THE USE OF PROTON AFFINITY DISTRIBUTIONS FOR THE CHARACTERIZATION OF ACTIVE-SITES OF ALUMINA-SUPPORTED CO-MO CATALYSTS

A series of MoO3/Al2O3 catalysts of varying weight loading were charac terized after calcination by their buffering capacity during potentiom etric titration. Strong buffering of the aqueous electrolyte occurred in distinct pH ranges, which indicated the formation of hydrolysis pro ducts of the surface compounds formed in these pH windows. Addition of cobalt, followed by calcination, revealed a new feature which signale d the formation of a possible surface heteropolymolybdate compound. If cobalt was added first this compound was not formed, however, if coba lt and molybdenum were coimpregnated it was detectable. As a promoter, Ni(II) had an effect similar to cobalt, but Fe(III) did not. The seri es of catalysts were further tested for their hydrodesulfurization act ivity using thiophene as a reactant. The thiophene conversion, as a fu nction of the amount of surface compound formed by addition of the cob alt promoter, resulted in a linear relation, indicating that the Co/Mo compound detected in the oxidic state could be correlated with the HD S activity of these catalysts. (C) 1996 academic Press, Inc.