Roles of Lewis and Brønsted acid sites in NO reduction with ammonia on CeO2-ZrO2-NiO-SO42− catalyst

Nickel and sulfate co-modified CeO2-ZrO2 catalysts were prepared by sol-gel method. The catalysts were characterized by XRD, FTIR, XPS, NH3 chemisorption and NH3-SCR activity tests. The results showed that the enhanced acidity of CeO2-ZrO2 catalysts by nickel and sulfate co-modification was responsible for the broadened temperature window and improved the selectivity to N2 in NH3-SCR deNOx. The introduction of nickel to CeO2-ZrO2 solid solutions resulted in more Ce3+ on surface of catalyst, leading to an increased Lewis acidity of catalyst. Higher Lewis acidity of catalyst facilitated ammonia activation at low temperature (<300 °C) and thereby improved the NH3-SCR activity. The enhanced high-temperature (>300 °C) activity and selectivity of catalysts arose from the introduction of Brønsted acid sites (less oxidative than Lewis acid sites) by sulfate modification.