TEMPERATURE-PROGRAMMED OXIDATION STUDIES OF AGED V-CONTAINING HYDROPROCESSING CATALYSTS

Temperature-programmed oxidation (TPO) of a NiMo/alumina hydrotreating catalyst aged with Kuwait resid showed the presence of two distinct t ypes of coke. A low-temperature coke (type I), showing a CO2 peak arou nd 460 degrees C, is attributed to a 'normal' coke, which is found on catalysts aged with lighter feeds. A high-temperature coke (type II), showing a CO2 peak around 620 degrees C, is associated with vanadium d eposits and appears to be consistent with the presence of asphaltenes. The presence of COS in the TPO profiles is taken as evidence of sulfu r in the coke. In addition, a low-temperature COS peak is observed, wh ich is ascribed to adsorbed CHx species in the inorganic sulfide phase . The coke effectively covers the inorganic sulfide phase. Hence, appr eciable loss of catalytic activity could be due to coverage of active sites by coke, aside from any specific poisoning effects of metal depo sits.