The Modification Of NiO And The Doping Of PbO On Mn-Ce/TiO₂ Catalyst For Selective Catalytic Reduction Of NO With NH₃ At Low Temperature

Large amounts of nitrogen oxides will cause a series of environmental problems,such as acid rain, fog and haze, photo-chemical smog and ozone depletion etc. It has been an essential task for atmospheric environment to control nitrogen oxide emission.Selective catalytic reduction of NOx with ammonia has been the most effective way of flue gas denitrification. V2O5-WO3（Mo O3）/TiO₂ catalyst is the most widely used commercial catalyst, which optimal reaction temperature is 300⁴00 ℃. That is to say,SCR catalysts are often in high sulfur, high dust and a large number of toxic components atmosphere, which shorten the service life of catalysts. Therefore, it is quite necessary to develop a new type of low temperature SCR catalyst with high NO conversion efficiency. Mn-Ce mixed oxides catalysts are considered as the most promising low temperature SCR catalysts because of its excellent low temperature catalytic activity. Catalyst poisoning is an inevitable problem in actual SCR reaction, it is related with fuel characteristics. PbO as one of the typical heavy metals in flue gas from coal-fired power plants and municipal solid waste incineration power plants will deposit on catalyst surface and poisoning SCR catalysts.First, we used equivalent-volumetic impregnation method to obtain Mn-Ce/TiO₂ and Ni-Mn-Ce/TiO₂ catalysts. We investigated the following problems:（1） the influence of different NiO loadings on the NO conversion efficiency of Mn-Ce/TiO₂catalyst;（2） the influence of different reaction conditions（such as calcination temperature, NH₃/NO ratio and O₂ concentration） on the NO conversion efficiency of Ni-Mn-Ce/TiO₂ catalyst;（3） the influence of NiO addition on the resistance of H₂ O and SO₂ over Mn-Ce/TiO₂ catalyst. Experimental results showed that the addition of NiO had a great promotion on the NO conversion efficiency of Mn-Ce/TiO₂ catalyst over the whole reaction temperature range when Pb:Mn mole ratio was 0.4. The highest NO conversion efficiency of Ni（0.4）-Mn-Ce/TiO₂ catalyst was 98.0%. Besides, the resistance of H₂ O and SO₂ over Mn-Ce/TiO₂ catalyst was obviously improved after the addition of PbO.Then, we used impregnation method to obtain Mn-Ce/TiO₂ and Pb-Mn-Ce/TiO₂ catalysts. We investigated the inhibitory effect of different PbO loadings on the NO conversion efficiency of Mn-Ce/TiO₂ catalyst and the poisoning reasons of Mn-Ce/TiO₂ catalyst caused by PbO. It showed that the doping of PbO would cause adecrease in NO conversion efficiency of Mn-Ce/TiO₂ catalyst. The NO conversion efficiency of Mn-Ce/Ti O₂ catalyst declined from 96.7% to about 40%.Characterizations such as BET, XRD, SEM, XPS, H₂-TPR, NH₃-TPD and FTIR were used to elucidate the poisoning reasons of Mn-Ce/TiO₂ catalyst caused by PbO. The decreasing of surface area, bad dispersion of manganese oxides, less reducible of manganese species, low concentration of Mn4+, Ce3+ and chemisorbed oxygen（Ob）, the alteration of acid sites, an obvious reducing of ammonia adsorbance, the vanishing of amide species, all of these were the deactivation reasons of Mn-Ce/TiO₂ catalyst caused by PbO doping.