Periodic density functional calculations of selected zeolite frameworks (MOR, FAU and IRR) were performed in order to investigate the formation of silanol nests, when T-atom are removed from their lattice positions. The existence of silanol nests is important for soption and catalytic performance of the zeolites. In addition they play a key role during the post-synthetic treatment procedures. The results allowed us to analyze the relative stability of vacancies in the modeled framework types depending on the type of the T-atom (Si, Al, or Ge for IRR framework) and its crystallographic position. In addition, we investigated the influence of the Al content of the zeolite and proximity of Al T-atoms on the stability of the vacancies. The modeling of the stepwise formation of silanol nests in the position of Si T-atoms after interaction with water molecules suggested that the complete process is exothermic but some of the individual hydrolysis steps are endothermic.The work is supported by Bulgarian Science Fund (DCVP 02/1), the European Commission (FP7 project Beyond Everest) and theBulgarianSupercomputerCenter.

Stepwise formation and relative stability of T-atom vacancies in zeolites: A periodic density functional study

248th National Meeting (2014)

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