In situ growth and assembly of microporous aluminophosphate nanosheets into ordered architectures at low temperature and their enhanced catalytic performance

Abstract

A low-temperature strategy to fabricate hierarchical aluminophosphate-based molecular sieves has been developed without the assistance of surfactants. The facile synthesis results in cylinder-like SAPO-5 (AFI) composed of oriented attached nanosheets with a thickness of 40–100 nm. The main exposed surface of the nanosheets is revealed by the SAED pattern to be the {001} plane, implying a short path for molecular diffusion in the one-dimensional 12-membered ring channel. Investigation on the crystallization process demonstrates that low temperature retards the crystal growth along the c-direction in SAPO-5 and the ordered architecture forms via a nanosheet formation and oriented attachment process. The aggregated morphology of SAPO-5 is template-dependent, which may be modified/changed by varying the template in the system. The low-temperature strategy is also successfully extended to the preparation of metal-containing aluminophosphate molecular sieves. The obtained MeAPO-5 (Me = Co, Mn, and Cr) and a novel CHA/AEI intergrowth CoAPO molecular sieve also possess hierarchical structures with nanosheet-assembled morphology. Remarkably, the present self-assembled AFI crystals exhibit an obvious improvement in catalytic reactions. This facile method provides a new way for the long-range organization of nanosized building blocks to fabricate hierarchical nanostructures.