In hydrodeoxygenation (HDO) on sulphided hydrotreating catalysts, addition of a sulphiding agent is typically required to maintain the catalyst activity. The effects of H2S and CS2 on the HDO of aliphatic esters on sulphided NiMo/gamma-Al2O3 and CoMo/gamma-Al2O3 catalysts were investigated in a fixed-bed flow reactor. The model compounds studied were methyl heptanoate, ethyl heptanoate, heptanol and heptanoic acid. The HDO produced C-7 and C-6 hydrocarbons in reactions where oxygen- and sulphur-containing compounds were formed as intermediates. Unlike CS2, H2S had a promoting effect on the HDO of the aliphatic oxygenates. The addition of H2S stabilised the selectivities as a function of time, and shifted the main products from C7 to C6 hydrocarbons, but did not prevent catalyst deactivation. The promoting effect of H2S was attributed to the increased catalyst acidity, which enhanced the acid-catalysed reactions (hydrolysis, esterification, dehydration, E-2 elimination and S(N)2 nucleophilic substitution). Both H2S and CS2 Suppressed the hydrogenation reactions on the NiMo catalyst but did not affect them significantly on the CoMo catalyst. H2S induced less hydrogen consumption and coke formation than CS2, but the carbon efficiency suffered in the presence of H2S. Thus, the use of H2S as sulphiding agent in the HDO of the aliphatic oxygenates was concluded to be more beneficial than the use of CS2. (C) 2007 Elsevier B.V. All rights reserved.