The influences of the hydrogen sulfide partial pressure and of a basic nitrogen compound (diaminopropane) on the activity of a sulfided CoMo/carbon catalyst in hydrodeoxygenation were studied from 10 to 150 kPa H2S, under a total pressure of 7 MPa, at 270 and 200 degreesC in the transformation of a mixture of guaiacol, ethyldecanoate, and 4-methylacetophenone in p-xylene, It is likely that three different active sites are responsible for hydrogenolysis, hydrogenation, and acid-catalysed reactions. An increase in hydrogen sulfide partial pressure decreases the average degree of reduction and uncoordination of the active sites and inhibits the hydrogenolysis and hydrogenation pathways, the first being affected to a larger extent. This accounts for the decrease of guaiacol dehydroxylation and the increase of 4-methylacetophenone conversion. The reactions catalysed by acid sites located on the metal sulfide, namely decarboxylation and alcohol dehydration, are promoted by hydrogen sulfide. The addition of diaminopropane strongly inhibits the conversion of guaiacol and ethyl decanoate. The decarboxylation selectivity is decreased as well. (C) 2001 Academic Press.