One-step direct synthesis of SAPO-36 using 4-pyrrolidinopyridine as an efficient structure-directing agent

Abstract

The synthesis of ATS-type aluminophosphate is challenging due to the formation of AFI-type aluminophosphate as a competitive phase when using traditional tripropylamine (Pr3N) as an organic structure-directing agent (OSDA). SAPO-36, the ATS-type silicoaluminophosphate, is less reported due to the rigorous synthetic conditions. Herein, a novel organic compound, 4-pyrrolidinopyridine (Ppyr), was found to be an effective OSDA for the first time to synthesize SAPO-36 via direct hydrothermal method. Various techniques, including XRD, SEM, TEM, nitrogen sorption, ICP-AES, XPS, TGA, solid NMR, NH3-TPD, and Py-IR, were carried out to characterize the synthesized SAPO-36 samples with different Si contents. It was experimentally and computationally demonstrated that Ppyr was a better OSDA than conventional Pr3N to direct the crystallization of the ATS-type structure. Heteroatom (Mg, Co, Fe, and Zn) isomorphically substituted ATS-type molecular sieve analogues can be successfully synthesized using Ppyr as OSDA.