Morphology and activity of multicomponent heterogeneous catalysts by binary cuts

Abstract

In oxidation of carbon monoxide, the activity of the Cu-Cr-Mn/γ-Al 2 O 3 catalytic system is correlated with its morphology. The phase composition and valence state of the metal ions in catalysts of different genesis were investigated by x-ray phase analysis (XPA) and diffuse-reflection electron spectroscopy (DRES). The sequence of application of the active components of the system over binary sections affects the catalytic activity. The undesirable copper-chromium combination is excluded by separation of the successively applied combinations of ingredients Cr-Cu and Cu-Mn through an intermediate stage.Key words: multicomponent heterogeneous catalysts, morphology and activity, oxidation of carbon monoxide, catalytic activity, binary composites and ternary combinations of different genesis, support, mechanism of oxidation, effective rate and adsorption constants, x-ray phase analysis, diffuse-reflection electron spectroscopy.Precious metals are traditional catalysts for removal of carbon monoxide from gases [1]. However, platinum and palladium compounds are sensitive to sulfur, nitrogen, and chlorine compounds and are rapidly poisoned during oil refining processes. Oxide catalytic systems, frequently of complex multicomponent composition, have been increasingly investigated in recent years. Of these systems, those containing copper combined with zinc, chromium, manganese, and other metal oxides are most frequently encountered.However, the introduction of new systems involves outlays for retooling catalyst plants and risks due to the lack of complete information on their chemical composition, method of synthesis, and reliability of use for a long time in optimum regimes. For this reason, it is necessary to deepen the concepts concerning the mechanism of the effect of the kinetic parameters of synthesis of the catalyst on its structural characteristics and to establish quantitative criteria for correlating the parameters of the selected kinetic model with the method of synthesis of the compound.The catalytic activity of supported heterogeneous catalysts is determined by the distribution of the active components over the inner surface and the phase space arising as a result by the radius of the catalyst granule. On the macroscopic level, the morphology is determined by the phase dispersion and distribution along a linear coordinate [2]. Control of the morphology during synthesis of the catalytic composition ensures a fine phase structure forming active sites in the near-surface region in which the reaction takes place.The method of preliminary surface activation is used in synthesis of a catalyst of the "sorption" type [3,4]. In the case of "impregnated" (nonadsorption type) [4] catalysts, the active components are uniformly

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