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

Abstract

Surface acidity and redox ability are critical factors affecting the NH3 and NO adsorption-activation in the selective catalytic reduction of NOx with NH3 (NH3-SCR). Herein, CuyNi3-yAlOx (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 CuyNi3-yAlOx (<80%), Cu1.5Ni1.5AlOx delivered a NOx conversion as high as 90% at 200 °C. Moreover, Cu1.5Ni1.5AlOx 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 CuyNi3-yAlOx 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. Cu1.5Ni1.5AlOx 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 Cu1.5Ni1.5AlOx. This study offered light on fabricating effective functionalized active sites to promote NH3-SCR performance.