PROMOTER-INDUCED ENHANCEMENT OF THE CRYSTALLIZATION RATE OF ZEOLITES AND RELATED MOLECULAR-SIEVES

ZE0LITES and other microporous molecular sieves(1-4) exhibit useful ca talytic, absorption and ion-exchange properties. Most synthetic zeolit es are made by hydrothermal methods, which generally suffer from the d rawback of long crystallization times(5). Here we show that the crysta llization rate of zeolites and related molecular sieves can be acceler ated by a factor of as much as about five by the addition of various ' promoter' ions, such as perchlorate, phosphate, nitrate, sulphate and carbonate. By using enhanced-sensitivity Si-29 NMR studies to monitor soluble silicate species during crystallization, we show that the prom oter ions enhance the rate of formation of the oligomeric (mainly tetr americ) silicate ions responsible for nucleation and growth of the cry stals.