The Research Of Benzaldehyde Synthesis Under FeO_x/C Catalyst

Benzaldehyde is widely used in cosmetics, perfumery, food and pharmaceutial industries. At present, benzaldehyde is mainly produced by the gas-phase oxidation of toluene or liquid-phase oxidation of benzyl alcohol on industrial and laboratory scales. However, these processes lead to generation of large amounts of by-products, and the selectivity is poor. Therefore, the efficient catalytic methods of producting higher-value benzaldehyde has received increasing attention in both academic and industry. In the present paper, FeO_x/C composites are prepared by the hydrothermal and heat-treating processes in argon atmosphere.The main contents of this work are listed as follows:(1) FeO_x/C(N) composites were prepared from glucose and Fe(NO3)3 by a hydrothermal method and then heat treatment in an argon atmosphere. The structural and surface features of the resulting composite were characterized by XRD, TG-DTA, XPS, XRF, SEM, TEM, FT-IR, and BET. The results showed that the FeO_x/C(N) composite are constructed of nanorods that are interconnected in three dimensions. The iron oxide nanoparticles of about 10-50 nm highly dispersed in the carbonaceous material. Treating the FeO_x/C(N) composite at higher temperatures could further gasify the carbonaceous material, increase the interreaction between iron oxide and carbon matrix, enhance the thermal and chemical stability of the composite, and change the phase of iron oxide. Moreover, the catalytic performance of the FeO_x/C(N) sample was investigated in selective oxidation of benzyl alcohol to benzaldehyde with hydrogen peroxide. With water or acetonitrile as solvent, the FeO_x/C(N) sample exhibited the higher activity and selectivity to benzaldehyde. The molar ratio of benzyl alcohol and hydrogen peroxide is 1:4 and the amount of catalyst is 0.1g. After reacting at 60 oC for 5h in water, the conversion of benzyl alcohol and selectivity to benzaldehyde are as high as 80.82% and 77.93%, respectively. Using acetonitrile as solvent, the conversion of benzyl alcohol and selectivity to benzaldehyde were 78.84% and 86.15%, respectively. The catalyst can be recovered and reused for six times without a significant loss in its activity and selectivity. The FeO_x/C(N) sample treated at 500 oC showed the best catalytic activity, in which the main iron species is Fe3O4.(2) FeO_x/C(A) composites are prepared by a hydrothermal method using glucose as carbon source and iron(III) acetylacetonate as precursors and then heat treatment in argon atomsphere at various temperatures. The structure and textural properties of the resulting composites are characterized by XRD, TG-DTA, XPS, XRF, SEM, TEM, Raman, FT-IR and BET. The results show that the iron oxide in the FeO_x/C(A) composites are highly dispersed and confined in the carbonaceous matter. The iron(III) acetylacetonate participates in the carbonization process of glucose and interferes with the formation of the irregular nano-flakes. The samples diameter is reduced after heat treatment in argon atmosphere. The iron oxide in the FeO_x/C(A)-0.5-180(300) composites is mainly Fe3O4 nanopariticles. At 500 oC, the formation of new phase α-Fe is observed. The as-synthesized FeO_x/C(A) composites could be used as heterageneous catalyst for the selective oxidation of styrene to benzaldehyde using 30% H2O2 as oxidizing reagent. The styrene conversion and benzaldehyde selectivity under optimal conditions are 90.3% and 68.2%, respectively. The FeO_x/C(A) catalyst is recycled for six times without loss of activity.