Conversion of dry gel to microporous crystals in gas phase

Recently the dry gel conversion (DGC) technique, where a hydrogel is dried and the resultant dry gel is converted into microporous crystals in steam o r in a mixed vapor of steam and organic structure-directing agents (SDAs), has been developed. It has been shown that a wide variety of microporous cr ystals, pure silica microporous crystals, aluminosilicates, metallosilicate s, and aluminophosphates, can be synthesized using the DGC method. Remarkab le results have been reported in the synthesis of BEA types zeolites, namel y aluminosilicate, titaniumsilicate, zincosilicate, and borosilicate with B EA topology, using tetraethylammonium hydroxide, a commercially available S DA. It has also been found that zeolite OU-1, probably analogous to SSZ-31 and NCL-1, is formed via phase transformation from BEA. Dense zeolite coati ngs like membranes are possible using this method. Characteristics of the D GC method are discussed in detail.