脱水处理对HZSM-5分子筛甲苯择形歧化性能的影响

Effect of dehydration treatment on the catalytic performance of HZSM-5 for shape-selective disproportionation of toluene

通过27AlMAS NMR、NH3-TPD和FT-IR等表征手段研究了脱水处理对HZSM-5分子筛催化剂的结构和催化性能的影响。HZSM-5分子筛经过371℃水蒸汽处理后,分子筛的部分骨架铝脱出,形成非骨架铝物种,该非骨架铝物种对甲苯择形歧化反应具有较大影响。HZSM-5分子筛的酸性变化主要是由于非骨架铝物种SiAl(OH)的变化而引起,随着脱水温度的升高,HZSM-5分子筛酸中心的强度下降,但酸中心数量增加,当脱水温度为400℃时,HZSM-5分子筛的酸中心强度和数量达到最佳,甲苯转化率为28.2%。脱水过程中,甲苯的引入可以阻止HZSM-5分子筛催化剂进一步脱水,起到稳定催化剂活性中心的作用,使催化剂的性能较为稳定。

Effects of dehydration treatment on the texture and catalytic performance of HZSM-5 were investigated by 27Al MAS NMR, NH3-TPD and FF-IR. Being treated by water vapor at 371 ℃, the non-framework aluminum species, transformed from part of the framework aluminum, had much effects on shape-selective disproportionation of toluene. The acidity of HZSM-5 was due to the non-framework aluminum species, i.e. , SiAl（OH）. The intensity of acid sites of HZSM-5 declined while the quantity of acid sites increased with dehydration temperature, with optimal intensity and quantity of acid sites and maximum toluene conversion of 28.2% at dehydration temperature of 400 ℃. Introduction of toluene during the dehydration inhibited further dehydration of HZSM-5 catalyst and thus stabilized the active sites and hence enhanced stability of HZSM-5 catalyst.