Impact of Parent Zirconia Crystallinity/Amorphicity on the n-heptane Isomerization over Pt/WO3-ZrO2 Catalysts

Abstract

A series of WO3-ZrO2 catalysts containing 18% of WO3 were prepared from Zr(OH)4 pre-calcined at temperatures between 25 to 700°C, before W-introduction by impregnation. Thus, in accordance with that, the resulting parent Zr(OH)4 support possessed different degree of crystallinity and proportion of monoclinic to tetrahedral (M/T) phases which directly influenced the same M/T ratio in the final Pt/WO3-ZrO2 catalyst. The resulting catalysts varied in nuclearity and reducibility of formed WOx species, as revealed by UV-Vis spectroscopy and TPR-H2. Despite widely different surface area of the final catalysts, ranged from 140 to 47 m2/g, related to the proportion of M/T phases, ranged from 10%/90% to 90%/10%; the activity of the corresponding Pt/WO3-ZrO2 for isomerization of C7 was found to be directly proportional only to the total surface area of the resulting catalysts without specific effect of the crystal modifications of the support. In accordance with that a correlation was observed between the isomerization activity in n-C7 conversion, ranged from 65 to 31%, and the population of formed poly-nuclear WOx species, ranged from 41 to 33%, directly controlled exclusively by the surface area of the support.