The Interaction of Water with Solid Surfaces: Fundamental Aspects Revisited

Reversible work transition state theory: application to dissociative adsorption of hydrogen

Surface science studies of model fuel cell electrocatalysts

Using XPS and x-ray-excited Auger electron spectroscopy (XAES), we have studied the variation in surface composition of CuO and Cu2O with a variety of high-vacuum treatments, including vacuum annealing, oxidation and hydrogen reduction. Prolonged annealing of CuO results in the formation of a thick layer of Cu2O at the surface whilst vacuum annealing of Cu2O produces a thin (possibly one monolayer) film of Cu metal. Both bulk Cu2O and the thick Cu2O film generated from vacuum-annealed CuO were oxidized to CuO by heating at 800 K in 1×10-4 mbar O2, the original surface being regenerated with vacuum annealing at the same temperature. Both CuO and Cu2O are reduced to metal at the surface by heating in 1×10-4 mbar hydrogen at 400 K. In the case of CuO, the extent of reduction varies with the thermal history of the sample, with prolonged vacuum annealing producing a more reducible surface. Hydrogen-reduced CuO and Cu2O were both reoxidized on vacuum annealing, demonstrating the diffusion of lattice oxygen to the surface.

Surface Oxidation and Reduction of CuO and Cu2O Studied Using XPS and XAES

Developments in water gas shift (WGS) catalysis, especially during the last decade, are reviewed. Recent developments include the development of 1 chromium‐free catalysts that can operate at lower steam to gas ratios and 2 more active catalysts that can operate at gas hourly space velocities above 40,000 h−1. A current challenge is to develop catalysts for use in fuel cell applications. Precious metal catalysts supported on partially reducible oxide supports (Pt‐ceria, Pt‐titania, Au‐ceria, etc.) are the current front runners. A critical review of the mechanism of the WGS reaction is also presented.

Water Gas Shift Catalysis

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)

Probing ensemble effects in surface reactions. 2. Benzene adsorption on clean and bismuth-covered platinum(111)

The dissociative adsorption of H2 and D2 on Cu(110): activation barriers and dynamics

Cu films on a Zn-terminated ZnO(0001) surface: structure and electronic properties

Un modele cinetique est propose pour expliquer la dissociation des especes adsorbees sur les catalyseurs ou les sites acides ont ete partiellement dilues

Probing ensemble effects in surface reactions. 1. Site-size requirements for the dehydrogenation of cyclic hydrocarbons on platinum(111) revealed by bismuth site blocking

J. M. Campbell

Papers

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

Probing ensemble effects in surface reactions. 2. Benzene adsorption on clean and bismuth-covered platinum(111)

The dissociative adsorption of H2 and D2 on Cu(110): activation barriers and dynamics

Cu films on a Zn-terminated ZnO(0001) surface: structure and electronic properties

Probing ensemble effects in surface reactions. 1. Site-size requirements for the dehydrogenation of cyclic hydrocarbons on platinum(111) revealed by bismuth site blocking