Modification of CrCeOx with Mo: improved SO2 resistance and N2 selectivity for NH3-SCR at medium–low temperatures

Abstract

NH₃-SCR at medium and low temperatures is an effective method for the removal of nitrogen oxides (NO_x) in industrial furnaces. Chromium (Cr) and cerium (Ce) based catalysts exhibit excellent NH₃-SCR potential at medium and low temperatures, but their sulfur resistance and N₂ selectivity need to be further improved. In this manuscript, the Mo(0.3)–CrCeO_x catalyst was synthesized via the citric acid method, and showed high catalytic activity with excellent sulfur resistance and N₂ selectivity. The mechanism of Mo doping was investigated. The highly dispersed amorphous MoO₃ was found, forming a Mo–O–Ce structure and generating more strong acid sites. The mechanism of Mo doping for enhanced SO₂ resistance and N₂ selectivity was further investigated by in situ DRIFTS. By effectively modulating the catalyst basicity, the generation of the active intermediate cis-N₂O₂²⁻ species was promoted. The change from the E–R to L–H mechanism is the key. The strong oxidation of Cr⁶⁺ species was appropriately suppressed, thus the N₂ selectivity was improved. It also prevents SO₂ from competing for basic sites on Cr species. In a word, all the improved performances were attributed to Mo doping. Finally, the SCR process is proposed.