Al-anchored platinum catalysts on reducible supports: High-temperature stability against redispersion during methane oxidation

The deactivation of noble metal catalysts due to the loss of active surface area, remains a significant challenge, especially under high-temperature oxidizing conditions. Such demanding conditions are often found in emission control systems for clean air application and during catalyst regeneration targeting to prolong the lifetime of a catalyst reducing the environmental costs associated to the process. The development of highly active catalysts with enhanced stability demands the synthesis of novel catalyst structures. However, novel catalyst formulations must rely on abundant additives to remain cost competitive and to find industrial application. Herein, we systematically explore the impact of doping support oxide surfaces (silica and titania) with AlOx and TiO$_x$ species on the activity and stability of platinum catalysts during complete methane oxidation. Conventional supports were compared with surface-modified silica supports with dispersed TiO$_x$ or AlO$_x$ species, prepared by facile wet chemistry-based surface modification (Pt/Ti-doped SiO$_2$, Pt/Al-doped SiO$_2$). While Pt/TiO$_2$ demonstrated high initial activity, it suffered severe deactivation due to platinum redispersion. ... mehrConversely, Pt/Ti-doped SiO$_2$ and Pt/Al-doped SiO$_2$ showed less activity than Pt/TiO$_2$ but enhanced stability and higher long-term activity. Consequently, AlO$_x$-doping of the rate-promoting titania surface yielded both high activity and stability, demonstrating that AlO$_x$ surface species prevent PtO$_x$ from migrating into the titania pocket sites that stabilize mono-dispersed platinum species. Additionally, AlO$_x$-doping prevented the partial anatase-rutile phase transformation of the TiO$_2$, which was observed for the unmodified Pt/TiO$_2$ catalyst. Combining the strong binding properties of alumina with the catalytic advantages of reducible oxides is a novel strategy for designing robust, high-temperature catalysts.