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The activation of reactants by catalytically active metal sites at metal-oxide interfaces is important for understanding the effect of metal-support interactions on nanoparticle catalysts and for tuning activity and selectivity. Using a combined experimental and theoretical approach, we studied the activation of H2 and the effect of CO poisoning on isolated Rh atoms completely or partially covered by a copper oxide (Cu2O) thin film. Temperature programmed desorption (TPD) experiments conducted in ultra-high vacuum (UHV) show that neither a partially nor a fully oxidized Cu2O layer grown on a Rh/Cu(111) single-atom alloy can activate hydrogen in UHV. However, in situ ambient pressure X-ray photoelectron spectroscopy (AP-XPS) experiments performed at elevated H2 pressures reveal that Rh significantly accelerates the reduction of these Cu2O thin films by hydrogen. Remarkably, the fastest reduction rate is observed for the fully oxidized sample with all Rh sites covered by Cu2O. Both TPD and AP-XPS data demonstrate that these covered Rh sites are inaccessible to CO, indicating that Rh under Cu2O is active for H2 dissociation but cannot be poisoned by CO. In contrast, an incomplete oxide film leaves some of the Rh sites exposed and accessible to CO, and hence prone to CO poisoning. Density functional theory calculations demonstrate that unlike many reactions in which hydrogen activation is rate limiting, the rate-determining step in the dissociation of H2 on thin-film Cu2O with Rh underneath is the adsorption of H2 on the buried Rh site, and once adsorbed, the dissociation of H2 is barrierless. These calculations also explain why H2 can only be activated at higher pressures. Together, these results highlight how different the reactivity of atomically dispersed Rh in Cu can be depending on its accessibility through the oxide layer, providing a way to engineer Rh sites that are active for hydrogen activation but resilient to CO poisoning. 

Cu-based catalysts are ubiquitous in many industrial reactions, including methanol synthesis. Under partially oxidizing conditions, Cu catalysts can have dynamic surface structures that greatly influence their reactivities. Therefore, elucidating the surface structures that are present on Cu, and looking for metastable structures, aids in the long term goal of understanding and controlling their catalytic behavior. Thin-film copper oxides such as the “29” and “44” structures have been described at length in the literature, but precursors to these thin-film oxides can be challenging to study because they exist only under certain conditions. Using a combination of experimental and computational surface science techniques, we discovered, modeled, and quantified a previously unreported O atom adlayer structure on Cu(111) with a p(2 × 1) unit cell. We used scanning tunneling microscopy to visualize the striped 2 × 1 structure and density functional theory (DFT) structure optimizations to identify the thermodynamically most favorable positions of Cu and O atoms in a p(2 × 1) unit cell. Using X-ray photoelectron spectroscopy and temperature-programmed desorption, we determined the stoichiometry of the structure to be 2:1 for surface Cu atoms to O adatoms, the same stoichiometry as that modeled by DFT. This work reports a new metastable structure formed on Cu(111) at the very initial stages of oxidation and is therefore worth considering in models of catalytically relevant redox processes at Cu surfaces. 

Chiral surfaces are of growing interest for enantioselective adsorption and reactions. While metal surfaces can be prepared with a wide range of chiral surface orientations, chiral oxide surface preparation is much more challenging. Herein, we demonstrate that the chirality of a metal surface can be used to direct the homochiral growth of a thin film chiral oxide. Specifically, we study the chiral ‘29’ copper oxide, formed by oxidizing a Cu(111) single crystal at 650 K. Surface structure spread single crystals which expose a continuous distribution of surface orientations as a function of position on the crystal, enabled us to systematically investigate the mechanism of chirality transfer between metal and oxide with high-resolution scanning tunneling microscopy. We discovered that the local underlying metal facet directs the orientation and chirality of the oxide overlayer. Importantly, single homochiral domains of the ‘29’ oxide were found in areas where the Cu step edges that templated growth were ≤20 nm apart. We used this information to select a Cu(239 241 246) oriented single crystal and demonstrate that a ‘29’ oxide surface can be grown in homochiral domains by templating from the subtle chirality of the underlying metal crystal. This work demonstrates how a small degree of chirality induced by very slight misorientation of a metal surface (~1 sites/ 20 nm2) can be amplified by oxidation to yield a homochiral oxide with a regular array of chiral oxide pores (~75 sites/ 20 nm2). This offers a general approach for making chiral oxide surfaces via oxidation of an appropriately miscut metal surface.