Study On The Pore-enlargement, Surface Modification And Catalytic Application Of γ-Alumina

In this paper, theγ-Al₂O₃ carrier with large pore diameter and appropriate pore size distribution was firstly prepared by using carbon black as enlarge agent, followed by the modification with ZSM-5 andβzeolite nanoclusters respectively, and used as the support of the hydrodesulfurization catalysts.For the pore enlargement ofγ-Al₂O₃ carrier, the effects of carbon black types, content and dispersion in theγ-Al₂O₃ power, such as the chemical properties and content of surfactant dispersant, on the pore distribution ofγ-Al₂O₃ were studied. The zeolite nanoclusters solution containing ZSM-5 andβzeolite secondary building units was synthesized in the absence of alkali metal ions respectively. The influences of crystallization temperature, crystallization time and the ratio of Si/Al were also examined. In the surface modification ofγ-Al₂O₃, the changes of the acidity and pore structure property before and after modification with zeolite nanoclusters were investigated.The samples were characterized by XRD, Py-IR, BET, NH3-TPD and EDS analytical techniques. The XRD and FT-IR results showed that no zeolite crystalline particle was detected in the clear solution (or zeolite nanoclusters) synthesized under the optimum synthesis conditions, and the nanoclusters particle size was suitable for the modification ofγ-Al₂O₃ carrier. In addition, the most probable particle size of ZSM-5 nanoclusters was smaller than ofβnanoclusters. The pore-enlargedγ-Al₂O₃ support with a large specific surface area, appropriate pore size distribution and sufficient mechanical strength was prepared by the Surfactant Dispersion Method (SDM). The acidity ofγ-Al₂O₃ support modified with zeolite nanoclusters was greatly improved, however, the changes of pore structure were unconspicuous. The EDS results revealed that the zeolite nanoclusters uniformly distributed in the modifiedγ-Al₂O₃ support, and the carrier modified with ZSM-5 nanoclusters had stronger acid strengthen and more uniform distribution than ofβnanoclusters.The hydrotreating catalysts were prepared by impregnating active components Ni-Mo onto the traditionalγ-Al₂O₃ and modifiedγ-Al₂O₃ respectively. The activity and selectivity of the catalysts in the HDS of DBT were also evaluated in a fixed-bed high pressure micro-reactor. Compared to the traditional catalyst, the catalyst modified with zeolite nanoclusters had stronger acidity, higher stacking number of active phase and improved HDS activity. It was found that although the DBT removal on the both catalysts occurred mainly through the hydrogenolysis route, the HDS proportion through the hydrogenation route was increased greatly on the modified catalyst, associated to the increased feed stock conversion and desulfurization rate. The catalyst using pore-enlargedγ-Al₂O₃ as carrier had higher HDS activity than that of traditional carrier.