Low temperature SCR denitration with NH₃ by highly dispersed Ni–Cu Sites: An insight into surface acidity and redox ability

Surface acidity and redox ability are critical factors affecting the NH₃ and NO adsorption-activation in the selective catalytic reduction of NO_x with NH₃ (NH₃-SCR). Herein, Cu_yNi_3-yAlO_x (y represents the Cu/Al ratio) mixed oxides with highly dispersed Ni-Cu dual active sites were constructed from the layered double hydroxide precursors to optimize the acidity and redox ability. Compared with other Cu_yNi_3-yAlO_x (<80%), Cu_1.5Ni_1.5AlO_x delivered a NO_x conversion as high as 90% at 200 °C. Moreover, Cu_1.5Ni_1.5AlO_x possessed superior N₂ selectivity (92% above 200 °C), catalytic stability (64 h), and H₂O and SO₂ resistance. Characterization demonstrated that Cu and Ni species in Cu_yNi_3-yAlO_x had interactions, and the interactions were derived from the electron transfer and influenced by the Ni/Cu ratio, inducing the formation of highly dispersed Ni–Cu sites. Cu_1.5Ni_1.5AlO_x with a Ni/Cu ratio of 1 achieved the strongest interaction. That interaction could inhibit nanosheet agglomeration, increase surface acidity, and improve low-temperature reducibility, in favor of NH₃ and NO adsorption/activation. It was discovered that the Ni–Cu sites participated in the NO and O₂ activation, respectively, and accounted for the NH₃ adsorption-activation, synergistically. More active intermediates (NH₃/NH₄⁺, bridging/bidentate nitrate) were produced by Langmuir-Hinshelwood and Eley-Rideal mechanisms over Cu_1.5Ni_1.5AlO_x. This study offered light on fabricating effective functionalized active sites to promote NH₃-SCR performance.