Acid centers in sulfated, phosphated and/or aluminated zirconias

Abstract

On sulfated ZrO2, the comparison of the effects of adsorbing water or ammonia on the infrared bands between 1400 and 1000 cm−1 suggests that besides structural Lewis sites on the surface of ZrO2, strong Lewis sites are made from chemisorbed SO3. Upon adsorption of water, SO3 is converted, partially, into a surface sulfated species which may act as strong Bronsted sites. At moderate surface hydration, both types of sites may coexist. The catalytic activity in the isomerization of isobutane is a function of the overall nominal surface density in SO4. The acid sites on the surface of phosphated mesoporous zirconia are attributable to surface P–OH groups working as weak Bronsted sites. On both sulfated and phosphated zirconia, surface coating of alumina stabilizes the porosity, but it does not modify the nature of their acid centers.