroxide was conducted on Ti-MWW, TS-1, Ti-MOR and Ti-Beta catalysts in order to produce methyl ethyl ketone oxime (MEKO) cleanly. Compared with other titanosilicates, Ti-MWW produced MEKO more efficiently and selectively, achieving a conversion and selectivity both over 99% under optimized conditions. Ti-MWW was particularly superior to TS-1 in MEKO selectivity, as TS-1 co-produced easily 2-nitrobutane byproduct as a result of consecutive oxidation of MEKO unless the ammonia/MEK molar ratio was increased to 4. The catalyst deactivated in repeated ammoximation, mainly owing to a partial dissolution of framework silicon in basic reaction media. Efforts were thus made in order to develop practicable regeneration methods. By adding a controlled amount of silica source into the reaction mixture, we could suppress the deactivation of Ti-MWW catalyst and then the lifetime was prolonged effectively.
Keywords: Ti-MWW; TS-1; Ammoximation; Methyl ethyl ketone; Methyl ethyl ketone oxime; Regeneration
Preparation of nanostructured Pd particles using a seeding synthesis approach—Application to the selective hydrogenation of buta-1,3-diene by Gilles Berhault; Laure Bisson; Cécile Thomazeau; Catherine Verdon; Denis Uzio (pp. 32-43).
Well-defined nanostructured Pd particles were successfully synthesized in aqueous solution using a seeding-mediated approach. Four well-defined nanoobjects were obtained: nanocubes, nanoprisms (or nanotetrahedra), nanopolyhedra, and nanorods. After deposition onto α-Al2O3, nanostructured Pd particles were found highly selective for the hydrogenation of buta-1,3-diene into butenes without further hydrogenation into butane.▪Well-defined nanostructured Pd particles were successfully synthesized in aqueous solution using a seeding-mediated approach with cetyltrimethylammonium bromide (CTAB) acting as both capping and structure-directing agent. Four well-defined nanoobjects were obtained: nanocubes, nanotetrahedra, nanopolyhedra, and nanorods. The anisotropic Pd nanorods exposed preferentially {100} facets due to the stabilization effect of CTAB.After deposition onto α-Al2O3, these nanostructured Pd particles were tested in the selective hydrogenation of buta-1,3-diene at 298K under 20bars of H2. Compared to an isotropic Pd catalyst, anisotropic Pd catalysts were found highly selective for the hydrogenation of buta-1,3-diene into butenes without further hydrogenation into butane. Moreover, on the nanostructured catalysts, further hydrogenation of but-1-ene into butane is reduced while but-2-enes were hardly converted. Finally, an unusual high level of cis but-2-ene isomer was observed. These results suggest a modification of the mechanism usually admitted for Pd catalysts when a well-defined nanomorphology is achieved.
Keywords: Palladium; Nanorods; Crystalline growth; Hydrogenation; Buta-1,3-diene
Cellobiose hydrolysis using organic–inorganic hybrid mesoporous silica catalysts by Jason A. Bootsma; Brent H. Shanks (pp. 44-51).
The hydrolysis of cellobiose, a model system for oligosaccharide hydrolysis, was examined using organic–inorganic hybrid mesoporous catalysts. The rate constants and apparent activation energies for three organic acid catalytic species in the hydrolysis reaction were determined. The kinetic parameters were also determined for the subsequent glucose degradation reaction. ▪The hydrolysis of cellobiose, a model system for oligosaccharide hydrolysis, was examined using organic–inorganic hybrid mesoporous catalysts. The activity of butylcarboxylic acid, propylsulfonic acid and arenesulfonic acid functionalized silicas were determined for cellobiose hydrolysis as well as glucose degradation. The hydrolysis rate constants for the three catalyst types were proportional to their pH values at ambient temperature and the apparent activation energies for the hydrolysis reaction were the same suggesting that hydrated protons were the catalytic species in the reaction. The apparent activation energy for glucose degradation was the same for each of the catalysts and was lower than that found for the hydrolysis reaction. As such, higher reaction temperature improved the selectivity of the hydrolysis reaction relative to the degradation reaction. The desirability of high reaction temperatures made the organic–inorganic hybrid materials preferable to polymer-based catalysts.
Keywords: Cellobiose; Disaccharide hydrolysis; Organic–inorganic hybrid catalysts; Mesoporous silica; Corn fiber
Catalytic effect of Fe/C powder on the formation of gas-phase products of vacuum pyrolysis of N,N′- ethylenebisstearamide by Gregory A. Poskrebyshev; Marc M. Baum; John A. Moss; Diran Apelian (pp. 52-65).
In the present work N,N′-ethylenebisstearamide ( EBS) in its free form and mixed with iron/carbon powder was thermolyzed in a closed system under vacuum to produce gas-phase products ( GPP). A catalytic effect of the iron/carbon surface on the gasification of thermolyzed EBS is observed over the 573–973K temperature range.▪In the present work N,N′-ethylenebisstearamide ( EBS) in its free form and mixed with iron/carbon powder was thermolyzed in a closed system under vacuum to produce gas-phase products ( GPP). A catalytic effect of the iron/carbon surface on the gasification of thermolyzed EBS is observed over the 573–973K temperature range. The overall yield of GPP measured after one hour of heating at a constant temperature increased with temperature ( T<973K) in both systems.The total yield, and the yields of the main identified GPP (CO, CH4, CO2 and C2H4), measured for free EBS are significantly lower (∼30 times) than those observed for mixture of EBS with iron/carbon powder. The catalytic formation of H2/N2, H2O and small amounts of other volatile11Compounds with a vapor pressure above 0.1Torr at room temperature. organic products is assumed at temperatures below 973K.The formation of GPP from low volatility products of EBS decomposition is assumed to proceed via at least two competing mechanisms ( EBS→ Primary products→2CO (1) or CO2 (2)). This mechanistical model can be used as a basis for understanding the delubrication mechanism of ferrous compacts and for the catalytic gasification of heavy amides ( EBS) or polyamides ( Nylon) widely used in industry.
Keywords: N,N; ′-ethylenebisstearamide; Pyrolysis; Thermolysis; Catalysis; Iron; Carbon; Amide
Kinetics of the N2O+CO reaction over steam-activated FeZSM-5 by M.N. Debbagh; A. Bueno-López; C. Salinas Martínez de Lecea; J. Pérez-Ramírez (pp. 66-72).
New insights into the kinetics of the N2O reduction by CO over steam-activated FeZSM-5 have been obtained. The scavenging mechanism, where gas-phase CO eliminates adsorbed atomic oxygen deposited by N2O properly describes the reaction. N2O activation generating adsorbed oxygen is 2–8 times faster than O* elimination by CO (rate-determining step). The fraction of free/oxidised sites in the catalyst was quantitatively determined as a function of the inlet partial pressure of CO and temperature. ▪The kinetics of the N2O reduction by CO as well as the direct N2O decomposition have been investigated over steam-activated FeZSM-5. To this end, steady-state experiments at different temperatures, partial reactant pressures, molar feed N2O/CO ratios, and space times were carried out in an integral fixed-bed micro-reactor. Different empirical and microkinetic models were evaluated in order to describe the experimental data and derive quantitative kinetic information. Depending on the molar feed CO/N2O ratio and temperature, the reduction occurs alone in the catalyst bed or simultaneously with direct N2O decomposition. The orders for N2O and CO in the N2O+CO reaction are 0.51 and 0.72, respectively, in contrast with the characteristic first-order behaviour of the direct N2O decomposition. The latter can be properly described by a two-step oxygen transfer mechanism. The scavenging mechanism (Eley-Rideal type), where gas-phase CO effectively eliminates adsorbed atomic oxygen properly describes the N2O+CO reaction. The removal of O* by CO is two orders of magnitude faster than by N2O, but the elimination of O* remains as the rate-determining step. The N2O activation generating adsorbed oxygen is 2–8 times faster than the O* elimination by CO. Elimination of O* by CO is more sensitive to temperature than N2O activation. The elementary step mechanism has been used to predict the fraction of free/oxidised sites. The inlet concentration of CO and temperature determines the degree of reduction of the catalyst surface. The obtained activation energies in direct N2O decomposition (141kJmol−1) and N2O reduction by CO (62kJmol−1) were in excellent agreement with values reported in the literature.
Keywords: FeZSM-5; N; 2; O; CO; Reduction; Direct decomposition; Kinetics; Rate law
Morphology changes of Pt-foil catalyst induced by temperature-controlled ammonia oxidation near atmospheric pressure by R. Kraehnert; M. Baerns (pp. 73-81).
Reaction-induced changes of a Pt foil catalyst during ammonia oxidation were investigated between 20 and 700°C, and close to atmospheric pressure. Reaction temperature and feed composition controlled the restructuring of the Pt surface, with reaction-induced faceting starting already at 286°C. Adsorbate-enhanced surface diffusion of Pt is suggested to account for the surface reconstruction well below temperatures reported for significant Pt transport through the gas phase via volatile PtO x.▪Reaction-induced changes of the morphology of a Pt foil catalyst during ammonia oxidation were investigated in a temperature-controlled way for partial pressures of oxygen and ammonia around 4.5 and 3kPa, respectively, and at temperatures between 20 and 700°C. The presence of the feed mixture (ammonia and oxygen) was required to induce surface roughening. Moreover, the reaction temperature controlled the type of restructuring of the Pt surface, that is, either into rows of parallel facets where facet size increased with temperature, or as bulky microcrystals protruding from the surface. Surprisingly, reaction-induced surface faceting was already observed at 286°C. Between 286 and 374°C adsorbate-enhanced surface diffusion of Pt is suggested to account for the surface restructuring well below temperatures reported for significant Pt transport through the gas phase via volatile PtO x.
Keywords: Catalytic ammonia oxidation; Platinum; Surface morphology; Restructuring; Faceting; SEM
Hydrogen production by ethanol steam reforming over Cu-Ni/SBA-15 supported catalysts prepared by direct synthesis and impregnation by A. Carrero; J.A. Calles; A.J. Vizcaíno (pp. 82-94).
Cu-Ni/SBA-15 supported catalysts prepared by direct synthesis and incipient wetness impregnation were characterized and tested in the ethanol steam reforming reaction. Lower water and ethanol conversion as well as hydrogen selectivity were obtained with catalysts prepared by direct synthesis. Products’ distribution was the result of the combined effects of metal particles’ size, metal content and Ni/Cu ratio. ▪Cu-Ni/SBA-15 supported catalysts prepared by the incipient wetness impregnation method were tested in the ethanol steam reforming reaction for hydrogen production. The effect of reaction temperature and metal loading was studied in order to maximize the hydrogen selectivity and the CO2/(CO+CO2) molar ratio. The best catalytic performance was achieved at 600°C. Products distribution was the result of the combined effects of metal particles size, metal content and Ni/Cu ratio on the catalyst. In addition, two catalysts were prepared by the method of direct insertion of Ni and Cu in the initial stage of the SBA-15 synthesis. X-ray powder diffraction (XRD), transmission electron microscopy (TEM), N2- adsorption and inductively coupled plasma atomic emission spectroscopy (ICP-AES) results evidenced that SBA-15 materials with long range hexagonal ordering were successfully synthesized in the presence of copper and nickel salts with the (Cu+Ni) contents around 4–6wt.%. However, lower hydrogen selectivity as well as ethanol and water conversions were obtained with catalysts prepared by direct synthesis in comparison with those prepared by incipient wetness impregnation method. Particularly, the best catalytic results were achieved with a sample impregnated with 2 and 7wt.% of copper and nickel, respectively.
Keywords: Ethanol steam reforming; SBA-15; Cu-Ni loading; Hydrogen production
The decomposition of ethanol over Mo2C/carbon catalysts by Róbert Barthos; Aleksandar Széchenyi; Ákos Koós; Frigyes Solymosi (pp. 95-105).
Mo2C prepared by the reaction of MoO3 with carbon Norit in H2 is an effective catalyst for the decomposition of ethanol to generate H2. A remarkable feature of the catalysts is its high stability. Adding potassium to Mo2C/Norit enhanced the formation of hydrogen. ▪The formation of Mo2C by the reaction of MoO3 with carbon Norit in H2 flow was followed by X-ray photoelectron spectroscopy. It was found that the conversion of MoO3 into Mo2C in the surface layer of Norit was complete at 973K. Mo2C prepared in this way on the surface of carbon Norit was found to be an effective catalyst for the decomposition of ethanol to generate H2; the extent of the reaction approached 100% even at 623–673K. Depending on the temperature and the Mo2C loading about 32–62% of hydrogen content of the decomposed ethanol has been converted into H2. Besides H2, acetaldehyde was the major product indicating that the dehydrogenation reaction of ethanol is the main process. The formation of CH4, CO, C2H4 and C2H6 also occurred in few percents. Another feature of the Mo2C/Norit catalysts is its high stability. The conversion of ethanol decreased only with few percent even after 75h at 723K. Adding potassium to Mo2C/Norit enhanced the catalytic efficiency of Mo2C and increased the formation of hydrogen. Mo2C prepared on multiwall carbon nanotube also proved to be active for the decomposition of ethanol. Adding water to ethanol enhanced the hydrogen production only to a small extent.
Keywords: Hydrogen production; Ethanol decomposition; Preparation of Mo; 2; C on Norit; Mo; 2; C on carbon nanotube; X-ray photoelectron spectroscopy; Mo; 2; C catalyst; Carbon as a support
Effect of the metal foam materials on the performance of methanol steam micro-reformer for fuel cells by Hao Yu; Hongqing Chen; Minqiang Pan; Yong Tang; Kai Zeng; Feng Peng; Hongjuan Wang (pp. 106-113).
Hydrogen production has been achieved in a laminated metal foam based micro-reformer for fuel cells. The strong interaction between the Ni and FeCrAl metal foams and catalyst results in the low activity for water gas shift reaction, therefore, increases the CO selectivity significantly. The optimal material for the fabrication of micro-reformer is CuZn foam. ▪A methanol steam micro-reformer was constructed to produce hydrogen (H2) for polymer electrolyte membrane fuel cells (PEMFCs), in which a Cu/Zn/Al/Zr catalyst was supported on metal foams. To optimize the performance of the micro-reformer, the effect of metal foams on the catalytic property was investigated in details, including catalytic activity, carbon monoxide (CO) selectivity and mechanical properties. It was found that the strong interaction between the Ni or FeCrAl metal foams and catalyst resulted in the low activity for water gas shift (WGS) reaction, therefore, increased the CO selectivity significantly. As a general principle, it was proposed that the metal materials poisoning or reducing the reforming activity should be excluded in the design of micro-reformers.
Keywords: Metal foam; Micro-reactor; Methanol steam reforming; Hydrogen production
Preparation of (Ga1− xZn x) (N1− xO x) solid-solution from ZnGa2O4 and ZnO as a photo-catalyst for overall water splitting under visible light by Xiaojun Sun; Kazuhiko Maeda; Maël Le Faucheur; Kentaro Teramura; Kazunari Domen (pp. 114-121).
A solid-solution of GaN and ZnO (Ga1− xZn x) (N1− xO x), is successfully prepared by nitriding ZnGa2O4 powder at 1123K for 15h under a flow of NH3, and the addition of an appropriate amount of ZnO to the starting material is shown to improve the photo-catalytic activity of the final product substantially.▪A solid-solution of GaN and ZnO (Ga1− xZn x) (N1− xO x), as a visible-light-driven photo-catalyst for overall water splitting, is successfully prepared using both ZnGa2O4 and a ZnGa2O4–ZnO mixture. The photo-catalytic activity of the catalyst is found to be dependent on both the Zn/Ga ratio of the starting material and the nitridation time, because both factors affect the crystallinity and atomic composition of the final (Ga1− xZn x) (N1− xO x) material. It is also revealed that the addition of ZnO promotes crystallization of the catalyst and controls the zinc concentration, thereby improving activity. By adjusting these two preparation parameters, it is possible to obtain a material with optimal crystallinity and atomic composition for overall water splitting under visible light ( λ>400nm).
Keywords: Heterogeneous photo-catalysis; Hydrogen production; Oxynitride; ZnGa; 2; O; 4