Solution-mediated transformation of natural zeolite to ANA and CAN topological structures with altered active sites for ethanol conversion

Abstract

In this study, one-pot syntheses of cancrinite (CAN) and analcime (ANA) frameworks from mordenite (MOR) natural zeolite were performed for the first time. The effects of the synthesis gel composition and alkalinity on the phase formation and crystallinity of the product were investigated. All studied zeolites were evaluated for their catalytic activities in ethanol conversion reactions from 473 K to 673 K and at 1 atm. The results suggested that the formation pathways of CAN and ANA are highly dependent on the alkalinity of the synthesis solution and the type of starting material regardless of synthesis template. The use of natural MOR zeolite (MORNZ) in the synthesis can contribute to highly crystalline ANA structures comparable to the ANA products obtained from fumed silica and sodium aluminate (NaAlO2). The quantity and locations of the acidic-cationic dual active sites of the proton-form product zeolites are suitable for synthesizing acetaldehyde from ethanol with over 90% product selectivity. However, further development of synthesis procedures to enhance the surface area is needed to improve the ethanol conversion of the resulting zeolites. This work provides a new perspective on highly crystalline and pure-phase zeolitic structural formations from natural zeolite and their potential application in ethanol conversion. (C) 2021 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.