Improving ceria-zirconia soot combustion catalysts by neodymium doping

Abstract

The effect of Nd doping on the physicochemical and catalytic properties for soot combustion of CeO2 and CeO2-ZrO2 oxides has been studied. Four oxides with composition CeO2, Ce0.9Nd0.1O2, Ce0.73Zr0.27O2 and Ce0.64Zr0.27Nd0.09O2 have been prepared by co-precipitation and calcination at 800 °C, characterized by XRD, Raman Spectroscopy, N2 adsorption and temperature programmed reduction by H2, and tested for soot combustion with NOx/O2. The catalytic activity for soot combustion of CeO2 and Ce0.9Nd0.1O2 was null due to thermal sintering (1 and 5 m2/g, respectively), and Zr-doping is mandatory to prevent such sintering. The best catalytic activity for soot combustion was obtained with Ce0.64Zr0.27Nd0.09O2 (37 m2/g), and as far as we know, it is the first time that this improvement on Ce-Zr soot combustion capacity by Nd doping is reported. Ce0.64Zr0.27Nd0.09O2 combines the beneficial effect of both Zr doping (improved thermal stability and redox properties) and Nd doping (additional benefit on redox properties by oxygen vacancies creation due to 3+ cations doping into the lattice). The highest activity for soot combustion of Ce0.64Zr0.27Nd0.09O2 is related with its highest NO oxidation capacity. As deduced by in situ DRIFTS experiments, Nd-doping into the Ce-Zr oxide favors the formation of less stable surface nitrogen species (nitrates and nitrites were detected) in comparison to those formed on Ce0.73Zr0.27O2 (only nitrates were detected) providing alternative and faster NO2 production pathways.