Synergic effect of Cu/Ce0.5Pr0.5O2-δ and Ce0.5Pr0.5O2-δ in soot combustion

• Cu/Ce0.5Pr0.5O2-δ catalysts are active in soot oxidation.
• Soot combustion activity is enhanced in the presence of Cu/Ce0.5Pr0.5O2-δ and Ce0.5Pr0.5O2-δ.
• Reduction of Ce and Pr in Ce0.5Pr0.5O2-δ is promoted to lower temperatures by copper.
• Cu supported on Ce0.5Pr0.5O2-δ particles promotes the NOx-assisted mechanism.
• Oxidation of soot over Ce0.5Pr0.5O2-δ occurs through the active oxygen mechanism.

A series of 5%Cu/Ce0.5Pr0.5O2-δ and Ce0.5Pr0.5O2-δ mixed oxides have been prepared and combined in different ratios. The resulting catalysts have been characterized by N2 adsorption, XRD, Raman spectroscopy and H2-TPR and tested for soot combustion by means of temperature-programmed experiments. The optimum catalyst for soot combustion in NOx/O2/N2 atmosphere is the mixture containing 40% Cu/Ce0.5Pr0.5O2-δ and 60% Ce0.5Pr0.5O2-δ. This mixture is more active than a reference catalyst containing the same amount of copper distributed in the whole Ce-Pr mixed oxide support. The benefit of mixing Ce0.5Pr0.5O2-δ particles with and without copper in a single catalyst formulation is that the participation of the two soot combustion mechanisms based on active oxygen and NO2, respectively, is optimized. The particles with copper mainly promote the catalytic oxidation of NO to NO2 (the NOx-assisted mechanism) while those without copper are more effective in promoting the active oxygen mechanism. If copper is loaded homogeneously in all the Ce0.5Pr0.5O2-δ particles, the positive effect of copper improving NO2 production is offset by the lower efficiency of the active oxygen mechanism, due to a lack of active oxygen on the Ce0.5Pr0.5O2-δ support.

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