The identification of the active sites in heterogeneous catalysis is important for a mechanistic understanding of the structure–reactivity relationship. Among others, the oxide/metal boundaries are expected to contain the active sites in various catalytic reactions. To reveal their nature and their chemical evolution under reaction conditions, the catalytic role of an oxide/metal system consisting of well-ordered ZnO nanoislands grown on Pt(111) in low-temperature CO oxidation was studied by near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) in operando conditions, and additionally by ultra-high vacuum scanning tunneling microscopy. To illustrate the special role played by the oxide/metal boundaries, a systematic comparative study of ZnO/Pt(111) with the pristine Pt(111) surface was undertaken. The regimes where mass transfer limitation starts to occur were identified using NAP-XPS and mass spectrometry measurements in combination, allowing a sound discussion on the relation between steady-state molar fractions of reactants/product and surface reactivity. Via the measurement of the steady-state CO2 molar fraction, we observed that the CO oxidation reaction rate over the ZnO/Pt(111) system is superior to that over Pt(111) in a temperature range extending to 410 K. The pivotal, albeit unexpected, role of ZnO-bound hydroxyls was clearly highlighted by the observation of the chemical signature of the CO + OH associative reaction at the ZnO/Pt boundaries. The carboxyl formed at low temperature (410 K) can be the intermediate species in the CO oxidation reaction, the OHs at the Pt/ZnO boundary being the cocatalyst, which explains the synergistic effect of ZnO and Pt. However, the species formed at higher temperature (from 445 K) are formates that would essentially be spectators.

We report on the shape, composition (from Pt95Zn5 to Pt77Zn23), and surface chemistry of Pt–Zn nanoparticles obtained by reduction of precursors M2+(acac)2 – (M2+: Pt2+ and Zn2+) in oleylamine, which serves as both solvent and ligand. We show first that the addition of phenyl ether or benzyl ether determines the composition and shape of the nanoparticles, which point to an adsorbate-controlled synthesis. The organic (ligand)/inorganic (nanoparticles) interface is characterized on the structural and chemical level. We observe that the particles, after washing with ethanol, are coated with oleylamine and the oxidation products of the latter, namely, an aldimine and a nitrile. After exposure to air, the particles oxidize, covering themselves with a few monolayer thick ZnO film, which is certainly discontinuous when the particles are low in zinc. Pt–Zn particles are unstable and prone to losing Zn. We have strong indications that the driving force is the preferential oxidation of the less noble metal. Finally, we show that adsorption of CO on the surface of nanoparticles modifies the oxidation state of amine ligands and attribute it to the displacement of hydrogen adsorbed on Pt. All the structural and chemical information provided by the combination of electron microscopy and X-ray photoelectron spectroscopy allows us to give a fairly accurate picture of the surface of nanoparticles and to better understand why Pt–Zn alloys are efficient in certain electrocatalytic reactions such as the oxidation of methanol.

Silicon oxide atomic layer deposition synthesis development over the last few years has open the route to its use as a dielectric within diamond electronics. Its great band-gap makes it a promising material for the fabrication of diamond–metal–oxide field effects transistor gates. Having a sufficiently high barrier both for holes and electrons is mandatory to work in accumulation and inversion regimes without leakage currents, and no other oxide can fulfil this requisite due to the wide diamond band-gap. In this work, the heterojunction of atomic-layer-deposited silicon oxide and (100)-oriented p-type oxygen-terminated diamond is studied using scanning transmission electron microscopy in its energy loss spectroscopy mode and X-ray photoelectron spectroscopy. The amorphous phase of silicon oxide was successfully synthesized with a homogeneous band-gap of 9.4 eV. The interface between the oxide and diamond consisted mainly of single- and double-carbon-oxygen bonds with a low density of interface states and a straddling band setting with a 2.0 eV valence band-offset and 1.9 eV conduction band-offset.