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
A theoretical approach to the dynamic analysis of deactivation and aging of heterogeneous catalysts is proposed -analysis of the rate derivative in a kinetic equation of a given form. Methodology was demonstrated for the simplest kinetic equations -zero-and first-order. Regardless of the form of the kinetic equation for the dynamic model of deactivation, the rate constant is a function of an independent reaction coordinate. The method can also be used for solving reactivation problems and for explaining the dynamics of cation exchange in zeolite. Problems related to aging and deactivation of solid catalysts arise in the course of heterogeneous catalytic reactions [1]. Empirical dynamic models based on intuition are used in practice for solving these problems. In particular, problems in cracking [2] and dehydrogenation [3-7] of hydrocarbons have been solved by this method.Gradual coking of the surface of the catalysts, up to total poisoning, take place in these processes in relatively severe conditions [8].We attempted to analyze how the second derivative of the concentration c changes in time t as a function of the form of the kinetic equation, i.e., the laws by which the reaction slows and in particular, how the kinetic order is reflected in the dynamics of the change in activity.The proposed methodology involves the analysis of the rate derivative in a kinetic equation of a given form. The simplest kinetic equations -zero-and first-order -are examined. It is shown that regardless of the form of the equation, rate constant k is a function of an independent coordinate of the reaction.During prolonged use of coked heterogeneous catalysts, the proposed approaches can be substantiated by previously used semiempirical models of deactivation. In a first approximation, this problem can be solved with the existing linear correlation in [9] between the activation energy and the preexponential factor.As the analysis of the literature shows, no attention was previously turned to the possibility of predicting the dynamics of deactivation with consideration of the form of the kinetic equation. Our proposed mathematical approach combined with additional methods of physicochemical investigation of the coked surface in situ can be a very useful tool for analyzing dynamic models of heterogeneous catalytic processes not only in block reactors but also in a continuous-flow system.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.