Effect of the chelating agent on the hydrodesulfurization activity of extruded Co-Mo/Al₂O₃ catalysts

γ-Al₂O₃ monolith support with high surface area and wide pore size distribution was obtained by extruding the mixture of pseudo boehmite and organic additives, as well as subsequent drying and calculation; a series of Co-Mo catalysts with ca. 8% molybdenum and 2% cobalt were prepared through co-impregnation of the support with solutions of ammonium heptamolybdate, cobalt nitrate and the chelating agent of citric acid (CA), oxalic acid (OA) and ethylenediamine tetraacetic acid (EDTA). The Co-Mo/Al₂O₃ catalysts were characterized by nitrogen sorption, XRD and H₂-TPR; the effect of chelating agents on their textural properties and activity in hydrodesulphurisation (HDS) of a commercial crude benzol was investigated. The results indicated that the catalyst precursors were mostly deposited over the surface of the mesopores with a diameter between 3 and 10 nm; the addition of chelating agent results in a high dispersion of Co-Mo species on the alumina support. The H₂-TPR results revealed that the addition of CA is able to improve the catalyst reducibility and shift the reduction temperature of Mo⁶⁺ to lower temperature. For the HDS reaction of the real-feedstock in a down-flow tubular reactor under 300 ℃, 3.0 MPa, a liquid hourly space velocity (LHSV) of 2 h^-1, and a hydrogen/oil volume ratio of 600, the removal of thiophene sulfur reaches 99.9% over the CA-promoted Co-Mo/Al₂O₃ catalyst.