(251b) High Reactivity Of Pt-Bha Nanocomposite Catalysts For Combustion Reactions

The large surface areas and reports of novel chemical reactivity make nanomaterials highly interesting for heterogeneous catalysis. The low stability of nanoparticles, however, typically restricts their use in reactive environments, in particular at high temperature conditions. We previously demonstrated the successful synthesis of unusually active and sinter-resistant nanocomposite materials which combine the high reactivity of nano-sized noble metal particles with the excellent high-temperature (~1000°C) stability of hexa-aluminates. In this contribution, we present the results of catalytic testing of these nanocomposite materials for two reactions: low-temperature CO oxidation and methane combustion. These reactions scan a wide range of reaction temperatures, and thus allow testing the versatility of these nanocomposite materials. For methane combustion, the ignition of highly dilute mixtures (1vol% CH4 in air) was investigated in a flow-tube reactor over a temperature range of 673-973 K. We find that 1wt% and 10wt% Pt-BHA catalyst reduce the ignition temperature by ~50-100 K compared to a pure BHA material. Furthermore, the catalyst does not show any signs of deactivation over repeated ignition cycles, demonstrating once again the excellent high-temperature stability of these nanocomposites. Low-temperature CO oxidation was performed by saturating a Pt-BHA sample with CO and then introducing oxygen at total pressures up to PO2 ~ 0.5 Torr. The reaction progress was monitored via FTIR over a temperature range of 200 ? 300 K. We find an activation energy for CO oxidation over Pt-BHA of ~9 kJ/mol, which is about three times lower than previously published values for more conventional Pt catalysts, indicating the exceptional high reactivity of these nanocomposite catalysts. It appears therefore that the embedding of metal nanoparticles into a nanostructured ceramic matrix allows to reconcile demands for high reactivity and high stability at reaction conditions.