Effect of H2S on the stability of CoMo/Al2O3 catalysts during hydrodeoxygenation

The effect of H2S addition on the activity and the stability of CoMo catalyst during hydrotreating of phenol and anisole was studied. The presence of H2S strongly decreased the HDO activity of the sulfided catalyst, and the ratio of the HDO reaction pathways depended on the H2S concentration. The hydrogenolysis route to aromatics was suppressed, whereas the conversion of the hydrogenation-hydrogenolysis route to alicyclics at moderate H2S concentrations remained the same as in the absence of H2S. This clearly supports the presence of two types of active sites for HDO on the catalyst. Sulfidation of the catalyst was not a prerequisite for demethylation of anisole to phenol, though it increased the activity of the catalyst. Demethylation proceeded effectively even on the acidic sites of the Al2O3 support and on the sulfhydryl groups formed on CoMo catalyst in the presence of H2S. In addition to desulfurization and changes in the structure of the active sulfided catalyst, the formation of coke and high molecular weight compounds on the catalyst decreased its activity but did not affect the selectivity of HDO. (C) 2000 Elsevier Science B.V. All rights reserved.