Localizing adsorption sites in zeolitic materials by X-ray powder diffraction: pyridine sorbed in B.ZSM-5

Abstract

Interpretation of X-ray powder diffraction spectra shows that it is possible to determine the locations of at least three distinct pyridine species in a saturated B.ZSM-5 zeolitic material (space group Pnma). Refinement of site occupancy factors leads to a total of ten pyridine molecules/unit cell distributed in the channel system of the MFI topology: four pyr1 molecules at the channel intersections (centred on 4cl sites), two pyr2 species in the sinusoidal channels (centred on 4c2 sites), and four pyr3 guests in the straight channels (centred on 4b inversion centres). Possible hydrogen-bond formation between pyridine molecules and framework oxygen atoms through silanol groups and/or charge-compensating protons is discussed. This work represents the first successful localization of more than eight aromatic molecules sorbed in an MFI topology.