载体孔结构对加氢脱硫催化剂催化性能的影响

Effect of Support Pore Structure on Hydrodesulfurization Performance of Catalyst

针对4,6-二甲基二苯并噻吩(4,6-DMDBT)等有位阻效应的大分子硫化物的加氢脱除,以获得合适孔结构分布的氧化铝载体为目标,通过调整拟薄水铝石制备的老化pH值和时间,并在成型过程中选择对载体孔结构破坏性小的弱酸作为胶溶剂,制得孔体积大、比表面积高、孔径适中的新型氧化铝载体。采用NH3-TPD和吡啶-TPD表征新型载体的酸分布与常规氧化铝载体的差异。以该载体制备Mo-Co加氢脱硫催化剂,并采用X射线光电子能谱和透射电子显微镜表征其表面的成分、价态及能级结构。结果表明,以分子直径小的NH3为吸附剂时,酸量无明显差异,但以分子直径较大的吡啶作为吸附剂时,新型氧化铝载体的酸量比常规氧化铝载体显著提高,显示出有利于大分子吸附的优势;新型氧化铝载体可以减弱活性金属与载体间的相互作用,生成更多的加氢脱硫活性中心。以新型氧化铝载体制备的催化剂具有良好的加氢脱硫、加氢脱氮及芳烃饱和活性,更有利于4,6-DMDBT的脱除。

Aiming at the deep hydrodesulfurization （HDS） of the compounds with strong steric hindrance effect such as 4, 6 DMDBT, a new type of alumina support was developed. Various preparation conditions were used to improve the pore structure of the support, including adjusting aging time and pH value during pseudoboehmite synthesis, and with a weak acid as peptizing agent during extruding. The new support possessed larger pore volume, larger specific surface area, suitable pore diameter and higher efficient pore channel ratio, compared to conventional support, which will benefit the adsorption of refractory compounds on the surface of catalysts. NHa-TPD and pyridine-TPD were used to characterize the acidity distribution of supports. X-ray photoelectron spectroscopy （XPS） and transmission electron microscope （TEM） were used to analyze the surface composition, the valence and energy level structure of the catalysts prepared with the new support. NH3-TPD results showed that no obvious acidity difference was detected between the new support and the conventional support, while pyridine TPD results indicated that the acidity of the new support was stronger than that of the conventional one, meaning that the new support favored the adsorption of large molecules. More hydrodesulfurization active sites were produced through reducing the interaction between active metals and the support. Catalyst prepared with the new support had fair activities of HDS, HDN and aromatic saturation, especially high activity in the removal of 4,6-DMDBT.