La promoted CuO-MnOx catalysts for optimizing SCR performance of NO with CO

Highlights: • La promoted CuO-MnO_x catalysts with different La/(Cu + Mn) molar ratios were constructed by co-precipitation method. • La-oxide controlled the CuO and MnO_x size to enable the strong synergistic interaction between ternary oxides. • The real active sites in La-Cu-Mn-O catalysts for DeNO_x reaction were discussed. • A possible catalytic mechanism of La-Cu-Mn-O complex for NO + CO model reaction was proposed. La-Cu-Mn-O catalysts with different La contents were prepared and evaluated for low-temperature selective catalytic reduction of NO by CO (CO-SCR) to study the structure–activity relationship. The results demonstrated that lanthanum was conducive to the decrease in the size of copper and manganese and preventing their agglomeration, enabling the enhancement in reducibility of the catalysts, which promotes the increase in exposed active sites and the reactivity between reactants (NO and CO). Furthermore, La³⁺ gains advantages from enhancing the redox couples of Mn⁴⁺+Cu⁺↔Mn³⁺+Cu²⁺, leading to the formation of high-proportioned active ions (Cu²⁺ and Mn³⁺) and surface oxygen defects in abundance, which favors the generation of numerous Cu^x+-□-La³⁺-□-Mn^y+ species (x = 2 or 1 and y = 3 or 4, □represents a surface synergetic oxygen vacancies). The abundant synergistic nodes promote the dissociation of NO and the transfer of dissociated oxygen, making the conversion of NO reach 100% at about 250 °C to reduce the active temperature. According to the in-situ DRIFTS results, we proposed a reasonable reaction mechanism for further understanding the routes in the NO + CO model reaction.