(7f) Unveiling the Mechanisms Underpinning Highly Active and Stable Emissions Control Catalysts

Correlating a catalyst’s physical and electronic structure to its activity and stability throughout a reaction is vital for developing cost-effective, high-performance materials. In this context, bimetallic alloys are one of the most important classes of heterogeneous catalysts because they can exhibit improved performance compared to monometallic systems while reducing the amount of scarce or expensive metals required. This presentation highlights our work investigating the fundamental mechanisms underpinning the exceptional activity of Pt alloy emission control catalysts. We demonstrate that incorporating small amounts (~10% atomic fraction) of base metal (Cu, Ni, Co) into Pt nanocrystal catalysts enhances their activity for a probe reaction (propene oxidation) up to an order of magnitude. Electronic structure calculations utilizing our newly developed alpha scheme model illustrate how the base metal alters the surface Pt electronic structure, modifying the binding of C_xH_y* and O* intermediates. Furthermore, kinetic measurements show that these highly active Pt alloys deactivate over time. These deactivated catalysts remain more active and exhibit distinct rate dependencies for adsorbed C_xH_y* and O* species compared to pure Pt catalysts. We then employ operando spectroscopic techniques (XAS, DRIFTS) to elucidate the deactivation mechanisms of these catalysts, revealing two processes: 1) rapid oxidation and partial segregation of the base metal and 2) gradual catalyst poisoning due to strongly bound intermediates. Finally, we show that this poisoning deactivation mechanism can be suppressed by interfacing these Pt alloy catalysts with an oxygen-donating support (Mn₂O₃), resulting in active and stable catalysts. This work presents a versatile approach for studying and designing Pt alloy catalysts tailored for low-temperature hydrocarbon oxidation reactions and beyond.