Green Synthesis of Low-Silica CHA Zeolite Without Organic Structural Directing Agents, Fluoride Media and Seeds

To spare the use of OSDA and fluorides, for the sake of reducing cost and environmental conservation, a green and efficient synthesis recipe of low-silica CHA zeolites has been demonstrated, without using seeds or any other zeolites. The main factors that determine the formation of CHA zeolites have been investgated systemmatically, and several rules are obtained. (i) just considering simple memallic cations acting as the SDA, K+ is indispensable for the formation of CHA framework, with noting that K+ can also direct to MER topology. (ii) working as catalyst or minerization agent, OH− and F− function almost identically, but when the concentration of F− has reached a really high level or even only F−was used, CHA framework can not form because the intermediate fluoride complexes are inclined to produce small melecules of fluoride salts with morderate solubility over to enter the zeolite framework. (iii) at conditions of this work, the second stirring after the RT aging should be adopted since the contrastive tests have showed the benifits of the second stirring in making fewer or smaller impurity grains. (iv) when the concentration of K+is too high in reactive gels, with the other same conditions, MER over CHA framework is preferentially to form. (v) it is reasonable to consider the as-synthesized K-CHA materials can be used to research the novel “trapdoor” effect later. The authors considered the discussions and conclusions would offer some beneficial references to the green synthesis of zeolites and further understanding of the mechanism of hydrothermal treatment.