title: Propene adsorption sites in zeolite ITQ-12: a combined synchrotron X-ray and neutron diffraction study.
abstract: The adsorption site of propene in the small-pore, pure silica zeolite [Si24O48]-ITW-ITQ-12 has been characterized via Rietveld refinement of the crystal structure of propene-loaded ITQ-12 on the basis of synchrotron X-ray and neutron diffraction data taken at 298 K. The structure can be described with a monoclinic unit cell having Cm symmetry and unit cell parameters a = 10.436 angstroms, b = 15.018 angstroms, c = 8.855 angstroms, beta = 105.74 degrees, and volume = 1335.9 angstroms3. Four-fold disordered adsorption sites that are nearly equivalent relative to the cage's 2/m pseudosymmetry are located near the center of each ellipsoidally shaped [4(4)5(4)6(4)8(4)] cage. At this site, the adsorbed propene molecule lies on a plane close and approximately parallel to the equatorial plane of the cage and is aligned with its methylene group pointing toward the pore's eight-ring window. The refined propene concentration, 1.8 per unit cell content, is close to one propene molecule per [4(4)5(4)6(4)8(4)] cage and the amount observed in adsorption experiments at 298 K and 1 atm propene partial pressure.
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA. Xiaobo.Yang@pci.uni-hannover.de
authors.forename: Xiaobo
authors.initials: X
authors.lastname: Yang
authors.forename: Brian H
authors.initials: BH
authors.lastname: Toby
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Camblor
authors.forename: Yongjae
authors.initials: Y
authors.lastname: Lee
authors.forename: David H
authors.initials: DH
authors.lastname: Olson