Zeolites最新文献

The adsorption properties of the clathrasil Deca-dodecasil 3R (DD3R) have been studied. This porous tectosilicate becomes microporous when the organic template 1-adamantanamine is removed by calcination, which gives this clathrasil zeolitical properties. By means of adsorption of water, DD3R has been proven to be very hydrophobic. These adsorption data, together with the isosteric heats of adsorption of carbon dioxide at different loadings, reveal the absence of strong adsorption sites for polar or polarizable molecules, in contrast to the adsorbent zeolite A.

The crystal structure of a natural erionite from Nizhnyaya Tunguska, Siberia (schematic formula K₂Ca_3.5Al₉Si₂₇O₇₂ · 32H₂O) has been refined to a residual wR of 0.044. The erionite framework can be described by a sequence AABAAC … of 6-membered rings of tetrahedra. The (Si, Al) distribution (24% of Al in T1 and 31% of Al in T2) is consistent with the strong disorder found in tetrahedral sites for all zeolites describable by a sequence of 6-rings. Erionite, as in the closely related zeolite offretite, shows a slight enrichment of Al in the single 6-ring. K is at the center of the cancrinite cage and coordinates 6 framework oxygen atoms. Ca atoms alternately occupy three sites, quite near each other, on the triad axis parallel to c, at the center of the erionite cage. Their coordination number varies between 6 and 9. The marked differences in T—O distances found between hydrated and dehydrated erionite are explained in terms of interactions between extraframework ions and framework oxygens.

Para-nitroaniline (pNA) has been incorporated into the one-dimensional channels of mesoporous MCM-41, the hexagonal member of the M41S family of ordered mesoporous silicate materials. The composite material shows a number of remarkable features, depending on the sorption procedure for the organic component, the after treatment, and the annealing time of the composite. In X-ray diffraction experiments different states of one-dimensional ordering of the sorbate molecules in the channel pores are observed. In agreement with the molecular dipole, chain-like coherent domains with the long axis of the sorbate molecule parallel as well as perpendicular to the host channel axis show up. In aged samples the periodic ordering of the pNA molecules is lost, and nonlinear optical properties of the composite have been measured in second harmonic generation experiments indicating the presence of a polar direction in the sample.

Symbols that specify the size and number of shortest rings at the angles of each of the 4-connected vertices of zeolite nets are given. Both the interpretation and the utility of these vertex symbols are discussed.

The crystal structure of an acetylene sorption complex of dehydrated fully Cd²⁺-exchanged zeolite X, Cd₄₆Si₁₀₀Al₉₂O₃₈₄ · 28C₂H₂ [a = 24.874(5) Å], has been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd$\text{3}$ at 21(1)°C. Cd₄₆−X was dehydrated at 450°C and 2 × 10⁻⁶ Torr for 2 d, followed by exposure to ca. 250 Torr of acetylene gas at 21(1)°C. The structure was determined in this atmosphere and was refined to the final error indices R₁ = 0.058 and R₂ = 0.067 with 661 reflections for which I > 3σ(I). In this structure, Cd²⁺ ions are found at three crystallographic sites: 13 Cd²⁺ ions are at site l, at the centers of the double six-oxygen rings; five Cd²⁺ ions lie at site I′, in the sodalite cavity opposite the double six-oxygen rings; and the remaining 28 Cd²⁺ ions are at site II, in the supercage near single six-oxygen rings. Each of these 28 is recessed 0.46 Å into the supercage where it coordinates laterally to an acetylene molecule (CC = 1.22(7) Å). These Cd²⁺ ions have a distorted tetrahedral environment, 2.192(8) Å from three framework oxygens and 2.79(5)Å from each carbon atom of an acetylene molecule (here counted as a monodentate). As compared to dehydrated Cd₄₆−X, five Cd²⁺ ions have relocated from sites I and II to I′, as they did in Cd₄₆−X · 28CO, primarily for electrostatic reasons.

A simplified pictorial description is given for the mesoporous inorganic structure MCM-48. Structure, symmetry, and pore architecture are all described in terms of this model.

The hydrothermal treatment of glasses of the composition 5 Na₂O : 4 CaO : 9 Al₂O₃ : 22 SiO₂ at 1 kbar pressure in a temperature range between 80°C and 200°C leads to the formation of the zeolite mineral gonnardite (NAT) with orthorhombic symmetry (a = 13.35 Å, b = 13.35 Å, and c = 6.65 Å). The formation of the mineral phase under these equilibrium conditions is restricted to the temperature interval between 80°C and 150°C.