Mechanistic aspects of NH3-SCR reaction over CeO2/TiO2-ZrO2-SO42− catalyst: In situ DRIFTS investigation

The solid superacid TiO2-ZrO2-SO42−-supported 20 wt.% CeO2 catalyst (20CeO2/Ti-Zr-S) was synthesized for selective catalytic reduction of NO with NH3 (NH3-SCR). The NH3-SCR performance was significantly enhanced by the construction of strong acid sites on the surface of 20CeO2/Ti-Zr-S and over 96% NO conversion was obtained at 225–425 °C. Meanwhile, the strong interaction between solid superacid and CeO2 resulted in excellent redox property and abundant surface oxygen species. Furthermore, the NH3-SCR reaction over 20CeO2/Ti-Zr-S catalyst mainly followed the Langmuir-Hinshelwood mechanism at low-temperature (250 °C). The M-NO2 (M = Ce, Ti, Zr) nitrate compounds, monodentate and bridging nitrates were the crucial intermediates in Langmuir-Hinshelwood mechanism. In addition, amide (–NH2) species were available at 350 °C over 20CeO2/Ti-Zr-S catalyst, which facilitated the high-temperature NH3-SCR activity via Eley-Rideal pathway.