The objective of the work was to elucidate the effect of coating alumina by carbon on the catalytic properties of CoMoS catalysts supported on carbon-coated alumina (CCA) in hydrodeoxygenation (HDO) reactions. The catalysts were synthesized using 12-molybdophosphoric heteropolyacid, cobalt citrate and CCA and characterized by N-2 physisorption, temperature-programmed desorption of ammonia, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. The catalytic properties were determined using a fixed-bed microreactor in HDO of guaiacol and oleic acid. It was found that using the CCA as supports of the CoMo/CCA catalysts altered the morphology and structure of the CoMoS active phase species. With the increase of carbon content up to 5.6 wt.%, the average length of CoMoS species passed through minimum at 2.4 nm and the average stacking number increased from 1.4 to 1.6. The increase of carbon content in the CCA led to rising the sulphidation degree of both metals and effective cobalt content into CoMoS phase. Using CCA supports instead of alumina for preparation of CoMo catalysts resulted in improving their activities in HDO of guaiacol and oleic acid and significantly reduced deactivation. Enhanced catalytic properties of CoMo/Cx/Al2O3 catalysts were related to lower acidity of CCA supports. CoMo/CCA catalyst with 2 wt.% of carbon had maximal activity in HDO of guaiacol and oleic acid thanks to an optimal balance between cobalt content into CoMoS phase particles and their average length. (C) 2015 Elsevier B.V. All rights reserved.