Alkylammonium-exchanged zeolite

Most zeolites have an intrinsic ability to exchange cations [1], This exchange ability is a result of isomorphous substitution of a cation of trivalent (mostly Al) or lower charges for Si as a tetravalent framework cation. As a consequence of this substitution, a net negative charge develops on the framework of the zeolite, which is to be neutralized by cations present within the channels or cages that constitute the microporous part of the crystalline zeolite. These cations may be any of the metals, metal complexes or alkylammonium cations. If these cations are transition metals with redox properties they can act as active sites for oxidation reactions. 

POMs can he immobilized onto anion-exchange resins and surface-modified metal oxides with quaternary ammonium cation- or amino-functional groups via anion-exchange. Jacobs and coworkers tethered Venturello s catalyst [P04(W0(02)2)4]3-on a commercially available nitrate-form resin with alkylammonium cations and have carried out the epoxidation of allylic alcohols and terpenes with this supported catalyst [166, 167]. The regio- and diastereoselectivity of the parent homogeneous catalysts were preserved in the supported catalyst. For bulky alkenes, the reactivity of the POM catalyst was superior to that of Ti- 3 zeolite with a large pore size. The catalytic activity of the recycled catalyst was maintained completely after several cycles. 

Ikeda, T., Sasaki, M., and Yasunaga, T. (1983). Kinetic studies of ion exchange of alkylammonium ion for sodium ion in aqueous suspensions of zeolite 4A using the pressure-jump method. J. Phys. Chem. 87, 745-749. 

The reverse of some of the above reactions may be seen in the decomposition by heating, perhaps in oxygen, of polyatomic non-metallic cations which have been ion exchanged into the zeolite, or which were present as templates from the synthesis. These include the ammonium, hydronium, and alkylammonium ions. In all cases, the final products are hydrogen ions. Depending upon the temperature and the zeolite, these may leave with oxide ions of the zeolite fi-amework as water vapor, so that the fiamework which remains is deficient in oxygens. 

Theng et al. (12) studied the exchange of several alkylammonium ions on a typical X and a typical Y zeolite. These ions could only exchange in the large cavities. They concluded that the exchange is lower than the limit imposed by possible space requirements. The limit to exchange was different for the X and Y zeolites although the available volume is almost the same. 

Exchange Procedure. Zeolite samples of 0.1 gram were equilibrated overnight in 40 ml of a solution containing appropriate proportions of Na+ and alkylammonium ions. A fixed temperature (4°, 17°, 25°, 40°, or... 

Materials. The methylammonium Y-zeolites (Table I) were prepared by ion-exchanging NaY (5 grams) with 4 100-ml portions of 1 N alkylammonium salt solution at 80 °C. Monomethylammonium (MMA) chloride, dimethylammonium (DMA) chloride, and tetramethylammonium (TTMA) bromide (Matheson, Coleman, and Bell) and the trimethyl-ammonium (TMA) chloride (Eastman Organic Chemicals) were used as received. 

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