Simultaneous reduction of NOx and decomposition of N2O over Fe and Cu zeolite catalysts
Fe-Beta and Cu-SSZ-13 catalysts were prepared by ion-exchange method,and composite catalysts were prepared using different mixing methods.Performance of the catalysts in catalyzing NOx reduction and N2O decomposition at the same time was investigated.Fe0.4Cu0.1catalyst,which was composed of Fe-Beta in the top layer and Cu-SSZ-13 in the bottom layer with mass ratio of 4:1,performed the best in catalyzing the removal of NOx and N2O simultaneously and broadening the reactive temperature window.Effects of inlet gas composition on the conversion of NOx,N2O,and NH3 were investigated.Physicochemical characteristics of the catalysts were characterized by N2 adsorption-desorption,XRD,NH3-TPD,UV-Vis DRS and H2-TPR techniques.The results showed that Cu-SSZ-13 and Fe-Beta had superior performance in catalyzing NOx reduction and N2O decomposition,respectively.In the tested temperature range,NOx was reduced by NH3 while N2O was decomposed over Fe0.4Cu0.1 when[NH3]/[NOx]was 1.NOx and N2O conversion reached 93.4%and 100%,respectively at 450℃.Oxidation of NH3 by O2 at high temperatures(>350℃)leads to decrease in NOx conversion with increasing temperature.And the formation of oxygen species from the decomposition of N2O at high temperatures(≥350℃)explains the efficient NOx reduction without O2 in the inlet gas.The presence of 2%H2O in the inlet gas hardly affected the reduction of NOx and oxidation of NH3 over Fe0.4Cu0.1 at high temperature(450℃),but did show reversible inhibitory effects on the conversion of N2O.Abundant isolated Cu2+ions were detected over Cu-SSZ-13,providing sufficient active centers for the NH3-SCR reaction.Both isolated Fe3+ions and FexOy species,which can catalyze NO oxidation and N2O decomposition,respectively,were detected over Fe-Beta.Using the top-Fe-bottom-Cu composite catalyst,NO oxidation occurs over Fe-Beta,which consumes oxygen species formed from N2O decomposition and thus promotes the conversion of N2O at low temperatures(≤450℃).However,the promotion effect of NO oxidation on NOx reduction was insignificant since NOx conversion was rather high in the temperature range for effective N2O decomposition.
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