CATALYTIC PROPERTIES AND PHYSICOCHEMICAL NATURE OF HIGHLY-ACTIVE PROTONS IN PARTIALLY REDUCED AG3PW12O40

The catalytic properties and the physicochemical nature of protons generated by the partial reduction of Ag+ cations in Ag3PW12O40 With hydrogen was investigated by examining the catalytic activities for isomerizations of l-butene and hexane and by H-1 MAS NMR spectroscopy. The catalytic activity of partially reduced Ag3PW12O40 reversibly changes with hydrogen pressure, indicating that on Ag3PW12O40 hydrogen molecules are reversibly transformed into protons which are active for the isomerizations of l-butene and hexane. When Ag3PW12O40 was partially reduced with hydrogen, the H-1 MAS NMR spectrum demonstrated the generation of two kinds of acidic protons, which are observed at 6.4 and 9.3 ppm. The protons at 6.4 ppm exist only in the presence of hydrogen in the gas phase. The amount of these protons reversibly changes with the hydrogen pressure. In contrast, the amount of protons at 9.3 ppm is independent of the hydrogen pressure. The protons at 9.3 and 6.4 ppm catalyze the isomerization of l-butene. Only the protons at 6.4 ppm are active for hexane isomerization, though the protons at 9.3 ppm are inactive. In both reactions, the reversible change of the activities with hydrogen pressure is caused by the reversible change in the number of the protons at 6.4 ppm.