Comparative study of transition metal (Mn, Fe or Co) catalysts supported on titania: Effect of Au nanoparticles addition towards CO oxidation and soot combustion reactions

Manganese, iron and cobalt oxides were supported on TiO2 by deposition-precipitation with urea method then gold nanoparticles were added as a second active phase. The catalysts were evaluated for soot combustion and CO oxidation to elucidate the individual and combined effect of both supported phases. The physicochemical characterization revealed that Mn, Fe and Co were in the form of oxides while Au was in metallic state. The catalytic evaluation for the soot combustion reaction showed a remarkable increase in the activity when the transition metal phase was dispersed on TiO2. It is noteworthy that the performance of the MnOx/TiO2 and CoOx/TiO2 catalysts was superior because they exhibited higher lattice oxygen mobility than the FeOx/TiO2 catalyst, while the effect of Au nanoparticles was to increase selectivity towards CO2. On the other hand, for the CO oxidation, Au active sites were essential and played an important role in carrying out the reaction at lower temperatures. The remarkable activity in the Au-CoOx/TiO2 and Au-FeOx/TiO2 catalysts suggests a promoting effect caused by the combination of the transition metal oxides and Au nanoparticles which helped create new adsorption sites at Au-MOx interfaces for the adsorption and activation of O-2 molecules.