Preparation of FeAPO-11 Molecular Sieves via Improved Solvent-Free Method and Their Catalytic Performances

Based on the solvent-free synthesis method of AEL-type molecular sieves in the literature, FeAPO-11 molecular sieves with high crystallinity, specific morphology or pore structure were synthesized by introducing some additional synthetic variables, including low temperature pretreatment, mechanochemical pretreatment, seed crystals and hydrogen peroxide. Their catalytic performance was investigated using phenol hydroxylation as a probe reaction. The synthesized FeAPO-11 molecular sieves were further characterized by XRD, SEM, N2 physisorption and UV-Vis DRS. Moreover, the effects of content and distribution of Fe species, and surface area of the catalysts on the phenol hydroxylation reaction were thoroughly studied. Characterization results indicate that combination of low temperature pretreatment and hydrogen peroxide can significantly improve the crystallinity of FeAPO-11 zeolite. Especially, under some specific conditions, FeAPO-11 molecular sieve with uniform nanocrystalline aggregates morphology can be successfully prepared. The catalytic reaction results suggest that the induction period of phenol hydroxylation reaction is mainly determined by the amount of multi-nuclear iron in the form of non-framework iron species in FeAPO-11 catalysts. Among the five selected catalysts, due to its regular nanocrystalline aggregates morphology, high external surface area and high iron content in the framework, FeAPO-11-LHSB exhibites the best performance with 33.6% dihydroxybenzene yield and 67.6% selectivity. © 2019, Editorial Office of Acta Petrolei Sinica(Petroleum Processing Section). All right reserved.