Periodic, self-consistent density functional theory (DFT-GGA) calculations are used to investigate the water gas shift reaction (WGSR) mechanism on Cu(111). The thermochemistry and activation energy barriers for all the elementary steps of the commonly accepted redox mechanism, involving complete water activation to atomic oxygen, are presented. Through our calculations, we identify carboxyl, a new reactive intermediate, which plays a central role in WGSR on Cu(111). The thermochemistry and activation energy barriers of the elementary steps of a new reaction path, involving carboxyl, are studied. A detailed DFT-based microkinetic model of experimental reaction rates, accounting for both the previous and the new WGSR mechanism show that, under relevant experimental conditions, (1) the carboxyl-mediated route is the dominant path, and (2) the initial hydrogen abstraction from water is the rate-limiting step. Formate is a stable “spectator” species, formed predominantly through CO2 hydrogenation. In addition...

On the mechanism of low-temperature water gas shift reaction on copper.

We have carried out a project to clarify the active site and the role of ZnO in Cu/ZnO-based catalysts for methanol synthesis from CO 2 and H 2 using both classical catalytic and surface science techniques. The active site model in which Zn species present on the Cu surface promote the methanol synthesis had been initially proposed based on the results of the powder catalysts such as a physical mixture of Cu/SiO 2 and ZnO/SiO 2 . The promotion of Zn has then been proved by a model catalyst of a Zn-deposited Cu(1 1 1) surface. The mechanism and kinetics of the methanol synthesis over Zn/Cu(1 1 1) as well as the structure of the active site have been studied on the atomic level by surface science techniques, such as XPS, AES, LEED, IRAS, and STM. A metallic Cu–Zn surface alloy is a catalytically active species for the methanol synthesis from CO 2 and H 2 .

The chemical modification seen in the Cu/ZnO methanol synthesis catalysts

A surface science investigation of the water-gas shift reaction on Cu(111)

Publisher Summary For chemisorption phenomena on transition metal surfaces, including surface reactivity, the bond-order conservation-Morse potential (BOC-MP) model appears to provide such a framework in which the intricacies of real phenomena are coherently interrelated. The BOC-MP model is a simple, truly “back-of-the-envelope’’ model that can be directly used by practitioners in the field. It efficiently describes and interrelates a wide variety of chemisorption phenomena. Most important, the model maps out metal surface reactions providing insight into both regularities and details. In principle, any metal surface reaction can be treated this way. The only requirement is to retain the rigor and simplicity of the model projections. This analytic model proved to be efficient for treating energetics of atomic and diatomic adsorbates on transition metal surfaces, particularly, the heat of chemisorption and activation barriers for dissociation and recombination. Recently, the BOC-MP model has been extended to treat energetics of polyatomic adsorbates as well, which made it possible to analyze mechanisms of catalytic heterogeneous reactions of practical importance. The chapter surveys major applications and implications of BOC-MP modeling to chemisorption and heterogeneous catalysis.

T.H. Ellis

Papers

New insights into the kinetics of formic acid decomposition on copper surfaces

Direct, Real-Time Measurement of Adsorption and Desorption Kinetics on Cu(100)