Copper(11) catalyzed oxidation of propylene on x and y type zeolites: Observation of Cu(II) migration by electron spin resonance during and after reaction

The copper(II) catalyzed oxidation of propylene on X and Y type zeolites in the presence of the different major cations, K⁺, Na⁺, Ti⁺ and Ca²⁺, in the temperature range of 260 - 300° C was studied in a flow system. Complete oxidation products, carbon dioxide and water, were formed over all catalysts. The catalytic activities and the location of the active copper species were studied by gas chromatography and electron spin resonance. The activity of CuK-X was greater than for other cations and demonstrated an important cocation effect. The migration of Cu(II) ions as active species is observed during réaction and depends on the specific cocation. The cupric ion is found to migrate from inaccessible site SI in the hexagonal prism to accessible site SIT near the six-ring of the zeolite lattice at which site coordination with propylene occurs prior to reaction. If propylene is then removed from the flow stream migration of cupric ion Pack to hexagonal prism sites is observed. Molecular oxygen is shown to play a role of reoxidizing reduced copper species so as to maintain the copper in the cupric ion form.