Simulation of oxidation of carbon particles at the surface of mixed oxide catalysts

A model of catalytic oxidation of a cylindrical carbon particle was suggested. The model considers the rate of layer-by-layer burning of the particle, variation of its geometry, and remote action of the catalyst. A software for calculations was developed; the data obtained correlate well with the experimental data for catalysts based on lanthanum cesium vanadate. The kinetics of carbon oxidation on catalysts of varied nature was compared.     

Preparation and characterization of modified aluminum oxide catalysts

The formation of individual and modified high-purity aluminum oxides (γ-Al₂O₃) prepared from aluminum alcoholates was studied. In the study of the hydrolysis of aluminum alcoholates and modified (Zr, Ti, and Si) aluminum alcoholates, it was found that an increase in the chain length of the alkoxy group and an increase in the aging temperature or aging time in mother liquor resulted in a decrease in the concentration of an amorphous phase, an increase in the concentration of a pseudoboehmite phase, and an improvement in its crystal structure. Hydrolysis in alkaline (a 0.5 wt % solution of ammonia) or neutral solutions made it possible to obtain samples with an almost 100% pseudoboehmite content. At the same time, the samples prepared by hydrolysis in an acidic solution (a 0.1 M solution of HCl) contained a considerable amount of an amorphous phase. It was found that the specific rate of dehydration of n-butanol on the modified aluminum oxide samples linearly decreased with the concentration of donor sites and linearly increased with the concentration of acceptor sites, whose concentration was measured using the spin probe method.     

Determination of the chemical nature of active surface sites present on bulk mixed metal oxide catalysts

CH3OH temperature programmed surface reaction (TPSR) spectroscopy was employed to determine the chemical nature of active surface sites for bulk mixed metal oxide catalysts. The CH3OH-TPSR spectra peak temperature, Tp, for model supported metal oxides and bulk, pure metal oxides was found to be sensitive to the specific surface metal oxide as well as its oxidation state. The catalytic activity of the surface metal oxide sites was found to decrease upon reduction of these sites and the most active surface sites were the fully oxidized surface cations. The surface V5+ sites were found to be more active than the surface Mo6+ sites, which in turn were significantly more active than the surface Nb5+ and Te4+ sites. Furthermore, the reaction products formed also reflected the chemical nature of surface active sites. Surface redox sites are able to liberate oxygen and yield H2CO, while surface acidic sites are not able to liberate oxygen, contain either H+ or oxygen vacancies, and produce CH3OCH3. Surface V5+, Mo6+, and Te4+ sites behave as redox sites, and surface Nb5+ sites are Lewis acid sites. This experimental information was used to determine the chemical nature of the different surface cations in bulk Mo-V-Te-Nb-Ox mixed oxide catalysts (Mo(0.6)V(1.5)Ox, Mo(1.0)V(0.5)Te(0.16)Ox, Mo(1.0)V(0.3)Te(0.16)Nb(0.12)Ox). The bulk Mo(0.6)V(1.5)Ox and Mo(1.0)V(0.5)Te(0.16)Ox mixed oxide catalytic characteristics were dominated by the catalytic properties of the surface V5+ redox sites. The surface enrichment of these bulk mixed oxide by surface V5+ is related to its high mobility, V5+ possesses the lowest Tammann temperature among the different oxide cations, and the lower surface free energy associated with the surface termination of V=O bonds. The quaternary bulk Mo(1.0)V(0.3)Te(0.16)Nb(0.12)Ox mixed oxide possessed both surface redox and acidic sites. The surface redox sites reflect the characteristics of surface V5+ and the surface acidic sites reflect the properties normally associated with supported Mo6+. The major roles of Nb5+ and Te4+ appear to be that of ligand promoters for the more active surface V and Mo sites. These reactivity trends for CH3OH ODH parallel the reactivity trends of propane ODH because of their similar rate-determining step involving cleavage of a C-H bond. This novel CH3OH-TPSR spectroscopic method is a universal method that has also been successfully applied to other bulk mixed metal oxide systems to determine the chemical nature of the active surface sites.     

Adsorption properties of Ni-Pd catalysts supported on aluminum oxide

The surface composition of Ni-Pd/Al₂O₃ catalysts has been studied using XPES and adsorption methods. The bimetallic catalysts differ from the single-metal Ni and Pd catalysts in the dispersivity of the metal phase which depends on the method of preparation and the presence of K⁺ promoter. A catalyst produced by the immersion method is strongly enriched in Pd compared with impregnated catalysts.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1746–1751, August, 1991.     

Physico-chemical properties of iron-tin mixed oxide catalysts in cyclohexane oxidation

The state of mixed iron-tin oxide catalysts with a variable ratio of their metallic components has been studied by Mössbauer and ESCA spectroscopy. The results are compared with the activity of these catalysts in cyclohexane oxidation.

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Valence states and solubility limits in ternary iron-tin-antimony mixed oxide catalysts

The electrical conductivity study of a series of ternary Fe–Sn–Sb mixed oxides with 5 at. % Fe has shown that iron dissolves in the structure of SnO₂ as ferric ions and, consequently creates acceptor centers which compensate the doping effect of Sb⁵⁺ ions simultaneously dissolved, thus increasing the maximum dissolution of pentavalent antimony and shifting thereby the apparition limit of Sb³⁺ ions towards higher Sb contents.

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Fe–Sn–Sb c 5 . %- Fe , SnO₂ , , Sb⁵⁺, . , Sb³⁺ Sb.

     

Cs-Fe-Co-Bi-Mn-Mo复合氧化物选择性催化氧化异丁烯

Mixed oxide catalyst Cs0.1 Fe2Co6BiMnMo12 Ox was prepared by the interprecipitation method, then the catalyst was calcined at different temperature. Selective oxidation of isobutene was carried out in a fixed-bed reactor. The results showed that the catalyst has high catalytic activity. Under the optimum reaction conditions ( n(-C4^= ) : n(O2) = 1:2-1:4, space velocity = 180h^-1, T = 360℃ ), the yield of methacmlein and methacrylic reached 80%, 8 %,respectively. The total yields of liquid products( methacrolein, methacrylic acid and acetic acid) reached about 90%.     

Oxidative ammonolysis of 3-picoline on mixed oxide catalysts

The oxidative ammonolysis of 3-picoline has been studied on the following catalysts: V₂O₅ on corundum, V₂O₅ with the addition of 1% of H₂WO₄ on corundum, V₂O₅ + MoO₃ + P₂O₅ (10.350.35) on silica gel, V₂O₅ + Al₂O₃, and a melt of V₂O₅ + TiO₂ (10.22). Mixed catalysts of vanadium and titanium oxides exhibited the highest activity and selectivity. With the passage of 25–45 moles of oxygen (in the form of air), 5–10 moles of ammonia, and 50–70 moles of water per mole of 3-picoline at a temperature of 390–410° C, the amount of nicotinonitrile formed on these catalysts amounted to 85–90% of the theoretically possible amount.Part LXIII of the series Oxidation of organic compounds; for part LXII, see [1].     

Oxidative ammonolysis of 3-picoline on mixed oxide catalysts

The oxidative ammonolysis of 3-picoline has been studied on the following catalysts: V₂O₅ on corundum, V₂O₅ with the addition of 1% of H₂WO₄ on corundum, V₂O₅ + MoO₃ + P₂O₅ (1∶0.35∶0.35) on silica gel, V₂O₅ + Al₂O₃, and a melt of V₂O₅ + TiO₂ (1∶0.22). Mixed catalysts of vanadium and titanium oxides exhibited the highest activity and selectivity. With the passage of 25–45 moles of oxygen (in the form of air), 5–10 moles of ammonia, and 50–70 moles of water per mole of 3-picoline at a temperature of 390–410° C, the amount of nicotinonitrile formed on these catalysts amounted to 85–90% of the theoretically possible amount.     

Hydrotalcite-derived Co-containing mixed metal oxide catalysts for methanol incineration

The Co–Mg–Al mixed metal oxides were prepared by calcination of co-precipitated hydrotalcite-like precursors at various temperatures (600–800 °C), characterised with respect to chemical (AAS) and phase (XRD) composition, textural parameters (BET), form and aggregation of cobalt species (UV–vis-DRS) and their redox properties (H₂-TPR, cyclic voltammetry). Moreover, the process of thermal decomposition of hydrotalcite-like materials to mixed metal oxide systems was studied by thermogravimetric method combined with the analysis of gaseous decomposition products by mass spectrometry. Calcined hydrotalcite-like materials were tested as catalysts for methanol incineration. Catalytic performance of the oxides depended on cobalt content, Mg/Al ratio and calcination temperature. The catalysts with lower cobalt content, higher Mg/Al ratio and calcined at lower temperatures (600 or 700 °C) were less effective in the process of methanol incineration. In a series of the studied catalysts, the best results, with respect to high catalytic activity and selectivity to CO₂, were obtained for the mixed oxide with Co:Mg:Al molar ratio of 10:57:33 calcined at 800 °C. High activity of this catalyst was likely connected with the presence of a Co–Mg–Al spinel-type phases, containing easy reducible Co³⁺ cations, formed during high-temperature treatment of the hydrotalcite-like precursor.     

Surface and catalytic properties of Cu/Zn mixed oxide catalysts

Copper catalysts supported on zinc oxide, with different loading (1–20 wt.% CuO), were prepared by impregnation of the basic zinc carbonate with a water solution of copper nitrate. The impregnated samples were dried at 120°C and calcined at 400–700°C. The surface and catalytic properties of CuO loaded on ZnO were determined by N₂ adsorption measurements conducted at −196°C and CO oxidation by O₂ at 150–300°C, respectively. The results obtained revealed that the surface and catalytic properties of different solids were dependent upon CuO content and calcination temperature. The specific surface areas of various adsorbents decreased monotonically as a function of both calcination temperature and extent of loading. However, the activation energy of sintering, ΔE_S, was found to increase by increasing the amount of CuO present. On the other hand, the CO oxidation activity on various catalysts was found to increase progressively by increasing the calcination temperature from 400 to 500°C, then decreased by increasing the temperature from 500 to 700°C. The augmentation of CuO content from 1 to 5 wt.% resulted in an increase in the CO oxidation activity, which decreased by increasing the extent of loading above this limit.     

The surface chemistry of VP mixed oxide

The surface chemistry of VP mixed oxides has been investigated by ESR, UV and Vis spectroscopy. The results are correlated with the yield of maleic anhydride in the oxidation of 1-butene. High yields of maleic anhydride are observed for catalysts that contain V⁵⁺ and V⁴⁺.

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VP , . 1-. , V⁺⁵ V⁺⁴.

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This work was sponsored by CNR Italy     

Deamination of butylamines on the surface of acidic oxide catalysts

Studies of the deamination of tert-, sec- and n-butylamines on several silicate and phosphate catalysts at 543–704 K have revealed that the reaction proceeds only with the participation of protonic cneters, its rate is independent of the strength of acidic centers and affected only by the amine structure. Butylammonium ion conversion is suggested to be the rate-determining step.

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-, - - 543–703 . , . , . , .

     

铈铁锆三元复合氧化物上碳烟的催化燃烧

采用水热法制备了纯CeO₂、Fe₂O₃和系列Ce₀.5Fe₀.5-xZr_{xO2复合氧化物催化剂,采用XRD、Raman、H2-TPR和BET等方法对其进行了表征,并利用程序升温氧化反应(TPO)技术研究了其碳烟燃烧催化性能。结果表明,Zr⁴+完全进入CeO2晶格中形成了固溶体,而Fe³+较难进入CeO2晶格中,部分Fe2O3分散在固溶体表面。固溶体形成产生的氧空位和表面高度分散的氧化铁协同作用是铈铁锆三元复合氧化物具有较高碳烟燃烧催化性能的关键。同时,与单纯的铈铁二元复合氧化物相比,Zr⁴+的掺杂明显提高了催化剂的抗老化能力,使Ce0.5Fe0.5-xZrxO2复合氧化物显示出更好的应用前景。在系列样品中,Ce0.5Fe0.30Zr0.20O2样品由于形成了最多的固溶体并具有良好分散性的表面Fe2O3,显示出最好的催化活性和稳定性。其催化碳烟的起燃温度(ti)和峰顶温度(tp)分别为251℃和310℃,长时间高温老化后其ti和tp仍较低,分别为273℃和361℃。}