Importance of metal-oxide interfaces in heterogeneous catalysis: A combined DFT, microkinetic, and experimental study of water-gas shift on Au/MgO

Abstract

The water-gas shift (WGS) reaction is central to a spectrum of industrially important catalytic processes, ranging from the manufacture of hydrogen to the processing of biomassderived feedstocks. Recently, oxide-supported Au catalysts have attracted attention for lowtemperature WGS reactions, but the role of the Au/oxide interface in promoting this chemistry remains under debate. In this contribution, we combine periodic Density Functional Theory (DFT) calculations, detailed microkinetic modeling, and rigorous kinetic measurements to elucidate the impact of this interface on the molecular-level features of WGS chemistry of a gold nanowire supported on a MgO(100) substrate. The results demonstrate that the barrier to activate water, which is prohibitively high (~2 eV) on a clean Au(111) surface, is decreased to essentially zero at the Au/MgO interface. From the DFTcalculated energetics, a dual-site microkinetic model of the Au/MgO interface is constructed. Rate and thermodynamic control analysis demonstrate both the high degree of kinetic control of COOH formation at the interface and a strong influence of competitive adsorption between CO and H. A procedure to refine the microkinetic predictions by iterative replacement of the energies of kinetically sensitive steps with a higher accuracy hybrid HSE06 prediction is introduced, and the determined effective activation barriers and reaction orders agree well with the results of detailed kinetic measurements on Au nanoparticles on MgO substrates. The results clearly show the critical role that the metal/oxide interface plays in WGS catalysis, and the approach introduced to predict kinetics at the metal/oxide interface should be applicable to a variety of catalytic processes on oxide-supported metal nanoparticles.

How Do Structurally Distinct Au/α‐Fe2O3 Interfaces Determine Surface OH/H2O reactivity, Intermediate Evolution, and Product Formation in Low‐temperature Water‐gas Shift Reaction?

“…XPS was employed to investigate the electronic and chemical properties of the interfacial structures. For the WGS reaction, the state of Au entities and the associated interfacial boundary are thought to play a crucial role in adsorbing CO and dissociating H 2 O . The results are shown in Figures and S4.…”

Water activation and carbon monoxide coverage effects on maximum rates for low temperature water-gas shift catalysis

“…Inspired by several works in the literature ( [34,35], we have made a model based on the idea of a maximum possible Sabatier rate [33,36], the rate at which the surface coverages are ideal for each reaction step. The water-gas shift reaction is often described to have a bi-functional mechanism which involves CO activation on a metal and water dissociation on the support or metal/support interface [7,14,[37][38][39][40][41][42].…”

Electrostatic Origins of Linear Scaling Relationships at Bifunctional Metal/Oxide Interfaces: A Case Study of Au Nanoparticles on Doped MgO Substrates

“…[19,20] One class of catalytic active sites that is prevalent in heterogeneous catalysis,b ut for which the physics and even existence of scaling relationships are essentially unknown, consists of sites at the interface between metal nanoparticles and oxide supports. [22][23][24] To analyze SRs on supported metal nanoparticles,weadopt astrategy of substitutionally doping Au/oxide interfaces.T his permits systematic perturbation of interfacial electronic properties while minimizing geometric changes that would be associated, for example,with changing the elemental nature of the metal or the metal nanoparticle size. [22][23][24] To analyze SRs on supported metal nanoparticles,weadopt astrategy of substitutionally doping Au/oxide interfaces.T his permits systematic perturbation of interfacial electronic properties while minimizing geometric changes that would be associated, for example,with changing the elemental nature of the metal or the metal nanoparticle size.…”