SOLID-STATE H-1 MAS NMR-STUDY ON THE HIGHLY-ACTIVE PROTONS IN PARTIALLY REDUCED AG3PW12O40

The physicochemical nature of protons generated by the partial reduction of Ag+ cations in Ag3PW12O40 with hydrogen was investigated by means of H-1 MAS NMR. When Ag3PW12O40 was partially reduced with hydrogen, the IH 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 amount of protons at 6.4 and 9.3 ppm depended on the degree of the reduction of Ag+ cations in Ag3PW12O40. When the degree of the reduction of Ag+ was 13%, the protons at 6.4 ppm were mainly observed and the protons at 9.3 ppm were only slightly observed. The amount of protons at 6.4 ppm increased by increasing the degree of the reduction of Ag+ cations from 13% to 32%. These protons were scarcely observed when the degree of reduction of Ag+ cations reached 67%. In contrast, the amount of protons at 9.3 ppm increased by increasing the degree of reduction of Ag+ cations from 13% to 67%. The acid strength of the protons observed at 6.4 ppm is higher than that of the protons at 9.3 ppm. The catalytic activity of partially reduced Ag3PW12O40 for the isomerization of 3,3-dimethylbut-1-ene and hexane reversibly changes with hydrogen pressure.