An Investigation On Molten Salt-derived Highly Efficient Catalysts For The Removal Of Volatile Organic Compounds

Most of volatile organic compounds(VOC) cause serious pollution to the atmosphere, and harmful effect on the human health. Catalytic oxidation is believed to be one of the efficient pathways for the removal of VOC, and the key issue is the development of active and cheap catalysts. Molten salt method is a novel strategy for the preparation of nanomaterials, with the advantages of environmental friendliness, simple process, and large scale production. In the present study,(1) according to the adjustment of the molten salt composition, the metal precursor, the weight ratio of molten salt and metal precursor, calcination temperature and time, we successfully fabricated nanowire-like Mn2O3, octahedral Co3O4, cubic CeO2, nanowire-/needle-/beam-/nanorod-like ZnO, flake-like CuO and MgO in the NaNO3-NaF molten salt system, via the molten salt method.(2) We developed a novel in situ molten salt method for the preparation of Mn2O3 nanowires supported ultra low loading of silver nanocatalysts. It was shown that the preparation methods had a great effect on physicochemical properties of the sample. Compared with the impregnation and polyvinyl alcohol-protected reduction routes, the molten salt method was beneficial for generation of highly dispersed Ag nanoparticles on the Mn2O3 nanowire support. The surface Mn4+/Mn3+ or Mn3+/Mn2+ molar ratios of the as-prepared samples were different from each other, while the difference in surface Ag+/Ag0 molar ratio was small. The Oads/Olatt molar ratio decreased in the order of Mn2O3-ms ≈ 0.12Ag/Mn2O3-redn > 0.12Ag/Mn2O3-imp > 0.13Ag/Mn2O3-ms, while the low-temperature reducibility decreased in the sequence of 0.13Ag/Mn2O3 > 0.12Ag/Mn2O3-imp > 0.12Ag/Mn2O3-redn > Mn2O3-ms > 0.23Ag/Mn2O3-bulk. Among these samples, 0.13Ag/Mn2O3-ms exhibited higher catalytic activity for toluene oxidation: T50% = 185 oC and T90% = 215 oC at a toluene/oxygen molar ratio of 1/400 and a SV of 40 000 mL/(g h). Compared to the supported Au or AuPd alloy nanocatalysts described in our previous studies, the 0.13Ag/Mn2O3-ms catalyst exhibited dozen times of toluene consumption rate per gram of noble metal. It is concluded that the high dispersion of silver nanoparticles on the Mn2O3 nanowire support and good low-temperature reducibility were responsible for the excellent catalytic activity of 0.13Ag/Mn2O3-ms.