Gold catalysts supported on ZnO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> for low-temperature CO oxidation

Gold catalysts with loadings ranging from 0.5 to 7.0 wt% on a ZnO/Al₂O₃ support were prepared by the deposition–precipitation method (Au/ZnO/Al₂O₃) with ammonium bicarbonate as the precipitation agent and were evaluated for performance in CO oxidation. These catalysts were characterized by inductively coupled plasma-atom emission spectrometry, temperature programmed reduction, and scanning transmission electron microscopy. The catalytic activity for CO oxidation was measured using a flow reactor under atmospheric pressure. Catalytic activity was found to be strongly dependent on the reduction property of oxygen adsorbed on the gold surface, which related to gold particle size. Higher catalytic activity was found when the gold particles had an average diameter of 3–5 nm; in this range, gold catalysts were more active than the Pt/ZnO/Al₂O₃ catalyst in CO oxidation. Au/ZnO/Al₂O₃ catalyst with small amount of ZnO is more active than Au/Al₂O₃ catalyst due to higher dispersion of gold particles.     

Selective oxidation of carbon monoxide in hydrogen-containing gas on CuO-CeO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts prepared by surface self-propagating thermal synthesis

The CuO-CeO₂/Al₂O₃ catalysts for the selective oxidation of CO in hydrogen-containing mixtures were prepared by surface self-propagating thermal synthesis (SSTS) with the use of cerium nitrate Ce(NO₃)₃, the ammonia complex of copper acetate [Cu(NH₃)₄](CH₃COO)₂, and citric acid C₆H₈O₇ as a fuel additive. The effect of the C₆H₈O₇/Ce(NO₃)₃ molar ratio on the catalyst activity and selectivity for oxygen was studied. The catalyst samples were studied by X-ray diffraction (XRD) analysis, temperature-programmed reduction (TPR-H₂), IR spectroscopy of adsorbed CO, and transmission electron microscopy (TEM). It was found that an increase in the C₆H₈O₇/Ce(NO₃)₃ ratio resulted in an increase in the degree of dispersion of the resulting CeO₂ phase. The greatest amount of dispersed CuO particles, which are responsible for catalytic activity in the oxidation of CO, was formed at C₆H₈O₇/Ce(NO₃)₃ = 1.     

Molecular mechanism of formation of supported platinum catalysts of the Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> family

Certain stages of the classical procedure for preparing aluminum-platinum catalysts, whose understanding is important from both the basic and practical viewpoints, are considered on the molecular level. Properties of both participants (active component precursor solution and oxide surface) are shown to be inhomogeneous, which can affect interaction of the components at the fixing stage. Existing views (and their evolution) on the mechanism of adsorption of platinum complexes from aqueous solutions on aluminum oxide surface are discussed. The role of chemical processes on the stage of fixing precursor on the electronic and structural properties of the supported metal is demonstrates. Strong metal-support interaction is shown to endow platinum with specific adsorption and catalytic properties in hydrocarbon transformation reactions.     

Composition of the gas phase over Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and the enthalpies of atomization of AlO,Al<Subscript>2</Subscript>O,and Al<Subscript>2</Subscript>O<Subscript>2</Subscript>

The A1, O, AlO, A1₂O, Al₂O₂, WO₂, and WO₃, partial pressures in the vapor over Al₂O₃ in a tungsten Knudsen effusion cell between 2300 and 2600 K were derived from A1⁺, O⁺, AlO⁺, A1₂O⁺, Al₂O₂⁺, WO₂⁺, and WO₃⁺, ion intensities. The mass spectrometer was calibrated against the equilibrium constant of the WO₃(g) = WO₂(g) + O(g) reaction. Refined values of the ionization cross sections of AlO and A1₂O₂ were used in the partial pressure calculations. The enthalpies of atomization of aluminum suboxides were determined to be Δ_at H ^o(AlO, g, 0) = 510.7 ± 3.3 kJ mol⁻¹, Δ_at H ^o(Al₂O, g, 0) = 1067.2 ± 6.9 kJ mol⁻¹, and Δ_at H ^o(Al₂O₂, g, 0) = 1556.7 ± 9.9 kJ mol⁻¹.     

Carbon black oxidation mechanism in loose and tight contacts with Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and CeO<Subscript>2</Subscript> catalysts

The catalytic combustion of carbon black was investigated in the presence of CeO₂ and Al₂O₃. The influence of contact type between carbon particles and these oxides was examined by thermal analysis, the BET specific area, and EPR spectroscopy. For tight contact carbon black-catalyst mixtures, a new paramagnetic species is observed and can be considered as a fingerprint of the contact between the two solids. These new paramagnetic species increase the reactivity of the catalytic reaction of carbon black (CB) combustion and take part in the oxidation mechanism of CB. Published in Russian in Kinetika i Kataliz, 2007, Vol. 48, No. 6, pp. 899–904. This article was submitted by the authors in English.     

Kinetic studies on the hydrogenation of nitrate in water using Rh/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and Rh-Cu/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts

Liquid-phase reduction NO ₃ ⁻ using monometallic and bimetallic catalysts (5% Rh/Al₂O₃, 5% Rh-0.5% Cu/Al₂O₃, 5% Rh-1.5% Cu/Al₂O₃, 5% Rh-5% Cu/Al₂O₃ and a physical mixture of 5% Rh/Al₂O₃ and 1.5% Cu/Al₂O₃) was studied in a slurry reactor operating at atmospheric pressure. Kinetic measurements were performed for a low concentration of nitrate (0.4 × 10⁻³−3.2 × 10⁻³ mol dm⁻³) and the temperature range 293–313 K. From the experimental data, it was found that the reduction of nitrate is first order with respect to nitrate. On the basis of the rate constants, the apparent activation energy was established using a graphic method. Published in Russian in Kinetika i Kataliz, 2007, Vol. 48, No. 6, pp. 881–886. This article was submitted by the authors in English.     

Oxidative dehydrogenation of propane on the VO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/CeZrO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> supported catalyst

The oxidative dehydrogenation of propane on a supported vanadium catalyst was studied (the support was a complex oxide system consisting of a ceria–zirconia solid solution deposited on γ-Al₂O₃ (CeZrO/γ-Al₂O₃)). A comparative analysis of the properties of the support and the catalyst prepared on its basis was performed. The support and catalyst were characterized by the BET method, scanning electron microscopy, X-ray diffraction analysis, and Raman spectroscopy. The catalytic properties of the catalyst and support were studied in propane oxidation at 450 and 500°C with pulse feeding of the reagent. The effect of propane on the support was found to improve the oxidative properties of the latter. This behavior of the support is related to the preparation procedure, which leads to the formation on its surface of the crystalline phase of the ceria–zirconia solid solution and amorphous ZrO₂ and Al₂O₃ phases and/or their solid solution. Similar processes occur with the catalyst support during the oxidative dehydrogenation, giving rise to additional active centers (CeVO₄).     

No-Glycerol rapid heterogeneous biodiesel production on K<Subscript>2</Subscript>CO<Subscript>3</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst by coupling process

Biodiesel containing almost no glycerol has been produced by coupling reaction carried out over K₂CO₃ supported by calcium oxide as solid base catalysts. The solid base catalysts synthesized by wet impregnation exhibit an exceedingly high activity in biodiesel production. It was found that the reaction time required for the highest yield of biodiesel, 99.2%, can be shortened to 30 min over K₂CO₃/Al₂O₃ under the optimum reaction conditions: 8: 1: 1 molar ratio of methanol/DMC/oil, 30 wt % K₂CO₃/Al₂O₃ catalyst, and 65°C reaction temperature. Solid basic catalysts examined in the study were characterized by BET surface area, XRD, CO₂-TPD, and SEM techniques. The strong interaction between K₂CO₃ and the support yields a new basic active site, which can be probably responsible for the high activity of K₂CO₃/Al₂O₃.     

An active phase transformation on surface of Ni-Au/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst during partial oxidation of methane to synthesis gas

It was studied the influence of gold addition on physico-chemical properties and catalytic activity of bimetallic Ni-Au/Al₂O₃ catalyst in partial oxidation of methane (POM). The reduction behavior in hydrogen, XRD crystal structure, XPS spectra and POM catalytic activity were investigated. The reduction of Ni-Au catalyst is a prerequisite condition to catalyze POM reaction. The formation of Ni-Au alloy during high temperature reduction in hydrogen and also in the conditions of POM reaction was experimentally proved. The addition of gold to Ni/Al₂O₃ system improves catalyst stability and activity in POM reaction.     

Sonochemical synthesis of vanadium complex nano-particles: a new precursor for preparation and evaluation of V<Subscript>2</Subscript>O<Subscript>5</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nano-catalyst in selective oxidation of methanol to methylal

In this study, an ionic complex of V(V) was synthesized by using ultrasonic method, and it was used as a precursor for production of a new catalyst for selective preparation of methylal or dimethoxymethane (DMM). By reaction between an ionic ligand [pyda.H₂]²⁺[pydc]^2? (LH₂), (pyda.H₂ = 2,6-pyridine diammonium and pydc = 2,6-pyridinedicarboxylate) and ammonium vanadate, the five coordinated V(V) complex, [pyda.H][V(pydc)O₂], {2,6- diaminopyridinum 2,6-pyridinedicarboxylatodioxovanadate(V)}, VLH₂ was synthesized. The prepared complex VLH₂ was characterized by SEM, thermal analysis TGA/DTA, FT-IR spectroscopy and X-ray diffraction studies. The results showed that the yield of the reaction was increased up to 64%. The average particle sizes of the obtained complex VLH₂ were about 50–60 nm. Also, the nano-catalyst of V₂O₅/Al₂O₃ was synthesized by impregnation method and was prepared as a nano-catalyst with average particles sizes of 50–60 nm, and its characterization was performed by XRD, EDX and SEM methods. Finally, the prepared catalyst was used to converting of methanol to methylal at different process conditions.     

Studies on the synthesis of higher alcohol over modified Cu/ZnO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

Higher alcohol has been considered as a potential fuel additive. Higher alcohol, including C₂–C₄ alcohol was synthesized by catalytic conversion of syngas (with a ratio of CO/H₂?=?1) derived from natural gas over modified Cu/ZnO/Al₂O₃ catalyst. Modified Cu/ZnO/Al₂O₃ catalysts promoted by alkali metal (Li) for higher alcohol synthesis (HAS) were prepared at different pH (6, 6.5, 7, 8, and 9) by co-precipitation to control Cu surface area and characterized by N₂ physisorption, XRD, SEM, H₂-TPR and TPD. The HAS reaction was carried out under a pressure of 45 bar, GHSV of 4000 h^?1, ratio of H₂/CO?=?1, and temperature ranges of 240 and 280 °C. It was found that the malachite phase of copper causes the size of copper to be small, which is suitable for methanol synthesis. Methanol and HAS share a common catalytic active site and intermediate. It was also found that the productivity to higher alcohol was correlated with Cu surface area.     

Initiation behaviour in hydrogenation of pyrolysis gasoline over presulphided Ni-Mo-Zn/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

A presulphided treatment was applied to the oxidic Ni-Mo-Zn/Al₂O₃ catalyst (nickel catalyst) in order to avoid thermal run-away during initiation of the hydrogenation of pyrolysis gasoline. The physico-chemical properties of the prepared oxidic nickel catalyst, the reduced and passivated (RP) nickel catalyst and the sulphided (RPS) nickel catalyst were characterised using N₂ adsorption-desorption, X-ray diffraction, temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). The TPR results showed that the reducibility of the RP Ni-Mo-Zn/Al₂O₃ catalyst was improved over the oxidic nickel catalyst. The XPS spectra confirmed the binding energy of the RPS nickel catalyst to be higher than that of the oxidic nickel catalyst. The catalytic performance was evaluated on a fixed-bed reactor (reaction temperature between 30 °C and 70°C, at 2.8 MPa of total pressure and weight hourly space velocity of 2.0 h^?1, the volume of H₂/pyrogasoline = 200: 1). The rising temperature of the RPS nickel catalyst was almost 20°C lower than that of the oxidic nickel catalyst during the initial stage of the hydrogenation reaction. The results indicated that the RPS nickel catalyst exhibited better stability than the oxidic nickel catalyst during the start-up period, thereby providing a better selectivity in long-term operation.     

Subsolidus phase relations in the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Li<Subscript>2</Subscript>O-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> (Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>) systems

The phase composition has been studied and an equilibrium phase diagram has been designed for the Al₂O₃-Li₂O-R₂O₅ (R = Ta or Nb) systems in the subsolidus region up to 1000°C and 85 mol % Li₂O. New phases with the composition Li_1+x Al_1?x O_2?x , where x = 0–0.67, have been found.     

Changes in the heat capacity of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> solid solutions near the point of antiferromagnetic phase transition in Cr<Subscript>2</Subscript>O<Subscript>3</Subscript>

Al₂O₃-Cr₂O₃ solid solutions with 0, 4, 7, 10 and 20 mol% of corundum were synthesized using a high-pressure/high-temperature apparatus and characterized by X-ray powder diffraction. Calorimetric measurements were carried out using DSC-111 (Setaram). Heat capacity was measured by the enthalpy method in a temperature range of 260–340 K, near magnetic phase transition in pure Cr₂O₃ (305 K). Magnetic contribution into the heat capacity was derived and found to change irregularly with the composition.     

Trimetallic NiMoW/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> hydrotreating catalyst based on H<Subscript>4</Subscript>SiMo<Subscript>3</Subscript>W<Subscript>9</Subscript>O<Subscript>40</Subscript> mixed heteropoly acid

Trimetallic NiMoW/Al₂O₃ catalyst was prepared using mixed H₄SiMo₃W₉O₄₀ heteropoly acid of Keggin structure and nickel citrate. Bimetallic NiMo/Al₂O₃ and NiW/Al₂O₃ catalysts based on H₄SiMo₁₂O₄₀ and H₄SiW₁₂O₄₀, respectively, were synthesized as reference samples. The use of mixed H₄SiMo₃W₉O₄₀ heteropoly acid as an oxide precursor allows the tungsten sulfidation degree and the degree of promotion of active phase particles to be increased. The hydrodesulfurization activity is enhanced as compared to NiW/Al₂O₃ catalyst. The synergistic enhancement of the activity of the NiMo₃W₉/Al₂O₃ catalyst relative to the bimetallic analogs is probably caused by formation of new mixed promoted active sites for direct desulfurization.     

Adsorption desulfurization performance and mechanism over nanocrystalline NiO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-1 adsorbent

Desulfurization performance was evaluated by an adsorption model or real oil (diesel and kerosene) at low temperature using nanocrystalline NiO/Al₂O₃-1 adsorbent in static equipment. The properties of the NiO/Al₂O₃ adsorbent samples were characterized by BET surface areas, transmission electron microscopy, FTIR spectra, and TG-DTG curves. Desulfurization experimental results indicated that the desulfurization efficiency for kerosene is much higher than that for diesel due to the π-electronic interaction and S–M bonds with NiO/Al₂O₃-1 adsorbent. Also, a performance of adsorbent regeneration was kept well for multiple cycles.     

Characteristics of CuAl<Subscript>2</Subscript>-Cu<Subscript>9</Subscript>Al<Subscript>4</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposites synthesized by mechanical treatment

Summary Reactive milling of Cu-hydroxycarbonate - powder aluminium mixture brings many complex chemical reactions such as decomposition, aluminothermic reduction and mechanical alloying resulting in the formation of nanometer size composites that contain intermetallic phases, -Cu₉Al₄ and -CuAl₂, with aluminium oxide.     

Laser assisted selective chemical metalization of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> films

Thick aluminum oxide films are prepared on Al plates by anodizing. On the ceramic surface thus obtained a very thin Ag film is deposited via vacuum thermal evaporation. The Ag/Al₂O₃/Al samples prepared are irradiated by Nd:YAG laser through a suitable metal mask in order to remove the top metal film in the exposed areas. Thus, a negative silver image of the copied mask is obtained. Further, the samples are processed in Ni electroless chemical bath activated by the rest of silver. All processing steps are studied by scanning electron microscopy (SEM). EDS X-ray mapping is applied to study the final distribution of Al and Ni in the processed areas. In addition, the DC conductivity of the fabricated Ni wires obtained is measured. The proposed new method for selective chemical deposition of electroconductive Ni onto laser microstructured Ag/Al₂O₃/Al samples is simple, versatile and not restricted to the metal/ceramic system studied as well as to the electroless deposited metal.     

Behavior of the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-ZrO<Subscript>2</Subscript> System at High Temperatures

The system Al₂O₃-ZrO₂ at temperatures of up to 2100°C was studied by differential thermal analysis.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 3, 2005, pp. 353–356.Original Russian Text Copyright © 2005 by Kamaev, Archugov, Mikhailov.