Ionothermal Synthesis of Hollow Aluminophosphate Molecular Sieves

Hollow AlPO4‐5 spheres (E‐AP and B‐AP) are synthesized ionothermally in tri‐substituted imidazolium bromide ionic liquids (ILs), that is, 1‐ethyl‐2,3‐dimethylimidazolium bromide and 1‐butyl‐2,3‐dimethylimidazolium bromide, respectively. Moreover, the morphologies of the hollow AlPO4‐5 particles vary with the type of ILs and the amounts of ILs, phosphoric acid, amine, and hydrofluoric acid. The thicknesses of the shells of the hollow spheres are substantially affected by the length of the alkyl chain on the imidazole ring of the ILs. The shell thicknesses significantly increase from 300–500 nm to 4–5 µm as the alkyl chain length increases, and solid AlPO4‐5 spheres (H‐AP) are generated in 1‐hexyl‐2,3‐dimethylimidazolium bromide IL. Furthermore, the experimental results suggest that the formation of hollow AlPO4‐5 spheres in an IL is consistent with Ostwald ripening theory. In addition, compared with ordinary solid AlPO4‐5 (S‐AP) prepared by hydrothermal methods, the hollow E‐AP particles are small and spherical. Moreover, the Co‐loaded hollow AlPO4‐5 (Co/E‐AP) catalyst exhibits excellent catalytic activities in the selective oxidation of tetralin. The reaction conversions are 73.5 and 5.7% over the Co/E‐AP catalyst and Co‐loaded solid AlPO4‐5 (Co/S‐AP) catalyst, respectively, which means that the hollow structure facilitates the mass transfer of the reactants and products in the catalytic reaction. Hollow aluminophosphate zeolites are first synthesized via an ionothermal approach. The mechanism of the formation of the hollow structure is consistent with Ostwald ripening theory. The Co‐loaded hollow AlPO4‐5 catalysts exhibit excellent catalytic activities in the selective oxidation of tetralin. The reaction conversion is 73.5%, which is 12.9 times that over the Co‐loaded solid AlPO4‐5 catalyst prepared by hydrothermal methods.