In situ imaging of the sorption-induced subcell topological flexibility of a rigid zeolite framework

The crystallographic pore sizes of zeolites are substantially smaller than those inferred from catalytic transformation and molecular sieving capabilities, which reflects flexible variation in zeolite opening pores. Using in situ electron microscopy, we imaged the straight channels of ZSM-5 zeolite with benzene as a probe molecule and observed subcell flexibility of the framework. The opening pores stretched along the longest direction of confined benzene molecules with a maximum aspect change of 15%, and the Pnma space group symmetry of the MFI framework caused adjacent channels to deform. This compensation maintained the stability and rigidity of the overall unit cell within 0.5% deformation. The subcell flexibility originates mainly from the topologically soft silicon-oxygen-silicon hinges between rigid tetrahedral SiO4 units, with inner angles varying from 135 degrees to 153 degrees, as confirmed by ab initio molecular dynamics simulations.

Automated summary

The crystallographic pore sizes of zeolites are smaller than previously inferred, due to the flexible variation in zeolite opening pores. In the study, it was found that the topologically soft silicon-oxygen-silicon hinges cause deformation of the zeolite channels, but this deformation does not affect the stability and rigidity of the overall unit cell.