Revealing and Controlling Atomic-Scale Stacking Disorder in SAPO-34 for Enhanced MTO Performance

SAPO-34 is the benchmark catalyst for the methanol-to-olefins (MTO) process, yet its catalytic lifetime remains limited, attracting increasing attention from both academia and industry. Here, we identify a previously unrecognized origin of SAPO-34 deactivation: stacking disorder, which is a type of structural defect difficult to detect by conventional PXRD, particularly in nanosized crystals. By combining advanced three-dimensional electron diffraction (3D ED), integrated differential phase-contrast scanning transmission electron microscopy (iDPC-STEM), and electron ptychography based on four-dimensional (4D) STEM data, we uncover atomic-level hidden stacking disorders in SAPO-34 synthesized using the conventional tetraethylammonium (TEA+) as the organic structure directing agent (OSDA). These disorders promote the formation of smaller aei cages, thereby accelerating catalyst deactivation. Guided by these structural insights, we identify a larger OSDA, N,N,N-trimethyladamantan-1-aminium (TMAda+), that suppresses aei-cage formation and yields stacking-disorder-free SAPO-34 with a markedly extended MTO lifetime. Furthermore, to circumvent the high cost of TMAda+, we develop a series of low-cost amine OSDAs that reproduce its structure-directing behavior, yielding SAPO-34 catalysts free of stacking disorder and with MTO performance comparable to that of TMAda+-directed catalyst, as confirmed by 3D ED and iDPC-STEM characterization. Among these catalysts, SAPO-34 directed by N,N-dimethylcyclohexylamine shows the highest catalytic durability. This work establishes a structural design strategy for producing stacking-disorder-free SAPO-34 with substantially enhanced MTO stability.