Influence of the active phase loading in carbon supported molybdenum-cobalt catalysts for hydrodeoxygenation reactions

The influence of the active phase loading on the physico-chemical properties and on the hydrodeoxygenation (HDO) activity of carbon supported catalysts was studied. Four molybdenum catalysts (Mo), with a MoO3 loading ranging from 6 to 15 wt.% and four cobalt promoted molybdenum catalysts (CoMo), with a total oxide content (MoO3 + CoO) ranging from 7.2 to 18 wt.% (with constant Co/(Co + Mo) ratio), were prepared and characterized. Both series of samples exhibit a non-uniform distribution of the active phase between the inside and outside of the carbon particles. The dispersion decreases with increasing metal loading. Cobalt seems to be mainly impregnated on the external particle surface and to be responsible for a partial remobilization of molybdenum which migrates towards the external part of the particles where cobalt is impregnated. Bulk cobalt oxide or bulk molybdenum oxide were never detected. For MoO3 contents higher than 6 wt.%, micropore blocking takes place. For a MoO3 content lower than 6 wt.%, most of the molybdenum is located in the microporous structure. It is fairly well dispersed and relatively strongly bound to the support. The CoMo catalysts were tested in HDO reactions. Due to the decrease of the dispersion, the catalytic activity does not increase proportionally with the amount of active phase. The most important parameter for the reaction of ketonic and ester groups is the dispersion of the active phase. (C) 2002 Elsevier Science Inc. All rights reserved.