SURFACE DISTRIBUTION AND HETEROATOM REMOVAL ACTIVITY OF EQUILIBRIUM ADSORPTION PREPARED, DOUBLY PROMOTED (ZN,CO)MO AL2O3 CATALYSTS/

Adsorption isotherms of Zn2+ and/or Co2+ ions on an 8 wt.% MoO3/alumin a catalyst have been obtained. The Langmuir parameters derived from re gression of the results indicate that preimpregnation of alumina with molybdate solutions notably decreased the adsorption of Zn2+ and Co2ions. In solutions containing both Zn2+ and Co2+ ions, the saturation capacity of Zn2+ was practically unaffected, while that of Co2+ was si gnificantly reduced owing to the higher intrinsic affinity of Zn2+ ion s for alumina sites. Adsorption of Co2+ ions occurs on two type of sit es, i.e. those on which Co2+ ions are loosely and strongly bound; the Co2+ on the latter type is not affected by the presence of Zn2+ ions. After calcination, the non-adsorbed Co, retained in the pores, was dep osited heterogeneously as a surface cobalt oxide bound loosely to the Al2O3. However, the homologous Zn was more homogeneously deposited, ow ing to its higher reactivity with Al2O3. These differences result in a n additional promotional effect in the gas-oil hydrodesulfurization (H DS) reaction, which has been observed on the catalysts prepared by sim ultaneous incorporation of Zn and Co. This effect is explained in term s of changes in the distribution and dispersion of promoters. These ch anges appear to be detrimental in hydrodenitrogenation (HDN).