Synergy between Metallic and Oxidized Pt Sites Unravelled during Room Temperature CO Oxidation on Pt/Ceria

International audiencePt-based materials are widely used as heterogeneous catalysts, in particular for pollutant removal applications. The nature of the active Pt phase responsible for CO oxidation has long been investigated with a view at designing more efficient formulations. The state of Pt has often been proposed to differ depending on experimental conditions, e.g. metallic Pt poisoned with CO being present at lower temperature before light-off, while an oxidized Pt surface prevails above light-off temperature. In stark contrast with all previous reports, we show here that both metallic and oxidized Pt are present in similar proportions under reaction conditions at the surface of ca. 1 nm nanoparticles showing high activity at 30 °C. The simultaneous presence of metallic and oxidized Pt enables a synergy between these phases. The main role of metallic Pt phase is to provide strong adsorption sites for CO, while that of oxidized Pt supposedly supplies reactive oxygen. Our results emphasize the complex dual oxidic-metallic nature of supported Pt catalysts and its evolving nature under reaction conditions, warranting a whole rethink of the mechanism of other reaction and metals, particularly redox and electrochemical reactions

Reducing two-level system dissipations in 3D superconducting Niobium resonators by atomic layer deposition and high temperature heat treatment

International audienceSuperconducting qubits have arisen as a leading technology platform for quantum computing which is on the verge of revolutionizing the world's calculation capacities. Nonetheless, the fabrication of computationally reliable qubit circuits requires increasing the quantum coherence lifetimes, which are predominantly limited by the dissipations of two-level system (TLS) defects present in the thin superconducting film and the adjacent dielectric regions. In this paper, we demonstrate the reduction of two-level system losses in three-dimensional superconducting radio frequency (SRF) niobium resonators by atomic layer deposition (ALD) of a 10 nm aluminum oxide Al2O3 thin films followed by a high vacuum (HV) heat treatment at 650 {\deg}C for few hours. By probing the effect of several heat treatments on Al2O3-coated niobium samples by X-ray photoelectron spectroscopy (XPS) plus scanning and conventional high resolution transmission electron microscopy (STEM/HRTEM) coupled with electron energy loss spectroscopy (EELS) and (EDX) , we witness a dissolution of niobium native oxides and the modification of the Al2O3-Nb interface, which correlates with the enhancement of the quality factor at low fields of two 1.3 GHz niobium cavities coated with 10 nm of Al2O3