| Nitrogen oxides (NOx) are major pollutants in air, which form acid rain and photochemical smog, causing serious damage to human body. NOx emissions in the flue gas is a major factor of atmospheric NOx pollution, the development of flue gas de-NOx catalysts for reduction of stationary source NOx emissions is therefore of great practical significance. In this paper, V-Ti type selective catalytic reduction (SCR) de-NOx catalyst based on titania nanowires on 304 stainless steel plates and Mn-Ti type SCR de-NOx catalyst based on nanoporous titania on metallic Ti plates were studied in detail. The composition, morphology and de-NOx property of the catalysts were investigated in detail utilizing the various techniques of field emission scanning electron microscope (FE-SEM), energy dispersive (EDS), X-ray diffraction (XRD) and a home-made de-NOx property testing system.The main results obtained are as follows:1) V-Ti type de-NOx catalyst:A TiN layer was firstly sprayed on 304 stainless steel plates by an arc-spraying procedure, which was then subjected to an oxidation reaction with 20 wt.% H2O2 solution containing 0.02 mg/ml HNO3 and 0.2 mg/ml C3H6N6, at 80℃for 6-72 h. The plates after the reaction were then calcinated in air at 450℃for 2 h. Titania nanowires were achieved for 6～12 h of the oxidation reaction. When the reaction duration prolonged to 18～72 h, nanoporous titania was achieved. After the calcination, the two titania mainly crystallized to anatase, with minor rutile phase. A V-W/TiO2 catalyst was then prepared by an impregnation method, using the titania nanowires as carriers. The SCR de-NOx property tests showed that, the efficiency to remove NOx kept constant at ca.88% when the NOx inlet concentration was in the range of 390～1100 ppm; when the reaction temperature ranged from 250℃to 350℃, the de-NOx efficiency only fluctuated insignificantly; when the N2 flowing rate fell in the range of 1.0～2.0 L·min-1, the de-NOx efficiency declined with the increasing flowing velocity. The de-NOx efficiency decreased significantly when the flowing rate increased to beyond 2.5 L·min-12) Mn-Ti type de-NOx catalyst:The nanoporous anatase TiO2 carrier was prepared by direct oxidation of metallic Ti plates with 10 wt.% H2O2. The Mn/TiO2 catalys were then prepared by dipping the Ti plate in the Mn (CH3COO)2 solution at 80℃. The FE-SEM observations indicated that MnOx loaded on the TiO2 surface was in the form of nanowires and nanorods. The SCR de-NOx property testing results showed that, with increasing MnOx load, the de-NOx efficiency first increased and then decreased, reaching a maximum of 85.5% at 250℃when the Mn/(Mn+Ti) molar ratio was 0.12. The additive of Fe element significantly improved the de-NOx efficncy of Mn/TiO2, which increased with increasing Fe/Mn molar ratio value. When the Fe/Mn molar ratio was 4.6, the efficiency reached 93.8% at 225℃. The additive of 5.08 wt.% Ce did not improve the catalytic property of the Mn/TiO2 catalyst. After the additive of V, MnOx in the form of plates appeared on the surface, instead of nanowires and nanorods. The additive of 0.71 wt.% V also failed to improve the de-NOx efficiency of Mn/TiO2. |
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