Abstract

We present a combined density functional theory (DFT) and Kinetic Monte Carlo (KMC) study of the
water gas shift (WGS) reaction on the Pd(100) surface. We propose a mechanism comprising both the
redox and the associative pathways for the WGS within a single framework, which consists of seven core
elementary steps, which in turn involve splitting of a water molecule followed by the production of an Hatom
and an OH-species on the Pd(100) surface. In the following steps, these intermediates then
recombine with each other and with CO leading to the evolution of CO2, and H2. Seven other elementary
steps, involving the diffusion and adsorption of the surface intermediate species are also considered for
a complete description of the mechanism. The geometrical and electronic properties of each of the
reactants, products, and the transition states of the core elementary steps are presented. We also discuss
the analysis of Bader charges and spin densities for the reactants, transition states and the products of
these elementary steps. Our study indicates that the WGS reaction progresses simultaneously via the
direct oxidation and the carboxyl paths on the Pd(100) surface.