Insight to sulfur species in the hydrodeoxygenation of aliphatic esters over sulfided NiMo/γ-Al2O3 catalyst Original Research Article

The hydrodeoxygenation (HDO) network of aliphatic esters was investigated over reduced and sulfided NiMo/γ-Al2O3 catalysts in a batch reactor at 250 °C and 7.5 MPa. Methyl and ethyl heptanoate and their main HDO reaction intermediates were used as reactants. The participation of surface OH− and SH− groups in the various reaction steps and the stability of the surface sulfur are discussed. Although the surfaces of the reduced and sulfided catalysts under H2 have identical properties, the reactivity of the oxygen-containing compounds is greater over the sulfided catalyst. This is due to the stronger nucleophilic strength of the SH− groups compared to the OH− groups. Methyl and ethyl heptanoate react via various reaction pathways, of which alkaline hydrolysis is demonstrated to be of special importance. Sulfur-containing intermediates are formed in the HDO reactions with surface SH− groups. Accordingly, sulfur level on the catalyst surface is diminished.