Chemical analysis with coordination

According to the chemical analysis and coordination distances, the Rietveld refinement of the crystal structure at room temperature revealed 1.2 Co2+ atoms per unit cell at the Col and Co2 sites, whereas the 1.4 Ag+ cations are spread over the Co3 site, from now on referred to as Ag5 for clarity, and two new sites, Ag2 and Ag3, located near Co2 in the 10-membered ring (Fig. 3). In addition, for this catalyst the presence of Ag° clusters outside the zeolite structure was recognized by the detection of a strong reflection at about 40° 28. In agreement with the lower Ag content, in Ag2.7Co2.8AF the Ag3 site... 

Equation (IS) provides the zeolite chemist with a powerful quantitative method for the determination of framework composition of zeolites. By comparing (Si/A1)NMR values with the results of chemical analysis, which gives bulk composition, the amount of nonframework (six-coordinated) aluminum can be calculated. This is of particular value in the study of chemically modified zeolites (see Sections III,J-III,M). 

NMR-characterization. 27 Corbin et al. (35) were able to show by a systematic study that Z/A1 MAS NMR gives the true Si/Al ratio with a mean error of 10 %, if two conditions are met a) The amount of paramagnetic species is less than 0.05 % and b) the sample does not contain "NMR-invisible" aluminium. Chemical analyses of the samples under study showed that condition one is fulfilled. If samples contain "NMR-invisible" aluminium a difference between the concentration determined by chemical analysis and the framework aluminium concentration determined by NMR should be observed. From the absence of such a difference we conclude that "NMR-invisible" aluminium species do not exist in our samples. Also a line at the position of about 0 ppm due to octahedrally coordinated non-framework aluminium and a broad line at about 30 ppm due to tetrahedrally coordinated nonframework aluminium (36) could not be observed. The values for the concentration of framework aluminium atoms derived from the intensities of the line at about 60 ppm (see below) are in good agreement with those corresponding to the amount of alumina used in the synthesis mixtures. In conclusion, through the Al MAS NMR measurements it was possible to show that all aluminium atoms are incorporated in tetrahedrally oxygen coordinated framework positions. 

The local environments of T-atoms in SAPO materials were examined using solid-state NMR, a bulk probe, and XPS, a surface sensitive probe. T-a-tom 2 p binding energies in XPS were found to vary in a predictable fashion with changes in NMR chemical shifts. The comparison demonstrates that XPS is sensitive to variations in the second coordination sphere for T-atoms in SAPO molecular sieves. XPS was also found to give a reasonable, quantitative measure of superficial (surface) T-atom fractions thus providing information about elemental homogeneity by comparison to bulk chemical analysis. 

Water could play a structure-directing role in the synthesis of microporous compounds, but such examples are very rare. The most remarkable one is the synthesis of VPI-5 by using dipropylamine as SDA.[111] However, chemical analysis indicated that the organic amine content in the framework of VPI-5 is very small (about one dipropylamine molecule/2.5 cells). The channels of VPI-5 were filled with a large number of water molecules instead of dipropylamine molecules. There are 7 water molecules in one cell of VPI-5. Two of them (I, II) coordinated to the A1 atom in the framework, and four of them (III-VI) formed three helical water molecule chains in the 18-membered-ring channel of VPI-5 via intermolecular H-bonds. These three helical water molecule chains connected all 6-coordinated A1 atoms. The last water molecule (VII) was located in the center of the channel. Therefore, it was proposed that these water molecules played a structure-directing role in the creation of the framework of VPI-5. The synthesis of VPI-5... 

A composition of the molecular complex of ZnDP with benzene and -propylamine can not be fixed from the thermogram because temperatures of destruction of ZnDP % -% complex with benzene and an axial complex with n-propylamine are slightly different (Table 1). That is why for three-component system ZnDP- benzene- -propylamine, the peak on the DTG curve at 62 °C may be explained by both evaporation of benzene and -propylamine. Chemical analysis of C,N,H indicate most accordance with ZnDPTLFL PA. formula. Thus, in the three-component in comparison with ZnDP-o-propylamine binary system, the coordination of the second -propylamine molecule does not occur. 

Aluminum-27 NMR spectra show that after crystallization, all the TOA-containing zeolites exhibit a well resolved resonance at <50 ppm, corresponding to framework Al(IV) atoms. However, following NH.- exchange and calcination in air at 500°C, a new band appears at abdut 0 ppm due to Al(VI) resulting from aluminum removed from the crystal lattice. In general, calculated Si/Al ratio from silicon-29 NMR data are in reasonable agreement with chemical analysis results. Thus, all the aluminum atoms in these siliceous mordenite and Al-rich pentasils are believed to be in tetrahedral coordination and incorporated into the zeolite lattice. 

Matter consists of electrons and atomic nuclei. We specify the spatial and spin coordinates of the i electron by and the spatial coordinates of the j nucleus by R,. According to quantum mechanics a system in a state is described as completely as is possible by a wavefunction, which is a function of the coordinates of all the particles. In general, the state is also time dependent however, we are concerned in this analysis with stationary states and with the solutions of the time-independent Schrodinger equation. The time dependence of the chemical reaction will be taken care of through transitions between stationary states. For a system of n electrons and N... 

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