| In order to remove the nitrogen oxides from flue gas, Cr-Ce/TiO2 catalysts were studied for the oxidation and reduction of NO in this paper. The following tasks were carried out:(1) The effects of molar ratio, loading of active component and calcination temperature along with the nature of supports on the performance of the catalytic oxidation of NO were examined. The microstructure of the catalysts calcined at different temperature was characterized by XRD and BET. The Cr-Ce/TiO2 which was calcined at 350 oC with total loading 30% and molar ratio Cr/Ce=2/1 showed perfect dispersity and stability. The high NO conversion of 80.7% was observed over it at 330 oC and space velocity 10,000 h-1.(2) The effects of operating condition on the catalytic oxidation of NO were also investigated. It was found that NO conversion increased with the enhancement of O2 concentration and decreased with the rise of NO concentration and GHSV.(3) The reaction kinetic equation was expressed as: rNO=kYNOaYO2b=332.62exp(-19968.93/RT)[NO]0.93[O2]0.21(4) The effects of H2O and SO2 on the catalytic oxidation of NO were studied by step transient response experiments and FTIR. H2O poisoning is reversible. After NO oxidation reaction in the presence of H2O and SO2, a few sulfates and sulfites were formed causing the irreversible deactivation of catalyst. The catalytic activity of deactivated Cr–Ce/TiO2 could recover mostly after heat treatment.(5) The effects of calcination temperature, molar ratio and loading of active component as well as operating condition on the performance of SCR were examined. The Cr–Ce/TiO2 catalyst showing high activity for catalytic oxidation of NO also performed high activity for NH3-SCR. The NO conversion of 99.6% was observed at 180℃and space velocity 10,000 h-1. NO conversion increased with the enhancement of O2 concentration and NH3/NO, and decreased with the rise of NO concentration and GHSV. The reaction of SCR followed Eley-Rideal mechanism.(6) The effects of H2O and SO2 on the performance of SCR were studied by step transient response experiments and FTIR. The 10% (φ) H2O had little negative effect on catalytic activity, and the NO conversion was kept at level of 97.7%. The catalyst was deactivated irreversiblly in the presence of SO2 due to the generation of excess amount of sulfate salts. The catalyst is expected to be applied to the removal of NOx from exhaust gas without SO2 at low temperature.
|
PDF Full Text Request