Hydrogen production reactions from carbon feedstocks: fossil fuels and biomass.

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

In this paper we report on the activity of Cu- and Ni-containing cerium oxide catalysts for low-temperature water-gas shift (WGS). Bulk catalysts were prepared in nanocrystalline form by the urea co-precipitation–gelation method. Lanthanum dopant (10 at.%) was used as a structural stabilizer of ceria, while the content of Cu or Ni was in the range of 5–15 at.% (2–8 wt.%). At low metal loadings, Cu or Ni were present in the form of highly dispersed oxide clusters, while at high loadings, clusters as well as particles of CuO or NiO (>10 nm in size) were present on ceria. Both Cu and Ni increased the reducibility of ceria, as evidenced by H2-TPR experiments. The WGS reaction activity of Ce(La)Ox was increased significantly by addition of a small amount (2 wt.%) of Cu or Ni. The catalysts were not activated prior to testing. Steady-state WGS kinetics were measured over the temperature range of 175–300 and 250–300°C, respectively, for Cu- and Ni–Ce(La)Ox. The activation energy of the reaction over Ce(La)Ox was 58.5 kJ/mol, while it was 38.2 and 30.4 kJ/mol, respectively, over the 5 at.% Ni–Ce(La)Ox and 5 at.% Cu–Ce(La)Ox catalysts in CO-rich conditions. A co-operative redox reaction mechanism, involving oxidation of CO adsorbed on the metal cluster by oxygen supplied to the metal interface by ceria, followed by H2O capping the oxygen vacancy on ceria, was used to fit the kinetics. Parametric studies were mainly performed with the 5 at.% Cu–(La)Ox catalyst. Notably, this material requires no activation and retains high WGS activity and stability at temperatures up to 600°C.

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Low-temperature water-gas shift reaction over Cu- and Ni-loaded cerium oxide catalysts

Catalysis by Supported Gold Nanoparticles: Beyond Aerobic Oxidative Processes

The rapid development in recent years of the proton-exchange membrane (PEM) fuel cell technology has stimulated research in all areas of fuel processor catalysts for hydrogen generation. The principal aim is to develop more active catalytic systems that allow for the reduction in size and increase the efficiency of fuel processors. The overall selectivity in generating a low CO content hydrogen stream as needed by the PEM fuel cell catalyst is dependent on the efficiency of the catalysts in each segment of the fuel processor. This article reviews the advances achieved during the past few years in the development of catalytic materials for hydrogen generation through fuel reforming, 1 water-gas shift and carbon monoxide preferential oxidation, as used or aimed to be of use in fuel processing for PEM fuel cell systems.

C. Rhodes

Papers

Water-gas shift reaction: finding the mechanistic boundary