Structural and catalytic characterization of mechanical mixtures of Pt/Wox-ZrO_2 and Al_2O_3

摘要

The effect of the Bronsted/Lewis acid ratio on isomerization of n-heptane using Al_2O_3 as a source of Lewis acidity and Wox/ZrO_2 as a source of Bronsted and Lewis acidity was studied and controlled using mechanical mixtures of these solids. These mixtures were characterized by surface area, infrared spec-troscopy of pyridine, X-ray diffraction and Raman spectroscopy. It was found that the presence of W=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 Brensted acidity of the W0x/ZrO_2 domains, the increase of Knudsen diffusivity and the loss of Pt metallic area by strong interaction of the Pt with the Wox/ZrO_2 explain this catalytic behavior.