Preparation of Hierarchical SAPO-18 via alkaline/acid etching

Abstract Hierarchical SAPO-18 molecular sieve was successfully post-synthesized in the alkaline tetraethyl ammonium hydroxide (TEAOH) solution and hydrochloride (HCl) acid solution. In the TEAOH solution, preferential dissolution occurs surrounding the defect sites in a controlled manner, leading to hierarchical SAPO-18 with well-preserved chemical compositions and crystallinities. In acidic solution, the dissolution is revealed to be sensitive to both the defects and the chemical compositions (selective dissolution of the Si-O-Al domains), which cooperatively contribute to the generation of meso-/macropores in the crystals. The crystallization of SAPO-18 precursor is thus inferred to proceed via an oriented nanoparticle attachment mechanism in the early stage. The twinning and intergrowth of nanoparticles occur in an ordered way, leading to the oriented arrangement of the crystallite boundaries. The defects located at the intergrowth interface are prone to acid/alkaline attacks, and play crucial role in the development of hierarchical pore systems. The hierarchical SAPO-18 sample exhibits excellent catalytic reaction performance in the liquid phase benzylation reaction of benzene and benzyl alcohol.