Single atom alloy (SAA) catalysts are promising new catalytic materials that combine the unique reactivity of isolated active catalyst atoms, such as Rh, and a less reactive base metal, such as Cu. These materials have been shown to deviate from linear scaling relationships and offer the promise of catalysts that deliver both high reactivity and selectivity. To date, detailed experimental studies of SAA reactivity have largely focused on lower barrier reactions that can be studied using thermal activation under surface science conditions, or higher barrier reactions whose kinetics are studied at elevated pressures. Our goal is to extend the detailed mechanistic studies of reactions on SAA's to high-barrier reactions whose low reaction probabilities generally prevent their study under controlled surface science conditions.<br/><br/>This presentation will focus on our experimental approach and recent results. We use a supersonic molecular beam to prepare a high-flux stream of energy-selected reactants with a tunable translational kinetic energy up to 150 kJ/mol and a state-selected vibrational energy up to 40 kJ/mol. The hyperthermal molecules in the beam replicate those in the high-energy tail of the Maxwell-Boltzmann distribution, but with much higher flux than could be obtained in a thermal gas sample under low-pressure conditions. As a result, our approach delivers the reactive flux needed to study high-barrier reactions while maintaining low-pressure conditions for detailed spectroscopic and mechanistic characterization. We are using this capability to extend the range of SAA reactions studied under highly controlled conditions to include high-activation-barrier reactions, including those that require C-H bond activation. Our initial measurements will focus on C-H activation of light alkanes (methane and ethane) on Rh-Cu SAA's, and we plan to report on measured reaction probabilities and subsequent reactivity of adsorbed alkyl fragments on the SAA surface.

Beam-surface scattering studies of energetic reactants on single atom alloy catalysts

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