Temperature-programmed oxidation of coke deposited by 1-octene on cracking catalysts

Abstract

The properties of coke deposited by 1-octene on fresh cracking catalysts have been investigated by analyzing CO, CO₂, and H₂O evolution during temperature-programmed oxidation (TPO). Of particular significance in the analysis is that the combustion mechanism dependence of the CO and CO₂ profiles were taken into account. Catalysts were laboratory coked at temperatures ranging from 200 to 600 °C under otherwise identical conditions. Two types of coke are identified, with the quantity of saturated coke decreasing and polyaromatic coke increasing as the coking temperature is raised. Trends, which are observed in the combustion rate-determining steps, indicate increased stability of the polyaromatic coke. Major differences in the TPO profiles of an industrial spent cracking catalyst, when compared with the laboratory-coked samples, suggest differences in the propensity for oxide formation. Reaction orders with respect to oxygen partial pressures indicate that the intrinsic rate of carbon monoxide evolution is independent of oxygen while carbon dioxide formation shows a more complicated dependence. It follows from the isokinetic temperature for the evolution of carbon dioxide from all substrates that the characteristic vibrational frequency is 674±31 cm-¹, which corresponds to the bending motion of CO₂.