Mechanism of hydrodenitrogenation. Final report, September 1, 1989--August 31, 1992

摘要

In this project it was proposed that the selectivity of the HDN reaction can be affected by an alteration of the catalyst acidity since it is possible that an acidic Hofmann-like deamination C--N--C bonds. Such a possibility was verified in this work by studying the denitrogenation of piperidine over acidic catalysts, and it was demonstrated that Bronsted acid sites are active for the denitrogenation of N-heterocycles, whereas Lewis sites are not. To better understand the role of acidic sites in the presence of hydrogenation and hydrogenolysis sites, molybdena was supposed on a series of acidic aluminas, and the resulting new acidity and molybdic phases were characterized. The oxidized catalysts supported on silica-aluninas showed increases from 3 to 150% of weak, medium and strong acid sites, which were produced by the molybdena phases. The new acidity was both of Lewis and Bronsted type, the predominance of one over the other depending upon support composition, as well as on loading and state of oxidation of Mo. High-alumina supports and low Mo loading favor dispersed Mo species, in particular bidentate and monodentate di-oxo Mo species. The latter is responsible for the new Bronsted acidity. Coordinative unsaturation of polymolybdates is responsible for the new Lewis acidity, which is increased upon reduction of Mo. High-silica supports favor monodentate species (high Bronsted acidity) up to 4 wt % MoO(sub 3). Beyond that, polymolybdate species and Lewis acidity predominate. The nature of the reduced molybdena phases is obviously affected by support composition. The HDN reaction of pyridine was utilized to assess the variation in activity and selectivity produced by the nature of the support.