Insights into copper-ZSM-5 supported cerium, zirconium catalysts to promote NH3-SCR activity and anti-thermal aging performance

Abstract

The effects of cerium and cerium + zirconium supported over Cu-ZSM-5 on SCR activity and anti-thermal aging performance in NOx abatement have been studied. X-ray diffraction, scanning electron microscopy, UV–vis diffuse reflectance, temperature-programmed technologies, Fourier transform infrared spectroscopy, and in-situ diffuse reflectance infrared Fourier transform spectroscopy were used to characterize the surface properties and transition-state species of the catalysts. The 6 %Ce-2 %Zr/Cu-ZSM-5 catalyst exhibits excellent NOx purification activity under dry and water vapor conditions and the best thermal aging resistance. Copper and zirconium species formed are in the nanometer size range and are well dispersed on the ZSM-5 surface, and cerium was formed with the low crystallinity of CeO2 as an increase of cerium content. Cerium and zirconium addition improve copper dispersion and the cooperative effect between copper and cerium/zirconium. Zirconium can promote the presence of copper in the form of ionic state rather than oxides, improve copper species dispersion, assist to stabilize the framework of ZSM-5, and prevent copper cations precipitation sintering. There were no obvious correlations between acid site strength and the SCR catalytic activity. The NH3-SCR reaction over 6 %Ce-2 %Zr/Cu-ZSM-5 catalyst co-follows the Eley-Rideal and Langmuir-Hinshelwood mechanism.