Microcalorimetric and catalytic studies on sulfated zirconia catalysts of different preparations

Sulfated and metal ion-promoted sulfated zirconia were synthesized by freez e-drying as well as by conventional and aerogel synthesis. The acidity of t he samples was studied by means of microcalorimetry; the catalytic performa nce of the samples was evaluated in the reaction between benzoic anhydride and anisole at 50 degreesC and RT. Supercritical drying and freeze-drying g ave access to sulfated zirconia with large pore diameters and pore volumes. As a result, high conversions in the Friedel-Crafts acylation were observe d; a further increase in activity was achieved by metal ion promotion. The results of the benzoylation reaction were related to data from microcalorim etric experiments. The adsorption was performed not only with ammonia and p yridine in the gas phase, but also with a mixture of pyridine in anisole, m uch more consistent with the catalysis conditions. Only from the latter exp eriments, the higher catalytic performance of cryogel and aerogel samples w as confirmed. Therefore, using such liquid mixtures might be a suitable met hod to distinguish between good acylation catalysts and less active samples . (C) 2001 Academic Press.