H-spillover and SMSI effects in paraffin hydroisomerization over Pt/WOx/ZrO2 bifunctional catalysts

The Pt-modified WOx/ZrO2 catalyst system is found to undergo various transf ormations in the presence of hydrogen, These transformations include the ge neration of spillover hydrogen at room temperature, the development of a st rong Pt-W interaction at elevated temperatures, and tungsten reduction. We have characterized these effects using hydrogen chemisorption and temperatu re-programmed reduction techniques. We have also employed pentane isomeriza tion as a test reaction to relate these changes to the acid catalysis of th ese materials. Our findings indicate that all of the above transformations are sensitive to tungsten loading. Room temperature hydrogen spillover is o bserved at 15.9 wt% tungsten, but is absent at tungsten loadings of less th an or equal to 8.4 wt%, The higher tungsten loading catalyst exhibits a Pt- W SMSI effect in hydrogen at >200 degrees C; at lower tungsten loadings muc h higher temperatures are required to induce this effect, This result agree s with the increasing reducibility of tungsten oxospecies at higher loading s. Platinum greatly facilitates the tungsten reduction, is involved in a re versible Pt-W strong metal interaction, and likely enhances hydrogen spillo ver during pentane isomerization. By facilitating tungsten reduction, Pt ca n have a deleterious effect on the high acid activity of these WOx/ZrO2 cat alysts. (C) 1999 Academic Press.