P. Blanchard et al., PREPARATION OF (CO)-MO-BASED HYDRODESULFURIZATION CATALYSTS - CHARACTERIZATIONS OF DEPOSITED SPECIES ON LANTHANUM-MODIFIED GAMMA-ALUMINA, Journal of molecular catalysis. A, Chemical, 135(2), 1998, pp. 143-153
The preparation of La-doped hydrodesulphurization (HDS) catalysts is i
nvestigated by deposition of Mo and Co from solutions containing their
salts on a gamma alumina previously modified by impregnation with lan
thanum nitrate solutions and further calcined at 773 K. Whatever the p
H of the impregnating solution, the n(Mo)/n(La) atomic ratio in the ox
ide precursor always governs the nature of the adsorbed oxomolybdenum
entities and a model of Mo distribution on the surface of the support
is proposed. The Mo surface distribution is mainly attributed to the s
elective adsorption of monomeric MoO42- species on sites associated wi
th La whereas poly-oxomolybdates adsorb on the alumina sites. Presence
of the promotor (Co) does not modify the Mo distribution. In addition
, it is shown that the presence of La in the catalyst formulation indu
ces a decrease of the thiophene HDS conversion due to the preferential
adsorption on the lanthanum hydroxyl groups of the oxomolybdate speci
es present in the impregnating solution as isolated monomeric entities
which are less easily sulphided, when deposited on the support, than
the poly-oxomolybdates. (C) 1998 Elsevier Science B.V. All rights rese
rved.