Rational design of novel CrZrOx catalysts for efficient low temperature SCR of NOx

Abstract

Novel CrZrOx catalysts were designed and synthesized by the co-precipitation method and the first time used for selective catalytic reduction of NOx with NH3 (NH3-SCR). The promotional effect of ZrO2 on Cr2O3 catalysts was investigated. The SCR performance of Cr2O3 was significantly enhanced with the appropriate addition of ZrO2 in CrZrOx, owing to the formation of solid solution structure and Cr-O-Zr conjunction bonds. Among the tested CrZrOx catalysts, the catalyst with Cr:Zr = 1:1 showed the optimal NOx removal efficiency at low temperatures, with the highest NO removal efficiency of 97.5% at 180 °C , excellent SO2 and H2O resistance at 300 °C with 50 ppm SO2 and 5% H2O. It appears that the reaction mechanisms followed the Langmuir-Hinshelwood model and NH3*, NH4+*, monodentate nitrates and nitrites were the major active intermediate species. The structure change modified the surface properties of the CrZrOx catalyst, increasing the concentrations of the acid sites, surface adsorbed oxygen Oa and Cr6+, which were responsible for the enhancement of SCR performance.