Ammonium zeolite

The work discussed here compares the relative site occupancies for three series of hydrated Y zeolites ammonium, calcium and lanthanum exchanged. The data for these same three series of samples in the dehydrated forms are also presented and the assignment of the observed resonances is discussed. 

Two cation exchanged series of hydrated Y zeolites, ammonium/sodium and calcium/sodium, have been studied by sodium-23 MASNMR methods. The differences in chemical shift of the lines were correlated with the cation locations in Y zeolite using previously published XRD and IR data. As a result, the simulations and various intensity plots discussed in this report provide an analysis of the distribution of the sodium cations among the various Y zeolite cages, and a method of monitoring how these distributions change as a result of zeolite hydration and other treatments. The results presented here strongly indicate that sodium-23 MASNMR can be used as an analytical tool... 

Figure C2.12.2. Fonnation of Br0nsted acid sites in zeolites. Aqueous exchange of cation M witli an ammonium salt yields tlie ammonium fonn of tlie zeolite. Upon tliennal decomposition ammonia is released and tire proton remains as charge-balancing species. Direct ion-exchange of M witli acidic solutions is feasible for high-silica zeolites.

A typical NaY zeolite contains approximately 13 wt% Na20. To enhance activity and thermal and hydrothermal stability of NaY, the sodium level must be reduced. This is normally done by the ion exchanging of NaY with a medium containing rare earth cations and/ or hydrogen ions. Ammonium sulfate solutions are frequently employed as a source for hydrogen ions. 

Ammonium salts of the zeolites differ from most of the compounds containing this cation discussed above, in that the anion is a stable network of A104 and Si04 tetrahedra with acid groups situated within the regular channels and pore structure. The removal of ammonia (and water) from such structures has been of interest owing to the catalytic activity of the decomposition product. It is believed [1006] that the first step in deammination is proton transfer (as in the decomposition of many other ammonium salts) from NH4 to the (Al, Si)04 network with —OH production. This reaction is 90% complete by 673 K [1007] and water is lost by condensation of the —OH groups (773—1173 K). The rate of ammonia evolution and the nature of the residual product depend to some extent on reactant disposition [1006,1008]. 

Quaternary ammonium bromides and hydroxides (quats) are applied as templates in the synthesis of zeolites with relatively high Si/Al ratio. Examples will be given of the use of mon-, di-, poly- and associated quats as templates in zeolite growth. Templated zeolites of the MFI-type can be grown in a lateral or in an axial way onto metal supports, providing promising composite systems, for separation and catalysis, respectively. 

Quaternary ammonium compounds (quats) are prepared - by moderate heating of the amine and the alkyl halide in a suitable solvent - as the chlorides or the bromides. Subsequently conversion to the hydroxides may be carried out. Major applications of the quat chlorides are as fabric softeners and as starch cationizing agent. Several bio-active compounds (agrochemicals, pharmaceuticals) possess the quat-structure. Important applications of quat bromides are in phase transfer catalysis and in zeolite synthesis. 

Quaternary ammonium compounds as structure directing agents in zeolite synthesis... 

Quaternary ammonium bromides play an important role in the synthesis of high silica zeolites... 

Since then, organic amines, quaternary-ammonium bases, metal complexes, and other compounds have been extensively used in zeolite synthesis, acting as space fillers with low specificity, structure-directing agent, or true templates ... 

Molybdenum/zeolite catalysts prepared by impregnating zeolites with ammonium hepiamolybdate solution generally give rise to poor dispersion of molybdenum [2]. In contrast, ion exchange would be an ideal method for loading active metal species onto supports. Few cationic forms are available as simple salts of molybdenum of high oxidation... 

A NaY zeolite (Al/Si atomic ratio 0.41) was supplied by Shokubai Kasei Kogyo Ltd. After an evacuation at 673 K for 1 h (lx 10 Pa), the zeolite powder was exposed to a vapor of Mo(CO)5 or Co(CO)jNO at room temperature, followed by an evacuation at room temperature for 10 min to remove physisorbed metal carlxrnyl molecules on the external surface of the zeolite. Mo(CO)yNaY or Co(CO)3NO/NaY was sulfided in a stream of an atmospheric pressure of 10% HjS/Hj (0.2 dm min ). The sulfidation temperature was increased from room temperature to 373 K at a rate of 2 K min and kept at the tempeiatiue for 1 h. Subsequently, the temperature was increased up to 673 K at a rate of 5 K min and kept at 673 K for 1.5 h. After the sulfidation, the sample was cooled in the HjS/Hj stream to room temperature. The Mo and Co sulfide catalysts thus prepared are denoted MoSx/NaY and CoSx/NaY, respectively. Mo sulfide catalysts, MoSj/NaY, were also prepared by a conventional impregnation method by using ammonium heptamolybdate, for companson. 

In liquid-solid processes reaction takes place between a liquid reactant and an insoluble or sparingly soluble solid which must be finely divided to speed up the process. Another measure to accelerate the process is to use an aqueous solution of a phase-transfer agent (typically a quaternary ammonium salt). The solid can also be a catalyst for reactions between liquid components, e.g. in acylations, carried out both conventionally in the presence of metal chlorides (mostly AICI3) or catalysed by zeolites and Grignard reactions. 

Quaternary ammonium ions have long been known to act as stmcture-directing agents in the crystallization of zeolites <1961JCS971 >. Millini and co-workers have more recently employed the azoniaspiro compounds 154,9, and 155 for this reason to produce novel microporous frameworks <1998MI199>. 

The formation of heavy carbonaceous compounds in 5A calcium exchanged zeolites depends on the calcium content. These zeolites are able to protonated ammonia molecules in ammonium ions. This Bronsted acidity results from the presence of CaOH+ species which are formed by water dissociation on Ca2+ ions and have an IR signature at 3515 cm"1. 

The SSZ-33 zeolite was synthesized using the template molecule derived from 8-keto tricycle [5.2.1.0] decane. The boron containing SSZ-33 was converted to Al-SSZ-33 by a one-step reflux in 1 M aluminum nitrate. The SSZ-35 zeolite was prepared with the template camphorquinone. SSZ-35 zeolite was then subjected to three-fold ion exchange in ammonium nitrate. 

The ZSM-5 zeolite had a SAR (silica-to-alumina ratio) value of 38 and were supplied by CENPES/PETROBRAS. These samples, as received, were submitted to two ion exchange processes with ammonium chloride solution at 323K for sodium content reduction, followed by calcinations at 773K under dry air flow for transformation to its acid form. 

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