Laws of selective CO oxidation over a Ru/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst in the surface ignition regime: II. Transition states

The kinetics of selective CO oxidation (or individual CO or H₂ oxidation) over ruthenium catalysts are considerably as affected by the heat released by the reaction and specifics of the interaction of ruthenium with feed oxygen. In a reactor with reduced heat removal (a quartz reactor) under loads of ∼701 g_Cat⁻¹ h⁻¹ and reagent percentages of ∼1 vol % CO, ∼1 vol % O₂, ∼60 vol % H₂, and N₂ to the balance, the reaction can be carried out in the catalyst surface ignition regime. When catalyst temperatures are below ∼200°C, feed oxygen deactivates metallic ruthenium, the degree of deactivation being a function of temperature and treatment time. Accordingly, depending on the parameters of the experiment and the properties of the ruthenium catalyst, various scenarios of the behavior of the catalyst in selective CO oxidation are realized, including both steady and transition states: in a non-isothermal regime, a slow deactivation of the catalyst accompanied by a travel of the reaction zone through the catalyst bed along the reagent flow; activation of the catalyst; or the oscillation regime. The results of this study demonstrate that, for a strongly exothermic reaction (selective CO oxidation, or CO, or H₂ oxidation) occurring inside the catalyst bed, the specifics of the entrance of the reaction into the surface ignition regime and the effects of feed components on the catalyst activity should be taken into account.     

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.     

Preferential oxidation of carbon monoxide on supported gold catalysts

Catalyst precursors containing 1% Au were synthesized by the impregnation of Al₂O₃ and CeO₂-Al₂O₃ supports with an aqueous solution of HAuCl₄ followed by drying, treatment with aqueous ammonia for the removal of chlorine residues, and final drying at 90°C. The oxidation of CO in gas containing ～1 vol % O₂, ～1 vol % CO, 60 vol % H₂, and the balance N₂ on the activated catalysts was studied. In a number of experiments, to 18 vol % water was added to the gas mixture. The activation of precursors by the initial gas was studied. It was found that the prolonged storage of a precursor in air made its activation difficult to perform. The 1%Au/Al₂O₃ catalyst activated by the gas mixture stably operated in the preferential oxidation of CO at room temperature with the occurrence of the reaction in the mode of catalyst surface ignition (a hot spot at the bed inlet) under a change in the feed gas flow rate by a factor of 3. The effect of the presence of additional CO₂ (to 39 vol %) on the oxidation of H₂ was studied: the catalyst activity decreased. Because the reaction of CO₂ reduction to CO did not occur, the effect can be due to the adsorption of CO₂ on gold. The effect of the addition of water vapor to the feed gas was studied with the use of 1%Au/CeO₂-Al₂O₃ as an example. The exo/endo effects related to the adsorption/desorption of water on the catalyst surface were detected upon steam supply and shutoff at a bed temperature of 100–150°C. It was noted that the addition of water vapor to a certain level favorably affected the selectivity (decreased the residual concentration of CO). The boundary water concentration, at which the effect became negative, depended on catalyst bed temperature. The higher was the bed temperature, the greater amount of water could be added until the manifestation of a negative effect.     

Chemo-bio catalyzed synthesis of <Emphasis Type="Italic">R</Emphasis>-1-phenylethyl acetate over bimetallic PdZn catalysts,lipase, and Ru/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>. part I

One-pot synthesis of R-1-phenyethylacetate at 70°C was investigated using three different catalysts simultaneously, namely a bimetallic PdZn/Al₂O₃ as a hydrogenation catalyst, an immobilized lipase as an acylation catalyst and Ru/Al₂O₃ as a racemization catalyst. The most active bimetallic catalyst was PdZn/Al₂O₃ calcined at 300°C and reduced at 400°C, whereas the most selective although less active catalyst was the one being calcined and reduced at 500°C. The highest selectivity to R-1-phenylethyl acetate over this catalyst was 32 at 48% conversion. Ru/Al₂O₃ was confirmed to have a positive effect on the formation of the desired product, although it was not very active in the racemization during one-pot synthesis.     

Chemo-bio catalyzed synthesis of <Emphasis Type="Italic">R</Emphasis>-1-phenylethyl acetate over bimetallic PdZn catalysts,lipase, and Ru/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>. Part II

One-pot synthesis of R-1-phenyethylacetate at 70°C was investigated using three different catalysts simultaneously, namely a bimetallic PdZn/Al₂O₃ as a hydrogenation catalyst, an immobilized lipase as an acylation catalyst and Ru/Al₂O₃ as a racemization catalyst. The most active bimetallic catalyst was PdZn/Al₂O₃ calcined at 300°C and reduced at 400°C, whereas the most selective although less active catalyst was the one being calcined and reduced at 500°C. The highest selectivity to R-1-phenylethyl acetate over this catalyst was 32 at 48% conversion. Ru/Al₂O₃ was confirmed to have a positive effect on the formation of the desired product, although it was not very active in the racemization during one-pot synthesis.     

Selective methanation of CO in the presence of CO<Subscript>2</Subscript> in hydrogen-containing mixtures on nickel catalysts

The screening of commercial nickel catalysts for methanation and a series of nickel catalysts supported on CeO₂, γ-Al₂O₃, and ZrO₂ in the reaction of selective CO methanation in the presence of CO₂ in hydrogen-containing mixtures (1.5 vol % CO, 20 vol % CO₂, 10 vol % H₂O, and the balance H₂) was performed at the flow rate WHSV = 26000 cm³ (g Cat)⁻¹ h⁻¹. It was found that commercial catalytic systems like NKM-2A and NKM-4A (NIAP-07-02) were insufficiently effective for the selective removal of CO to a level of <100 ppm. The most promising catalyst is 2 wt % Ni/CeO₂. This catalyst decreased the concentration of CO from 1.5 vol % to 100 ppm in the presence of 20 vol % CO₂ in the temperature range of 280–360°C at a selectivity of >40%, and it retained its activity even after contact with air. The minimum outlet CO concentration of 10 ppm at 80% selectivity on a 2 wt % Ni/CeO₂ catalyst was reached at a temperature of 300°C.     

Mechanism of the initiation of combustion in CH<Subscript>4</Subscript>(C<Subscript>2</Subscript>H<Subscript>2</Subscript>)/Air/O<Subscript>3</Subscript> mixtures by laser excitation of the O<Subscript>3</Subscript> molecules

The possibility of enhancing the ignition and combustion of the CH₄/air/O₃ and C₂H₂/air/O₃ mixtures by exciting the asymmetric vibrations of the O₃ molecule with CO₂ laser radiation is considered. Even the admixture of small amounts of O₃ (2.5–5.0 vol %) into the hydrocarbon/air mixtures intensifies ignition and shortens the induction period. The excitation of the O₃ molecules with 9.7-μm radiation speeds up the chain process and further reduces the induction period and the ignition temperature. The induction period can be shortened by a factor of 10–100 even at low radiation energies absorbed by the gas (E _S = 10^?3-10^?2 J/cm³).     

Thermal activation effect on catalytic systems MnO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> for deep oxidation of hydrocarbons

The effect of thermal activation, sharp increase in the catalytic activity of the system MnO _x -Al₂O₃ in reactions of deep oxidation of CO and hydrocarbons after calcination of the catalyst at 900–1000°C was discovered and investigated. With the use of X-ray phase analysis, X-ray electron spectroscopy, EXAFS, IR spectroscopy, electronic spectroscopy of diffuse reflections, electron microscopy etc. it was established that the effect of thermal activation is related to reversible phase transitions in the system at heating and cooling. On cooling from 1100°C to 650°C disperse particles of cubic spinel of composition Mn_{2.1 ? x} · Al_{0.9 + x} O₄ are conserved on the corundum surface. On further cooling the spinel decomposes and finally the nanocristalline species of β-Mn₃O*₄ containing up to 15 at% of Al³⁺ form and govern the activity.The thermal activation effect was implemented in an industrial catalyst IK-12-40. Joint Stocks Co “KATALIZATOR” produced and supplied to customers hundreds of tons of this catalyst. The catalyst was awarded with a silver medal of the International exhibition EUREKA in Brussels (1995).     

The effect of spinel type support FeAlO<Subscript>3</Subscript>, ZnAl<Subscript>2</Subscript>O<Subscript>4</Subscript>, CrAl<Subscript>3</Subscript>O<Subscript>6</Subscript> on physicochemical properties of Cu,Ag, Au,Ru supported catalysts for methanol synthesis

The comparative study of the role of binary oxide support on catalyst physico-chemical properties and performance in methanol synthesis were undertaken and the spinel like type structures (ZnAl₂O₄, FeAlO₃, CrAl₃O₆) were prepared and used as the supports for 5% metal (Cu, Ag, Au, Ru) dispersed catalysts. The monometallic 5% Cu/support and bimetallic 1% Au (or 1% Ru)-5% Cu/support (Al₂O₃, ZnAl₂O₄, FeAlO₃, CrAl₃O₆) catalysts were investigated by BET, XRD and TPR methods. Activity tests in methanol synthesis of CO and CO₂ mixture hydrogenation were carried out. The order of Cu/support catalysts activity in methanol synthesis: CrAl₃O{ia6} > FeAlO₃ > ZnAl₂O₄ is conditioned by their reducibility in hydrogen at low temperature. Gold appeared more efficient than ruthenium in promotion of Cu/support catalysts. Published in Russian in Kinetika i Kataliz, 2009, Vol. 50, No. 2, pp. 242–248. The article is published in the original.     

Liquid phase selective hydrogenation of phenol to cyclohexanone over Ru/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocatalyst under mild conditions

Highly monodispersed ruthenium nanoparticles were prepared via wet impregnation technique using RuCl₃ · nH₂O as a precursor. Ru nanoparticles were supported on Al₂O₃ to synthesize Ru nanocatalyst. The nanocatalyst was characterized by various techniques like XRD, SEM, TEM and BET analysis. The catalyst was used for hydrogenation of phenol under mild condition. The activity of the catalyst was checked by varying different parameters such as reaction temperature, time, H₂ partial pressure, metal loading and catalyst amount. The catalyst was recovered from product and reused up to four times without significant loss in its catalytic activity. After a reaction time of 1 h, Ru/Al₂O₃ nanocatalyst showed high reactivity (82% conversion) and selectivity to cyclohexanone (67%) at 80°C and 20 bar hydrogen pressure.     

Effect of CeO<Subscript>2</Subscript> on the properties of the Pd/Co<Subscript>3</Subscript>O<Subscript>4</Subscript>/cordierite catalyst in the conversion of CO,NO, and hydrocarbons

The effect of CeO₂ on the properties of the Pd/Co₃O₄-CeO₂/cordierite catalyst is a function of the method of its preparation. The catalyst obtained by the simultaneous deposition of cerium oxide and cobalt oxide showed high activity in the oxidation of CO (CO + O₂, CO + NO) and extensive oxidation of hexane (C₆H₁₄ + O₂). This behavior is due to the increased mobility of surface oxygen and increased dispersion of the catalyst components.     

Selective oxidation of CO under conditions of catalyst surface ignition

The oxidation of CO in the presence of an excess of hydrogen and to 20% CO₂ and H₂O in the starting mixture was studied in flow reactors with high and low rates of heat removal. The ignition of the catalyst surface was observed in the reactor with a low rate of heat removal; catalyst surface ignition initially occurred at a “hot” spot (section) of the catalyst bed and gradually propagated along the bed. Experimental data on the relaxation dynamics of residual CO concentration and temperature in a catalyst bed under conditions of small heater temperature disturbances near and at the critical temperature of ignition and the effect of oxygen concentration in the starting mixture on this process are reported. It was found exprimentally that the ignition regime in the tested cases was more favorable for the selective oxidation of CO in an excess of hydrogen than the reaction in an isothermal reactor; this was likely due to the more favorable temperature distribution over the length of the catalyst bed.     

The monooxidation of ethylene with hydrogen peroxide on the per-FTPhPFe<Superscript>3+</Superscript>OH/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> biomimetic

The gas-phase monooxidation of ethylene by hydrogen peroxide on a biomimetic heterogeneous catalyst (per-FTPhPFe³⁺OH/Al₂O₃) was studied under comparatively mild conditions. The biomimetic oxidation of ethylene with hydrogen peroxide was shown to be coherently synchronized with the decomposition of H₂O₂. Depending on reaction medium conditions, one of two desired products was formed, either ethanol or acetaldehyde. The kinetics and probable mechanism of ethylene transformation were studied.     

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.     

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.     

Carbon monoxide and oxygen interaction with Ru/MgF<Subscript>2</Subscript> catalyst: IR and EPR studies

Electron paramagnetic resonance (EPR) and infrared (IR) spectroscopy were used to study the formation of ruthenium and adsorbed species appearing on the catalyst upon the adsorption of CO and O₂ on 1.37 wt% Ru/MgF₂ catalysts derived from Ru₃(CO)₁₂. The presence of Ru ^x+ sites in spite of a reductive H₂ treatment at 673 K was observed by EPR and IR spectroscopy beside metallic Ru⁰ species. Both IR and EPR results provided clear evidence for the interaction between surface ruthenium and probe molecules. The IR spectra recorded after admission of CO showed a band at approx. 2000 cm⁻¹, due to linearly adsorbed CO on Ru⁰/MgF₂ and two bands at higher frequencies (approx. 2140 and approx. 2070 cm⁻¹), related to CO on oxidized Ru ⁿ⁺ species, e.g., to Ru(CO)₃ complex with Ru in the 1+ and/or 2+ state of oxidation and Ru(CO)₂ with Ru in the 3+ and/or 4+ state of oxidation. A weak anisotropic EPR signal with g _‖ = 2.017 and g _⊥ = 2.003 is due to O ₂ ⁻ radicals and a formation of Ru⁴⁺-O ₂ ⁻ complex is postulated. The Ru³⁺ appears to oxidize to Ru⁴⁺ and the resulting dioxygen anion is coordinated to the ruthenium. The strong, isotropic EPR signal at g ₀ = 2.003 detected upon admission of CO is attributed to CO radical anion rather than to any ruthenium carbonyl complexes.     

Oxidative conversion of methane and methanol on M/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/cordierite structured metal oxide catalysts (m = Ni,Cu, Zn)

A study was carried out on the properties of Ni/Al₂O₃ and Cu-ZnO/Al₂O₃ composites supported on ceramic honeycomb monoliths made from synthetic cordierite in the carbon dioxide conversion of methane and the partial oxidation of methanol. The structured nickel-alumina catalysts are significantly more efficient than the conventional granulated catalysts. The improved working stability of these catalysts was achieved by adjusting the acid-base properties of the surface by introducing sodium and potassium oxides, which leads to inhibition of surface carbonization. The hydrogen yield was close to 90% in the partial oxidation of methanol with a stoichiometric reagent ratio in the presence of the Cu-ZnO/Al₂O₃/cordierite catalyst. A synergistic effect was found, reducing the selectivity of CO formation in the presence of the Cu-ZnO catalyst relative to samples derived from the individual components Cu and ZnO. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 5, pp. 299–306, September–October, 2007.     

Formation of Co-Ru/MgO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for the Fischer-Tropsch synthesis: A magnetic method for the estimation of cobalt particle size

The physicochemical properties of Co-supported catalysts were studied, and the particle size of Co in Co/MgO/Al₂O₃ and Co-0.2% Ru/MgO/Al₂O₃ catalysts for the Fischer-Tropsch synthesis (FTS) was estimated using a magnetic method. It was found that a considerable fraction of superparamagnetic Co particles, which increase selectivity for C₅₊ hydrocarbons and decrease the yield of methane in the FTS, was present in a ruthenium-containing catalyst along with single-domain ferromagnetic particles. In this case, the catalyst activity increased by a factor of 10.     

Kinetic model of coherent synchronized ethylene monooxidation by hydrogen peroxide on a biomimetic catalyst,per-FTPhPFe<Superscript>3+</Superscript>OH/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

A kinetic model that fits the experimental data is studied on the basis of the most probable mechanism of ethylene oxidation by hydrogen peroxide over a biomimetic catalyst, perfluorinated iron (III) tetraphenylporphyrin, deposited on aluminum oxide (per-FTPhPFe³⁺OH/Al₂O₃). Effective rate constants for the catalase and oxygenase reactions and their effective activation energies are found.     

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.