Synthesis of high-silica offretite by the interzeolite conversion method

High-silica offretite (Si/Al = 7.6–8.0) with no or very little amount of erionite was successfully obtained by the interzeolite conversion of faujasite used as a starting material in the presence of both benzyltrimethylammonium hydroxide and the structure-forming alkali metal cations such as Li+ and Na+. Hydrothermal conversion of faujasite into offretite depended on the Si/Al ratio of the starting faujasite. Only faujasite with Si/Al ratio of 16–31 was converted into offretite. In this conversion, offretite was obtained in 1 day, indicating that the crystallization rate was enhanced by using faujasite as the starting material. Based on 13C CP/MAS NMR measurements, most of benzyltrimethylammonium cations were presented intact within zeolitic pores of the obtained offretite. As offretite was not obtained from amorphous materials (amorphous SiO2 and γ-Al2O3 or Al(OH)3), the advantage of the interzeolite conversion was demonstrated.