Catalytic activity of molybdena/alumina catalysts for the hydrogen-deuterium equilibration at low temperature

The H2-D2 equilibration has been studied at low temperature (78 to 110 K) over reduced (H2 at 673 or 773 K) MoO3/gamma-alumina (Mo content 5% in atoms). From the e/Mo ratio (No. of H equivalents/No. of Mo atoms) it was possible to determine the surface composition with respect to Mon+ (n=4,5,6) and surface vacancies. It was therefore possible to correlate the catalytic activity for H2-D2 with specific surface configurations. The correlation plots (catalytic activity vs. surface composition) strongly suggest the presence of active sites cosisting of Mo4+...Mo4+ pairs or, possibly, vacancies pairs. A comparison with H2 adsorption at 78 K shows that the same sites and hydrogen forms are active in the case of H2 adsorption and H2-D2 equilibration. The relationship with the centres active for hydrogenation reactions is briefly discussed.