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Applied Catalysis A, General (v.314, #1)
Preparation and chiral activation of cinchonidine modified Pt nanoclusters deposited on an alumina support: Influence of catalyst nature on obtained enantiomeric excess in ethyl pyruvate hydrogenation at low pressures by A. Kraynov; R. Richards (pp. 1-8).
Research and development towards catalysts that can induce high enantiomeric excess (ee) under mild reaction conditions is important from both academic and applications perspectives. In particular, a heterogeneous system capable of inducing high ee under mild conditions without additional external forces (i.e. sonication) would be of interest. A novel preparation of Pt nanoclusters (3nm) deposited on a non-porous alumina support and modified with cinchonidine was found to be very efficient for hydrogenation of ethyl pyruvate at low pressures. The catalyst demonstrated 80–88% of enantiomeric excess in ethyl pyruvate hydrogenation under mild reaction conditions (2.5–10bar of hydrogen pressure) in acetic acid. Further, the catalyst was found to be very stable and could be recycled at least four times without an observable decrease of activity or enantioselectivity. The influence of the nature of the catalyst and modifier on the obtained enantiomeric excess was investigated via DRIFTS (diffuse reflectance infra-red fourier transform spectroscopy) measurements.
Keywords: Enantioselective hydrogenation; Cinchonidine; Activation; Heterogeneous catalysis; Nanoclusters; Pt; DRIFTS
Effect of supports and Ni crystal size on carbon formation and sintering during steam methane reforming by K.O. Christensen; D. Chen; R. Lødeng; A. Holmen (pp. 9-22).
Steam methane reforming was studied at 823K, a total pressure of 20bar and steam to carbon ratios from 0.08 to 2.4 over conventional NiO/α-Al2O3 and NiO/CaO-Al2O3 catalysts as well as catalysts supported on hydrotalcite derived materials. Catalyst activity, coke formation and deactivation at steam reforming conditions were studied using the tapered element oscillating microbalance (TEOM). Nickel supported on hydrotalcite derived materials had a smaller crystal size and a higher resistance to coke formation than the conventional NiO/α-Al2O3 and NiO/CaO-Al2O3. The higher resistance to carbon formation could be due to a higher saturation concentration of carbon in the smaller nickel crystals. Sintering experiments were performed at 903K and 20bar on the hydrotalcite derived catalysts and compared with an industrial NiO/CaAl2O4 catalyst. The particle growth for the hydrotalcite derived catalysts was larger than for the industrial catalyst, but the hydrotalcite derived catalysts had the smallest size of stabilized Ni crystals.
Keywords: Methane reforming; Coke formation; Nickel catalyst; Hydrotacite; Sintering
Characterization and catalytic properties of montmorillonite pillared with aluminum/lanthanum by Oscar Macias; Julio Largo; Carmen Pesquera; Carmen Blanco; Fernando González (pp. 23-31).
This work describes the synthesis, characterization and catalytic properties of montmorillonite pillared with mixed aluminum/lanthanum pillars. This material presents characteristics that are very different from montmorillonite pillared only with aluminum. It shows a bimodal micropore structure, through generation of pores at the limit between microporosity and mesoporosity. The textural parameters show higher values and it is thermally more stable, maintaining high values of specific surface area and micropore volume up to 700°C. The acidity of aluminum/lanthanum pillared material reveals that its surface shows more acid centers, mainly Lewis-type. The increase of the conversion in dehydration of 1-butanol as in hydroisomerization of heptane shows its better behavior as an acid catalyst. The study of 1-butanol dehydration shows that there is an increase in the acidity and the thermal stability and a smaller deactivation by carbonaceous deposits in the aluminum/lanthanum pillared material.
Keywords: Montmorillonite; Pillared; Lanthanum; Acid catalysis; Bifunctional catalysis
Preparation and application of nickel-containing smectite-type clay materials for methane reforming with carbon dioxide by Nobuhiro Iwasa; Masanori Takizawa; Masahiko Arai (pp. 32-39).
Mesoporous smectite-type clays containing different metals, such as Mg, Fe, Co, or Ni, were synthesized by a hydrothermal method and tested for reforming of methane with carbon dioxide. The synthesized clays had smectite-type structure with mesopores and high surface areas. After hydrogen reduction, the synthesized smectite materials containing Ni are highly active for the reforming reaction. Their activity depends on the synthetic conditions used. The smectite materials prepared at lower slurry pH values and lower hydrothermal temperatures exhibit higher activity than a reference catalyst of Ni/SiO2 prepared by impregnation method. The most active Ni-containing smectite catalyst is superior to the conventional supported Ni catalysts reported in the literature. The turnover frequency (TOF) of Ni smectite catalysts significantly depends on the size of Ni crystallites, which are formed on the reduction; those having smaller Ni crystallites show higher TOF values.
Keywords: Smectite; Nickel; Mesoporous materials; Methane reforming; Crystallite size effect
Sol–gel-derived super-hydrophilic nickel doped TiO2 film as active photo-catalyst by Sunil Dutta Sharma; Davinder Singh; K.K. Saini; Chander Kant; Vikash Sharma; S.C. Jain; C.P. Sharma (pp. 40-46).
Pure and nickel doped TiO2 thin films on soda glass substrates were prepared by sol–gel dip coating process. The resulting films were annealed at 500°C for 1h and characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and UV–vis-near IR techniques. AFM reveals that doping of Ni ions suppresses the grain growth of crystal in the TiO2 film. The contact angle with water of these films was measured by sessile drop method. The undoped films could be entirely wetted by water after 1h UV illuminations, while 0.5mol% Ni ion-doped films become entirely wetted after 20min UV illumination. The photo-catalytic activity was characterized by photo-catalytic degradation of aqueous methyl orange under UV radiation. It is found that, with a suitable amount (2–10mol%), the Ni dopant increases the photo-catalytic activity of TiO2 films. The mechanism can be attributed to these processes: (1) as the anatase grain sizes decrease with Ni doping and the specific surface areas of doped TiO2 films increase, the charge transfer in TiO2 film is promoted; (2) by enhancing the electron–hole pair separation and inhibiting their recombination, the Ni dopant enhances the charge pair separation efficiency for doped TiO2 films.
Keywords: Titanium dioxide; Sol–gel; Hydrophilicity; Photo-catalyst
Preferential methanation of CO in a syngas involving CO2 at lower temperature range by Muhamad B.I. Choudhury; Shakeel Ahmed; Mazen A. Shalabi; Tomoyuki Inui (pp. 47-53).
Preferential elimination of CO in a model syngas involving CO2 at a low temperature range was studied on a series of Ni-based multi-component composite catalysts supported on θ-alumina spheres. The catalysts were characterized by TPR to evaluate the change of reduction temperature with the catalyst composition, which corresponded to the catalytic performance. Performance of CO methanation on these catalysts was compared in a continuous flow reactor under atmospheric pressure. The Rh-modification onto the known highly active three-component methanation catalyst Ni-La2O3-Ru exhibited an evident enhancement in the activity. Complete conversion of CO to methane preferentially occurred on this four-component catalyst, Ni-La2O3-Ru-Rh, as low as 230°C. As long as CO remained in the syngas, methanation of CO2 was completely retarded. It was reconfirmed that La2O3 increases Ni dispersion, and Rh and Ru enhance H2 adsorption, and induce the reduction of main catalyst component NiO x at a low temperature range by hydrogen spillover. These are the causes of the very high performance of this catalyst.
Keywords: Preferential methanation of CO; Rh-modified Ni-based composite catalyst; Hydrogen spillover; TPR measurements
Analysis of the simultaneous catalytic combustion of chlorinated aliphatic pollutants and toluene over ceria-zirconia mixed oxides by Beatriz de Rivas; Jose I. Gutiérrez-Ortiz; Rubén López-Fonseca; Juan R. González-Velasco (pp. 54-63).
In the present work the oxidation of representative VOCs, such as toluene, 1,2-dichloroethane and trichloroethylene, present in trace amounts in air streams over a series of Ce xZr1− xO2 oxides (CeO2, Ce0.8Zr0.2O2, Ce0.68Zr0.32O2, Ce0.5Zr0.5O2, Ce0.15Zr0.85O2, ZrO2) as catalysts was investigated with focus on the difference in catalytic performance in the oxidation of single and chlorinated VOC/toluene mixtures, and on the mixture effects on product selectivity. In general, the efficiency for the single VOC destruction decreased in the following order: toluene>1,2-dichloroethane>trichloroethylene. For chlorinated compounds the best performance was observed for the mixed oxides with 50 and 85mol% of zirconia content, while ceria exhibited the best behaviour for toluene oxidation. With regard to chlorinated compounds the combination of surface acidity and accessible lattice oxygen appeared to control the catalytic performance of the mixed oxides. On the contrary, the combustion of toluene was essentially controlled by surface oxygen species.Notable ‘mixture effects’ on both activity and selectivity were noticed when a given chlorinated feed was decomposed in the presence of toluene. On one hand, mutual inhibition took place but the conversion of trichloroethylene was retarded much more severely. On the other hand, the destruction of toluene was less affected by the presence of 1,2-dichloroethane. Competitive adsorption played an important role in the inhibition detected with CeO2-based catalysts. However, no one species was able to dominate the adsorption sites and thereby completely prevent the adsorption and reaction of other species. On the other hand, HCl selectivity was greatly enhanced by the presence of toluene in the feed stream.
Keywords: Catalytic combustion; VOCs; Ceria-zirconia mixed oxides; Binary mixtures; 1,2-Dichloroethane; Trichloroethylene; Toluene
Bimetallic Rh-Ge and Pt-Ge catalysts supported on TiO2 for citral hydrogenation by T. Ekou; A. Vicente; G. Lafaye; C. Especel; P. Marecot (pp. 64-72).
Bimetallic TiO2-supported Rh-Ge and Pt-Ge catalysts were prepared by surface redox reaction between hydrogen activated on a parent monometallic rhodium or platinum catalyst and a germanium salt dissolved in water (catalytic reduction method). They were characterized by elemental analysis, transmission electronic microscopy (TEM), temperature-programmed reduction (TPR) and by their activity for the gas phase dehydrogenation of cyclohexane.Elemental analysis of the bimetallic catalysts showed that germanium can effectively be deposited by the catalytic reduction method on titania-supported Rh and Pt catalysts. Moreover, the different characterization methods (TEM, TPR and cyclohexane dehydrogenation) proved that germanium is in great interaction with rhodium and platinum. Nevertheless, some germanium deposition occurred also separately on the titania support.TEM and cyclohexane dehydrogenation results revealed that both rhodium and platinum particles were stable on titania support under the conditions of bimetallic catalyst preparation contrary to previous results obtained with silica or alumina supports. Effectively, no sintering has been observed when they were immersed in an aqueous solution under hydrogen bubbling (catalytic reduction protocol). Their catalytic performances for the cyclohexane dehydrogenation reaction indicate that all the catalysts reduced at high temperature (500°C versus 300°C) developed the strong metal–support interaction (SMSI) effect, which implied the formation of TiO(2− x) species. Whatever the nature of the parent metal (Rh and Pt), this effect was totally destroyed by air exposure of the samples at ambient temperature whereas one part of the TiO(2− x) moieties remained after immersion of the catalysts in an aqueous medium.
Keywords: Rhodium; Platinum; Germanium; Titania; Bimetallic catalysts; SMSI effect
Bimetallic Rh-Ge and Pt-Ge catalysts supported on TiO2 for citral hydrogenation by T. Ekou; A. Vicente; G. Lafaye; C. Especel; P. Marecot (pp. 73-80).
Bimetallic Rh-Ge/TiO2 and Pt-Ge/TiO2 catalysts prepared by surface redox reaction (catalytic reduction method) were tested for the selective hydrogenation of citral. Samples were reduced either at 300°C or at 500°C (SMSI effect). For both Rh and Pt series, the unsaturated alcohols (UA) selectivity goes through an optimum as a function of the germanium content whatever the reduction temperature. For low Ge loadings, it was possible to combine the bimetallic and SMSI effects, inducing a high UA selectivity on bimetallic catalysts supported on TiO2. On the other hand, at high Ge loadings the bimetallic effect was predominant and led also to a high UA selectivity. Moreover, TiO2 support contributed to stabilize the bimetallic Rh-Ge and Pt-Ge particles prepared by catalytic reduction toward an air exposure at ambient temperature.
Keywords: Citral hydrogenation; Rhodium; Platinum; Germanium; Titania; Catalysts
Soot combustion with K/MgO as catalyst by Romel Jiménez; Ximena GarcÃa; Caroline Cellier; Patricio Ruiz; Alfredo L. Gordon (pp. 81-88).
This paper explores the possible effect of the potassium precursor on the activity of K/MgO catalysts for soot combustion and, in particular, which of previously described potassium roles would be more affected. The catalytic activity of the prepared K-catalysts was evaluated through thermogravimetric assays using catalyst-carbon black mixtures. Selected catalyst samples were characterized by XPS, AAS, BET surface area, carbothermic reduction, DRIFTS and XRD. The effect of physical contact was also assessed.The experimental results show that the addition of potassium from different precursors (KOH, KNO3) affects the basic nature of the catalyst surface and its interaction with active species, and this is reflected in the catalytic activity. With KNO3 as the precursor, a more active catalyst was obtained, a result that is attributed to: (i) higher concentration and dispersion of potassium, (ii) greater mobility and reactivity of the activated oxygen species, and (iii) lower stability of surface carbonates and OH groups, facilitating the formation of active species and favoring the mobility of surface activated oxygen.
Keywords: Soot; Catalytic combustion; Potassium
A comparative study of supported aqueous- and ethylene glycol-phase catalysts in stilbene hydrogenation: Influence of the different modes of dispersion of supported liquids by Shin-ichiro Fujita; Yoko Sano; Balchandra M. Bhanage; Masahiko Arai (pp. 89-93).
Supported liquid phase catalysts (SLPC) containing water-soluble Pd complexes were used for hydrogenation of stilbene in toluene. When water is loaded on a silica gel support, the catalytic activity of SLPC increases with the amount of the water. In contrast, when ethylene glycol (EG) is used as the supported liquid, the activity does not depend on the amount of EG loaded. These results can be explained by differences in the mode of dispersion of the supported liquids over the support.
Keywords: Supported liquid phase catalyst; Metal complex; Hydrogenation; Catalyst preparation; Palladium
Controlling factors in the direct formation of H2O2 from H2 and O2 over a Pd/SiO2 catalyst in ethanol by Qingsheng Liu; Jack H. Lunsford (pp. 94-100).
The direct formation of H2O2 in ethanol over a Pd/SiO2 catalyst has been studied under conditions that yield good selectivities for the peroxide, moderate rates of formation, and concentrations of H2O2 that approach 2wt.%. Several factors, including the partial pressures of H2 and O2, the presence of protons along with chloride and/or bromide ions, and the reaction temperature significantly affect the rate of H2O2 formation, the selectivity of the reaction, and the loss of palladium from the support. Mass transport, which is a function of a particular system, may also limit the rate of peroxide formation. Halide ions (Cl− or Br−) and protons (derived from H2SO4 in this study) are essential for limiting the combustion reaction; i.e., in the absence of these ions almost no peroxide was formed. A selectivity for H2O2 approaching 80% was achieved using 2×10−5M Br− and 0.12M H2SO4 with an O2/H2 ratio of 15. Bromide is particularly useful as the halide because it inhibits the loss of Pd from the support. The net formation rate for H2O2 was found to be first order with respect to H2 and zero order with respect to O2. The effects of changing the temperature from 5 to 15°C were evaluated, and it was observed that the system was most stable at the lowest temperature. As might be expected, the initial rate of peroxide formation and the conversion of H2 was the largest at 15°C, but as the reaction proceeded the rate of peroxide formation and the selectivity decreased. These results further establish the complexity of this three-phase system that involves a network of reactions and the possibility that the catalyst undergoes change with time.
Keywords: Hydrogen peroxide; Hydrogen; Oxygen; Palladium/silica catalyst; Mass transport
Growth of mordenite on monoliths by secondary synthesis by Juan M. Zamaro; MarÃa A. Ulla; Eduardo E. Miró (pp. 101-113).
Mordenite films were grown on FeCrAl alloy, CSi foam, and cordierite monoliths in order to study the influence of chemical and physical characteristics of the support on the structure of the coatings and its catalytic activity for the SCR of NO x with CH4 as test reaction, using In as the active ingredient. The method of secondary synthesis from nanometric seeds was selected because of the higher coating homogeneities achieved. The FeCrAl alloy and cordierite yielded ordered crystals growths, preferentially with the b-axis perpendicular to the metallic surface, and with the c-axis perpendicular to the cordierite support, respectively. While high crystal intergrowth was observed for the FeCrAl alloy, in the cordierite case it was limited to the interphase. The CSi foam yielded disordered film structures, forming a dense phase in the shape of cumulus laying at the top of mordenite crystals with high intergrowth. The differences are mainly attributed to chemical characteristics that originate different local environments in which the seeds are immersed and the growth takes place, the topography of the substrates not being so important. The order in maximum NO x conversions was InHMOR/FeCrAl>InHMOR/cordierite>InHMOR powder>InHMOR/CSi, and it can be related, among other factors, to the accessibility of the reactants to the active sites.
Keywords: In-mordenite; Hydrothermal synthesis; Monoliths; SCR of NO; x; with CH; 4
Autocatalysis-like behavior of hydrogen sulfide on hydrodesulfurization of polyaromatic thiophenes over a synthesized molybdenum sulfide catalyst by Hamdy Farag; Kinya Sakanishi; Takenaka Sakae; Masahiro Kishida (pp. 114-122).
Hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene over a synthesized nanosize-MoS2 catalyst were investigated in a batch reactor. The catalytic activity in hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene increased remarkably with H2S being remained in the reaction zone. The HDS reactions of the two substrates over the present catalyst were found to proceed via a network where direct desulfurization and hydrogenation routes are essentially involved. The product contribution from the hydrogenation route is much more pronounced. Isomerized components were also identified. Dibenzothiophene and 4,6-dimethyldibenzothiophene exhibited almost identical results in terms of the reactivity and selectivity. The increase in the catalytic activity with H2S is probably due to the increase in the number of the potentially active sites modified by H2S. The kinetic investigation of the hydrodesulfurization reactions revealed the autocatalysis-like phenomena attributed to the potentially modified active sites by self-produced H2S. TEM image reveals that the synthesized MoS2 may consist of a bent and/or a closed round layers which might play an important role in such autocatalysis behaviors of H2S in the hydrodesulfurization of polyaromatic thiophenes.
Keywords: Hydrodesulfurization; H; 2; S; MoS; 2; Dibenzothiophene; 4,6-Dimethyldibenzothiophene
Enhanced photocatalytic activity of TiO2− xN x loaded with copper ions under visible light irradiation by Takeshi Morikawa; Yoshihiro Irokawa; Takeshi Ohwaki (pp. 123-127).
Nitrogen-doped TiO2 (TiO2− xN x) photocatalysts loaded with various transition metal ions, including Cu, Pt, Ni, Zn and La, were prepared using a wet impregnation method. Photocatalytic activity of the catalysts under visible light irradiation ( λ>410nm) for acetaldehyde oxidation was examined. As a result, it was found that photocatalytic activity over TiO2− xN x (concentration of nitrogen was found to be ∼0.25at.%) was markedly enhanced by Cu or Pt loading, while Ni, Zn or La loaded TiO2− xN x showed similar photodegradation rate to the bare TiO2− xN x. Among them, the enhancement effect of Cu ion was found highest. The optimum concentration of Cu was found to be 0.5wt%, and X-ray photoelectron spectroscopy (XPS) and X-ray induced Auger electron spectroscopy (XAES) analyses suggested the presence of Cu2O or Cu hydroxides on the catalyst surface. In terms of the long-term stability of the catalysts, it was confirmed that more than 2100μmol of CO2 was produced when acetaldehyde was continuously photooxidized over 1100μmol of Cu loaded TiO2− xN x under visible light for 100 consecutive days (>410nm, 0.9mW/cm2, in a 1L vessel).
Keywords: Photocatalysis; Nitrogen-doped TiO; 2; Visible light; Acetaldehyde; Photooxidation; Carbon dioxide; Metal loading; Copper; Nitrogen doping; Antibacterial; Bactericidal
Selective hydrogenation of acetylene in excess ethylene on micron-sized and nanocrystalline TiO2 supported Pd catalysts by Joongjai Panpranot; Kunyaluck Kontapakdee; Piyasan Praserthdam (pp. 128-133).
Physicochemical properties and catalytic performances of Pd catalysts supported on commercial micron-sized and nanocrystalline TiO2 synthesized by sol–gel and solvothermal method were studied for the selective hydrogenation of acetylene in the presence of excess ethylene. While acetylene conversions were found to be merely dependent on Pd dispersion, ethylene selectivity appeared to be strongly affected by the presence of Ti3+ in the TiO2 samples. The use of pure anatase TiO2 (either micron- or nano-sized) that contained significant amount of Ti3+ as supports for Pd catalysts gave high ethylene selectivities, while the use of pure rutile TiO2 (without Ti3+ present) resulted in ethylene loss. The results suggest that the effect of Ti3+ on the TiO2 supports was more important for high ethylene selectivity than the effect of TiO2 crystallite size for selective acetylene hydrogenation over Pd/TiO2 catalysts.
Keywords: Selective acetylene hydrogenation; Pd/TiO; 2; Nanocrystalline TiO; 2; Sol–gel; Solvothermal; Defect
Erratum to “Dehydration of butanediols over CeO2 catalysts with different particle sizes� [Appl. Catal. A: Gen. 300 (2006) 50–57]
by Ai Igarashi; Naoki Ichikawa; Satoshi Sato; Ryoji Takahashi; Toshiaki Sodesawa (pp. 134-134).