The characterization of tungsten-oxide-modified zirconia supports for dual functional catalysis

The results of catalytic titration measurements indicated that WOx/ZrO2 catalysts prepared by coprecipitation have higher acid site density and strength, and are more active for pentane isomerization. than catalysts prepared by impregnation. The coprecipitated WOx/ZrO2 contains similar to0.004 meq-H+/g-catalyst. XPS of chemisorbed 2,6-dimethylpyridine and pyridine revealed the presence of Lewis acid sites as well as strong and weak Bronsted acid sites on the surface of these catalysts. The concentration of strong Bronsted sites was close to the concentration of Lewis sites, suggesting that the high acidity of these materials may originate from a conjugate Bronsted-Lewis site. Pt/WOx/ZrO2 undergoes a reversible loss of hydrogen chemisorption capacity with increasing hydrogen pretreatment temperature, accompanied by a reversible loss of pentane isomerization activity. This loss can be attributed to a strong Pt-reduced tungsten oxo species interaction (SMSI). Room temperature hydrogen spillover is observed in the Pt/WOx/ZrO2 (similar to16% W) catalyst, consistent with the presence of bulk WO in this material as observed by TPR.