CHARACTERIZATION OF RESIDUAL COKE DURING BURNING

Coke remaining from the partial burning of coke deposited during the commercial re-forming of naphtha on a Pt-Re/Al2O3 catalyst was studied. Burning temperatures were 623-923 K, and the remaining coke was characterized by temperature-programmed oxidation, X-ray diffraction, electron diffraction, IR, C-13 CP-MAS NMR, electron spectroscopy for chemical analysis, electron paramagnetic resonance, and chemical analysis. After coke is burned at 673 K, the residual coke shows the minimum value in the H/C ratio and the maximum in the thickness of the aromatic layers, degree of organization, C = O concentration, binding energy of C 1s, peak width, and g value. This agrees with the model of coke burning: at low temperatures, the burning is selective; the more hydrogenated and amorphous carbonaceous species are burnt first. At high temperatures, the burning is nonselective and all species are simultaneously burnt. Coke is partially oxidized during burning, and intermediate species with C = O and C-OH groups are formed.