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Applied Catalysis A, General (v.300, #2)
Comparison of liquid-phase olefin epoxidation over MoO x inserted within mesoporous silica (MCM-41, SBA-15) and grafted onto silica by Paul Célestin Bakala; Emmanuel Briot; Laurent Salles; Jean-Marie Brégeault (pp. 91-99).
Molybdenum(VI)-containing siliceous-MCM-41 and -SBA-15 mesoporous molecular sieves and silica-supported molybdenum(VI) complexes have been prepared according to an original pathway by the reaction between low-cost Mo(VI) peroxo species and silica precursors (tetraethylorthosilicate), silica beads (pure SiO2) or precipitated silica in an acidic and peroxidic medium (peroxo route). Hydrogen peroxide is added to avoid the formation of iso-(or hetero-)polyoxometalates in the direct one-pot synthesis of mesoporous solids, or in the case of pure SiO2. The resulting calcined materials have been characterized by chemical analysis, X-ray powder diffraction, nitrogen sorption isotherms, TEM and EDX analysis, UV–vis diffuse reflectance spectroscopy, Raman spectrometry and catalysis tests. The peroxo routes lead to inserted and/or supported molybdenum oxide zones which are restricted in size due to the porous structure of the silica-based materials and to the involment of low-condensed and even mononuclear oxoperoxo species. This allows to support MoO x species in a dispersion which cannot be achieved with the systems using heptamolybdate [Mo7O24]6− salts or heteropolyoxometalates, which favor the anchoring of MoO3 clusters. Catalysis tests show that the very dispersive structure of the MoO x-siliceous-MCM-41, -SBA-15 and MoO x/SiO2 promotes the generation of fairly active oxidation catalysts for liquid-phase olefin epoxidation (cyclooctene, R-(+)-limonene from ambient to 40°C) using anhydrous tert-butylhydroperoxide (TBHP) as oxidant. Under specific conditions, leaching of redox-active species has been minimized (less than 2ppm) especially with MoO x/SiO2 which is proposed as the simplest catalyst for these oxidations. MCM-41 and SBA-15 do not show clear advantages over silica in epoxidation reactions with TBHP.
Keywords: Mesoporous solids; Silica; Oxoperoxo species; Epoxidation; Hydrogen peroxide
Epoxidation with hydrotalcite-intercalated organotungstic complexes by Jorge Palomeque; François Figueras; Georges Gelbard (pp. 100-108).
W(VI)-based catalysts for epoxidation were incorporated into hydrotalcite either by anionic exchange or by complexation with phosphonic acids previously incorporated between the sheets. Phenyl- and dodecylphosphonic acids and peroxotungstic salts were intercalated into hydrotalcite as attested by the expansion of the lamellar lattice and the complexation of phosphonic acids with W-peroxo species was made possible when using a lipophilic quaternary ammonium peroxotungstic salt [W(VI)-Aliquat] which maintains the layered structure. These catalysts were checked in the epoxidation of cyclohexene with hydrogen peroxide or terbutylhydroperoxide as external oxidants. The materials prepared by anionic exchange gave only epoxycyclohexane but with moderate yields, whereas those prepared from previously incorporated phosphonic acids gave rather high selectivity (50–72%) in allylic oxidation products.
Keywords: Peroxotungstate; Olefin epoxidation; Hydrotalcite; Hydrogen peroxide; Dodecylphosphonic acid; Epoxidation; Peroxotungstic acid; Phenylphosphonic acid
A new class of highly dispersed VOx catalysts on mesoporous silica: Synthesis, characterization, and catalytic activity in the partial oxidation of ethanol by Ja Hun Kwak; Jose E. Herrera; Jian Zhi Hu; Yong Wang; C.H.F. Peden (pp. 109-119).
The morphology of vanadium oxide supported on a titania-modified mesoporous silica (MCM-41), obtained by means of a careful grafting process through atomic layer deposition, was studied using a variety of characterization techniques. The X-ray diffraction (XRD) together with transmission electron microscopy (TEM),51V nuclear magnetic resonance (51V-NMR), Raman, FTIR and DRS-UV/Vis results showed that the vanadia species are extremely well dispersed onto the surface of the mesoporous support; the dispersion being stable upon thermal treatments up to 400°C. Studies of the catalytic activity of these materials were performed using the partial oxidation of ethanol as a probe reaction. The results indicate an intrinsic relationship between dispersion, the presence of a TiO2–VOx phase, and catalytic activity for oxidation and dehydration.
Keywords: Vanadium oxide; MCM-41; Atomic layer deposition; Ethanol partial oxidation; 51; V-NMR; UV–vis DRS; Raman
Modification of catalytic properties over carbon supported Ru–Cu and Ni–Cu bimetallics by E. Asedegbega-Nieto; B. Bachiller-Baeza; A. Guerrero-Ruíz; I. Rodríguez-Ramos (pp. 120-129).
Two series of bimetallic catalysts, Ru–Cu and Ni–Cu, supported on a high surface area graphite were prepared. These catalysts were characterized by TPR, H2 chemisorption and X-ray photoelectron spectroscopy. The results obtained with these techniques indicate that for the Ru–Cu series, Ru and Cu atoms are in more intimate contact for the catalyst with lowest Cu content than for the other bimetallic catalysts belonging to this series. This conclusion was also reached when these catalysts were employed in the hydrogenation reactions of citral and cinnamaldehyde. For both substrates similar selectivity patterns were obtained over each of the Ru–Cu catalysts. As for the Ni–Cu series, characterization results proved the existence of alloy formation between Ni and Cu. When these catalysts were employed in the hydrogenations of citral and cinnamaldehyde the saturated aldehydes were the main products obtained owing to the high selectivity of Ni towards the formation of these hydrogenation products. Therefore when Cu, which is not very active in these reactions, is added significant changes in the selectivity are not observed.
Keywords: Bimetallic catalysts; TPR; H; 2; chemisorption; X-ray photoelectron spectroscopy; Citral; Cinnnamaldehyde
Improving hydrogen storage/release properties of magnesium with nano-sized metal catalysts as measured by tapered element oscillating microbalance by Xiaochun Xu; Chunshan Song (pp. 130-138).
An effective catalyst doping method was developed for directly depositing nano-particles of various metal catalysts (palladium, platinum and ruthenium) on the outer surface of magnesium powders through a wet chemistry process. The catalyst-doped magnesium was characterized by powder X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). Catalysts of nano-meter size were uniformly deposited on the outer surface of the magnesium particles. The hydrogen storage and hydrogen release properties of magnesium and catalysts-doped magnesium were measured in situ by the tapered element oscillating microbalance (TEOM), and also by the volumetric method. Both the hydrogen absorption and hydrogen release kinetics of magnesium were significantly improved by doping the nano-particle catalysts. Among the three metals-doped and examined, palladium showed the best catalytic effect. Upon doping 0.5mol% nano-particle palladium, the hydrogen absorption and hydrogen release rates of magnesium increased 1 and 14 times, respectively, as revealed by the dynamic measurement of storage/release by TEOM, which indicated a strong catalytic effect.
Keywords: Catalysts; Fuel cell; Hydrogen storage; Magnesium; Nano-particle; Palladium; TEOM; Volumetric method
Structure and reactivity of zirconium oxide-supported ammonium salt of 12-molybdophosphoric acid catalysts by K. Narasimha Rao; K. Mohan Reddy; N. Lingaiah; I. Suryanarayana; P.S. Sai Prasad (pp. 139-146).
A series of catalysts with varying quantities of ammonium salt of 12-molybdophosphoric acid supported on zirconium dioxide was synthesized. The catalysts were characterized by nitrogen adsorption for BET surface area, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and31P MAS NMR techniques to study the nature of the interactions of the active component with the support as a function of salt loading. The nature of the Keggin ion species (intact, fragmented or decomposed) formed on the support varies with the extent of loading of the heteropolyacid salt. A good correlation was obtained between the extent of formation of lacunary Keggin ion species and the activity of the catalysts during the ammoxidation of 2-methylpyrazine at different reaction temperatures.
Keywords: Ammonium salt of 12-molybdophosphoric acid; Zirconia; Ammoxidation of 2-methylpyrazine
Platinum group metals as catalysts in enantioselective 1-phenylpropane-1,2-dione hydrogenation by E. Toukoniitty; S. Franceschini; A. Vaccari; D.Yu. Murzin (pp. 147-154).
Different γ-Al2O3 supported Ir, Pd, Ru, Rh and Pt catalysts were tested in enantioselective 1-phenylpropane-1,2-dione hydrogenation using cinchona alkaloid modifiers. Activity and enantioselectivity over Ir and Ru catalysts were low. Pd catalyst was active in the hydrogenation of 1-phenylpropane-1,2-dione, however, the enantioselectivity over this catalyst was almost negligible. Over Pd hydrogenation proceeded mainly via hydrogenation of the C1O1 carbonyl group, which is attached to the phenyl ring. Hydrogenation over Pd did not proceed in the second hydrogenation step via an enol form as found for ethyl pyruvate hydrogenation over Pd. The structure-selectivity relationship and solvent effects are similar over Pt and Rh in the first hydrogenation step. However, in the second hydrogenation step of hydroxyketones to diols large mechanistical differences between Pt and Rh were observed. Although the activity over Rh catalysts was lower than over Pt after optimization the best result obtained with Rh/γ-Al2O3 (5754 Lancaster) was 60% ee in toluene at maximum yield of 28%, which makes Rh a promising metal for enantioselective hydrogenation.
Keywords: Hydrogenation; Diones; Enantioselectivity; Regioselectivity; Pd; Rh; Ru; Ir; Pt
Methanol steam reforming over paper-like composites of Cu/ZnO catalyst and ceramic fiber by Shuji Fukahori; Takuya Kitaoka; Akihiko Tomoda; Ryo Suzuki; Hiroyuki Wariishi (pp. 155-161).
Copper–zinc oxide catalyst powders were successfully prepared into paper-like composites, called catalyst paper in this study, using ceramic fibers as the carrier matrix of the catalyst. A papermaking technique with a dual polyelectrolyte retention system was used. Catalyst particles were supported on the ceramic fiber networks tailored in the catalyst paper having various types of pores. Pieces of catalyst paper were subjected to methanol steam reforming (MSR) to produce hydrogen gas for fuel cell applications. They demonstrated a higher performance for methanol conversion and hydrogen production in the MSR reaction than commercial Cu/ZnO catalyst pellets, exhibiting an efficacy equivalent to that of the original catalyst powders. The concentration of carbon monoxide, which acts as a catalytic poison for fuel electrode catalysts, decreased remarkably, without any carbon monoxide reduction system. Moreover, the porous structure of catalyst paper influenced the MSR efficiency. It was assumed that the macropores ca. 20μm in diameter greatly contributed to the MSR performance, rather than the mesopores on the catalyst surfaces. Thus, the porous, flexible and easy-to-handle catalyst paper is a promising material for practical MSR applications.
Keywords: Cu/ZnO catalyst; Catalyst paper; Papermaking technique; Methanol steam reforming; Hydrogen production; Carbon monoxide; Porous structure; Fuel cell
High performance Pd/beta catalyst for the production of gasoline-range iso-paraffins via a modified Fischer–Tropsch reaction by Zhong-Wen Liu; Xiaohong Li; Kenji Asami; Kaoru Fujimoto (pp. 162-169).
The direct synthesis of gasoline-range iso-paraffins from synthesis gas (CO+H2, syngas) via a modified Fischer–Tropsch (FT) reaction was intensively studied under a wide range of reaction conditions by the combination of Co/SiO2 and Pd/beta in a consecutive dual reactor system. Results indicate that high selectivity of gasoline-range iso-paraffins ( iso-paraffins relative to C4+ hydrocarbons was about 80%) could be achieved with the presence of Pd/beta catalyst in the lower reactor. Moreover, the performance of the Pd/beta catalyst for the titled reaction and the product composition can be significantly regulated by independently changing the reaction conditions such as catalyst amount, reaction temperature, and hydrogen partial pressure in the lower reactor. It was found that the Pd/beta catalyst used in this work was very active and stable even at a reaction temperature as low as 503K. With the increase of hydrogen partial pressure in the lower reactor, the long-term stability of the Pd/beta catalyst was significantly enhanced.
Keywords: iso; -Paraffin synthesis; Fischer–Tropsch; Beta zeolite; Bifunctional catalyst
Nanosized iron and iron–cobalt spinel oxides as catalysts for methanol decomposition by E. Manova; T. Tsoncheva; Cl. Estournès; D. Paneva; K. Tenchev; I. Mitov; L. Petrov (pp. 170-180).
Nanosized iron and mixed iron–cobalt oxides supported on activated carbon materials and their bulk analogues prepared by thermal synthesis are studied by X-rays diffraction, Mössbauer spectroscopy, magnetic measurements and temperature programmed reduction. Their catalytic behavior in methanol decomposition to H2, CO and methane is tested. Phase transformations in the metal oxides affected by the reaction medium are also investigated. Changes in the reaction mechanism of the methanol decomposition after the metal oxides deposition on the support as compared to the bulk phases are discussed.
Keywords: Nanoparticles; Iron and/or cobalt oxide catalysts; Mössbauer spectroscopy; Methanol decomposition; Magnetism
Carbon-supported cobalt–iron catalysts for ammonia synthesis by W. Raróg-Pilecka; A. Jedynak-Koczuk; J. Petryk; E. Miśkiewicz; S. Jodzis; Z. Kaszkur; Z. Kowalczyk (pp. 181-185).
The cobalt, iron and Co–Fe catalysts deposited on carbon were prepared, characterised (XRD, H2 TPD) and studied in ammonia synthesis at 90bar (H2:N2=3:1). Partly graphitised carbon material obtained via high temperature treatment (1900°C) of commercial activated carbon was used as a support for the active metals (10wt.%) and barium or potassium were used as promoters. XRD studies of unpromoted materials have shown that cobalt (5–20% in Co+Fe) dissolves in the iron phase (alloy formation); the average sizes of crystallites (20–30nm) are roughly independent of the metal kind (Co, Fe, Co–Fe). The effect of Ba and that of K on the catalyst performance proved to be strongly dependent on the choice of an active phase (Co or Fe or Co–Fe). In the case of Co/C, the promotional effect of barium was extremely large. Furthermore, the Ba–Co/C system was found to be less inhibited by the ammonia product than Ba–Fe/C. At low temperature (400°C) and at high conversion (8% NH3 in the gas), the surface-based reaction rate (TOF) for Ba–Co/C is about six times higher than that for Ba–Fe/C.
Keywords: Ammonia synthesis; Cobalt–iron catalyst; Carbon support; Barium potassium promoter
Photocatalytic activity of hydrothermally synthesized tantalate pyrochlores for overall water splitting by Shigeru Ikeda; Minori Fubuki; Yoshiko K. Takahara; Michio Matsumura (pp. 186-190).
Tantalate and niobate pyrochlores, Ca2M2O7 (M=Nb, Ta) and A2Ta2O6 (A=Na, K), were prepared by a hydrothermal method. These oxides were crystallized directly from tantalum or niobium alkoxide in the presence of sodium, potassium or calcium cation in basic solutions at temperatures between 373 and 448K, and their crystallinity was improved by calcination in air. Stoichiometric liberations of H2 and O2 were achieved over tantalate pyrochlores loaded with a small amount of nickel oxide (NiO) as a catalyst for H2 production, while the NiO-loaded niobate pyrochlore showed no photocatalytic activity. The photocatalytic functions of the tantalate pyrochlores were attributed to their energy levels of the bottom of conduction bands being much more negative than those of the niobate pyrochlores.
Keywords: Overall water splitting; Photocatalysis; Tantalate pyrochlores; Hydrothermal synthesis; Crystallinity; Band gap energy