Understanding Heterogeneous Catalysis Through the Transient Method

Abstract

Although catalysis can be understood through steady-state ex periments, it seems clear that transient experiments will usually furnish much additional information. Often steady-state data can be explained by a number of different models, but the results of transient experiments are usually so rich that only a detailed, complex model will come close to explaining the results. These ideas have long been applied in other fields, but in heterogeneous catalysis they have come into acceptance only during the last 15 years or so. Pioneering experiments were done by Wagner (1) in 1938, and Tamaru (2)

Forty years of temporal analysis of products

“…However, it should be noted that the number of active sites based on chemisorption measurements may significantly differ from the number of reactive sites. 168,169 To address this issue, the SSITKA method, proposed by Happel 170,171 and developed by Bennett 172 and Biloen, View Article Online provides an elegant technique 174 which allows the determination of the surface concentration of the most active reaction intermediates (mari) under reaction conditions. According to the idea of the SSITKA approach, after a step-change between two reactant streams containing different isotopes, distributions of isotopically labelled products are monitored using a MS. SSITKA studies are used to determine the amount of substance stored/released by a surface.…”

Transient Response Methods for Assisted Design of Gas Phase Heterogeneous Catalysts: Experimental Techniques and Mathematical Modeling

“…The first one is the classical approach (Bennett, 1967(Bennett, , 1976(Bennett, , 1982Furusawa et al, 1976;Happel, 1972;Kobayashi, 1972, 1974;Tamaru, 1964;Yang et aL, 1973) in which the imposed transient is introduced by means of a pulse, step-up, or step-down perturbation in the feed gas concentration. The second approach uses more recently developed concepts (Lyberatos et aL, 1984;Shanks and Bailey, 1989) whereby the feed concentration is manipulated in response to the effluent concentrations according to some forcing function c^t) through time modulation.…”

“…Experimental verification of these mathematical models for the transient kinetics was provided by Kobayashi and Kobayashi (1972) and Yang et al (1973). Since these pioneering efforts, the transient response method in catalysis has been the subject of a significant number of both developments and applications which have been summarized in various review papers (Bennett, 1976(Bennett, , 1982Bhatia et al, 1990;Christoffel, 1982;Falconer and Schwarz, 1983;Furusawa et al, 1976;Happel, 1972;Kobayashi and Kobayashi, 1974;Tamaru, 1991;Villermaux, 1981), monographs (Bell and Hegedus, 1982;Christoffel, 1989;Happel, 1986;Matros, 1990;Tamaru, 1978;Yablonskii, 1991), and recent symposia (Cutlip and Gulari, 1989) to which the interested reader is referred for details. The subsequent sections will briefly discuss classification of various laboratory types that are used in catalyst testing, summarize some general concepts behind transient response methods in catalysis, review selected laboratory types, and provide an overview on modeling of the transient reactor behavior along with illustrations of their usage.…”

Assessment of kinetic modeling procedures of TAP experiments

“…In the 1960s renewed interest was shown in transient methods and the first fundamental transport-kinetics model for a pulse reactor was developed [10,11]. Since then a number of groups have made contributions to the theoretical and experimental developments of transient response methods, summarized in numerous review papers and monographs [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27].…”