Temporal Analysis of Product (TAP)

Abstract

The Temporal Analysis of Products (TAP) pulse response method for characterization of catalyst kinetic properties and mechanistic features is presented. Beginning with details of the instrument configuration and different experimental formats, the basic experimental concepts that distinguish the TAP method from kinetic tools such as molecular beam scattering and pulse response in advecting reactors are discussed. Three guiding principles that define the TAP experiment are (i) insignificant perturbation of the catalyst state, (ii) spatial uniformity of the gas within the active zone of the reactor, and (iii) well-defined diffusion in the Knudsen transport regime. In the Knudsen regime, only gas/solid collisions are significant and an intrinsic measurement of catalyst kinetic properties becomes possible. Theoretical tools for extracting kinetic information from TAP pulse response data are described, including numerical solutions, moment-based analysis, and time-dependent analysis of rate and concentration data. Experimental studies are presented that demonstrate the TAP approach to characterization of coverage-dependent sticking coefficients, active site titration at working temperatures for both irreversibly and reversibly adsorbing molecules (heat of adsorption), multiple active sites working within mixtures, mechanistic features including adsorption processes and microkinetic network discrimination, and lifetime of surface intermediates as well as connection of kinetic features across the pressure gap.