Kinetics of CO and CO2 evolution during the temperature-programmed oxidation of coke deposited on cracking catalysts

The reaction kinetics of evolved carbon monoxide and carbon dioxide during the temperature programmed oxidation (TPO) of an industrially spent fluid cracking catalyst have been investigated. Two pathways to CO and two to CO(2) evolution, all involving either undissociated or dissociated surface oxide complexes, were assumed. Rate coefficient parameters and O(2) reaction orders were then optimized to simulate the TPO profiles recorded over a range of conditions: heating rates of 2, 5 and 10 degrees C and O(2) partial pressures of 0.939, 1.11, and 5.0% in an atmosphere of N(2). Evolution rates of CO during TPO are independent of the O(2) partial pressure, whereas an order of 0.75 is indicated for CO(2) formation. Because of differences in assumed mechanisms and carbon substrates, calculated preexponential factors and activation energies can not be readily compared with literature values, although some comparisons are made. If the heating rate is high (greater than or equal to 5 degrees C min(-1)) and the oxygen partial pressure is low (less than or equal to 1%), the shape of TPO profiles for highly saturated hydrocarbon coke deposited on cracking catalyst are affected by changes in the rate-determining step with increasing temperature. (C) 1998 Academic Press.