Sastre German, Corma Avelino
Instituto de Tecnologia Quimica UPV-CSIC, Universidad Politecnica de Valencia, Avda. Los Naranjos s/n, 46022 Valencia, Spain.
J Phys Chem B. 2006 Sep 14;110(36):17949-59. doi: 10.1021/jp060505x.
The stability of rings in pure silica zeolite frameworks is investigated through a new method. The energetic terms influencing the stability of rings are evaluated through the short-range plus electrostatics corresponding to SiO bonds and OSiO and SiOSi angles. Several atomistic force fields have been evaluated, and a reparametrization of the Vessal-Leslie-Catlow force field has been chosen because of its physical meaning and good structural accuracy. The ring energetics are analyzed and discussed in terms of local strain in the framework and in terms of geometric variables. This methodology allows to differentiate between the strain of rings of a given size in different zeolite structures. In particular, it is found that double four rings (D4Rs) are not necessarily, as previously stated, a strained secondary building unit. The analyses of D4Rs in the topologies AST, BEC, and LTA allow the calculation of its stability in the different structures showing high energy in BEC and LTA and low energy in AST. Implications of these results on nucleation of zeolites are drawn regarding the facility with which D4Rs are inserted in different frameworks.
通过一种新方法研究了纯硅沸石骨架中环的稳定性。通过对应于Si - O键以及O - Si - O和Si - O - Si角的短程加静电作用来评估影响环稳定性的能量项。已经评估了几种原子力场，并且由于其物理意义和良好的结构准确性，选择了对Vessal - Leslie - Catlow力场进行重新参数化。从骨架中的局部应变和几何变量的角度对环的能量学进行了分析和讨论。这种方法能够区分不同沸石结构中给定尺寸环的应变情况。特别是，发现双四元环（D4R）并不一定如先前所述是一种应变的二级结构单元。对AST、BEC和LTA拓扑结构中D4R的分析使得能够计算其在不同结构中的稳定性，结果表明在BEC和LTA中能量较高，而在AST中能量较低。关于D4R在不同骨架中插入的难易程度，得出了这些结果对沸石成核的影响。
