Ammonium ion exchange

Structure Modification. Several types of stmctural defects or variants can occur which figure in adsorption and catalysis (/) surface defects due to termination of the crystal surface and hydrolysis of surface cations (2) stmctural defects due to imperfect stacking of the secondary units, which may result in blocked channels (J) ionic species, eg, OH , AIO 2, Na", SiO , may be left stranded in the stmcture during synthesis (4) the cation form, acting as the salt of a weak acid, hydrolyzes in aqueous suspension to produce free hydroxide and cations in solution and (5) hydroxyl groups in place of metal cations may be introduced by ammonium ion exchange, followed by thermal deammoniation. 

Acid Sites. Acidic zeoHtes have outstanding catalytic activity. The hydrogen form may be produced by ammonium ion exchange, foUowed by thermal deammoniation. The unsolvated proton forms an OH group with a bridging O ... 

The azide form of the quaternary ammonium ion exchange resin IR-400 (which exhibits low lfiction-sensitivity) reacts with bromoform, analogously to dichloro-and dibromo-methane, to form the highly explosive triazidomethane. Solutions of above 50% concentration explode in contact with a pipette or on injection into a GLC inlet port. 

Calcined and steamed FAU samples also have complex hydroxyl IR spectra. Figure 4.25 shows the difference between an ammonium ion-exchanged FAU before and after steaming and calcination. The very simple, easily interpretable hydroxyl spectrum of the ammonium exchanged FAU sample is transformed into a complex series of overlapping hydroxyl bands due to contributions from framework and non-framework aluminum atoms in the zeolite resulting from the hydrothermal treatment conditions [101]. 

Polystyrene has been used most often as the support for phase transfer catalysts mainly because of the availability of Merrifield resins and quaternary ammonium ion exchange resins. Although other polymers have attrative features, most future applications of polymer-supported phase transfer catalysts will use polystyrene for several reasons It is readily available, inexpensive, easy to functionalize, chemically inert in all but strongly acidic media, and physically stable enough for most uses. Silica gel and alumina offer most of these same advantages. We expect that large scale applications of triphase catalysis will use polystyrene, silica gel, or alumina. 

To provide an estimate of constants, Ktex, suitable for use in Eq. 11-55, let us try to isolate the contribution of the sorbate s hydrophobicity using some available data. For the alkyl ammonium ions exchanging with sodium cations in the data of Cowan and White (1958), we have (see Eqs. 11-37 to 11-44) ... 

These NMR results are confirmed by the IR spectra of ammonium-exchanged Al-MCM-41. In the spectral range of NH deformation modes, a vibration band at ca. 1450 cm 1 is observed which is assigned to the deformation mode of ammonium ions (BS band). Its presence evidences the incorporation of A1 into tetrahedrally coordinated framework positions, because ammonium ion exchange requires a negatively charged framework. The intensity of the NH4+ deformation mode increases with increasing aluminum content until a Si/Al (gel) ratio of 7.3. 

The appearance of the hydroxyl bands at 3650 and 3550 cm-1 upon heating the ammonium form accompanies the decrease and disappearance of the NH-stretching bands as ammonia is evolved. The rate of decomposition of the ammonium ions appears to be influenced by the calcination conditions. Ward observed that most of the ammonium ions decomposed between 200° and 350°C, and at 420° only discreet hydroxyl bands were present (148). With extensively exchanged samples (>90% of the exchange sites occupied by ammonium ions), the 3550-cm I band was more intense than that at 3650 cm-1, in contrast to the intensity relationship observed at lower ammonium-exchange levels. Angell and Schaffer also noted the variability of the relative intensities of the two bands with different extents of ammonium ion exchange. 

The preparation of ammonium ion exchanged Y zeolites has long been known to be a precursor step in the preparation of H Y zeolites. The former materials have been characterized by thermo-gravimetric experiments, while the latter zeolites that contain the H atoms as hydroxyl groups have been intensively examined by infrared spectroscopy (1 .2 A systematic description of the... 

Figure 1. The extent of ammonium ion exchange of Na Y zeolite (A) at 23°C and at (O) 85°C. Equilibrations of the solutions with v/m = 20 cm3/g were carried out for 4 hr each.

Figure 2. The degree of ammonium ion exchange of Na Y zeolite following triple equilibrations at selected temperatures. Points C and F correspond to the designated data points in Figure 1.

Table I lists the zeolite samples used in this study along with their chemical composition and source of manufacture. Either ammonium ion-exchanged or acid-washed zeolites were employed to...

Steaming usually produces extra framework aluminum, but even in the case of leaching some extra framework aluminum may be left on the mordenite. In some cases they can be removed by ammonium ion exchange, if desired, followed by calcination. However, depending on the amount and location of the extra framework aluminum, as the case may be, these species may increase or decrease the catalyst activity. An early review on the dealumination of mordenite was given by Karge and Weitkamp (14). In particular for hydroisomerization of paraffins, this effect has been studied by A. Corma et al. (15, 16). 

Zr(P04NH4)2-H20. The same compound is formed by ammonium ion exchange with Q -Zr(P04)2K2-H20. Heat treatment of the ammonium exchanged form at 300 °C gives back the hydrogen phosphate. Primary alkylamines react very readily to form bilayer intercalation compounds analogous to those formed by clays (the layer area per proton is 24 A ). 

According to the XRD pattern all samples are well crystallized and show the typical feature of the MFI structure. Its largely pure formation is confirmed by the results of n-hexane adsorption. The values of the micropore volume (at p/ps = 0.5) are fairly close to the theoretical ones calculated for an ideal MFI-structure (0.19 cm /g, see Table 1). Table 1 gives the Si/Me ratios of the fnunework as further characteristic data. An equal concentration of Me in the lattice have been strived for. However, the results of the chemically determined Me concentration and the ammonium ion exchange capacity disagree especially for the In-Sil. It is less pronounced for Fe-Sil. Therefore the creation of extra-framework species in In-Sil and Fe-Sil has to be considered which do not contribute to the Bronsted acidity but to other kinds of acidic sites. This is in agreement with the results of the TPD measurements. 

Figure 11 Measured Brensted acid site density as a function of the nominal concentration from ammonium ion exchange, (o) infrared spectroscopy ( ) 2-propanol dehydration ) TPD of ammonia. Line represents perfect agreement. ...

The trichlorosilane is separated by distillation from unreacted tetrachlorosilane, which is returned to the reactor. The trichlorosilane is then passed through quaternary ammonium ion exchange resins that catalyze the following two reactions. 

A wide variety of electrodes of this type have been febricated, including ones selective for K (based on valinomycin), Cl (based on quaternary ammonium ion-exchanger molecules) and more recently, acetylcholine [based on ion exchangers (J3)], Na" " (Sll), Mg " (LI), and H+ (A2) microelectrodes have been introduced with the latter three based on ffie neutral carriers illustrated in Fig. 2 of this article. In general, these liquid membrane micro-ISEs possess response characteristics including selectivities comparable to the macroelectrode designs prepared with the same organic liquid membrane phases. 

Tt is interesting to note that while aqueous ammonium ion exchange of the calcined Nd,NaY zeolite results in the removal of the non-framework aluminum, as seen in the Al NMR spectrum, the si NMR spectrum remains practically unchanged (Figure lB,c). The persistence of the broad resonance and associated SSB suggests that the paramagnetic cation is irreversibly trapped in the smaller cages. 

Proton-deuteron exchange reactions are most easily studied by n.m.r. Examples are the exchange of aromatic protons in phenols under alkaline conditions, exchange of the a-protons in methoxy-acetone in aqueous solution, exchange of NH protons in triethyl-ammonium ion, exchange of the nuclear protons of hydroxy-indoles in deuterium oxide under mildly basic conditions and exchange of aromatic protons of substituted benzophenones in deutero-sulphuric acid. ... 

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