| Nitrogen oxides, as one of the main atmospheric pollutants, have aroused extensiveattention, due to its contribution to acid rain, light pollution, ozone depletion, greenhouseeffects and some other negative effects. Selective catalytic reduction (SCR) of NOx withNH3is one of the most effective flue gas cleaning technologies for stationary sources.Catalyst is the core of the SCR technology that determinate the efficiency of the SCRsystem.At present, the commercial catalysts (V2O5–WO3(MoO3)/TiO2) for this process arehighly active within the narrow temperature window of300–400℃. In order to meet theneeds of the reactive temperature, SCR catalysts are often distributed in an atmosphere withhigh dust and volatile compounds, but this way often causes deactivation by highconcentration of dust and toxic components. Considering the cost and the pollution,Regeneration of deactivated catalyst is the priority. In this study, a commercialvanadium-titanium-based SCR De-NOxcatalyst was selected and simulation of poisoning inlaboratory. The poisoning mechanism of the catalysts by typical components of toxicity (K,Na, Ca, and As) are studied respectively, providing a theoretical basis for catalystregeneration methods, processes, life extension of the catalyst and reduction of the costs ofoperating denitrification system.Firstly, the influence of different concentrations of K, Na, Ca on the performance ofcatalysts were investigated, catalysts before and after poisoning were characterized by N2adsorption-desorption, XRD, Raman, H2-TPR, XPS and FT-IR. Results show that the K, Na,Ca all had toxic effects on catalysts, and the toxicity of K was the strongest and the Ca wasthe weakest. The introduction of K、Na、Ca to catalyst could lead to a decline of surface areaand pore volume. V2O5and WO3were still in amorphous form or highly dispersed on thesurface of TiO2carrier after poisoning. The oxidation ability of the catalysts was decreasedand the surface chemical adsorption oxygen was reduced obviously. The chemical form ofsurface active components was not affected; With the increase of toxicity components, theV5+=O peak disappeared gradually.Secondly, the influence of trace arsenic on catalyst activity has been investigated andphysic chemical properties of fresh and poisoned catalysts have been analyzed with relevant characterization methods. The results reveal that arsenic has intense poison effect on thecatalysts and causes a significant decrease on catalyst activity; Trace arsenic has low impacton catalyst surface area, pore volume and pore size; On the condition of arsenic’s existence,VOxspecies which are on the surface of catalysts become diversification, the V5+=O peakdisappeared gradually, while chemical forms of tungsten and titanium on catalyst surface areaffected little.Finally, by integrating NH3-TPD with FT-IR experiment, the catalyst surface acidity andcatalytic reaction pathway influenced by K, Na, Ca and As were investigated. Results showedthat the total amount of acid on the catalyst significantly decreased after K, Na, Ca poisoning,the capacity of NH3adsorption declined seriously (especially Bronsted acid), acid strengthweakened and weakly adsorbed NH3increased, as a result the key step of SCR reaction isdifficult to occur. K, Na, Ca do not affect the pathway of catalytic reaction, but they suppressthe formation of the intermediate product by reducing the surface adsorbed oxygen. As hadfew influence on the amount of total acid and acidly of the catalyst, but the amount of weaklyadsorbed NH3increase will also affect the SCR reaction. |
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