Directly Synthesis of ZSM-22 Particles by Adding Polyurethane Foam in Ionic Liquid-directed Dry-gel-conversion

Abstract

Pure-silica ZSM-22 particles with millimeter size were directly synthesized by adding polyurethane foam (PU foam) in ionic liquid-directed dry-gel-conversion process, where the dry gel was prepared under the unusual acidic condition for hydrolyzing the silica precursor with 1,3-alkylimidazolium ionic liquid as the structure direct- ing agent (SDA). Both the PU foam and the ionic liquid-directed dry-gel-conversion process played essential roles in the formation of macroscopic morphology, because only powder-like sample could be obtained in the absence of foam, and moreover, no such special morphology could be achieved on ZSM-22 zeolite prepared by the PU foam-added traditional hydrothermal synthetic route. Various synthetic parameters were systematically studied, in- cluding the influence of PU foam, adding time and adding amount of PU foam, as well as the crystallization time. Pure phase ZSM-22 particles with the highest crystallinity can be obtained by adding appropriate volume of PU foam after microwave aging. Finally, the directly synthesized ZSM-22 particles were modified by impregnating CuO, which exhibited superior N2O adsorption property to the CuO-impregnated post-molded ZSM-22 particles with binding materials. The results indicate that there is an important influence of the macro-morphology on the adsorption performance of zeolites.