Characterisation and reactivity of Re/carbon catalysts in hydrodesulphurisation of dibenzothiophene:Effect of textural and chemical properties of support

摘要

This work examines the effect of the textural and chemical properties of two activated carbons on the activity of carbon-supported Re catalysts for the hydrodesulphurisation(HDS)of dibenzothiophene(DBT).For this purpose,two series of Re-containing catalysts with Re loadings between 0.06 and 0.33 atoms Re nm~2 were prepared by impregnation of microporous(CMI)and micro-mesoporous(CME)activated carbons with solutions of NH4ReO4.Characterisation of the carbon supports by textural analysis showed that the CMI carbon was exclusively microporous while the CME was micro-and mesoporous.Temperature-programmed decomposition(TPD),FTIR and electrophoretic migration and acidity measurements showed that the CMI presented a greater amount of highly stable oxygen surface groups(carbonyl and quinone type)and less strong acidic carboxylic groups than CME.The textural properties of the catalysts indicated that the oxidic Re species of the catalyst precursors were mostly deposited over the external surface of the carbons.Upon sulphidation,XPS results showed that Re was fully sulphided for both catalyst series,and that the deposited oxidic Re species were redistributed during sulphidation due to the interaction with the stable oxygen surface groups of the carbons.The greater concentration of these oxygen surface groups on the CMI carbon led to better Re dispersion in the Re(x)/CMI catalysts than in the Re(x)/CME catalysts,especially at low Re loadings.Thus,the Re(x)/CMI catalysts showed higher HDS activity and greater increases in activity with increasing Re loadings up to about 0.15 Re atoms nm~(-2)than the Re(x)/CME catalysts.Above this Re content,the texture of the carbons controlled the HDS activity.The activity of the Re(x)/CM1 catalysts decreased markedly due to a decrease in ReS2 dispersion caused by formation of Re multilayers and plugging of micropores,while the activity of the Re(x)/CME catalysts continued increasing because the presence of larger pores on the CME carbon delayed the effects of pore blocking and ReS2 sintering to higher Re loadings.