Properties of chemisorbed hydrogen species on Ag-A zeolite partially reduced with hydrogen as studied by 1H MAS NMR

Heterolytic dissociation of H-2 proceeded to form acidic protons and silver hydride species, Ag-3-H upon exposing Ag-A to hydrogen. The effects of the degree of Ag+ ion exchange and the temperature of hydrogen exposure on the formation of hydrogen chemisorbed species were examined with H-1 MAS NMR. Furthermore. the thermal stability of silver hydride species and the temperature dependence of the line shape of the peak due to acidic protons were studied with raising the temperature stepwise from 298 to 513 K. The thermal stability of Ag-3-H and the mobility of acidic protons decreased with increasing the Ag+ content in zeolite. Ag-3-H reacted with acidic protons to form H-2 and Ag-3(+) at 353 K. This result was in conformity with the mechanism of hydrogen adsorption proposed in our previous work. (C) 2001 Published by Elsevier Science B.V.