无定形硅铝载体的酸性对费托蜡加氢裂化反应中柴油选择性的影响

利用逐梯度铵交换处理的方法合成了三个织构性质相似、酸性不同的无定形硅铝载体，并通过XRD、N₂吸附-脱附、NH₃-TPD、Py-FTIR和NMR等手段对载体的物化性质进行了研究。经等体积浸渍负载贵金属Pt，制成加氢裂化催化剂，以费托蜡加氢裂化生产柴油为探针反应，研究了无定形硅铝载体的酸性与柴油选择性之间的构效关系。结果表明，柴油选择性主要与载体的B酸性质有关，受L酸的影响很小；催化剂载体的强B酸含量与柴油选择性成相反关系，载体强B酸的含量越低，柴油选择性越高；催化剂Pt/B-1具有相对最高的柴油选择性，在反应压力7.0 MPa，H₂/wax（volume ratio）=1 000：1，LHSV=1.0 h^-1，温度为370℃的条件下，C₂₂₊转化率为62.52%时，对柴油的选择性达87.12%，具有比文献报道及商业化无定形硅铝载体ASA制备的催化剂Pt/ASA相对更高的活性和柴油选择性。

Study of the relationship between the acidity of amorphous silica-alumina supports and diesel selectivity in Fischer-Tropsch wax hydrocracking

Three amorphous silica-alumina supports with similar textural properties and different amounts of acidity were successfully synthesized through ammonium exchange processing and their structures, acidity properties and the coordination of Si and Al in the as-synthesized supports were characterized using XRD, N₂ adsorption-desorption, NH₃-TPD, Py-FTIR and NMR. Amorphous silica-alumina was impregnated into a solution of H₁₂N₄PtCl₂·XH₂O to obtain hydrocracking catalysts. The relationship between acidic properties of supports and catalytic performance was studied by hydrocracking of Fischer-Tropsch (F-T) wax to diesel in a continuous-flow type fixed-bed reactor as a model reaction. The results illustrated that the diesel selectivity was mainly related to Brønsted acid properties of the supports while Lewis acid showed little correlation. The amount of strong Brønsted acid was reversely related to the selectivity of diesel:the smaller the amount, the higher the selectivity. The as-synthesized Pt/B-1 catalyst showed high selectivity of 87.12% to diesel at the conversion of F-T wax of about 62.52%, under the reaction conditions of 370℃, 7.0 MPa, LHSV of 1.0 h^-1 and a hydrogen-to-wax ratio of 1 000:1. Pt/B-1 had better catalytic performance than Pt/ASA prepared by commercial amorphous silica-alumina (ASA).