Reactions of methyl heptanoate on sulphided NiMo/gamma-Al2O3 and CoMo/gamma-Al2O3 catalysts in gas and liquid phases were investigated in detail. Experiments with heptanol and heptanoic acid were carried out in support of the conclusions. Hydrodeoxygenation (HDO) of the ester produced C-7 and C-6 hydrocarbons. Alcohols, aldehyde, carboxylic acid and ethers were formed as intermediates. In addition, a few sulphur-containing compounds were formed as intermediates and they led to desulphurisation of the catalysts. The reactions of the ester and the intermediates are explained in terms of hydrogenation and acid-catalysed reactions such as hydrolysis, esterification and dehydration. The E-2 elimination and S(N)2 nucleophilic substitution mechanisms are proposed to play a role in the reactions. HDO and hydrogenation activities were higher on the NiMo catalyst than the CoMo catalyst. The NiMo catalyst might thus seem to be preferred for the conversion of aliphatic esters, alcohols and carboxylic acids. According to the proposed reaction scheme, however, hydrogen consumption will be greater with this catalyst. (c) 2006 Elsevier B.V. All rights reserved.