Porous structure and surface area of oxide, reduced and sulphided forms of alumina-supported cobalt molybdena catalyst

Abstract

The porous structure and surface area of alumina-supported cobalt molybdena catalysts were examined as functions of their activation conditions. It was revealed that the process of reduction by hydrogen as well as simultaneous reduction — sulphiding by a hydrogen and hydrogen sulphide mixture — results in the disappearance of pores of larger diameters. This is caused by the formation of monomeric, dimeric and/or polymeric species on pore surfaces as a result of thermal activation in hydrogen and H₂-H₂S atmospheres.

On the basis of the shapes of the hysteresis loops of nitrogen adsorption-desorption isotherms and on t plots of the samples investigated it was found that the dominant pores are those with diameters in the mesopore range.

The shapes of the mesopores resemble tubular capillaries with diameters o of various size and/or tubular capillaries with short necks and wide sloping bodies. Some of the mesopores can be closed at one end.

The uniformity of pore sizes appearing after the H₂-H₂S treatment provides good conditions for the diffusion of reactant molecules of large diameter. This is especially important for such catalytic reactions as depolymerization of asphaltenes, hydrodemetallization of metal porphyrins and other hydrotreatment processes.