Atomic and Electronic Structures on a Mordenite Zeolite

Atomic structures of an insulating and hydrophobic zeolite sample of mordenite were measured by high-energy X-ray diffraction, and a pair distribution function analysis was carried out. Valence- and conduction-band O 2p partial densities of states (DOSs) in a mordenite were measured by soft X-ray emission and absorption spectroscopies (SXES and SXAS), respectively. The SXAS spectrum for the conduction band O 2p orbital has characteristic structures like that of crystalline SiO2, while pre-shoulders are observed in mordenite. By choosing characteristic energies in the SXAS spectrum for the incident photon energies, SXES spectra were obtained, in which a large peak and three small peaks or shoulders can be assigned by a lone pair orbital and bonding (σ) ones, respectively. A density functional theory was applied to determine the exact atomic structures and electronic states, and they are in good agreement with the corresponding experiments. It is concluded that the O 2p partial DOS is mainly O-Si covalent bonds, and the Al and Na atoms have minor contributions for them. From this study, it was found that the fundamental properties of complex zeolites can only be obtained in combination of experimental and theoretical investigations as mentioned above, which can open feasibilities to uncover the origin of active sites in functional zeolites.