Influence of the impregnation order of molybdenum and cobalt in carbon supported catalysts for hydrodeoxygenation reactions

This work concerns the role of the impregnation order of molybdenum and cobalt in carbon supported catalysts. Four activated carbons have been used as supports and the effect of the impregnation order (either cobalt or molybdenum at first) has been considered. The samples were characterized by N-2 physisorption, XPS and SEM. The sulfided catalysts have been tested in hydrodeoxygenation, using a model mixture containing: 4-methylacetophenone, ethyldecanoate and guaiacol. Both series of samples exhibit a low dispersion of the active phase, but CoMo is more uniformly distributed than MoCo. This result was interpreted to be consequence of the position occupied by the metal impregnated at first and of the strong interactions existing between cobalt and molybdenum. In the samples containing only one metal, cobalt is mainly impregnated at the exterior of the grains, while molybdenum is impregnated at the interior of the grains, causing micropore blocking. When the second metal is added, cobalt seems to bring about the remobilization of molybdenum outside the grains in CoMo catalysts and the formation of molybdenum oxide on the external grain surface in MoCo. Concerning catalytic activity, CoMo catalysts show higher hydrogenation properties for the conversion of ketonic groups and higher decarboxylation selectivity in the conversion of the ester