Calculations of Hydrogen Associative Desorption on Mono- and Bimetallic Catalysts
Huiling Zheng, Hao Li, Weiyu Song, Zhen Zhao, Graeme Henkelman
Abstract
Transition-metal-based materials can activate C–H and O–H bonds in industrially significant reactions such as hydrocarbon and alcohol reforming. Recently, bimetallic alloys based on Au, Ag, and Cu have shown unique chemistry including coke-resistance, promising reaction activity, and interesting product selectivity. However, the mechanism of their key reaction step, the hydrogen associative desorption process, is not well-understood. In this work, density functional theory calculations were used to study the kinetics and thermodynamics of hydrogen associative desorption on 8 monometallic and 70 bimetallic Au–, Ag–, and Cu–X (X = Ir, Ni, Pd, Pt, and Rh) close-packed surfaces. We identified two different mechanisms for hydrogen associative desorption on these surfaces, which are selected by the density of states overlap between a gas-phase H2 molecule and the d-band of the surface metal. We show that specific bimetallic atomic ensembles have significantly lower kinetic barriers for hydrogen associative desorption. A linear correlation between the hydrogen desorption barriers and the reaction energies was found for most of the surfaces studied. More importantly, we show that a Au-/Ag-/Cu-rich ensemble alloy with a small portion of a strong-binding metal can effectively lower the hydrogen associative desorption barrier. This finding is significant for the design of highly active and selective catalysts for H2 production through the activation of organic molecules.