Application of periodic operation to kinetic study of NO–CO reaction over Rh/Al2O3

Abstract

Abstract A concentration forcing periodic operation has been applied incorporating with a conventional steady-state rate measurement in order to study the kinetics of NO–CO reaction over Rh/Al2O3 at 423 K. The steady-state rate data obtained using a differential fixed-bed reactor showed that the order of the reaction was 0 with respect to CO concentration (CCO) and 0.4 with respect to NO concentration (CNO). Under the periodic condition, where a square wave was applied for NO and CO feeding, a deformation of the CNO wave was observed at the outlet of an integral fixed-bed reactor. Shape of the deformed CNO wave indicates that both reactants were strongly adsorbed on catalytic active sites. Three plausible mechanisms that could explain the strong adsorption of these two reactants together with insignificant self-inhibition effect of the strong adsorption on the rate were considered: (I) Langmuir–Hinshelwood (L–H), (II) Eley–Redial-like (E–R-like) and (III) combined L–H and E–R-like mechanisms. A one-dimensional pseudohomogeneous reactor model coupled with the reaction mechanisms was employed to simulate the characteristics of the rate data and the shape of the deformed CNO wave. Only the E–R-like mechanism could predict these characteristics of steady and periodic operations by employing one set of kinetic parameters while the other mechanisms needed different sets of the parameters to predict the characteristics. Sensitivity of each parameter to the shape of the CNO wave was analyzed and value of each parameter was determined for the E–R-like mechanism. The reliabilities of the proposed mechanism and its parameters were evaluated.