B、Al、Ga同晶取代丝光沸石的从头计算

用从头计算Hartree Fock方法研究了B、Al、Ga等同晶取代进入丝光沸石骨架后可能存在的位置，确定了与电荷平衡质子结合的氧位置，考察了B、Ga等杂原子进入骨架对丝光沸石Brnsted酸性的影响.能量分析表明B、Al、Ga在丝光沸石骨架中最容易进入T3和T4位；当Al、Ga在T4位时，质子与O10结合为能量最低即最稳定结构，而当B在T4位时，质子与O2或O10结合比较稳定.质子亲合势分析表明与硅铝丝光沸石相比， B和Ga进入骨架导致丝光沸石分子筛的Brnsted酸性有所减弱，其酸性依次为：B ZSM 5Ga ZSM 5< Al ZSM 5.

Ab initio Study on B, Al or Ga Isomorphously Substituted Mordenites

The siting of B, Al or Ga and the bridging hydroxyl group in mordenite framework were studied by using ab initio Hartree- Fock methods. The influence of the presence of B or Ga in the framework on the Bronsted acidity of mordenite was investigated. It was shown that energetically, heteroatoms including B,Al or Ga prefer the same T- sites, T3 and T4, when replacing Si in mordenite framework. For the preferred substitution site T4, the charge- compensating proton prefers to attach to O10 in case of Al and Ga substitution while the proton prefers to bond with O2 or O10 in case of B substitution. The proton affinity calculations showed that the acidity of isomorphously substituted mordenite increases in the order:B- MOR<< Ga- MOR< Al- MOR.