SODIUM AZIDE IMPREGNATION

The samples can be prepared by alkali metal vapor treatment of the zeolite, treatment of the molecular sieve with a solution of the alkali metal in liquid ammonia or in primary amines, treatment of the zeolite with organolithium compounds, or decomposing sodium azide previously impregnated on sodium zeolites [59-62]. 

In order to take benefit of the strong geometrical constraints of the zeolite voids, so as to improve the basic properties, basic moities insertion inside the pores was achieved by several authors [2-4,9,12,13]. The direct incorporation of alkali hydroxide during their synthesis by treatment of aqueous or methanolic solution [13] can lead to loss of crystallinity by Al-0 solvolysis. This phenomena can be avoided by using a mild method consisting of a thermal decomposition of neutral alkali salts previously occluded inside the zeolite void cavities [9]. In this respect. Martens et al. prepared supported sodium clusters on zeolites generated by impregnation of sodium azide followed by its thermal decomposition [2-4]. 

Iodine-sodium azide solution Filter paper impregnated with 2%... 

An alternate method for the preparation of such dusters [213] is based on the impregnation of a dehydrated zeolite with alcoholic solutions of sodium azide, followed by the controlled decomposition of the azide. The ionic sodium clusters were shown by ESR spectroscopy to be Na4 and are formed in the zeolite pores. The clusters exhibit catal)dic properties for both isomerization and hydrogenation reactions of alkenes and alkynes. 

Microporous superbasic catalysts based on zeolites suitable for alkene isomerization were developed by Martens et al. [28-30]. They have high activity in the 1-butene isomerization and side-chain alkenylation of xylene [31], and are prepared by impregnating a dehydrated zeolite (NaY) with NaN3 in alcoholic solution. Subsequent decomposition of the azide inside the zeolite pores produces metallic sodium particles Nax°and cationic sodium clusters Na43+. The high catalytic activity was attributed to the ionic sodium clusters as they could be detected using ESR spectroscopy. 

---