含磷模板剂和不同硅源对多级孔ZSM-5分子筛结构和催化性能的影响

EFFECTS OF PHOSPHORUS TEMPLATE AND SILICON SOURCES ON STRUCTURE AND CATALYTIC PERFORMANCE OF HIERARCHICAL ZSM-5 ZEOLITE

通过采用不同比例的四丁基氢氧化磷(TBPOH)和四丙基氢氧化铵(TPAOH)混合作为模板剂合成多级孔ZSM-5分子筛,采XRD,BET,SEM,TEM,NH3-TPD,MAS NMR等方法对分子筛进行物化性质表征,考察TPAOH和TBPOH的协同作用,期望得到较高结晶度的含P的多级孔ZSM-5。结果表明:以正硅酸乙酯(TEOS)为硅源,在TBPOH和TPAOH物质的量比为1∶1时,合成的多级孔ZSM-5形貌较为规整,由ZSM-5小晶粒堆积而成并呈现出丰富的介孔结构,具有较大的比表面积和孔体积,孔径分布集中于3~7nm处。相比常规ZSM-5分子筛,合成的多级孔ZSM-5分子筛表现出更强的弱酸性和更多的总酸量。在1,3,5-三异丙苯的裂解反应中,相同转化率下,微孔ZSM-5分子筛表现出较好的苯和二异丙苯的选择性,而多级孔ZSM-5表现出更加优异的丙烯和异丙苯选择性。

ZSM-5 molecular sieves with hierarchical porous structure were synthesized by using mixture of phosphorus-containing template TBPOH and TPAOH with different proportions,and characterized by XRD,BET,SEM,TEM,NH 3-TPD and MAS NMR.The synergistic effect of TPAOH and TBPOH was investigated,by which the phosphorus-containing hier-ZSM-5 with fairly high degree of crystallinity can be obtained.The results showed that the morphology of ZSM-5 is regular and it shows higher specific surface area and pore volume when the molar ratio of TBPOH and TPAOH is 1∶1 with TEOS as the silicon source.The pore size distribution is cocentrated at 3-7 nm.ZSM-5 zeolite rich in mesoporous structure was constituted by accumulation of small grains.Compared with conventional ZSM-5 molecular sieve,hier-ZSM-5 shows greater weak acidity and total amount of acidity.At same conversion of 1,3,5-triisopropylbenzene cracking reaction,the microporous ZSM-5 zeolite shows better selectivity for benzene and diisopropylbenzene,while the hier-ZSM-5 with mesopores shows more excellent selectivity for propylene and cumene.