Hydrodeoxygenation of guaiacol using NiMo and CoMo catalysts supported on alumina modified with potassium

Bio-oils require the elimination of most of the oxygen they contain to stabilize them before their use as fuels. The hydrodeoxygenation (HDO) process consists on eliminating oxygen from the bio-oil at high hydrogen pressures over a solid catalyst. However, catalysts often suffer from prompt deactivation due to extensive coke deposition. Therefore, searching more stable catalysts for HDO is still a challenge for biorefiners. In this work, the HDO of guaiacol as a model compound from bio-oil was carried out in a batch reactor at 523 K, pH2 = 5.5 MPa over potassium modified γ-Al2O3 supported CoMo and NiMo catalysts. Potassium was shown to be an effective activity and selectivity modifier. It led to an increase in the yields to products that may hinder catalysts coking by shifting selectivity from demethylation and methyl substitution reactions to direct CAromaticOH bond scission and hydrogenation reactions. Changes on selectivity were accompanied by a decrease in guaiacol conversion. The effect produced by potassium was shown to be related to: a reduction in acidity, a decrease in the relative number of Mo species in octahedral coordination, and to an increase in the relative concentration of catalytically inactive NiAl2O4 and CoAl2O4 species. Results of this work contribute to design more stable HDO catalysts from a rather simple modification of conventional hydrotreatment catalysts.