E. Hillerova et M. Zdrazil, EFFECT OF LOADING ON HYDRODESULFURIZATION ACTIVITY OF MO AL2O3 AND MO/C SULFIDE CATALYSTS PREPARED BY SLURRY IMPREGNATION WITH MOLYBDIC ACID/, Applied catalysis. A, General, 138(1), 1996, pp. 13-26
The MoO3/alumina and Mo/active carbon catalysts of various loadings we
re prepared by the new slurry impregnation method (SIM). The slurry of
MoO3 in water was added to the support. The pH of the slurry was 2.5
and this was favourable for the adsorption of molybdate anions on alum
ina and active carbon with the point of zero charge 7.0 and 7.5, respe
ctively. The low solubility of MoO3 was sufficient to transport molybd
enum species from solid MoO3 to the adsorbed phase. The equilibrium wa
s achieved after 5 weeks at 30-50 degrees C. The calcination was not n
ecessary and was left out. This was especially advantageous for active
carbon support which is susceptible to oxidative damage. The maximum
loading achieved was 18 and 31 wt.-% MoO3 for Al2O3 (195 m(2) g(-1)) a
nd active carbon (1100 m(2) g(-1)), respectively. The activity was tes
ted in the hydrodesulfurization of thiophene at 1.6 MPa and 250-400 de
grees C. The activity of the SIM samples was similar to the activity o
f the catalysts prepared by the conventional impregnation method (CIM)
with ammonium heptamolybdate. The dependence of the activity on loadi
ng for the SIM samples was the same as reported in the literature for
CIM catalysts. On alumina the activity per unit of molybdena was const
ant in the whole range of the loading 0-18 wt.-% MoO3. On active carbo
n it gradually decreased in the whole range of the loading from 0 to 3
1 wt.-% MoO3. It is concluded that the nature of the SIM catalysts is
the same as of the CIM catalysts but the SIM possesses several advanta
ges.