Green synthesis route for MCM-49 zeolite using a seed-assisted method by virtue of an ultraphonic aging procedure

Abstract

The organic structure-directing agent (OSDA)-free synthesis of MCM-49 is strongly desired because OSDA makes synthesis cost expensive and environment unfriendly. In this work, an efficient, eco-friendly and simple route to synthesize MCM-49 zeolite is developed, via seed-assistance, without deliberately adding OSDA, with ultraphonic aging treatment. For comparison, the effect of microwave aging, mechanical stirring aging and without any aging processes on the synthesis is investigated. Due to the acoustic cavitation, the ultraphonic aging treatment shows superiority over the others. Ultraphonic aging not only keeps the MCM-49 seed integrity but also promotes both the silica species and aluminum species to the solid phase, which is beneficial for the growth of MCM-49 and the suppression of MOR formation in the absence of OSDA. ²⁷Al MAS NMR data show that the seed-assisted MCM-49 almost has no extra-framework aluminum, but dealumination will happen upon ammonium exchange. ²³Na MAS NMR results demonstrate that the interaction between Na ions and framework of the seed-assisted MWW product is strengthened after calcination, which makes the exchange of Na species difficult. Alternatively, ammonium exchange upon the as-made sample is an effective method to remove Na species, which improves the micropore volume, external surface area, and acid amount of the seed-assisted MCM-49.