Mesoporogen-free construction of highly meso-/macroporous silicoaluminophosphate zeotypes via non-classical...

The development of a facile and sustainable synthetic route for hierarchical silicoaluminophosphate (SAPO) zeotypes remains a significant challenge. Herein, we present a novel mesoporogen-free strategy for the direct synthesis of hierarchical SAPO-11 and SAPO-5 possessing substantial meso-/macroporosity. This approach utilizes triethyl phosphate (TEP) as the phosphorus source within a low-water-content alkaline gel system, which not only markedly reduces the consumption of microporous organic structure-directing agents (OSDAs) but also effectively promotes a non-classical crystallization pathway governed by nanoparticle attachment and fusion. The resulting materials retain well-defined microporous frameworks while exhibiting exceptionally large meso-/macropore volumes (up to 0.52 cm³ g^-1) and high external surface areas (up to 156 m² g^-1). For the gas-phase Beckmann rearrangement of cyclohexanone oxime (CHO), the optimized hierarchical SAPO-11 achieves high ε-caprolactam (CPL) selectivity (96.8%), prolonged catalyst stability (>15 h), and excellent reusability (> 5 cycles). This is attributed to its highly mesoporous and macroporous structure, which enhances mass diffusion capacity and carbon accommodation capability. This work establishes a general and cost-effective platform for constructing hierarchical zeotypes with enhanced mass transport properties, holding great potential for industrial catalytic processes.