Use of linear modeling in steady-state isotopic-transient kinetic analysis of surface-catalyzed reactions: Application to plug-flow reactors

Abstract

Determination of kinetic parameters from steady-state isotopic transient kinetic analysis (SSITKA) requires modeling of the reactor system and the catalyst surface. In this work, a novel application of linear-modeling methods was developed for SSITKA, using transfer functions for non-differential-length catalyst beds in non-ideal plug-flow reactors (PFR's), which are often employed in SSITKA. Various linear relationhips between the catalyst surface and the gas phase were derived - including linear convolution, which provides a new rigorous method for generating calculated isotopic transient responses from catalyst-surface and reaction-system models. Incorporation of linear convolution - which avoids a priori gas-phase behavior correction which is problematic when using non-ideal PFR's - in parametric and nonparametric kinetic analyses provides for increased accuracy in the determination of kinetic parameters in SSITKA. The linear modeling techniques developed were applied to a PFR transient-response model for an irreversible reaction occurring in a non-differential-length catalyst bed. It was determined that the dependency upon the catalyst-bed length in PFR's is unimportant if gradientless conditions - differential conversion of reactant and irreversible reaction - are maintained in a catalyst bed of non-differential length. The results illustrate how the linear modeling techniques developed can be used with SSITKA to test assumed catalyst-surface reaction models.