Tungsten –zirconia sopported over silica as a catalyst for acid catalyzed reactions

C. R. VERA, K. SHIMIZU, C. L. PIECK, J. M. GRAU, M. E. LOVATO, J.M. PARERA

Angra dos Reis, Brasil

Congreso; 12º Congresso Brasileiro de Catálise; 2003

The synthesis of novel complex catalysts of tungsten promoted zirconia (WZ) supported over silica and the study of its activity in I-butene isomerization, n-butane isomerization and isomerization-cracking of n-octane was performed in this work. In order to disperse WZ over silica, zirconia was first dispersed over silica. Highly dispersed zirconia with a great resistance to sintering was got by controlled hydrolysis of zirconium alkoxide impregnated by incipient wetness. This resistance is crucial for the synthesis of W promoted catalysts which needed to be calcined at 700-800 OC in order to become catalytically active. Tungsten promoted catalysts were prepared by impregnation of silica supported Zr(OH)4 with ammonium metatungstate. Catalysts with zirconia contents equal to 1-1.5 monolayers (1 monolayer=30% zirconia in thiscase) were the most active. Catalysts with lower and higher zirconia contents wepe less active. The optimum calcination temperature was 750ºC, a value which is similar to that of bulk WZ. The activity of silica supported WZ taken as a whole (silica + WZ) was only in a few cases higher than the activity of bulk WZ. ow ever the activigper unit mass of zirconia was always higher in the case of the supported catalysts. The activity in isornerization of n-butane was low while it was high for isomerization of 1-butene and isomerization-cracking of n-octane, indicating that most active sites on rhese catalysts had medium strength. In the case of the n-octane reaction, the stability displayed by the new catalysts was higher than the activity of bulk WZ.