Mordenite zeolite with ultrahigh SiO2/Al2O3 ratio directly synthesized from ionic liquid-assisted dry-gel-conversion

Abstract

SiO2/Al2O3 ratio (SAR) is one of the most important parameters for zeolite materials, and tuning of SAR towards required topology is crucial for applications of zeolites. Mordenite (MOR) zeolites normally possess the moderate SARs of about 4–32. In this work, a breakthrough for straightforward synthesis of high-silica MOR zeolites was achieved without using seed or fluoride additive, attaining well crystallized MOR with wide window of SARs in the range of 11–263, in which the ultrahigh SAR of 263 represented the highest value for MOR up to date. The synthesis relied on the gel preparation by acidic hydrolysis of the silica precursor with the ionic liquid (IL), 1-butyl-3-methylimidazolium bromide ([BMIm]Br), as the structure-direct-agent, followed by dry-gel-conversion (DGC). Besides mordenite, ZSM-5 could be also obtained from this route. Thermal stability tests demonstrated that the obtained ultrahigh-silica MOR zeolites preserved the crystalline structure up to 800 °C, and the higher SAR, the better thermal stability. Our synthesis largely expands the SAR range of MOR zeolites and provides a series of highly thermal stable high-silica MOR zeolites as promising catalyst supports.