Yang Xiaobo, Toby Brian H, Camblor Miguel A, Lee Yongjae, Olson David H
Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
J Phys Chem B. 2005 Apr 28;109(16):7894-9. doi: 10.1021/jp050778c.
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.
通过基于在298 K下获取的同步加速器X射线和中子衍射数据，对负载丙烯的ITQ - 12晶体结构进行Rietveld精修，表征了丙烯在小孔径纯硅沸石[Si24O48]-ITW-ITQ-12中的吸附位点。该结构可用具有Cm对称性的单斜晶胞来描述，晶胞参数为a = 10.436埃，b = 15.018埃，c = 8.855埃，β = 105.74度，体积 = 1335.9埃³。相对于笼的2/m伪对称性几乎等效的四重无序吸附位点位于每个椭圆形[4(4)5(4)6(4)8(4)]笼的中心附近。在此位点，吸附的丙烯分子位于靠近笼赤道平面且大致平行于该平面的平面上，其亚甲基指向孔的八元环窗口。精修得到的丙烯浓度为每晶胞含量1.8个，接近每个[4(4)5(4)6(4)8(4)]笼一个丙烯分子，这与在298 K和1 atm丙烯分压下吸附实验中观察到的量相符。
