Direct Synthesis of Zeolites from a Natural Clay, Attapulgite

Presently, chemical Si/Al sources are predominantly used as raw materials for the synthesis of zeolites in spite of their high cost. Here, we report for the first time the direct synthesis of a ZSM-5 zeolite by using a natural clay, attapulgite (ATP), as the low-cost and environmentally benign Si/Al source through a vapor-induced transformation (VIT) method, in which the vapor diffuses into ATP and interacts with the framework. In a crystallization recipe, ATP is well present with a pristine crystal structure, and the yield of zeolite reaches 96%. The resultant zeolite exhibits well-defined crystallinity and porosity, which are comparable to the counterpart synthesized from traditional chemical Si/Al sources. In the synthetic process, the formation of Si-F species plays an important role, which promotes the transformation of an ATP crystal to a zeolite crystal. Meanwhile, the metal elements (e.g., Al, Fe, and Mg) of ATP exist in the zeolite products, and at least part of them are located in the zeolite framework, which endows the zeolite with excellent catalytic activity. Direct synthesis of various zeolite crystals including TON, MOR, and∗BEA from ATP is also realized via the VIT method. Our work provides a green and economic alternative for the synthesis of zeolites using natural clays instead of chemical raw materials.