TMA ions

Figure 25. Ion mass peaks at different two-photon energies. Broadenings of trimethylamine (TMA ) ion peaks as a function of the ionization energy. A hv2 > 3.875 eV B hv2 = 3.688 eV C hv2 = 3.607 eV. Excitation energy of paraxylene (PX) in the Si state = 3.90 eV. The broadenings in B and C correspond to time constants of 160 20 and 200 20 ns, respectively. Peaks corresponding to TMA H+ are also observable. Taken with permission from Int. J. Mass Spectrom. Ion Proc. 1994, 131, 233-264.

Table 4 summarizes the experimental conditions and the nature of the solid phases obtained from the system involving Na+ and TMA+ ions, n-propylamine or n-octylamine in presence or in absence of Al. The source of Si and Al only Influences the crystallization kinetics but not the nature of... 

The presence of a certain amount of TMA ions in the reaction mixture appears to be necessary for the synthesis of zeolite 12. The minimum... 

These experiments indicate that the TMA ions are encaged in the gmelinite cages and can be removed only by heat treatment, e.g., at 450° C. The sodium ions appear to be either in the gmelinite cages or in the minor... 

When TMA-hydroxide pentahydrate was heated under vacuum or in nitrogen to modest temperatures, the following products were identified by mass spectrometry (mole %) water, 5 methanol, 5 dimethyl ether, 70 and trimethylamine, 20. This product structure can be rationalized in terms of further reaction of the methanol from Reaction 1 with TMA ions. 

In the zeolite, most of the TMA ions are encaged in the gmelinite units, their charge being satisfied by the negative framework charge. We designate this cation site I. 

From the general inaccessibility of both the sodium and TMA ions, we postulate that most of the acidic sites generated by thermal treatment of the derived NH4+/TMA+ zeolite will also be inaccessible to reactant molecules. Likewise, catalytically active metals such as Pt and Pd introduced by ion exchange are expected to be located in or near these same inaccessible sites. This may explain the poor approach to equilibrium observed with the isomerization catalysts, and the poor hydrogenation activity of the hydrocracking catalyst indicated by excessive coking and catalyst decline, even in the presence of a massive 3.1 wt % palladium. 

The research below focusses on the NMR parameters for poly(dA-dT) in 1 M tetramethylammonium chloride (TMA+) relative to their value in the same concentration of sodium chloride. The methyl groups shield the charged nitrogen in the TMA+ ion and it was of interest to determine whether conformational changes occur in the synthetic DNA when the counterion was changed from Na+ to TMA+. 

TMA is essential to the synthesis of ZK-4. With TMA products having Si/Al atomic ratios up to about three have been produced(7). Essentially all sodalite units in ZK-4 contain a TMA ion(8). In the absence of TMA the isostructural zeolite A, with Si/Al invariably equal to one, is produced. 

NMR using the Intensity for sodalite cages in ZK-4 (which are completely filled with TMA) as a standard. The results are compared in Table V with values calculated for random filling by one TMA ion or by either two or three sodium ions based on the reactant compositions. 

Our synthetic routes to ZK4 were modifications of those described by Kerr (21). An amorphous, basic aluminosilicate gel containing tetramethylammonlum (TMA) Ion was heated at 100°C to promote formation of ZK4 crystals. Preparation of the gel Involved the vigorous mixing at room temperature of one component acting as a source of sodium and alumina, with another component acting as a source of TMA and silica. The alumina used was sodium... 

In order to obtain a good correlation of lattice parameter with composition, sodium-exchanged samples of several materials were obtained from the Initial products by calcining them In air at 5208C to remove trapped TMA+ Ion by oxidation to gaseous products and H+ followed by sodium-exchange with excess 2M NaCl (aq) at 60°C. Elemental analysis showed that this treatment was In fact Inadequate for the exchange,... 

Often organic ions (e.g. tetraalkylammonium cations such as tetramethylammo-nium, TMA+, ions) or neutral molecules are used as templates (i.e. structure-directing agents). In the past certain templates were introduced empirically although they are now widely used, their action is still not fully understood. 

FIGURE 6.1 Factors that influence the nature of electrostatic cation adsorption at oxide surfaces, and thus, PL membrane structure, (a) Percentage of surface sites occupied by TMA+ ions compared to Na+ ions. This number is another way of representing AGexcTMA+/Na+. (b) Standard state entropy of cation adsorption. (Modified and reprinted from Sahai, N., J. Colloid Interface Sci., 252, 309, copyright 2002, and Sahai, N., Geochim. Cosmochim. Acta, 64, 3629, copyright 2000. With permission from Elsevier Science.)... 

FIGURE 11.8. SHG spectra of azoprobe 1 at the heptane/water interface containing alkali metal and tetram-ethylammonium (TMA) ions (as chloride salts). The concentration of azoprobe 1 in bulk aqueous phase is 1.0 X 10- M. 

A layered structure of OL-1 with different interlayer distance of H-OL-1 was got when TMA permanganate was reduced by alcohol. TMA cations were not in between the layers according to the TMA ion diameter size. The structures of those samples of TEA-, TPA-, and TBA-OL-1, directly reduced by their TAA permanganates, were related to type III, II, and II models. 

Fig. 2.42. Orientational change of a water molecule in the first hydration shell of a tetramethylammonium ion (TMA ). (a) A water molecule in the first hydration shell is attached to the TMA ion by charge-electric dipole interaction, (b) Orientational change of a water molecule in the first hydration shell is complemented by formation of another hydrogen bond to an outer water molecule. (Reprinted from Y. Nagano, H. Mizuno, M. Sakiyama, T. Fujiwara, and Y. Kondo, J. Phys. Chem. 95 2536, 1991.)...

In the synthesis of faujasite type zeolite, the sequence of the phase evolution amorphous faujasite "P", is well known. Dwyer and Chu( l demonstrated that when TMA ions was added to the initial synthesis mixture a new sequence amorphous faujasite —> ZSM-4, prevailed. In the present work, we utilised a nucleation gel, usually used for directing faujasite phase( ), to the new synthesis system for omega zeolite. Here, we report the effects of nucleation gel on the crystallization processes. 

---