Simultaneous catalytic oxidation of carbon monoxide, hydrocarbons and soot with Ce-Zr-Nd mixed oxides in simulated diesel exhaust conditions

Ce0.73-xZr0.27NdxO2 mixed oxides (x <= 0.3) were prepared, characterized by XRD, Raman spectroscopy, N-2 adsorption isotherms and H-2-TPR, and tested for simultaneous CO, propylene, benzene and soot oxidation in a gas mixture containing O-2, NOx, H2O, CO2, CO, propylene (model aliphatic hydrocarbon) and benzene (model aromatic hydrocarbon) that simulates a diesel exhaust. Ce-Zr mixed oxide doping with a low atomic fraction of neodymium (0.01 <= x <= 0.09) promotes the creation of oxygen vacancies, has a minor effect in the BET specific surface areas of the oxides, increases the surface ceria reducibility and has a positive effect in the catalytic activity. On the contrary, higher neodymium atomic fractions (x=0.2 and 0.3) promote sintering, with a drastic decrease of the BET specific surface area, surface reducibility and catalytic activity. The Ce0.73-xZr0.27NdxO2 catalysts with x <= 0.09 are able to accelerate simultaneously soot, propylene and benzene combustion, and as a general trend, the catalytic behavior of Ce0.73Zr0.27O2 is improved by low atomic fraction neodymium doping (0.01 <= x <= 0.09). These Ce0.73-xZr0.27NdxO2 mixed oxides with 0.01 <= x <= 0.09 are also able to accelerate CO oxidation in a certain extent, but there is a net production of CO during soot combustion because the oxidation capacity of these oxides is not high enough to oxidize all CO released as soot combustion product. (C) 2014 Elsevier B.V. All rights reserved.