Structural and catalytic characterization of mechanical mixtures of Pt/WOx-ZrO₂ and Al₂O₃

The effect of the Brønsted/Lewis acid ratio on isomerization of n-heptane using Al₂O₃ as a source of Lewis acidity and WOx/ZrO₂ as a source of Brønsted and Lewis acidity was studied and controlled using mechanical mixtures of these solids. These mixtures were characterized by surface area, infrared spectroscopy of pyridine, X-ray diffraction and Raman spectroscopy. It was found that the presence of W{double bond, long}O stretching mode which was consistent with the presence of oxotungstate species which were the precursors of the acid sites. It was found out that as the oxotungstate structures increased, the selectivity to n-heptane isomers increased while the hydrocracking and dehydrocyclization selectivity decreased. The presence of Brønsted acidity of the WOx/ZrO₂ domains, the increase of Knudsen diffusivity and the loss of Pt metallic area by strong interaction of the Pt with the WOx/ZrO₂ explain this catalytic behavior.