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

Mixed oxides of 4% Cu/CexZr1−xO2 (x = 0, 0.25, 0.50, 0.75, 1) were synthesized by flame spray pyrolysis and characterized by N2 adsorption, XRD, XPS, O2-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/Ce0.75Zr0.25O2 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/CexZr1−xO2 (x < 1.0), with essentially no intermediate N2O detected in the exhaust gas stream. An organonitrogen mechanism is occurring in this case.