螯合剂对Co-Mo/Al_2O_3成型加氢脱硫催化剂性能的影响

以拟薄水铝石为原料,添加有机溶剂,经挤条成型、干煅、焙烧制备了比表面积大、孔分布宽的柱状γ-Al2O3载体;采用共浸渍法制备了系列Co-Mo/Al2O3催化剂(CoO和MoO3质量分数分别为2%和8%)。利用低温氮吸附、XRD和H2-TPR技术对催化剂进行了表征,考察了螯合剂柠檬酸(CA)、草酸(OA)和乙二胺四乙酸(EDTA)对成型催化剂粗苯加氢脱硫活性的影响。结果表明,添加螯合剂后,催化剂的前驱体主要沉积在载体的3~10 nm中孔内,活性组分以无定形态高度分散在载体上。添加CA可提高催化剂的还原性,显著降低Mo6+的还原温度。在300℃、3.0 MPa、液体空速(LHSV)为2 h-1和氢油体积比为600的条件下,噻吩硫的脱除率可达到99.9%以上。

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.