Preparation and Evaluation of Copper Manganese Oxide as a High-Efficiency Catalyst for CO Oxidation and NO Reduction by CO

In this work, highly efficient Cu-x-Mn composite catalysts (0 <= x <= 0.20) were synthesized by an improved hydrothermal-citrate complex method and tested in the catalytic total oxidation of CO and the removal of NO by CO. The influence of Cu on manganese oxide materials was characterized by several techniques, including FESEM, HRTEM, XRD, BET analysis, H-2 TPR, O-2 TPD, XPS, and DRIFTS. Possible reaction mechanisms for the NO + CO model reaction and CO oxidation were also tentatively proposed. The Cu-modified manganese oxide materials showed higher catalytic activity in CO oxidation and the selective catalytic reduction (SCR) of NO with CO than pure MnOx materials. The improved catalytic activity in CO oxidation observed for the copper-manganese oxide catalyst was associated with a greater amount of adsorbed oxygen species and high lattice oxygen mobility due to the formation of a Cu1.5Mn1.5O4 spinel active phase (Cu-x(2+)-Mn-x(3+)-[O(y-z)circle dot(z)] species). Furthermore, in terms of the CO-SCR model reaction, the surface-dispersed Cu-x+-O-2-Mny+ active species could be reduced to a Cu+-rectangle-Mn(4x)+ active species, which was considered to be the primary active component in the reduction of NO by CO. The results of the catalytic performance testing indicated that Cu0.075Mn had the highest catalytic activity in CO oxidation, whereas Cu0.15Mn exhibited the best CO-SCR catalytic performance.