Synthesis and Catalytic Properties of MeAPO-5 Molecular Sieves for Selective Oxidation of Cinnamyl Alcohol

A series of metal ion-substituted aluminophosphate molecular sieves of MeAPO-5 (Me=Co, Fe, Cu, Zn, Mn) were hydrothermally synthesized. The as-synthesized and calcined samples were characterized by X-ray diffraction (XRD), diffuse reflectance (DR) UV-Vis spectroscopy, thermogravimetric-differential thermal analysis (TG-DTA), and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) techniques. The as-synthesized single-phase MeAPO-5 molecular sieves all had high crystallinities. The type of metal significantly influences the states and amounts of the incorporated metal species, as indicated by DR UV-Vis and ICP analysis results. Co2+, Zn2+, Fe3+, and Mn2+ can be incorporated into the framework through the substitution of Al3+, while Cu2+ substitution is difficult. Selective oxidation of cinnamyl alcohol with molecular oxygen over various MeAPO-5 molecular sieves was conducted to probe the effects of the nature and states of metal species on their catalytic performances. CoAPO-5 showed higher catalytic activity and selectivity than the other MeAPO-5 molecular sieves. 1,4-Dioxane should be of the choice of solvent. A decrease in the reaction temperature favors the formation of cinnamaldehyde whereas an increase in the reaction temperature remarkably promotes the epoxidation of cinnamyl alcohol regardless of the occurrence of deep oxidation processes.