Effect of structural and chemical factors on the acidity and IR spectroscopic characteristics of bridging hydroxyl groups in zeolites

Abstract

The rotational diffusion coefficients for rodlike micelles of C14DAC and C14DAB are smaller than those of dodecyldimethylammonium chloride and poly(7-benzyl L-glutamate)s, depending on the long contour length.Schmidt and Stockmayer23 presented approximately an equationfor semiflexible polymer chains. If ( 23) is transcribed to semiflexible rodlike micelles, the contribution by the anisotropy of the translational diffusion, which is omitted in (8), can be described by -(/>" -D±)/3 = -(1 /4)Z>0[ 1 -0.5(¿C/2«)V4] (24)Numerical values can be calculated by using the contour length and persistence length of rodlike micelles and the translational diffusion coefficient listed in Table I. The -(Z)¡| -Z)±)/3 values are definitely small in comparison with the Da and (Lc* 2/ 12)0r values, as seen in Table I. This proves that the assumption of the negligible contribution by the anisotropy of the translational diffusion in ( 7) is reasonable.At high micelle concentrations above 2 X 10"2 g cm"3 4which belong to the semidilute or concentrated regime, mutual diffusion coefficients for 2.6 M NaCl solutions of C14DAC and 4.3 M NaBr solutions of C14DAB reached a constant value at high µ2. Constant values are listed in Table II, where the Z>(0) and Afl(°°) values are also included. The AZ)(=°) values are negative, and their (23) Schmidt, M.; Stockmayer, W. H. Macromolecules 1984, 17, 509. absolute values increase with an increase in micelle concentration, independent of the temperature.The AZ> d(°°) values in the semidilute and concentrated regimes change from ( 13) to (20), with increasing micelle concentration.At the high limit of micelle concentration, where the rotational diffusion and the perpendicular translational diffusion are restricted ADM/D(0) = D'¿?°)D\{c^v")/DW)D\{c-c"Q) -1 » -1 (25) from ( 1) and ( 19). The AD(=°)/Z)(0) values were calculated and included in Table II. They approach -1 as micelle concentrations are increased.It is stated that, in solutions of rodlike molecules at higher concentrations, the field correlation functions at nonzero scattering angles decay in a double-exponential fashion.24 It is due to the coupling of the restricted rotational diffusion to the translational diffusion, in which the perpendicular translational diffusion is precluded. Such non-single-exponential curves of the field correlation function at finite scattering angles were observed for aqueous sodium halide solutions of surfactants at the semidilute and concentrated regimes examined here. This observation must confirm that rodlike micelles in such surfactant solutions behave similar to the rodlike molecules at high concentrations.Acknowledgment. I am grateful to Drs. S. Fujime and T. Maeda for their valuable suggestions to apply their theory.

Lattice relaxation of zeolites

“…Lattice-energy minimisation-studies by Kramer [6c] have shown that structure-relaxation due to protonated oxygen-atoms bridging Si-and Al-tetrahedra in faujasite is considerable and comparable to that in clusters. This contrasts with earlier suggestions of lattice-rigidity [12]. Its consequences for Bronsted acidity in zeolites are analysed in the third section.…”

Characterization of Gallosilicate MFI-Type Zeolites by IR Spectroscopy of Adsorbed Probe Molecules

“…[66][67][68][69][70] However, isolated OH groups having a range of force constants should be equally well probed by CO and by N 2 . In principle, this heterogeneity could be ascribed to a range of O-H force constants stemming from local variations of bond lengths and bond angles in the zeolite framework.…”

Structure and Dynamics of a Brønsted Acid Site in a Zeolite: An ab Initio Study of Hydrogen Sodalite

“…[20][21][22][23] There is only one exception in recent results of Campana et al, 24 where for a structure in protonated offretite the calculated Al-O distance is 1.93 Å . The values found for the Al-O-Si angle, which is believed to be the main parameter affecting the O-H stretching frequency, 25 are in the range 130°-140°and strongly depend on the particular structure. Figure 2 shows the radial distribution functions (rdf) calculated for the framework atoms in the H sodalite and Na sodalite simulations.…”