Study Of Deactivation Mechanism And Regeneration Method Of Deactivated Commercial V₂O₅-WO₃-MoO₃/TiO₂SCR Catalysts

Nitrous oxides emitted from power plants can turn to acid rain and photochemical smogin the air. As a result, they could corrode the iron and constructions, damage the growth ofbotany and the health of human beings.According to a recent survey,50%of the exhaustedNOx in China were produced by power plants. Therefore, it is necessary and urgent to controland govern the emission of nitrous oxides from power plants due to environmental protectionof China. SCR method has been widely applied to eliminate nitrous oxides. worldwide.Nowadays catalyst V₂O₅-WO₃/TiO₂was widely used. This the cost of the catalyst is veryexpensive, and what’s more,the catalyst is easy to be deactivated. Therefore, the study ofregeneration of deactivated catalyst is very important for reducing the cost of purchasing andthe environmental harm of deactivated catalyst.This paper is mainly concerned with study ofthe deactivation mechanism and regeneration method of SCR catalyst.The deactivation mechanism of commercial de-NOx V₂O₅–WO₃/TiO₂catalysts whichwere used in Coal-fired power plant was investigated by means of characterizations via BET,XRD, XPS and TPO-MS. The result showed that there are amounts of carbonaceous speciesdeposited on the deactivated catalyst. Thus the application of ozone to regenerate thedeactivated catalysts was proposed. the activity tests showed that deactivated catalysts treatedby180mg/L ozone restored its activity obviously. By characterizations via BET, XRD, XPSand TPO-MS, it was found that after the regeneration with ozone, the carbonaceous specieson the surfaces of the catalyst was completely eliminated.The spent V₂O₅/TiO₂catalyst used in another power plant was characterized by SEM,EDS, XRD and BET techniques to reveal the deactivation mechanism. It was found that thespent catalyst was heavily covered by ash which blocked the active sites and plugged thepores, and the main composition of the ash was silicon dioxide and so on. Then, theregeneration of the spent V₂O₅/TiO₂catalyst was conducted by washing with aqueous solutionof0.5mol/L H₂SO₄and0.01mol/L hydrofluoric acid. The activity test showed that theregenerated catalysts which were washed by0.01mol/L hydrofluoric acid gained a significantincrease in its activity, which was ascribed to the good chemical encroaching effect ofhydrofluoric acid on silicon dioxide,then deactivated catalyst was washed by hydrofluoric acid in different concerntration,it was found that the regenerated catalyst1.0mol/LHF-Rwhich was washed by1.0mol/LHF gained90%conversion of fresh catalyst.The sulfur resistance stability of regenerated catalyst was studied, and the effect of Niloading on the regenerated catalyst which was washed by hydrofluoric acid wasdiscussed.The result showed that the impregnation of Ni on the regenerated catalyst canimprove its sulfur resistance stability. These may result from the decline in the number ofactive site for the oxidation of SO₂by the addition of Ni onto the regenerated catalyst whichwere washed by hydrofluoric acid.