Energetic homogeneity of thermally stabilized metal and metal-oxide surfaces, new oscillation theory of catalysis (OTCAT), and unification of catalytic mechanisms

详细信息    查看全文

• 作者：Victor E. Ostrovskii ; Elena A. Kadyshevich
• 关键词：Calorimetric measurements ; Calorimeters differential ; Calorimetry of chemisorption ; Catalytic theory ; Surface homogeneity ; Catalytic kinetics
• 刊名：Journal of Thermal Analysis and Calorimetry
• 出版年：2017
• 出版时间：January 2017
• 年：2017
• 卷：127
• 期：1
• 页码：819-850
• 全文大小：
• 刊物类别：Chemistry and Materials Science
• 刊物主题：Physical Chemistry; Analytical Chemistry; Polymer Sciences; Inorganic Chemistry; Measurement Science and Instrumentation;
• 出版者：Springer Netherlands
• ISSN：1588-2926
• 卷排序：127

文摘

New phenomenological Oscillation Theory of stationary heterogeneous CATalysis (OTCAT) is developed on the basis of a wide generalization of original calorimetric and kinetic studies and the available literature; it bears on the following principal conclusions: (1) the thermally stabilized metals and metal-oxides are homogeneous relative to the chemisorption and catalytic activity of their surface places, i.e., chemisorption (ChS) of a substance at the surface of a thermally stabilized crystal of a definite composition under definite ambient conditions proceeds with formation of a definite chemadphase (chemically adsorbed two-dimensional phase, ChPh) with a constant differential heat effect independently of the surface coverage by this ChPh, and the surface of a thermally stabilized crystal catalyzing any chemical reaction reveals itself as a comprehensive whole rather than as a conglomerate of places of different activities; (2) the frequency of the acts of ChS of gases at free surface places is of the same order of magnitude or is only one–two–three orders of magnitude lower than the frequency of collisions of gas molecules with these surface places, is much higher in order of magnitude than the rate of catalysis, and proceeds with a minor temperature coefficient; the observable high temperature coefficients of reaction rates represent the products of the reaction rate constants by some partial equilibrium constants, and thus, the observable reaction rate temperature dependences are made up of the rate constant temperature dependences plus the equilibrium constant temperature dependences; (3) ChS is of island nature, i.e., the surfaces of working catalysts pose island-archipelago structures rather than monomolecular films similar to two-dimensional solutions. According to the OTCAT, the catalyst of any stationary chemical reaction under some external conditions in any gaseous or liquid mixture containing source substances and a desired product is a solid capable of forming at its surface an island ChPh or a set of island ChPhs that are in equilibrium with the source substances and product; catalytic processes are one step, the rate of any catalytic reaction is determined by the rate of this unique step (rate-determining step, RDS), and another portion of the reaction is equilibrium. The OTCAT is applied to clarify the mechanisms and to deduce the kinetic equations for seven manifold catalytic reactions; these equations describe well the experimental rates of the corresponding reactions over wide ranges of variations in reaction parameters.