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.

Copper-Zinc Oxide-Alumina Methanol Catalysts Revisited

The activation of O2 on metal surfaces is a critical process for heterogeneous catalysis and materials oxidation. Fundamental studies of well-defined metal surfaces using a variety of techniques have given crucial insight into the mechanisms, energetics, and dynamics of O2 adsorption and dissociation. Here, trends in the activation of O2 on transition metal surfaces are discussed, and various O2 adsorption states are described in terms of both electronic structure and geometry. The mechanism and dynamics of O2 dissociation are also reviewed, including the importance of the spin transition. The reactivity of O2 and O toward reactant molecules is also briefly discussed in the context of catalysis. The reactivity of a surface toward O2 generally correlates with the adsorption strength of O, the tendency to oxidize, and the heat of formation of the oxide. Periodic trends can be rationalized in terms of attractive and repulsive interactions with the d-band, such that inert metals tend to feature a full d band ...

O2 Activation by Metal Surfaces: Implications for Bonding and Reactivity on Heterogeneous Catalysts

The structural sensitivity of the water-gas shift (WGS) reaction (CO + H2O → H2+ CO2) over metallic copper is addressed here by comparing its kinetics over the atomically clean Cu(110) surface with prior results for Cu(111). The surfaces were prepared and characterized with UHV surface analysis (AES, LEED, XPS), then transferred to an attached microreactor for medium-pressure [10–1000 Torr (1 Torr = 101 325/760 Pa)] kinetic measurements and finally returned to UHV for post-reaction surface analysis. For both surfaces, the rate is nearly first-order in H2O pressure and zero-order in CO. Depending upon the temperature, Cu(110) is four- to ten-fold more active than the more densely packed Cu(111) surface. The apparent activation energy is also ca. 7 kcal mol–1(1 cal = 4.184 J) lower on Cu(110). This is attributed to a lower barrier for O—H bond cleavage in the rate-determining step: i.e. the dissociative adsorption of water. Strong evidence for a ‘surface redox’ mechanism involving oxygen adatoms is provided by comparing the known kinetics of reverse WGS with the rate of dissociative CO2 adsorption on Cu(110). A potential-energy diagram is presented which explains the known kinetics and energetics for the elementary steps as occurring in the forward or reverse direction, as well as the overall WGS reaction on clean Cu(110). The influence of adsorbed Cs on the reaction kinetics is also presented, and compared to earlier results on Cs/Cu(111). In both cases, Cs strongly accelerates the reaction. In the case of Cu(110), the rate-determining step is even changed. The reaction mechanism involves Cs · CO3, a and Cs · Oa.

Kinetics and mechanism of the water-gas shift reaction catalysed by the clean and Cs-promoted Cu(110) surface: a comparison with Cu(111)

C.M.A.M. Mesters

Papers

The adsorption and incorporation of oxygen on Cu(100) and its reaction with carbon monoxide; Comparison with Cu(111) and Cu(110)

Interaction of hydrogen with oxygen on Cu(111)

The adsorption of carbon monoxide on Cu(110)-Ni surfaces prepared by dissociation of nickel carbonyl

Preparation and characterization of Cu(111)-Ni and Cu(110)-Ni surface alloys

Preparation and reactivity of Cu(100)-Ni surfaces