Enhanced Catalytic Activity and SO2/H2O Tolerance for Selective Catalytic Reduction of NOx with NH3 over Titanate Nanotubes Supported MnOx–CeO2 Catalyst at Low Temperature

Abstract

An environment-friendly selective catalytic reduction (SCR) catalyst with high catalytic activity and strong anti-poisoning performance at low temperature is strongly needed to achieve the wide application of low temperature NH₃-SCR technology. Selection of appropriate carrier is one of the most important measures to improve catalytic activity as well as anti-poisoning capability of SCR catalyst. Manganese oxide-cerium oxide supported on traditional titanium dioxide (denoted as MnCe/TiO₂) and titanate nanotubes (denoted as MnCe/TiNTs) were prepared by impregnation method and their catalytic activities towards NH₃-SCR of NO were evaluated in flue gas with or without SO₂ & H₂O. The results indicate that TiNTs with optimum morphology and microstructure can be obtained when P25 TiO₂ is hydrothermally treated at 130 °C for 24 h. Supporting MnO_x–CeO₂ composite on TiNTs not only enhances the catalytic activity at low temperature, but also improves N₂ selectivity and widens active temperature window of catalyst. The main reason is the large specific surface area as well as the unique hollow tubular structure of TiNTs facilitates high dispersion of catalytic active components on the inner and outer walls of TiNTs, which enriches surface acid sites and surface reactive oxygen species to fulfill low temperature SCR reaction cycle. Moreover, TiNTs significantly enhances the SO₂ & H₂O tolerance of catalyst, for the competitive adsorption between SO₂, H₂O and reactants is alleviated and the deposition of ammonium sulphate or ammonium bisulphate becomes more difficult on MnCe/TiNTs catalyst. Besides, the confinement effect of TiNTs makes partial toxicants be trapped inside the tubular channel of TiNTs. So that protects the active components, which are distributed on the out wall of TiNTs, from being poisoned.