Alkali-ion exchange

The Na in the ceramic is 80% of the alkali content. Stress-development in the P-AljOj component is markedly different at 850 °C and 1200 °C °. At 800 °C, the P-AI2O3 phase assimilates K to 0.3, then remains constant with increasing mole fraction in the melt (0.2 to 0.85Xk+). 

The p -Al203 expands. The Na retained in the P-AI2O3 eventually decohesizes the electrodes of a working electrolyte. 

Increasing the temperature to 1200 C minimizes the stresses. 8N4 is ion-exchanged in KCl vapour at 1200 C to give 100% K p -Al203 textured ceramics. 

K /Rb ion-exchange is conducted above an RbCl melt at 1200 C for two days. 

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Growth of a Si02-rich layer by diffusion-controlled alkali ion exchange. 

Finally, our observations regarding the longterm impact of alkali ion exchange on glass dissolution now provide a mechanistic basis for the empirical residual rate of reaction appended to the TST rate law articulated by Grambow (1985). The residual rate was appended to prevent calculated glass dissolution rates from dropping to zero under silica-saturated conditions, which is not in accord with experimental observations. 

Micro- and meso- Alkali ion-exchanged zeolites and mesoporous materials... 

Other basic zeolites are those prepared by Baba et al. [79], consisting of low-valent Yb or Eu species introduced into alkali ion-exchanged Y zeolites by impregnation with Yb or Eu metal dissolved in liquid ammonia then heating under vacuum at ca 470 K. These materials catalyze the Michael addition of cyclo-pent-2-enone and dimethyl malonate at 303 K, without solvent, yielding, after 20 h reaction, 81 % Michael adduct with 100% selectivity [80,81]. 

Ion conductivity Electrodialysis Concentration or desalination of electrolytes, separation between electrolyte and non-electrolyte, bipolar ion exchange membrane process to produce acid and alkali, ion-exchange reaction across the membrane, electro-deionization (EDI, CDI), etc. 

The development of environmentally friendly solid catalysts for the production of fine chemicals has known a recent growing interest and recent review articles have been devoted to catalysis by solid bases. Several solid bases have been proposed such as alkali ion-exchanged zeolites [1], alkaline oxides supported on microporous [2] and mesoporous solids [3], sodium metal clusters in zeolites... 

Shape selectivities in base-catalyzed reactions were reported by Corma et al. for alkaline-substituted sepiolites and alkali ion exchanged zeolites in the reaction of benzaldehyde with esters[40]. 

Chemisorption of COj leads to carbonate structures. Carbonate formation is accelerated by preadsorbed water (cf. also [543]). According to Boese et al. [608], the assignment of the corresponding bands is difficult because of band overlap. However, the authors tentatively attributed a band pair found with CO2 on Nai jLiio.y-A at 1660 and 1365 cm to a bidentate structure and a second one at 1588 and 1421 cm to a monodentate structure (cf. [543,641]). From alkali ion-exchanged zeolites, carbonates could be removed by pumping at elevated temperatures, which was, however, not possible in the case of alkaline earth-exchanged zeolites. 

Zeolites. Zeolites are usually used as solid-acid catalysts. However, alkali ion-exchanged zeolites, especially faujasites, are weak bases and show unique... 

The base strength of alkali ion-exchanged zeolites can be estimated by using the Knoevenagel condensation reactions of benzaldehyde with ethyl cyanoac-etate (pFTa = 8.6) [reaction (12)], ethyl acetoacetate (pKa = 10.7), and ethyl mal-onate(pKa = 13.3) over alkali ion-exchanged X and Y zeolites (55). 

Modified Zeolites. As described above, alkali ion-exchanged zeolites are weak bases. Various efforts have been made to increase the base strength of alkali metal-ion exchanged zeolites. Metallic sodium particles in zeolites are formed by the decomposition of occluded sodium azide (59). These sodium particles are capable of performing base-catalyzed reactions. These catalysts catalyze the isomerization of butenes at 300 K and the side-chain alkylation of toluene with ethylene at 523 K. 

The ring transformation of y-butyrolactone into y-butyrothiolactone proceeds over alkali-ion exchanged faujasite (117). A 100% conversion was attained over CsY at 603 K... 

Side Chain Aikyiation ofAikyiaromatiCS. Alkylation of alkylbenzenes with alkenes or alcohols over base catalysts yield the products alkylated at the side chain, while ring-alkylation proceeds over acidic catalysts. To abstract a proton from the alkyl groups, strongly basic catalysts are required. The pKa values of toluene and cumene are 35 and 37, respectively. In the vapor-phase reaction of toluene with methanol, alkali ion-exchanged zeolites, especially, RbX and CsX give ethylbenzene and styrene as products, while acidic zeollites afford xylenes (52). 

The reaction of phenol with DMC in vapor phase over alkali-ion exchanged zeolites selectively jdelds the 0-methylation product, anisole. Over NaX, 92% of anisole 3deld was obtained at 533 K (118). 

Aniline is selectively A -methylated with DMC over alkali ion-exchanged zeolites, no ring-methylation products being formed (120). The ratio of the two products, A -methylaniline and A, A -dimethylaniline, depends on the reaction conditions and the zeolites used. The higher selectivity for A(-methylaniline was obtained at lower DMC/aniline ratio of lower contact time. Over KY, A -methylaniline was selectively formed at 453 K. The selectivity for N-methylaniline was 93.5% at aniline conversion of 99.6% at 453 K and DMC/aniline ratio of 1.25. Over NaX, A, A -dimethylaniline was obtained at 95.6% at 100% conversion of aniline at 513 K and DMC/aniline ratio of 2.5. Alkali ion-exchanged EMT zeolites, especially K-EMT, are also very effective for N-alkylation of aniline with DMC (121). 

Alkylation of Phenylacetonitrile. Phenylacetonitrile is very selectively monomethylated with DMC into 2-phenylpropionitrile over alkali ion-exchanged zeolites, as mentioned before, [reaction (13)] (58). Phenylacetonitrile is also methylated with methanol over alkali ion-exchanged zeolites (58). 

Table 9.5. N2 and O2 adsorption capacities of alkali ion-exchanged Zr02-PILC at 25 °C and 1 atm...

Orville, P.M. Alkali ion exchange between vapour and feldspar phases. Amer. J. Sci., 26l, 201-237 (1963). 

Bachinski and Muller (l9Tl)- High-temperature, metastable portions of the two-phase region in the system microcline - low albite were determined at 6OO to 900°C and 1 atm by means of alkali ion-exchange and exsolution - dissolution experiments. Compositional data are fitted to two-coefficient Margules expressions using the method of Thompson (1967) and the "r-s" method of Thompson and Waldbaum (1969b). 

The ketones 56,57, and 58 are some of the monocychc P,y-enones whose photochemical reactions upon sensitized irradiation have been examined. Irradiation of the dienone 56 in ether is reported to give the bicyclic ketone 59 via oxa-di-Ji-methane reaction. Recently, the photoreaction of cyclohexadienone 56 and its derivatives having chiral auxiliaries was examined in alkali ion exchanged Y zeolites. Thus, irradiation of 56 in dry (-)-ephedrine-modified zeoHte gave the ODPM product in 30% ee. Significant... 

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