Effect of ammonium salts on hydrothermal synthesis of high-silica mordenite

Abstract

Effect of ammonium salts on the direct hydrothermal synthesis of high-silica mordenite (MOR) zeolite with tetraethylammonium hydroxide was investigated. The addition of NH 4NO 3 to the system restrained the formation of MFI zeolite and quartz, and accelerated the crystallization rate of high-silica MOR zeolite. The MOR zeolite synthesized with NH 4NO 3 was very poorer in framework defects as compared with sample obtained without NH 4NO 3 as indicated by IR and 29Si MAS NMR techniques. It was also indicated by nitrogen adsorption study that the micropore and external surface areas of the MOR zeolites synthesized with ammonium salts are considerably larger than that of sample without ammonium salts. Under well-optimized conditions, the highly crystalline and pure MOR zeolite with a Si/Al ratio of ≈34 was successfully prepared by adding seed crystals and NaF as well as NH 4NO 3.