Makoto Misono

Advances in designing perovskite catalysts

Abstract Recent advances in the basis for designing perovskite catalysts (ABO3, A: rare earths, B: transition metals of the first row) are reviewed. The main strategies of the catalyst design are; (1) selection of B-site elements which principally determine the catalytic activity, (2) valency and vacancy controls by selection of A-site elements including partial substitution, (3) synergistic effects of constituting elements, mainly B-site transition elements, (4) enhancement of surface area by forming fine particles or dispersing on supports, and (5) addition of precious metals with their appropriate regeneration to realize a high-performance automotive catalyst.

Catalysis by heteropoly compounds—recent developments

Abstract Recent developments for catalysis by heteropoly compounds as both acid and oxidation catalysts have been described. The acid strength of typical heteropoly acid, H3PW12O40, was found to be higher than that of H2SO4 in liquid-state and that of H-ZSM-5 in solid-state. The catalytic activity for acid-catalyzed reactions was greatly enhanced by supporting it on mesoporous silica (MCM-41) and the formation of an acidic Cs salt, Cs2.5H0.5PW12O40. The Cs2.5H0.5PW12O40 is hydrophobic and active for “water-tolerant catalysis”. Bifunctional catalysts Pt-Cs2.5H0.5PW12O40 and its SiO2-supported catalyst were effective for skeletal isomerization of n-alkanes. Isotopic study using 13 C -n-butane revealed that the isomerization of n-butane proceeds mainly via monomolecular mechanism over Pt-Cs2.5H0.5PW12O40. The Pt-Cs2.1H0.9 PW12O40 possessed ultramicropores with the width between 0.43 and 0.50xa0nm and exhibited shape selectivities for oxidation, hydrogenation, and skeletal isomerization of n-butane. As a typical example for oxidation catalyzed by heteropoly compounds, selective oxidation of methane with hydrogen peroxide has been focussed. The H4PVMo11O40 was found to be very efficient for the reaction. The reaction scheme, active species, and the role of heteropoly anion have been proposed.

Heteropolyacids. Versatile green catalysts usable in a variety of reaction media

Basic characteristics of heteropolyacids as green catalysts are overviewed, focusing on the various reaction fields in which the heteropolyacid catalysts function as acid and oxidation catalysts, and then two industrial processes which were made very green by the use of heteropolyacid catalysts in liquid biphase systems are described. In this context an interesting new reaction field formed at the interfacial layer of a solid heteropolyacid and liquid has also been reported.

Catalytic activity and structural stability of La0.9Ce0.1Co1-xFexO3 perovskite catalysts for automotive emissions control

Abstract One of the most important issues of automotive catalysts is the endurance of fluctuations between reductive and oxidative (redox) atmospheres at high temperatures exceeding 1173xa0K. The catalytic activity and structural stability of La0.9Ce0.1Co1−xFexO3 perovskite catalysts (x=0, 0.2, 0.4, 0.6, 0.8 and 1.0), both in powder and monolithic forms, were investigated after aging treatments in real and simulated “model” automotive exhaust gases. For powder catalysts before and after treatment both in the redox model gas and in air, the activity for oxidation of propane was evaluated and correlated with the crystal structure. For monolithic catalysts, the activities for reduction of NO, oxidations of CO and hydrocarbons (HC) were evaluated before and after aging in the flow of an engine exhaust gas at 1173xa0K. With increasing Co in La0.9Ce0.1Co1−xFexO3 perovskite catalysts, the catalytic activity increased and the structural stability decreased. La0.9Ce0.1Co0.4Fe0.6O3 indicated the best balance of activity and durability in the automotive exhaust gas at high temperatures. When the fraction of Co exceeded 0.6, the activity diminished due to the structural transformation from perovskite to K2NiF4-type layered structure. These observations, in general, corresponded to the results obtained for Pd-promoted perovskite monolithic catalysts. Specifically Fe at B-site gave the durability, and Co as well as Pd improved the activity of perovskite catalysts applied to automotive emissions control.

Selective oxidation of butanes. Toward green/sustainable chemistry

The importance of selective oxidation for the progress of green/sustainable chemistry is pointed out and the state of the art of heterogeneous selective oxidation of alkanes described, taking for examples the selective oxidations to form oxygenated products (1) of isobutane catalyzed by heteropoly-based mixed oxides and (2) of n-butane to maleic anhydride catalyzed by vanadium phosphorous mixed oxides. In addition, efforts necessary to bring about breakthroughs in this field are discussed.

Acid catalysts for clean production. Green aspects of heteropolyacid catalysts

Abstract A view of green/sustainable chemistry (GSC) and catalysts for GSC is first discussed. It is pointed out that easily applicable methods for the evaluation of greenness (or green index) are necessary for the sound development of GSC movement. Then, green/sustainable aspects of heteropolyacid (HPA) catalysts are described referring to examples of the achievements of basic studies and successful practical applications: (i) water-tolerant acid catalysis, (ii) catalysis in pseudoliquid phase, (iii) solid-phase catalysis, (iv) bi-functional catalysis in combination with noble metals, and (v) green processes in bi-phase systems.