碱处理改性对Zn/HZSM-5分子筛催化剂性能的影响

以不同浓度的NaOH溶液对HZSM-5分子筛进行碱处理改性后所得多级孔ZSM-5分子筛作为活性组分制备甲醇制芳烃催化剂,采用XRD、SEM、NH3-TPD和N2吸-脱附等手段对催化剂进行了表征,分别考察了碱处理改性对分子筛催化剂骨架结构、酸性质、孔结构以及催化性能的影响.结果表明,通过合适浓度的NaOH碱溶液处理后,HZSM-5分子筛在保持微孔骨架结构的同时,可以调变其晶内介孔孔道结构分布以及酸性质.随着NaOH碱溶液浓度升高,HZSM-5分子筛的酸量、介孔孔容、介孔表面积都增加、孔容分布变宽,催化剂的活性和稳定性等催化性能得以改善.HZSM-5分子筛碱处理改性适宜的NaOH溶液浓度为0.4 mol/L,改性后的催化剂芳烃收率由25.07％增加到32.22％,使用寿命由8d增加到16d,但NaOH溶液浓度超过0.6 mol/L后会严重破坏HZSM-5分子筛骨架结构,催化活性下降较快.

Effect of Alkali Treatment on the Performance of Zn/HZSM-5 Catalyst

The HZSM-5 zeolite was alkali treated with NaOH solution at different concentrations,and the hierarchical ZSM-5 zeolite was prepared as the active component for the catalyst of methanol to aromatics,the catalysts were characterized by XRD,SEM,NH3-TPD and N2 adsorption-desorption,the effects of alkali treatment on the structure,acid properties,pore structure and catalytic performance of the zeolite catalyst were investigated.The results show that the size of mesoporous distribution and acid properties of the HZSM-5 zeolite can be changed with the treatment of appropriate concentration of NaOH solution but the Microporous structure of the HZSM-5 zeolite can be maintained.With the increasing concentration of NaOH solution,the amount of acid sites,mesopore volume,and specific surface area increase,the pore size distribution become broader.Therefore,the catalytic performance for the reaction is effectively improved.As the HZSM-5 was treated by the suitable NaOH concentration of 0.4 mol/L,the yield of aromatics increase from 25.07％ to 32.22％,and the stability of catalyst increase from 8 d to 16 d.When the NaOH concentration is over 0.6 mol/L,the framework of HZSM-5 zeolite is found to be severely destroyed and catalytic activity decrease rapidly.