Synthesis, Characterization And Catalytic Combustion Properties Of Manganese Oxide Octahedral Molecular Sieve

Cryptomelane-type manganese oxide octahedral molecular sieve(OMS-2) for VOCs catalytic combustion was synthesized by solvent-free solid-state and refluxing synthesis methods.Catalytic combustion of Toluene and Formaldehyde over OMS-2 catalysts have been investigated.The properties of the sieve catalysts,such as the structure morphology,surface oxygen and thermal stability were characterized by X-ray diffraction(XRD),Field emission scanning electron microscopy(FE-SEM), Hydrogen-temperature programmed reduction(H₂-TPR),Oxygen-temperature programmed desorption(O₂-TPD),Temperature programmed desorption-Mass spectroscopy(TPD-MS) and Nitrogen adsorption-desorption.The results indicated that the catalytic activity of OMS-2 is correlated to the oxygen species and surface area in the catalytic combustion of Toluene and Formaldehyde.The activity of catalytic combustion for Toluene obviously depends on the surface properties of OMS-2 and the amount ofαoxygen species,andβoxygen species can mainly contribute to the catalytic combustion of small-size Formaldehyde molecule.Catalysts of Ce-OMS-2 with different Ce content were subsequently prepared by impregnation and ions-exchange of aqueous solution of Ce³⁺.The structure morphology and surface oxygen properties of the sieve catalysts Ce-OMS-2 were investigated by XRD,TPD-MS and H₂-TPR techniques.The results indicated that the catalytic activity of Ce-OMS-2 for formaldehyde combustion was reduced with the increasing of Ce content.The Ce ion doped onto the surface of OMS-2 may block up the micropore tunnel with the surface area dropping dramatically.In conclusion,the possible reaction mechanism of VOCs catalytic combustion and the catalytic cycle of oxidation reaction were discussed in accordance with the experimental results.The mechanism of catalytic combustion over OMS-2 catalyst may be corresponding with Mars-van Krevelen mechanism.