控ZSM-5分子筛酸性的方法研究进展(Ⅱ)非金属及金属改性

调控ZSM-5酸性一直是ZSM-5分子筛改性研究的重点。采用非金属、碱土金属及过渡金属等对ZSM-5分子筛进行元素掺杂改性是调控其酸性能的主要手段。可通过筛选改性元素种类、控制改性元素用量、对内外表面酸中心同时或分别改性等方法调控ZSM-5分子筛的酸性能。通常在一定范围内,磷、镁、钙元素掺杂改性后的ZSM-5分子筛强酸位点减少,而弱酸位点增加;硼元素掺杂改性后的ZSM-5分子筛只对弱酸位点发生作用;锌、镓元素掺杂改性后的ZSM-5分子筛会导致其B酸量减少,L酸量增加;铜、银元素掺杂改性后的ZSM-5分子筛由于发生氧化还原作用,其还原态Cu-ZSM-5和Ag-ZSM-5的B酸量较高,蒸汽稳定性较好,且裂解性能较高;钨元素掺杂改性后的ZSM-5分子筛也会使其酸量及酸强度降低。同时探讨了不同反应体系中分子筛酸性能与催化性能间的关系,为提高ZSM-5分子筛在各反应的催化性能提供依据。

Research development in acidity adjustment method of ZSM-5 zeolite II.Metal and nonmetal modification

Acidity adjustment had been the key point of ZSM-5 molecular sieve modification research.Doping of non-metals,alkaline earth metals and transition metals was the main ways to regulating acidity of ZSM-5 molecular sieve.The acidity of ZSM-5 zeolite was improved by changing the types and the amounts of modified elements and tuning the acid sites of inner or outer surface.Normally,within the specific limits and on ZSM-5 zeolite modified by P,Mg and Ca,the strong acid sites decreased and the weak acid sites increased.Boron element only affected the weak acid sites of ZSM-5 zeolite.B acid sites decreased and L acid sites increased on ZSM-5 zeolite modified by Zn and Ga.For Cu,Ag modified ZSM-5 zeolite,the reduced state,Cu-ZSM-5 and Ag-ZSM-5,which caused by the oxido-reduction,had higher B acid sites,better steaming stability and higher cracking activity.Acid content and strength of acid sites on ZSM-5 zeolite modified by W decreased.Additionally,the relationship between the acid properties of molecular sieves and the catalytic performance in different reaction systems was also discussed,which provided support for the fabrication of ZSM-5 zeolite with high catalytic performance.