C K-EDGE XAS ANALYSIS OF COKE MATERIALS DEPOSITED ON CATALYSTS

Coke materials deposited on spent catalysts were characterized by C K- edge x-ray absorption spectroscopy (XAS). An alumina supported nickel catalyst used in steam reforming gave a XAS spectrum similar to that o f graphite, indicating highly developed polynuclear aromatic (PNA) str uctures of the coke material. The spectrum of a zeolite catalyst used in fluid catalyst cracking (FCC) exhibited pi features which were ass igned to less developed PNA structures. Some pi features were observe d in the spectra of three Ni-W sulfide catalysts used in hydrotreatmen t but the development of PNA structures was much less significant as c ompared with the above two catalysts. These results implied that the p oisoning by the coke materials were very different among these catalys ts.