Microstructural Properties and HDS Activity of CoMo Catalysts Supported on Activated Carbon, Al2O3, ZrO2 and TiO2

Abstract

Unconventional supports of CoMo catalysts, such as activated carbon, ZrO₂ and TiO₂ and conventional Al₂O₃ support in the form of cylindrical extrudates were studied using inverse gas chromatography with single pellet- string column (SPSC) configuration, high pressure mercury porosimetry and nitrogen adsorption methods to assess both the transport and textural characteristics. The supports were saturated from an aqueous slurry of MoO₃. MoO₃ supported catalysts were promoted from the aqueous slurry of CoCO₃.Co(OH)₂. The transport and textural parameters of all CoMo catalysts prepared in their both oxidic and sulfide form were compared with that of the parent supports. It was concluded that the support effect, represented in the present work by surface area, CoMo loading and mainly the mean transport-pore radius, govern resultant activity of CoMo catalysts. The increasing mean transport-pore radii either of the support or of the sulfide catalyst correlated well qualitatively with the increasing activity in HDS of 1-benzothiophene in the order: ZrO₂ ~ TiO₂ < Al₂O₃ < C. The unconventional ZrO₂- and TiO₂-supported systems exhibited low microstructural changes in terms of textural and transport characteristics after deposition of CoMo and low HDS activities. In contrast, Al₂O₃- and C-based systems revealed significant changes in microstructure after deposition of the CoMo phases onto the supports and high HDS activities. The activated carbon supported CoMo catalyst exhibited the highest HDS activity and the mean transport-pore radius despite the highest volume of micropores.