Selective catalytic reduction of NO by hydrocarbons (HC-SCR) is one of the promising technologies for removal of NO in exhausts containing excess oxygen, such as diesel and lean burn gasoline engines. Supported Ag catalysts, especially Ag/Al₂O₃, are thought to be the promising candidates for use in diesel exhausts, as confirmed by several reports on engine bench tests. The HC-SCR performance of supported Ag catalysts is very sensitive to the reaction conditions, especially the type of hydrocarbons and the addition of H₂. The control of reaction conditions would be key for practical use. The current research of supported Ag catalysts is reviewed from the viewpoints of practical use and the reaction mechanism, i.e., the reaction scheme, the role of surface adsorbed species, and the structure of active Ag species.

Design of solid acid catalysts is one of the key technologies to establish environmental friendly catalytic processes. Featuring cation-exchanged clay and metal salts of heteropolyacids as model solid acid catalysts, a strategy for design of active catalysts for green chemical and biomass conversion processes is discussed. The important role of solid Lewis acids was suggested in acetylation of alcohols with acetic anhydride by cation-exchanged clay, Friedel–Crafts acylation and alkylation of aromatic compounds with metal salts of heteropolyacids, and hydrolysis of cellulose into saccharides. The significant influence of reactor design and reaction conditions on dehydration of saccharides into 5-hydroxymethylfurfural (HMF) is also discussed.

The size control of Ag into nanoclusters generates unique catalytic features of Ag on automotive emission control and environmentally friendly organic reactions. Hydrogen-assisted selective catalytic reduction of NO by hydrocarbons (H₂–HC–SCR), which is one of the promising technologies for removal of NO in the diesel engine exhausts, results in the formation of Ag clusters on alumina or zeolites and enhancement of the conversion of NO into N₂. A mechanistic study using in situUV-Vis, EXAFS, and FT/IR revealed that the promotion of partial oxidation of hydrocarbons by active oxygen species is the essential role of Ag clusters. Hydrogen is suggested to be indispensable for the formation of the Ag cluster and the active oxygen. The important role of hydride on the formation of H₂O₂-like active chemical species on Ag clusters was confirmed by density functional theory (DFT) calculation. Knowing the high activity of Ag nanoclusters for the formation of Ag-hydride, supported Ag clusters were applied for various organic reactions. Supported Ag clusters on appropriate metal oxide, especially Al₂O₃, are recyclable and show very high activity and selectivity for atom-economic reactions, i.e., alcohol dehydrogenation, C–C coupling reaction of alcohols, direct amide synthesis from alcohols and amines, N-benzylation of anilines with alcohols, and selective hydrogenation of nitroaromatics.

Acidic metal oxides, in particular Ta ₂ O ₅ , significantly enhanced the conversion of 5-hydroxymethylfurfural to a cyclopentanone derivative.

To elucidate the reaction mechanism of NO–C₃H₆–CO–O₂ over NiFe₂O₄, we investigated the dynamics of the adsorbed and gaseous species during the reaction using operando Fourier transform infrared (FTIR). The NO reduction activity dependent on the C₃H₆ and CO concentrations suggested that NO is reduced by C₃H₆ under three-way catalytic conditions. From FTIR measurements and kinetic analysis, it was clarified that the acetate species reacted with NO–O₂ to form N₂ via NCO, and that the rate-limiting step of NO reduction was the reaction between CH₃COO^– and NO–O₂. The NO reduction mechanism of the three-way catalyst on NiFe₂O₄ is different to that on platinum-group metal catalysts, on which NO reduction proceeds through N–O cleavage.