Temperature-programmed reduction of metal-exchanged zeolite-A catalysts

The reduction of metal (Co, Ni, and Cu)-exchanged zeolite-A was studied by a temperatureprogrammed reduction (TPR) technique. The TPR profiles indicat e that the metals are in a dispersed form. The hydrogen consumption in the reduction process demonstrates that the metals are present in monovalent an d divalent forms. High-temperature reduction peaks are also observed in the cases of CoA and NiA. Nitrogen adsorption reveals that, on heating at high temperature, the pore capacity of zeolite-A increases when exchanged with transition metals because more space is occupied by water molecules. This i s confirmed by thermal analysis. After dehydration, the cations are in chan ged positions; they are often located in hidden sites (hexagonal prism and sodalite cages). The activation energy for the reduction process is calcula ted.