Catalytic reduction of NO by CO over Cu/CexZr1- xO2 prepared by flame synthesis

Mixed oxides of 4% Cu/Ce_xZr_1-xO ₂ (x = 0, 0.25, 0.50, 0.75, 1) were synthesized by flame spray pyrolysis and characterized by N₂ adsorption, XRD, XPS, O ₂-TPD and H₂-TPR. The as-prepared catalysts were assessed for the equimolar reduction of NO by CO (3000 ppm each, space velocity 50,000 h^-1). Incorporation of Zr⁴⁺ in the form of solid solution with CeO₂ stabilizes the Cu⁺ species, which was in turn beneficial for the initial reductive chemisorption of NO to N₂O. A peculiar low-temperature activity giving 40% N₂ yield was found with the composition of Cu/Ce_0.75Zr_0.25O₂ at 150 °C. This is traced to the low-temperature activation of rapid CO oxidation (as probed by in situ DRIFTS), related to the abundance of surface reactive lattice oxygen sites and their high reducibility. At 250 °C and above, a N₂ yield of >85% (and ∼100% at 350 °C) was obtained for all Zr-containing catalysts i.e. Cu/Ce_xZr_{1- x}O₂ (x <1.0), with essentially no intermediate N ₂O detected in the exhaust gas stream. An organonitrogen mechanism is occurring in this case. © 2010 Elsevier Inc.