Temperature-programmed Reduction of Metal-exchanged Zeolite-a Catalysts

The reduction of metal (Co, Ni, and Cu)-exchangedzeolite-A was studied by a temperature programmed reduction (TPR) technique. The TPR profiles indicate that the metals are in a dispersed form. The hydrogen consumption in the reduction process demonstrates that the metals are present in monovalent and 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 is confirmed by thermal analysis. After dehydration, the cations are in changed positions; they are often located in hidden sites (hexagonal prism and sodalite cages). The activation energy for the reduction process is calculated. This revised version was published online in July 2006 with corrections to the Cover Date.