Dispersion and adsorption of dibenzothiophene on the surface of CoMo/γ-Al2O3 catalyst

Dibenzothiophene (DBT) and alkyl substituted dibenzothiophenes are the main sulfur compounds which cannot be removed easily from diesel fuel. In this paper, the dispersion and dispersion threshold of DBT on the surface of the CoMo/gamma-Al2O3 catalyst were studied, and its possible adsorption state was analyzed. DBT powder is mixed with CoMo/gamma-Al2O3 catalyst powder, which contains 16% MoO3 and 2.8 % CoO, and the m (DBT)/m (CoMo/gamma-Al2O3) is 0.05, 0.10, 0.15, 0.20, 0.25, 0.30 and 0. 40, respectively. It is found that DBT can disperse spontaneously onto the surface of CoMo/gamma-Al2O3 at temperatures (e. g. 80 degreesC) lower than its melting point. The XRD peaks of the residual crystalline DBT appear for the samples with m(DBT)/ m(CoMo/gamma-Al2O3)>0.15, but they disappear for the samples with m(DBT)/m(CoMo/gamma-Al2O3)less than or equal to0.15. It can be inferred that the adsorption of DBT on the surface of CoMo/gamma-Al2O3 may have the end-on manner through the adsorption of sulfur atoms on active sites. The FTAR result of the sample m (DBT)/m (CoMo/gamma-Al2O3) = 0.10 shows that the in-plane stretching vibration (similar to3 000 cm (-1)) and out-of-plane deforming vibration 744 cm of C-H, and the vibration of aromatic ring ( 1400 similar to 1600 cm(-1)) of adsorbed DBT do not shift significantly. These results suggest that DBT may be adsorbed on the surface of CoMo/gamma-Al2O3 vertically rather than horizontally. The LRS result of the m (DBT) /m (CoMo/gamma-Al2O3) = 0.10 sample also shows that the Raman diffraction band of the aromatic ring (similar to 1570 cm (-1)) of adsorbed DBT does not shift significantly. The adsorption of DBT on the surface of CoMo/gamma-Al2O3 may include two states, one is the end-on manner through the adsorption of sulfur atoms, the other is the flat manner through the adsorption of pi electrons of DBT molecules, and the main states may be the former.