Designed synthesis of single-crystalline silicoaluminophosphate zeolite via interzeolite transformation for n-dodecane hydroisomerization

Single-crystalline zeolites are highly desirable in this field owing to their high hydrothermal stability and high mass transfer efficiency. However, the preparation of single-crystalline silicoaluminophosphate SAPO-11 zeolite remains a significant challenge due to its complex synthesis process. Herein, we firstly report a facile and direct approach to synthesize single-crystalline SAPO-11 by interzeolite transformation via a kinetic-modulated process. The crystallization process of single-crystalline SAPO-11 was monitored by the time-dependent characterizations. A panel of characterizations by XRD, SEM, N2-adsorption and solid-state NMR provided evidence that the formation mechanism of single-crystalline SAPO-11 involved fast interzeolite transition process between two different topologies from AlPO4-8 (AET) to SAPO-11(AEL), thus it avoids the aggregation of small nanocrystals during the conventional polycrystalline SAPO-11 synthesis. In addition, the Brønsted acid sites of the prepared samples could be precisely regulated. The resulting single-crystalline catalyst exhibits superior isomer selectivity (92.3% vs. 70.6%) and yield (77.9% vs. 62.3%) in the n-dodecane hydroisomerization compared with the conventional polycrystalline sample due to the unique morphology and suitable acidity. This synthetic strategy provides a new orientation to design other single-crystalline zeolite catalysts.