脱水处理对HZSM-5分子筛甲苯择形歧化性能的影响

通过²⁷Al MAS 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。

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

Effects of dehydration treatment on the texture and catalytic performance of HZSM-5 were investigated by ²⁷Al MAS NMR, NH₃-TPD and FT-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.