(549b) The Effect Of Calcination Conditions On Structure And Properties Of Pt-Bha Nanocomposites

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 that the embedding of metal nanoparticles into a nanostructured ceramic matrix results in unusually active and sinter-resistant nanocomposite materials which combine the high reactivity of metals with the excellent high-temperature (~1000°C) stability of ceramics. The synthesis of these nanocomposites is based on a reverse microemulsion-templated sol-gel route. While such microemulsion-templating offers a versatile platform and is widely used in nanomaterials synthesis, it typically results in residual surfactant remaining on the nanomaterial surface or in the nanomaterial structure and hence blocking and/or altering the active site available for catalytic reactions. Despite the importance of these residual surfactants, very little effort has been devoted to the study of this effect. In the present contribution we report the investigation of the influence of calcination conditions on structure, stability, and reactivity of these nanocomposites. Metal nanoparticle size (TEM), pore structure (BET), specific surface area (chemisorption), and catalytic reactivity were monitored as a function of calcination conditions over a wide range of temperatures (473 - 1473 K) for a Pt - barium hexaaluminate (Pt-BHA) nanocomposite catalyst. We find strong evidence of a particle caging effect by the pore network of the hexa-aluminate phase. Furthermore, calcination in air or hydrogen alone was less effective in removing the residual surfactant and exposing the full metal surface area than a combination of both. This can be explained by a rapid and efficient removal of residual surfactant without significant platinum particle growth. Correspondingly, we find higher reactivity of these materials as evidenced by lowered ignition temperatures in methane combustion.