Al_(2)O_(3)基材作载体制备MoP加氢脱硫催化剂的研究

Preparation of Al_(2)O_(3)-based material supported MoP catalyst for hydrodesulfurization

采用低温燃烧法和溶剂热法分别合成了富含五配位Al^(3+)物种的氧化铈改性Al_(2)O_(3)(Ce-Al_(2)O_(3))和介孔-大孔Al_(2)O_(3)(M-Al_(2)O_(3));通过程序升温还原浸渍法负载的Mo的磷酸盐前驱体制备了MoP催化剂。以二苯并噻吩(DBT)为模型含硫化合物评价了其加氢脱硫(HDS)性能。结果表明,M-Al_(2)O_(3)上制备纯相MoP所需磷酸盐前驱体的P/Mo摩尔比在1~1.2之间。DBT在MoP催化剂上转化率大小为MoP(1)/SiO_(2)>MoP(1)/Ce-Al_(2)O_(3)>MoP(1.2)/M-Al_(2)O_(3)。动力学研究表明,DBT在MoP(1)/Ce-Al_(2)O_(3)和MoP(1.2)/M-Al_(2)O_(3)上的HDS反应活化能几乎相同,显著小于MoP(1)/SiO_(2)上的活化能。在MoP催化剂上,直接脱硫(DDS)路径选择性随温度的增加而增加。在较低的温度下(如280℃),DBT主要通过加氢(HYD)反应路径脱硫;在较高的温度下(如360℃),DDS和HYD两条反应路径并重。

A cerium oxide modified Al_(2)O_(3)(Ce-Al_(2)O_(3))and a macro-mesoporous Al_(2)O_(3)(M-Al_(2)O_(3)),which are both rich in pentahedrally coordinated Al^(3+),are synthesized via a low-temperature combustion method and a solvothermal method,respectively.MoP catalysts are obtained through temperature-programmed method to reduce the supported molybdenum phosphate precursors prepared via an impregnation method.The hydrodesulfurization performances of MoP catalysts are evaluated through using dibenzothiophene(DBT)as model sulfur-containing compound.It is indicated that the P/Mo molar ratio in the phosphate precursor required for the formation of phase-pure MoP over M-Al_(2)O_(3)is between 1 and 1.2.The conversion of DBT over MoP catalysts drops in the order of MoP(1)/SiO_(2)>MoP(1)/Ce-Al_(2)O_(3)>MoP(1.2)/M-Al_(2)O_(3).It is demonstrated by the kinetic study that the hydrodesulfurization activation energy of DBT over MoP(1)/Ce-Al_(2)O_(3)is nearly same as that over MoP(1.2)/M-Al_(2)O_(3),both are much lower than that over MoP(1)/SiO_(2).Over these MoP catalysts,the selectivity of the direct desulfurization pathway increases with the rising temperature.At a relatively low temperature(e.g.280℃),the desulfurization of DBT occurs mainly through the hydrogenation pathway;while at a high temperature(e.g.360℃),both the direct desulfurization and hydrodesulfurization pathways play an equal role.