Controlling Heterogeneous Catalysis of Water Dissociation Using Cu-Ni Bimetallic Alloy Surfaces: A Quantum Dynamics Study.

Abstract

Copper-Nickel bimetallic alloys are emerging heterogeneous catalysts for water dissociation which is the rate-determining step of the industrially important water gas shift (WGS) reaction. Yet, the detailed quantum dynamics studies of water-surface scattering in the literature are limited to pure metal surfaces. We present here a three-dimensional wave packet dynamics study of water dissociation on Cu-Ni alloy surfaces, using a pseudodiatomic model of water on a London-Eyring-Polanyi-Sato (LEPS) potential energy surface in order to study the effect of initial vibration, rotation, and orientation of the water molecule on the reactivity. For all the chosen surfaces, reactivity increases significantly with vibrational excitation. In general, for lower vibrational states the reactivity increases with increasing rotational excitation but it decreases in higher vibrational states. Molecular orientation strongly affects reactivity by helping the molecule to align along the reaction path at higher vibrational states. For different alloys, the reaction probability follows the trend of barrier heights and the surfaces having all Ni atoms in the uppermost layer are much more reactive than the ones with Cu atoms. Hence the nature of the alloy surface and initial quantum state of the incoming molecule significantly influence the reactivity in surface catalyzed water dissociation.