镍盐前驱体对Ni改性HZSM-5择形催化甲苯与甲醇合成对二甲苯反应性能的影响

Effects of Ni Precursor on the Catalytic Performance of Ni-Modified HZSM-5 in Shape-Selective Alkylation of Toluene With Methanol to p-Xylene

分别以硝酸镍、氯化镍、硫酸镍和乙酸镍为前驱体,采用浸渍法制备了Ni改性HZSM-5催化剂,并考察了其对甲苯甲醇烷基化反应合成对二甲苯的催化性能。采用XRD、TG-DTG、N2吸附-脱附、H2-TPR和NH3-TPD手段对催化剂进行了表征。结果表明,由于镍盐前驱体中阴离子种类的不同,活性Ni物种在催化剂中的分散状态和存在形式不同,导致Ni改性催化剂具有不同的烷基化催化活性和加氢活性;与母体催化剂相比,催化甲苯甲醇烷基化反应的甲苯转化率降低,对二甲苯选择性呈现不同变化,并且Ni的加氢作用延缓了催化剂的积炭过程。以硝酸镍为前驱体制备的Ni改性催化剂中活性Ni物种晶粒尺寸较小,分散度较高,具有较高的烷基化催化活性和加氢活性,并且稳定性也比母体催化剂有所提高。

Ni-modified HZSM-5 catalysts were prepared by the method of impregnation with nickel nitrate, nickel chloride, nickel sulfate and nickel acetate as Ni precursors, respectively, and were characterized by XRD, TG-DTG, N2 adsorption-desorption, H2-TPR and NH3-TPD methods. Their catalytic performances for toluene alkylation with methanol to p-xylene were investigated. The results showed that the status and dispersion of active Ni species in the Ni-modified catalysts were apparently different due to different anions in Ni precursors. So the Ni-modified catalysts exhibited different alkylation catalytic performance and hydrogenation ability. With the Ni-modified HZSM-5 as catalyst, the toluene conversion of toluene alkylation with methanol was reduced and p-xylene selectivity was changed, compared to its parent catalyst. Meanwhile, the process of coking was postponed by hydrogenation of Ni. The Ni-modified catalyst prepared with nickel nitrate as Ni precursor had smaller crystal particle with higher dispersion of active Ni species, thus possessed better alkylation catalytic activity and hydrogenation performance. The catalytic stability of theNi-modified catalyst in toluene alkylation with methanol was also better than that of its parent catalyst.