Active oxygen by Ce–Pr mixed oxide nanoparticles outperform diesel soot combustion Pt catalysts

A Ce0.5Pr0.5O2 mixed oxide has been prepared with the highest surface area and smallest particle size ever reported (125 m2/g and 7 nm, respectively), also being the most active diesel soot combustion catalyst ever tested under realistic conditions if catalysts forming highly volatile species are ruled out. This Ce–Pr mixed oxide is even more active than a reference platinum-based commercial catalyst. This study provides an example of the efficient participation of oxygen species released by a ceria catalyst in a heterogeneous catalysis reaction where both the catalyst and one of the reactants (soot) are solids. It has been concluded that both the ceria-based catalyst composition (nature and amount of dopant) and the particle size play key roles in the combustion of soot through the active oxygen-based mechanism. The composition determines the production of active oxygen and the particle size the transfer of such active oxygen species from catalyst to soot.

Effect of the CeZrNd mixed oxide synthesis method in the catalytic combustion of soot

Ce0.64Zr0.27Nd0.09Oδ mixed oxides have been prepared by three different methods (nitrates calcination, coprecipitation and microemulsion), characterized by N2 adsorption, XRD, H2-TPR, Raman spectroscopy and XPS, and tested for soot combustion in NOx/O2. The catalyst prepared by microemulsion method is the most active one, which is related to its high surface area (147 m2/g) and low crystallite size (6 nm), and the lowest activity was obtained with the catalyst prepared by coprecipitation (74 m2/g; 9 nm). The catalyst prepared by nitrates precursors calcination is slightly less active to that prepared by microemulsion, but the synthesis procedure is very straightforward and surfactants or other chemicals are not required, being very convenient for scaling up and practical utilization. The high activity of the catalyst prepared by nitrates calcination can be attributed to the better introduction of Nd cations into the parent ceria framework than on catalysts prepared by coprecipitation and microemulsion, which promotes the creation of more oxygen vacancies.

Opportunities for ceria-based mixed oxides versus commercial platinum-based catalysts in the soot combustion reaction. Mechanistic implications

The aim of this paper is to study the activities of ceria–zirconia and copper/ceria–zirconia catalysts, comparing with a commercial platinum/alumina catalyst, for soot combustion reaction under different gas atmospheres and loose contact mode (simulating diesel exhaust conditions), in order to analyse the kinetics and to deduce mechanistic implications. Activity tests were performed under isothermal and TPR conditions. The NO oxidation to NO2 was studied as well. It was checked that mass transfer limitations were not influencing the rate measurements. Global activation energies for the catalysed and non-catalysed soot combustion were calculated and properly discussed. The results reveal that ceria-based catalysts greatly enhance their activities under NOx/O2 between 425 °C and 450 °C, due to the “active oxygen”-assisted soot combustion. Remarkably, copper/ceria–zirconia shows a slightly higher soot combustion rate than the Pt-based catalyst (under NOx/O2, at 450 °C).