Characterization of nitrogen on aged hydroprocessing catalysts by temperature-programmed oxidation

Temperature-programmed oxidation studies were carried out on: (1) sulfided hydroprocessing catalysts treated with-ammonia or aniline; (2) catalysts coked with ethylcarbazole or pyrene; and (3 ) aged catalysts derived from a vacuum gas oil feed. Oxidation of nitrogen on the catalysts gave nitric oxide, while oxidation of carbon gave carbon dioxide and carbon monoxide. Two types of nitrogen on the catalysts were detected, a low-temperature form, ascribed to adsorbed NH_x species, and a high-temperature form, ascribed to strongly adsorbed organic-N species. It is proposed that the high-temperature form of nitrogen consists of either strongly adsorbed organic-N species with a separate coke phase, or coke-N species, in which the coke covers the N-species. In either case, the nitrogen atom appears to be attached to the catalyst surface and is not in the bulk of the coke itself.