Hydrodenitrogenation on Pt/silica–alumina catalysts in the presence of H2S: Role of acidity
Résumé
The effect of the support acidity on the HDN activity of a series of Pt/silica–alumina catalysts was investigated. Catalyst containing 1 wt.% of Pt supported on silica–aluminas with silica content varying between 10 and 50 wt.% were prepared by incipient wetness impregnation. The acidity was characterized by IR spectroscopy of adsorbed pyridine and isooctane hydrocracking and a good correlation with the silica content of the supports was observed. All the catalysts presented similar metal dispersion as measured by hydrogen chemisorption. The conversion pathway of 1,4-tetrahydroquinoline (1,4-THQ), used as model molecule for HDN study, on Pt/silica–alumina catalysts was similar to the one previously reported for sulfided catalysts, having as main steps the complete saturation of this molecule followed then by C-N bond scission to form completely denitrogenated products. Hydrogenation and HDN activities increased with the Brønsted acidity of the catalysts. As the thiotolerance of these catalysts does not seem to be affected by the support acidity, it is proposed that the 1,4-THQ activity increase would be related to a bifunctional mechanism involving neighboring Pt sites and Brønsted sites of the silica–alumina support.