Synergistic effect between copper and cerium on the performance of Cu_x-Ce_0.5-x-Zr_0.5 (x = 0.1–0.5) oxides catalysts for selective catalytic reduction of NO with ammonia

A series of Cu_x-Ce₀._5-x-Zr_0.5 oxides catalysts with different Cu/Ce ratio were synthesized by citric acid method. The catalysts were characterized by XRD, BET surface area, H₂-TPR, NH₃-TPD, NO-TPD, XPS and in-situ DRIFTS. The synergistic effect between copper and cerium on the catalytic performance of Cu_x-Ce₀._5-x-Zr_0.5 for selective catalytic reduction of NO with ammonia was investigated. It was found that the Cu_0.2-Ce_0.3-Zr_0.5 catalyst show the excellent SCR activity, N₂ selectivity and H₂O/SO₂ durability in a low temperature range of 150–270 °C even at high gas hourly space velocity of 84,000 h⁻¹. The strong interaction leads to the improvement of the acidity and the increase in the amount of active oxygen species (oxygen vacancy), which are responsible for the higher activity at low temperatures. The SCR reaction process over Cu_0.2-Ce_0.3-Zr_0.5 was also examined using in-situ DRIFTS. The DRIFTS results indicate that abundant ionic NH₄⁺ (Brønsted acid sites), coordinated NH₃ on the Lewis acid sites, as well as highly active monodentate nitrate and bridging nitrate species were the key intermediates in the SCR reaction.