II. Structure of Perovskites 1982 A. Crystal Structure 1982 B. Nonstoichiometry in Perovskites 1983 1. Oxygen Nonstoichiometry 1983 2. Cation Nonstoichiometry 1984 C. Physical Properties 1985 D. Adsorption Properties 1986 1. CO and NO Adsorption 1986 2. Oxygen Adsorption 1987 E. Specific Surface and Porosity 1987 F. Thermal Stability in a Reducing Atmosphere 1989 III. Acid−Base and Redox Properties 1990 A. Acidity and Basicity 1990 B. Redox Processes 1991 1. Kinetics and Mechanisms 1992 2. Reduction−Oxidation Cycles 1993 C. Ion Mobility 1993 1. Oxygen Transport 1993 2. Cation Transport 1994 IV. Heterogeneous Catalysis 1995 A. Oxidation Reactions 1995 1. CO Oxidation 1995 2. Oxidation of Hydrocarbons 1996 B. Pollution Abatement 2001 1. NOx Decomposition 2001 2. Exhaust Treatment 2002 3. Stability 2004 C. Hydrogenation and Hydrogenolysis Reactions 2004 1. Hydrogenation of Carbon Oxides 2004 2. Hydrogenation and Hydrogenolysis Reactions 2006

Chemical structures and performance of perovskite oxides.

Dimethyl ether (DME) as an alternative fuel

This review examines recent developments in the complete oxidation of methane at low temperature over noble metal based catalysts in patents and open literature. The abatement of natural gas vehicle (NGV) methane emissions is taken as one example among possible applications. The review develops current ideas about the properties of palladium and platinum catalysts supported on silica and alumina supports in the complete oxidation of methane under oxidising conditions, focusing on low-temperature reaction conditions. The influence of residual chloride ions on the catalytic activity, the kinetic aspects of the oxidation of methane over these catalysts, the nature of the active sites, the influence of metal particle size and reaction products on the activity, the observed changes in catalytic activity with reaction time and the effect of sulphur containing compounds are examined. The latest studies concerned with improved palladium and platinum supported catalysts which would exhibit enhanced and stable catalytic activity at low temperature in the presence of water and sulphur containing compounds are reported. Possible routes for preparing catalysts able to meet future regulations concerning methane emissions from lean-burn NGV vehicles are discussed.

Complete oxidation of methane at low temperature over noble metal based catalysts: a review

A large number of studies can be found in the literature regarding the production of new catalysts for methanol steam reforming. This work summarizes the latest developments on catalysts for this application and is divided in two main groups: copper-based and group 8–10 metal-based catalysts. In each section, the strategies proposed by several authors to enhance the performance of the catalysts are described. An overall comparison between the two groups shows that copper-based catalysts are the most active ones, while the 8–10 group catalysts present better results in terms of thermal stability and long-term stability. Very promising results were reported for both groups, enhancing the value of methanol as a hydrogen carrier for fuel cell applications.

Catalysts for methanol steam reforming—A review

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.

Review of fuel processing catalysts for hydrogen production in PEM fuel cell systems

Catalytic combustion, as an alternative to conventional thermal combustion, has received considerable attention during the past decade. Research efforts have been promoted by the need to meet governmental demands concerning pollution and the wish to use energy sources more efficiently. The two main advantages offered by catalytic combustors over flame combustors apply to these goals: Catalytic combustion can be carried out over a wide range of fuel concentrations in air and at low temperatures. These low temperatures result in attaining NO, emission levels substantially lower than possible with conventional combustors.

Catalytic Materials for High-Temperature Combustion

The influence of catalyst properties on the activity and selectivity of hydrogen generation by methanol reforming over copper-based catalysts impregnated on γ-alumina pellets has been investigated. In the experiments, three sets of copper-based catalysts with various compositions were tested: Cu/Zn/Al 2 O 3 , Cu/Cr/Al 2 O 3 and Cu/Zr/Al 2 O 3 . The catalysts were characterized using temperature programmed reduction (TPR), temperature programmed oxidation (TPO), SEM–EDS, Brunauer–Emmett–Teller (BET) surface area measurement and X-ray diffraction (XRD). The copper surface area was determined by pulse chemisorption using N 2 O. We found a correlation between the copper surface area and catalytic activity. The activity tests were performed in a fixed bed reactor with 15 g of spherical catalyst pellets using a gas hourly space velocity (GHSV) of 25,000. The results of the activity tests indicate that the choice of promoter and the catalyst composition greatly influence the activity as well as the selectivity for CO 2 formation. The highest conversions were achieved for the zinc-containing catalysts (Cu/Zn/Al 2 O 3 ) for both steam reforming and the combined reforming process. Complete conversion of methanol was only obtained for the zinc-containing catalysts when running the steam reforming process. The combined reforming process generally yielded a product stream containing lower carbon monoxide concentrations compared to steam reforming at the equivalent reactor temperature for all of the catalysts tested.

Activity and characterization of Cu/Zn, Cu/Cr and Cu/Zr on γ-alumina for methanol reforming for fuel cell vehicles

Preparation and characterization of LaCrO3 and Cr2O3 methane combustion catalysts supported on LaAl11O18- and Al2O3-coated monoliths

A single-step dip-coating technique was developed to produce stable films or washcoats of controlled thickness, surface area and pore-size distribution on alumina whisker-covered metal substrates (both flat plates and monoliths). Dip-coating slurries were prepared by dispersing fine porous powder in a colloidal silica sol. The method provided control over coating thickness and coating properties, such as pore-size distribution and surface area. The coating thickness could be varied between approximately 2 and 40 μm by selecting slurry composition and withdrawal speed in the dipping procedure. The pore-size distribution and surface area could be varied by changing type and amount of porous filler material in the dipping slurry. Uniform and bimodal pore-size distributions were obtained using silica and ZSM-5 molecular sieves, respectively, yielding coatings with surface areas between 60 and 400 m2g−1.

Preparation of anchored ceramic coatings on metal substrates: a modified sol-gel technique using colloidal silica sol

A brief review is given of the evolution of our ideas on the mechanism of catalytic reforming reactions over the last 40 years. The early bifunctional reaction mechanism, though criticized much, led first to an understanding and optimization of the reforming process and later to several other catalyst and process innovations. Kinetic and tracer studies on model catalysts using single hydrocarbons as reactants and the surface-science approach revealed the finer nuances of the mechanism involved. Simultaneously, the roles of S, Cl, coke, and hydrogen and of a second metal component like Re, Ir, or Sn in the industrial catalyst were also understood to a greater or lesser extent. All these results make the mechanism of reforming reactions a field of fascinating complexity in fundamental and industrial catalysis.

P. Govind Menon

Papers

Catalytic Materials for High-Temperature Combustion

Activity and characterization of Cu/Zn, Cu/Cr and Cu/Zr on γ-alumina for methanol reforming for fuel cell vehicles

Preparation and characterization of LaCrO3 and Cr2O3 methane combustion catalysts supported on LaAl11O18- and Al2O3-coated monoliths

Preparation of anchored ceramic coatings on metal substrates: a modified sol-gel technique using colloidal silica sol

Some Aspects of the Mechanisms of Catalytic Reforming Reactions