Resolving and Controlling Silicoaluminophosphate Zeolite Intergrowths and Mixtures.

Achieving controlled synthesis of silicoaluminophosphate (SAPO) zeolites is critical for optimizing their catalytic performances, yet it remains difficult due to the complex coupling of synthesis variables and insufficient atomic-level structural understanding. Herein, we systematically investigate the multi-scale characterization and controllable synthesis of SAPO zeolites. We explore the effects of critical synthesis parameters (pH, Si content, the concentration and composition ratio of structure-directing agents) on the structural selectivity and distribution of SAPO-5 (AFI) and SAPO-34/18 (CHA/AEI) intergrowths and mixtures, identify the selective synthesis window for each structural component, and interpret the underlying selectivity mechanism from a perspective of competitive thermodynamics and kinetics. Low-dose electron microscopy enables the atomic-resolution imaging of beam-sensitive SAPO-34/18 intergrowths for revealing their stacking sequences and spatial distributions under the regulation of Si content and structure-directing agent ratio. This work provides a methodology for investigating the structure-property relationship of zeolite structures by combining controllable synthesis with atomic-resolution electron microscopy, thereby enabling the controllable design of these zeolite catalysts with tailored topology and porous structure.