Microcalorimetric and catalytic studies on sulfated zirconia catalysts of different preparations

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