Synthesis of catalytically active sulfated zirconia aerogels

Sulfated zirconia aerogels were synthesized by a sol-gel method followed by high temperature supercritical drying. Aerogels with sulfur introduced during the gelation step had high surface areas and pore volumes. Their textural properties could be tuned by variation of the preparation conditions. Samples synthesized by this procedure and those obtained by incipient wetness impregnation of zirconia aerogels with (NH4)(2)SO4 were shown to exhibit catalytic activity in the isomerization of n-butane comparable to conventional precipitated zirconia. Maximum catalytic activity of impregnated aerogels was observed at lower nominal sulfur loadings. They were shown to retain more surface sulfates after calcination compared to samples prepared by two other methods. The most active samples had close to monolayer surface coverage with sulfates with the decomposition peak at 820-830 degrees C. Over-monolayer surface sulfates hindered the isomerization activity whereas bulk sulfates had little effect. (C) 1998 Academic Press.