Elementary Reactions and Intermediate Species Formed during the Oxidative Regeneration of Spent Fluid Catalytic Cracking Catalysts

The surface chemistry of coke precursors on spent fluid catalytic cracking catalysts during the oxidative regeneration process was investigated by temperature-programmed desorption and temperature-programmed oxidation experiments and IR spectroscopy. NH3 and HCN are formed via cracking and hydrolysis reaction of coke above 350 °C. The amount of NH3 released depends on the concentration of water in the samples. In contrast to water-free conditions, in the presence of 5% water, significantly lower amounts of coke N (40% vs 74%) were converted to NOx during the regeneration process. Temperature-programmed oxidation experiments indicated that polyaromatic nitrogen compounds are cracked to CO and HCN, which are subsequently oxidized in part to NO. The addition of Pt-based CO combustion promoters enhances the oxidation of reduced nitrogen intermediates and leads to an increase of NO emissions. Isotope-labeling experiments indicate that NO reacts to N2 with CO generated during the regeneration and HCN/NH3 formed during pyrolysis of the coke species.