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Applied Catalysis A, General (v.286, #2)
Preferential oxidation of CO under excess H2 conditions over Ru catalysts by Soo Yin Chin; Oleg S. Alexeev; Michael D. Amiridis (pp. 157-166).
The preferential oxidation of CO in the presence of excess H2 (PROX reaction) has been examined over SiO2- and Al2O3-supported Ru catalysts. The effects of various parameters (pretreatment conditions, nature of support and precursor) on catalyst structure and performance were investigated through the use of O2 chemisorption, HRTEM, FTIR, and kinetic measurements. The combination of a direct hydrogen treatment and use of a nitrate precursor results in the synthesis of finely dispersed Ru catalysts capable of completely eliminating CO in the temperature range of 120–150°C for Ru/SiO2 and 160–180°C for Ru/Al2O3 at a space velocity of 120000mL/gh. Addition of 10% H2O essentially has no effect on the CO oxidation over Ru/SiO2, while a relatively small effect (negative below 180°C and positive above 200°C) is observed with Ru/Al2O3. In contrast, the addition of 15% CO2 suppresses the CO oxidation over both catalysts at the high temperature end, with the effect being more pronounced over the SiO2-supported sample. Both effects can be attributed to the onset of the forward and reverse water gas shift reactions. Overall, in the presence of both H2O and CO2 the H2O effect dominates, due to the high value of the water gas shift equilibrium constant at these temperatures.
Keywords: Selective oxidation; CO oxidation; PROX; Ruthenium
Effect of oxidant treatment of date pit active carbons used as Pd supports in catalytic hydrogenation of nitrobenzene by N. Bouchenafa-Saïb; P. Grange; P. Verhasselt; F. Addoun; V. Dubois (pp. 167-174).
Two active carbons from Algerian date pits prepared by chemical activation at moderate temperature (500–600°C) with H3PO4 and ZnCl2 and one commercial active carbon (from Darco) have been oxidized with air at different temperatures (300–450°C) and with nitric acid in severe conditions during a short time. It has been demonstrated that air treatment generates surface oxygenated groups (XPS) that have an acidic character (simplified Boehm titration), without degrading the specific surface area (BET). Each active carbon has an optimal oxidation temperature depending on its activation procedure and corresponding to 20% in weight loss during the oxidation process. This optimal temperature achieves the highest surface oxygen content, which is directly correlated to the global acidity. It also means that when the support is loaded with 5% Pd by incipient wetness method, the catalyst exhibits the best activity for the liquid phase hydrogenation of nitrobenzene to aniline. In general, the metallic dispersion of the catalysts (CO chemisorption) remained appreciable even after oxidizing treatments. Exception is noted when nitric acid is used as oxidant while the active carbon has been prepared using zinc chloride.
Keywords: Nitrobenzene; Hydrogenation; Pd/C; Active carbon; Support acidity; Date pits
Preparation of copper catalyst washcoats for methanol steam reforming in microchannels based on nanoparticles by P. Pfeifer; K. Schubert; G. Emig (pp. 175-185).
The demand of fast load alternations for hydrogen generation by methanol steam reforming for automotive fuel cell application may be met in an excellent manner by microstructured reactors. However, catalyst incorporation is difficult in the micrometer size. By the use of dispersed nanoparticles a washcoating procedure was developed and is explained on the basis of a copper catalyst system. The mixing of CuO particles with other necessary materials like ZnO was examined during high energy ball milling (dry mixing) or dispersing the powders in a solution of cellulose derivatives (wet mixing). For the latter technique the shearing of agglomerates and re-agglomeration were investigated for the pure substances using laser diffraction. The influence of ball milling on particle sizes was determined by adsorption experiments and X-ray diffraction. All mixtures were characterized by temperature programmed reduction (TPR) followed by the measurement of the Cu(0) particle size (X-ray diffraction). A special method based upon X-ray structure analysis was applied for determination of the mixing quality. The relationship between these catalyst properties and additional measurements of the catalyst activity/degradation done was obvious.
Keywords: Microstructured reactor; Microchannel reactor; Methanol steam reforming; Nanoparticle washcoat; Copper oxide; High energy ball milling; Dispersing; Mixing quality
Surface-selective infiltration of thin-film catalyst into microchannel reactors by H. Chen; L. Bednarova; R.S. Besser; W.Y. Lee (pp. 186-195).
A thin-film Pt/Al2O3 catalyst was synthesized by a sol–gel synthesis method with hydrogen hexachloroplatinate hydrate and aluminum isopropoxide as precursors in a water-based solvent. The catalyst contained ∼5nm Pt particles dispersed on Al2O3 support, which was mostly amorphous with a specific surface area of 400–450m2/g and a pore size distribution in the range of 2–8nm. For uniform infiltration of the sol–gel catalyst precursor into the microchannel of Si-based reactors, a hydrophobic film was applied to the top surface of the reactors while reactive ion etched microchannel surface of the reactors remained hydrophilic. Under these surface conditions, the catalyst precursor infiltrated selectively into the microchannel without spilling over to the reactor surface. In comparison to other infiltration methods, this surface-selective approach provided an effective means of precisely controlling the amount of catalyst loaded into the reactors and keeping the reactor surface clean for subsequent sealing via anodic bonding. However, as delamination occurred preferentially at the sharp corners of the microchannel, the thickness of the catalyst layer that could be practically incorporated into the reactors was limited to ∼3μm.
Keywords: Thin-film catalyst; Pt/Al; 2; O; 3; Sol–gel synthesis; Surface-selective infiltration; Microchannel reactor
Interaction between Ni and V with USHY and rare earth HY zeolite during hydrothermal deactivation by Alyne S. Escobar; Marcelo M. Pereira; Ricardo D.M. Pimenta; Lam Y. Lau; Henrique S. Cerqueira (pp. 196-201).
The effect of Ni and V in the hydrothermal deactivation of an ultrastable Y zeolite with and without rare earth elements is presented and discussed. Although in the presence of steam, vanadium itself is the main factor responsible for zeolite loss of surface area, for the rare earth containing sample the presence of nickel increased the vanadium effect. Temperature-programmed reduction of these zeolites further support this observation by showing an increased amount of mobile readily reducible vanadium species while nickel and rare earth interact. The same deleterious effect of nickel was also observed in rare earth containing FCC catalysts after hydrothermal deactivation.
Keywords: Y zeolite; Nickel; Vanadium; Deactivation; Rare earth
Reductive amination of cyclopentanone by P. Doležal; O. Machalický; M. Pavelek; P. Kubec; K. Hrádková; R. Hrdina; R. Šuláková (pp. 202-210).
The kinetics of heterogeneous catalytic reductive amination of cyclopentanone has been studied on a pilot plant PARR autoclave. N-cyclopentyliminocyclopentane was detected as the main intermediate in a reaction mixture. It was found that, at the given conditions, the main intermediate does not form the undesirable N, N-dicyclopentylamine but undergoes slow hydrolysis, and the desired product, cyclopentylamine, results in a good yield. Slight amounts of by-products such as cyclopentanole and N, N-dicyclopentylamine were obtained. The experimental data were confronted with the suggested kinetic model.
Keywords: Cyclopentanone; Cyclopentylamine; N; -cyclopentyliminocyclopentane; Heterogeneous catalytic reductive amination; Kinetics
Hydrotalcite like compounds with low Mo-loading active catalysts for selective oxidation of cyclohexene with hydrogen peroxide by Rodica Zǎvoianu; Ruxandra Bîrjega; Octavian Dumitru Pavel; Anca Cruceanu; Mihai Alifanti (pp. 211-220).
Several Mo-containing hydrotalcite-like compounds (HTlcs-Mo) were prepared by different ionic exchange procedures using as parent a synthetic hydrotalcite Mg3Al(OH)8(CO3)0.5·2H2O with a composition similar to the natural occurring mineral. Their physico-chemical properties determined by chemical and TG–DTA analyses, XRD, BET, FTIR, SEM-EDX, DR–UV–vis and Raman spectroscopy, were compared to those of two HTlcs-Mo prepared by direct synthesis at constant pH=10 and low or respectively high supersaturation. The catalytic activity of these solids towards cyclohexene oxidation with hydrogen peroxide was investigated. The catalytic activity was mainly influenced by the basic properties of the catalysts, which varied depending on the preparation procedure. The best catalysts for hydroperoxidation were found to be those having a low Mo content (about 2.5–2.8%) in the form of MoO42− species, and higher Mg concentration in the brucite layer. The catalysts containing also Mo7O246− species were more active for epoxidation.
Keywords: Layered double hydroxide; Hydrotalcite; Molybdate; Heptamolybdate; Cyclohexene oxidation; Hydrogen peroxide
Biomimetic catalysis of an organophosphate by molecularly surface imprinted polymers by Rıdvan Say; Murat Erdem; Arzu Ersöz; Hayrettin Türk; Adil Denizli (pp. 221-225).
A synthetic polymer selective for paraoxon was prepared by a molecular surface imprinting technique. We have combined molecular imprinting with the ability of histidine to chelate metal ions to create active centrum of phosphotriesterase on microbead surfaces. For this purpose, methacryloyl–histidine–copper(II) [MAH–Cu(II)] and methacryloyl–histidine–copper(II)–paraoxon [MAH–Cu(II)–paraoxon] metal chelating monomers were synthesized; paraoxon imprinted polymers were produced and the binding characteristics of the polymers were evaluated. The optimum pH was determined applying different pH values and the hydrolytic activity of phosphotriesterase was evaluated in the framework of Micheaelis–Menten kinetics. In addition, the values of maximal rate: Vm (4.58×10−2μM/min) and Micheaelis–Menten constant, Km (1.28×10−3M), were obtained from Lineweaver–Burk plots for the imprinted polymeric catalyst.
Keywords: Molecular imprinting; MIP; Nerve agent; Detoxification; Enzyme analogue; Biomimetic catalysis
Effect of catalytic activity on methane steam reforming in hydrogen-permeable membrane reactor by Jianhua Tong; Yasuyuki Matsumura (pp. 226-231).
Steam reforming of methane, mainly to hydrogen and carbon dioxide, proceeds over nickel catalysts at 800K in an equilibrium-shift reactor with a thin palladium membrane 11μm-thick supported on a stainless steel porous metal filter. The methane conversion greatly exceeds its equilibrium conversion due to the hydrogen separation with the membrane. The catalytic activity affects the conversion much more than in the cases using an equilibrium reactor. The conversion in the membrane reactor decreases with an increase in the space velocity of the reaction mixture, mainly because of a decrease in the hydrogen separation ratio (rate of hydrogen separation/total production rate of hydrogen). The rate of hydrogen separation depends basically on the hydrogen permeability of the membrane, but an active catalyst also increases the rate; that is, the hydrogen production rate depends on the catalytic activity. Thus, the higher rate causes the higher partial pressure of hydrogen in the reactor, while the hydrogen flux through the membrane depends on the pressure.
Keywords: Membrane reactor; Hydrogen separation; Palladium membrane; Methane steam reforming; Nickel catalyst
Deposition ofγ-Al2O3 layers on structured supports for the design of new catalytic reactors by Valérie Meille; Stéphanie Pallier; Gabriela V. Santa Cruz Bustamante; Marilyne Roumanie; Jean-Pierre Reymond (pp. 232-238).
Structured objects of different characteristic size have been coated withγ-Al2O3. The oxide layers are characterised in terms of thickness, surface area, crystalline phase, adherence on the support surface, etc. According to the structured object, adherent oxide layers from less than 1 to around 200μm have been obtained.
Keywords: Washcoating; Spray-coating; Suspensions; Al; 2; O; 3; Structured catalytic reactors
Catalysts based on Co/zirconium doped mesoporous silica MSU for the hydrogenation and hydrogenolysis/hydrocracking of tetralin by A. Infantes-Molina; J. Mérida-Robles; E. Rodríguez-Castellón; B. Pawelec; J.L.G. Fierro; A. Jiménez-López (pp. 239-248).
Zirconium doped mesoporous silica (MSU) has been used as a support of Co catalysts with different Co-loadings. These catalysts have been characterised by several techniques such as XRD, XPS, textural properties, H2-TPR, NH3-TPD, chemisorption of H2, DRIFTS and FT-IR of adsorbed NO. The performance in the hydrogenation and hydrogenolysis/hydrocracking of tetralin at different temperatures has been examined in a high-pressure fixed-bed continuous-flow stainless steel catalytic reactor operating at 6.0MPa of pressure. The incorporation of cobalt by using the incipient wetness method with an aqueous solution of cobalt nitrate is effective for preparing catalysts with 5–20wt.% Co. The behaviour of these catalysts demonstrates that the higher the metallic loading, the contact time between catalyst and reactants, and the H2/tetralin molar ratio, the better the results with conversions in the steady-state near to 100% and better the yields of hydrogenation and hydrogenolysis/hydrocracking products. Thus, the catalyst with 15wt.% of Co, operating at 315°C, with a contact time of 3.6s and an H2/tetralin molar ratio of 15, gives rise to a conversion of tetralin of nearly 100%, yields of hydrogenation of 71%, and of hydrogenolysis/hydrocracking of 28% after 6h on-stream. In addition, the thiotolerance of these catalysts has been tested with a feed of 425 and 850ppm of dibenzothiophene (DBT). With 425ppm of DBT, the performance of the best catalyst is only reduced by 17% after 5h on-stream. However, with 850ppm of DBT, a dramatic decrease in the activity is observed, although this activity can be recovered after new thermal and reduction treatments.
Keywords: Mesoporous MSU molecular sieves; Cobalt catalysts; Tetralin hydrogenation; Hydrogenolysis/hydrocracking; Sulfur tolerance
Effect of noble metal particle size on the sulfur tolerance of monometallic Pd and Pt catalysts supported on high-silica USY zeolite by Takashi Matsui; Masaru Harada; Yuichi Ichihashi; Kyoko K. Bando; Nobuyuki Matsubayashi; Makoto Toba; Yuji Yoshimura (pp. 249-257).
The size effect of monometallic Pd and Pt clusters was investigated for the sulfur tolerance of these noble metal catalysts supported on high-silica USY zeolite, using the CO adsorption method and the extended X-ray adsorption fine structure (EXAFS) method. Both Pd and Pt particles show the highest surface sulfur tolerance in the form of <20Å-diameter particles, although the bulk phase of these clusters is subject to penetration by adsorbed sulfur atoms. For noble metal particles >25Å in diameter, the bulk phases of the Pd and the Pt particles approach that of the metallic structure. With increased cluster size, the surface sulfur tolerance of Pt particles decreases gradually, while that of Pd particles decreases rapidly. For large noble metal particles >50Å in diameter, EXAFS spectra show that sulfidation in the bulk phase of the noble metal particles is suppressed for Pt but promoted for Pd.
Keywords: Pd; Pt; Noble metal catalyst; USY zeolite; Size effect; Sulfur tolerance; EXAFS