Structural changes of nano-Pt particles during thermal ageing: support-induced effect and related impact on the catalytic performances

The simultaneous reduction of NO and N2O has been investigated on Pt-based catalysts supported on γ-Al2O3 and perovskite materials (LaFeO3). Particular attention has been paid to the catalyst resistance to thermal sintering processes occurring under reaction conditions at elevated temperature in the presence of oxygen and water. Bulk and surface modifications have been examined using appropriate physicochemical techniques (H2-TPR, XPS, and HRTEM) and have been tentatively correlated to the catalytic performances in terms of activity and selectivity. It has been found that a significant particle growth occurs on 4 wt.% Pt/γ-Al2O3 having a strong detrimental effect on the conversion of N2O at high temperature. On the other hand, 4 wt.% Pt/LaFeO3 exhibits a higher resistance to thermal sintering. Such a behaviour has been explained by the occurrence of strong metal/support interactions highlighted by high resolution TEM observations. The formation of epitaxially oriented Pt particles on the LaFeO3 crystal lattice during thermal activation, still observable after thermal ageing would partly explain the best resistance of 4 wt.% Pt/LaFeO3 to deactivation towards the conversion of N2O at high temperature. Hence, supported catalysts on LaFeO3 with lower Pt loading were prepared. It has been finally found a striking enhancement of the catalytic performances, opening a new practical interest for minimising the noble metal loading

Support-Induced Effects of LaFeO3Perovskite on the Catalytic Performances of Supported Pt Catalysts in DeNOxApplications

International audienceA comparative investigation of the catalytic performance in the simultaneous conversion of NOx and N2O has been achieved on supported nanosized Pt particles interacting with conventional alumina and perovskite based materials. Particular attention has been paid to successive thermal treatments under reductive and oxidative atmospheres which induce bulk and surface reconstructions. Those modifications considerably alter the catalytic behavior of Pt in interaction with LaFeO3 or γ-Al2O3 in terms of activity and selectivity toward the selective transformation of NOx to nitrogen at low temperature. Changes in physicochemical properties have been examined using appropriate techniques, such as H2-temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) of CO adsorption. It has been found that oxidic Pt4+ species initially stabilized on LaFeO3 lead after subsequent H2 reduction to the formation of metallic nano-Pt particles in stronger interaction than on γ-Al2O3 support and then become more resistant to sintering during thermal aging in 1000 ppm NO, 1000 ppm N2O, 3 vol % O2, 0.5 vol % H2O, and 0.5 vol % H2 at 500 °C. Correlatively, significant improvements have been observed in the selective reduction of NOx to nitrogen. This study opens new prospects in the development of supported catalysts containing low Pt loadings because of the existence of stronger interactions with perovskite supports