Behaviour of Co-Mo-Al 2O 3 catalysts in the hydrodeoxygenation of phenols

Abstract

The activity of a number of ring alkyl-substituted phenols in the direct hydrodeoxygenation reaction (i.e. C-O bond scission without prior ring hydrogenation) in the presence of a commercial Co-Mo-Al 2O 3 catalyst has been investigated. The results indicate that the catalytically active site is stereochemically demanding. It is proposed that the phenol ring hydrogenation and the direct hydrodeoxygenation reaction proceed on the same catalytic site. The ease of the direct hydrodeoxygenation reaction is retarded mainly when transfer of the substrate hydroxyl group onto a co-ordinatively unsaturated metal site on the catalyst is inhibited. This occurs when the catalyst hydroxyl group receptor site is occupied by a co-ordinating ligand (poison) or when substituents on the substrate direct the phenolic hydroxyl group away from this metal site. The catalytic behaviour of Co-Mo-Al 2O 3 can be ‘transformed’ to resemble more closely that of Ni-Mo-Al 2O 3 (high reductive capacity) when the reaction medium contains both excess H 2S and a co-ordinating ligand. It is proposed that this ‘transformed’ species is of importance in hydrodenitrogenation reactions in an H 2S-rich environment.