Gravimetric study of reduction by H2 of hydrodesulphurization CoMo/γ-Al2O3 catalysts in their oxidic precursor forms

Abstract

A CoMo/γ-Al₂O₃ oxidic catalyst series, where the r= Co/(Co + Mo) atomic composition changes from 0.00 to 1.00 and the total cobalt and molybdenum oxide content remains constant (≈ 15% wt. since Co and Mo are present as Co₃O₄ and MoO₃), were prepared. Their hydrogen reducing capabilities were studied gravimetrically and compared with those of well defined crystalline bulk oxide phases. This technique allows a better understanding of the structure of these amorphous solids and confirms other physico-chemical measurements.

The simultaneous presence of a molybdenum monolayer and bulk like MoO₃ explains well the reduction behaviour of molybdenum-rich catalysts. Reduction of catalysts containing only Mo is very heterogeneous, but no independent molybdenum oxide species were found.

Much of the cobalt in cobalt-rich catalysts behaves as Co₃O₄ during their reduction. Several independent cobalt oxide species are present in catalyst containing only cobalt.

Inhibition of the reducing capability is observed in catalysts whose composition lies in the r= 0.25–0.75 range. It is proposed that a strong interaction between the oxides causes this phenomenon.