Tetsuo Takaishi

Determination of the ordered distribution of aluminum atoms in zeolitic frameworks. Part I

A new method was developed to determine the ordered distribution of Al atoms in a zeolitic framework by combining X-ray structural and 29Si MAS n.m.r. data. The configuration of Al atoms sought must give populations of 29Si(OSi)4−n(OAl)n′ with n = 0 ∼ 4, which are very close to the observed. The procedure consists of two steps. First, a configuration in an ideal (stoichiometric and disorder-free) crystal is determined by using connectivity relations between T sites (sites occupied by Si or Al atom). Then, the configuration is modified by introducing disorders so as to give the desired population spectrum. The method was applied successfully to ZK19, synthetic counterpart of phillipsite, and mined chabazite.

Ordered distribution of Na ions in dehydrated NaX zeolite

An ordered distribution of Na ions in Na 88 X zeolite is deduced on the basis of a framework with an Al-Si ordering given in a preceding paper. Calculated populations of Na ions on nine kinds of sites are in excellent agreement with those observed recently by Olson.

Galliation and 18O-exchange Reactivities of ZSM-5 and ZSM-11

Abstract The 18 -exchange between CO 2 and ZSM-5 and ZSM-11 was measured, along with their galliation. There was a strong correlation between the reactivities for these two processes, and they markedly depended upon the sources of starting materials. The reactivities stem from defects the concentration of which may depend upon the know-how of synthesis of the suppliers. About 6 framework oxygen atoms became reactive for exchange per Ga atom inserted, which suggests that Ga occupies a corner of the 4-membered oxygen ring. The initial heats of adsorption of NH 3 , calorimetrically determined, were ca. 160 kJ·mol −1 in H-Ga-ZSM-5 and ZSM-11. The catalytic activity on galliated zeolites is due to the fact that one acid site is produced by each Ga atom in the framework.

Effects of Structural Disorder on the Generation of Acidic Sites in Zeolite L

Acidic properties of zeolite L were observed to correlate well with its structural disorders. The 29 Si-MAS-NMR spectrum of zeolite L having a Si/Al ratio different from 3 revealed that Al distribution deviated from the ideal and suggested the presence of six different boat-shaped 8-ring patterns. Differential molar heats of adsorption of ammonia changed step-wise with the adsorbed amount, which reflects the difference in the acid strength of protons located in structurally different 8-rings.

Al–Si ordering in the framework of leucite and Cs-exchanged leucite

Ordered distributions of Al atoms in the frameworks of leucite and Cs-exchanged leucite (pollucite) are determined, under the restriction of the Al–O–Al avoidance rule. The observed 29Si MAS NMR spectra of pseudo-tetragonal leucite and Cs-exchanged leucite cannot be explained by an Al-configuration of tetragonal symmetry, but are consistently explained by one of P1121/a symmetry. On the other hand, an XRD pattern of a single crystal of leucite supports pseudo-tetragonal symmetry. This discrepancy is interpreted by the pseudo-tetragonal crystal consisting of twins of monoclinic microcrystallites. A detailed analysis of the 29Si MAS NMR spectrum of Cs-exchanged leucite of the high temperature phase (pseudo-cubic) shows that the domain size of the monoclinic phase is only several unit cells. The origin of an abnormal twist of the framework of tetragonal leucite and a driving force to transform it to the pseudo-cubic phase at higher temperature are discussed. The degree of the long-range order, S, is newly defined for this system, and estimated from 29Si MAS NMR data as S = ca. 0.8.

O4 molecule in the pore of Ca6-A zeolite

The existence of O 4 , dimer of O 2 molecules, has been subjected to long discussion, without a decisive conclusion. Recently we caught diamagnetic O 4 molecule in the pore of Ca 6 -A zeolite at near liq. N 2 temperature. The dimerization heat, from two adsorbed O 2 to adsorbed O 4 , was 2.1 ± 0.1 kJ/mol, and O 4 has a linear shape.

Ordered Distribution of Cations in Zeolite A

Various patterns of configuration of Na2 in Na-A zeolites were derived and assigned to respective space groups and types of dielectrics. Differences between Na 12 - and Na 10 Ca-A zeolites were discussed. In Na 10 Ca-A zeolite, the phase change takes place twice, according to heat capacity measurements. This complication is interpreted in terms of cation distributions.