Monoclinic and tetragonal high surface area sulfated zirconias in butane isomerization:: CO adsorption and catalytic results

In the present study high surface area monoclinic and tetragonal sulfated zirconia samples both active in n-butane isomerization were prepared from the same hydroxide precursor in a navel one-step hydrothermal process. The process is studied via analysis of intermediate stages of the product formation. The monoclinic samples show a catalytic activity in n-butane isomerization lower by about a factor of 4 compared to the tetragonal samples, although the acidity as analyzed by CO adsorption was found to be similar. This suggests, that it is not only the acidity of sulfated zirconia that determines the catalytic performance. The results support the bimolecular mechanism, for which a favorable arrangement of surface groups is necessary. The surface structure of tetragonal zirconia seems to be better suited than that of the monoclinic zirconia, although the presented monoclinic zirconia performs substantially better than claimed in many publications, where the monoclinic phase is typically assumed to be inactive. (C) 2001 Academic Press.