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

摘要

The simultaneous reduction of NO and N_2O has been investigated on Pt-based catalysts supported on γ-Al_2O_3 and perovskite materials (LaFeO_3). 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 (H_2-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-Al_2O_3 having a strong detrimental effect on the conversion of N_2O at high temperature. On the other hand, 4 wt.% Pt/LaFeO_3 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 LaFeO_3 crystal lattice during thermal activation, still observable after thermal ageing would partly explain the best resistance of 4 wt.% Pt/LaFeO_3 to deactivation towards the conversion of N_2O at high temperature. Hence, supported catalysts on LaFeO_3 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.