An improved microkinetic model for the water gas shift reaction on copper

Abstract

A previously developed 13 elementary step microkinetic mechanism for the WGSR on Cu(1 1 1) [Surf. Sci. 512 (2002) 229] is extended by including four new elementary steps. Employing a systematic reaction route analysis, the microkinetic model is further analyzed, simplified and reduced. It is shown that from the total of 70 possible overall reaction routes (RRs), the kinetics of the WGS reaction on Cu is still dominated by only three RRs. Two of them, namely, the formate and associative RRs, are dominant at lower temperatures. The third one, referred to as a modified redox RR, is dominant at higher temperatures. Utilizing the quasi-equilibrium and steady-state assumptions, the microkinetic model is further reduced to a two-step mechanism similar to that of Temkin. The corresponding explicit rate expression with all parameters predicted a priori provides excellent agreement with the complete microkinetic model as well as with new experimental data provided here.