Influence of sodium on the structure and HDS activity of Co-Mo catalysts supported on silica and aluminosilicate

Structural changes and catalytic performances of hydrodesulfurization (HDS) Co-Mo catalysts, supported on amorphous aluminosilicate (ASA) and amorphou s SiO2 were investigated as a function of the amount of sodium ions added t o the supports. The catalysts were prepared according to the incipient wet impregnation method using (NH4)(6)Mo7O24 as molybdenum precursor and CoCl2 or Co(NO3)(2) as cobalt precursor. Structural and morphological characteris ations of the materials were performed with X-ray diffraction (XRD) and sur face area measurements (BET). In the case of the ASA-supported catalysts, i ncreasing the amount of sodium resulted in a gradual decrease of the cataly st surface areas and allowed formation of the beta-CoMoO4 phase. In the SiO 2-supported catalysts, the beta-CoMoO4 phase formed in the absence of sodiu m. Moreover, addition of the alkali ions to the amorphous silica induced th e phase transition to cristobalite resulting in a drastic decrease of the s urface area. The catalytic behaviour of the materials was tested in the HDS of thiophene carried out in a continuous-flow system at atmospheric pressu re, in a range of temperature between 603 K and 673 K. Unlike the silica-su pported catalysts that were strongly inhibited by the addition of sodium, t he ASA-supported catalysts exhibited a maximum of the HDS activity in corre spondence with a specific amount of sodium. A correlation between structure and activity is proposed. (C) 2000 Academic Press.