Pd/ZSM-5/MCM-41催化剂加氢脱硫性能研究

Hydrodesulfurization Performances of Pd Catalysts Supported on ZSM-5/MCM-41 Composite Zeolite

本工作将三种材料:全硅MCM-41(Si-MCM-41)、通过机械混合Si-MCM-41和HZSM-5得到的Z-MCM-41-M、通过在HZSM-5外部包覆Si-MCM-41制备得到的Z-MCM-41,采用XRD、N_2吸附-脱附、NH_3-TPD、Py-IR手段进行了表征.分别以这些材料为载体,制备出负载型贵金属Pd催化剂,以二苯并噻吩(DBT)为模型化合物,在固定床反应器上进行加氢脱硫(HDS)性能考察.反应结果表明,载体的表面积或分散程度并不是影响负载型Pd催化剂HDS性能的关键性因素,催化剂的HDS性能受到载体的孔尺寸和载体的酸性双重影响.负载在酸性载体上表现出较好的HDS性能和加氢选择性,与溢流氢有关.其中,在三种催化剂中,Pd/Z-MCM-41催化剂表现出最高的HDS活性和优异的加氢活性,说明在载体的介孔孔道结构中引入微孔的酸中心对提高加氢脱硫活性有重要影响,仅靠机械混合方式制备的载体不能将介孔的孔道优势与微孔的酸性优势表现出来,不能产生较好的协同催化作用,具有介孔孔道结构和适中酸性的Z-MCM-41复合材料是潜在的贵金属加氢脱硫催化剂载体.

Siliceous MCM-41 （Si-MCM-41）, two micro-mesoporous materials obtained either by physically mixing Si-MCM-41 with HZSM-5 zeolite （Z-MCM-41-M） or by coating Si-MCM-41 over HZSM-5 zeolite particles （Z-MCM-41）, were prepared and characterized by means of XRD, N2 adsorption-desorption, pyridine adsorbed FT-IR. The hydrodesulfuri- zation （HDS） performances of the supported Pd catalysts thereof, were evaluated with dibenzothiophene （DBT） as the model sulfur-containing molecule. The close relationship between the surface area of the support and the HDS performance for the supported Pd catalysts was not observed. The result indicated that the surface area of the support or the dispersion of the cat- alyst might not be the key parameter affecting the HDS performance of the supported Pd catalyst. However, the HDS perfor- mances of Pd catalysts were significantly influenced by the pore structures and acid properties of the supports. Pd catalysts supported on the acidic supports showed the enhancement of HDS and hydrogenation activities that was thought to be the effect of hydrogen spillover. Among the catalysts studied, Pd/Z-MCM-41 exhibited the highest HDS activity and excellent hydrogenation activities. The results demonstrated that mesoporous materials introducing to microporous zeolite was benefi- cial to the improvement of HDS activities, but only physically mixing Si-MCM-41 with HZSM-5 zeolite couldn＇t show the combination advantage of pore of mesoporous materials and acid properties of microporous zeolite, and further generate bet- ter synergistic catalytic action. Z-MCM-41 composite material with the regular structure and uniform distribution acidity was potential carriers for precious metal catalysts.