Simulation of transients in heterogeneous catalysis: a comparison of the step- and pulse-transient techniques for the study of hydrocarbon oxidation on metal oxide catalysts

The responses to step and pulse transients with reactants have been simulated for conventional step-transient conditions at atmospheric pressure and pulsing under vacuum using a temporal analysis of products (TAP) reactor, respectively. Propene oxidation over an oxide catalyst with the participation of lattice oxygen was chosen as a model reaction. The mechanism comprises adsorption of the reactants, a series of surface reaction steps and desorption of the products. For this type of reaction one of the reactants, namely oxygen, is a constituent of the catalyst and the oxygen coverage is assumed to be one at the start of the transient, Simulations were performed for all variants with one of the reaction steps becoming rate limiting at steady-state conditions. Both types of transients are compared for the same reaction mechanism and rate constants, neglecting catalyst restructuring. The results show that the visual features of step responses are often quite conclusive about the rate limiting step of the reaction mechanism, while pulse responses in this regard are less conclusive unless they are modelled or a desorption step is rate limiting. The two transient methods are compared regarding their usability for the study of reaction mechanisms. (C) 2000 Elsevier Science Ltd. All rights reserved.