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

Four activated carbons were used as supports and the effect of the impregnation order (either cobalt or molybdenum first) was considered and tested in hydrodeoxygenation reactions. Both series of samples exhibit a preferential impregnation of the metal oxides at the exterior of the carbon grains, but CoMo (molybdenum first) is more uniformly distributed than MoCo (cobalt first). When molybdenum is added after cobalt (MoCo), the molybdenum-cobalt interactions cause a thick layer of metal oxide crystals to be formed; it covers the external grain surface and it is only in partial physical contact with the carrier. When cobalt is added after molybdenum (CoMo), it seems to bring about the remobilization and migration of molybdenum to the external part of the grains. Finally it is shown that inorganic impurities, like calcium and iron, which are present in low amounts in the activated carbon can interact with molybdenum and form mixed oxides. Concerning the catalytic activity, MoCo catalysts show lower hydrogenation properties for the conversion of ketonic groups and lower decarboxylation selectivity in the conversion of the ester. (C) 2002 Elsevier Science Ltd. All rights reserved.