Silica supported superacid isomerization catalysts

Oxoanion promoted ZrO2 and TiO2 catalysts are isomerization catalysts which are usually prepared in bulk form. High activation temperatures and low sintering resistance usually yield low surface area materials. The replication of the structure of these catalysts over silica was studied in this work as a means of increasing the number of available active sites. The acid activity was assessed by means of the test of isomerization of cis-butene. The dispersion of tungsten-zirconia, tungsten-titania, boron-zirconia and boron-titania over silica was accomplished by sequentially impregnating Zr and Ti organic compounds and W and B inorganic salts. Supported ZrO2 displayed the highest sintering resistance, crystallizing at 700 °C, while supported TiO2 crystallized at a lower temperature, 550 °C. As a consequence, only supported zirconia could match the range of activation of WOx species (700–800 °C) and a bimodal pattern of activity was found, with maxima at 550 and 750 °C when the W-ZrO2/SiO2 catalyst was used in the isomerization of cis-butene. W-TiO2/SiO2 was fairly inactive.