(214g) Structural Sensitivity of the Water Gas Shift Reaction in Platinum Surfaces

In view of recent economical and environmental pressures, the necessity of a paradigm shift in the production and utilization of energy has emerged. In this shift, hydrogen is envisioned to play a central role, being regarded as a potential "fuel of the future". Hydrogen can be produced via the water-gas shift (WGS) reaction taking place during the catalytic reforming of oxygenated hydrocarbons derived from biomass. Latest research focuses on the use of precious metals, such as platinum and gold, as catalysts for WGS, and several studies have elucidated the underlying reaction mechanism. However, the contribution of different site types, namely steps and terraces, on the overall reaction rate is an open question and it remains unclear how structure sensitive is the WGS reaction. The present work addresses these questions using a multiscale modeling approach that integrates density functional theory (DFT) calculations and kinetic Monte Carlo (KMC) simulation. Using DFT we calculate the reaction barriers for the elementary steps of the WGS mechanism occurring at the two different site types, steps or terraces. These elementary steps include adsorption-desorption events, water and hydroxyl decomposition, and the formation of carboxyl and formate intermediates. We subsequently incorporate the calculated values into a KMC framework, and perform simulations for different step-site densities. For an extended temperature range we show that the reaction rates of stepped surfaces depend on step-site density. Our results indicate that the WGS reaction is structure sensitive and that the steps are the active sites for this chemistry.