Study On Properties Of V₂O₅/CeO₂ Catalyst For Selective Catalytic Reduction With NH₃ At Low Temperature

Nitrogen oxides（NOx） are one of the major source of airpollution. Extensive studies and commercial operation have shown that selective catalytic reduction （SCR） with NH₃ is the most effective technology for DeNOx removal from the flue gas of burning coal plant. The temperature of the flue gas from burning coal plant is lower than 200℃, and the main industrial catalysts which need reheat the flue gas back to the SCR operating temperature（ over 350℃） to avoid catalyst poisoning by SO₂. However, boiler power plant NOx emissions is large. State Environmental Protection Administration as amended by the“thermal power plant air pollution emission standards”（GBl3223-2004） of thermal power plant NOx emissions regulations and has made clear to meet the new addition to the existing power plant emissions standards. It is needed to set aside for smoke removal of nitrogen oxides device space. The corresponding emissions charges will be formally implemented soon, then nitrogen oxides and sulphur dioxide will implement the same standards on sewage charges. Faced with increasingly severe environmental pollution situation and chargeing on the nitrogen oxides sewage, SCR technology research is imminent. Since a low-temperature SCR process can be located at downstream of a boiler system, after removing of dust and SO₂, it is relatively easy to retrofit in the existing boiler, which will result in reduced plugging by dust and reduced poisoning by SO₂, and avoid preheating of flue gas. All these will contribute to reduce cost for NOx removal. Catalyst is the key to the selective catalytic reduction （SCR） of NOx, and its properties are directly related to the effect of NOx removal, the SCR for low emperature has received much attention due to its economics.In our experiment, the support ceria （CeO₂） was obtained by thermal decomposition of cerous nitrate（Ce（NO₃）₃·6H₂O） to support vanadium oxide （V₂O₅）. A series of V₂O₅/CeO₂ catalysts were prepared by using the isometric incipient impregnation method with different calcination temperatures（400℃, 500℃, 600℃） and various V₂O₅ loadings（1²0 wt%）. It was found: the vanadium content ranging from 1 to 20%, the temperature increased from 100 to 300℃, the V₂O₅/CeO₂ catalysts show a high activity for SCR, with compared to pure CeO₂. By the analysis of the catalytic effect of the catalysts, we abtainted: the best loading of catalyst was 5 wt% while calcination temperature of catalyst was 400℃; When the calcination temperature was 500℃, the best loading was 15 wt%; When the calcination temperature was 600℃, the best loading was 10 wt%. Via the comparison and analysis of the best catalysts with the three different calcination temperatures, we considered that the best catalyst was the 5 wt% V₂O₅ loading and the 400℃calcination temperature. And with its further analysis, the effect of the calcination temperature, O₂, SO₂, NH₃ on the catalytic activity of 5%V₂O₅/CeO₂ catalyst were studied. We also studied the relationship between the catalytic activity and the reaction time at 200℃. A combination of various physicochemical techniques such as BET surface area, X-ray diffraction （XRD） and SEM were used to characterize the physico-chemical properties of the catalysts.