MoO3 and Mo2C have emerged as remarkable catalysts for the selective hydrodeoxygenation (HDO) of a wide range of oxygenates at low temperatures (i.e.,  673 K) and H 2 pressures (i.e., ≤ 1 bar). While both catalysts can selectively cleave CO bonds, the nature of their active sites remains unclear. Here, we used operando nearambient pressure X-ray photoelectron spectroscopy to reveal important differences in the Mo 3d oxidation states between the two catalysts during the HDO of anisole. This technique revealed that although both catalysts featured a surface oxycarbidic phase, the oxygen content and the underlying phase of the material impacted the reactivity and product selectivity during HDO. MoO3 transitioned between 5+ and 6+ oxidation states during operation, consistent with an oxygen vacancy driven mechanism wherein the oxygenate is activated at undercoordinated Mo sites. In contrast, Mo 2 C showed negligible oxidation state changes during HDO, maintaining mostly 2+ states throughout the reaction.

promising properties for redox applications, including gravimetric oxygen storage up to 4% by mass, high stability and rapid reversibility, with re-oxidation in less than 1 min at 400 C. Finally, the redox chemistry of Ca 0.8 Sr 0.2 MnO 3 was also investigated using in situ X-ray photoelectron spectroscopy and near-edge X-ray absorption measurements at near ambient pressure in oxygen atmospheres.

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One of the main goals in catalysis is the characterization of solid/gas interfaces in a reaction environment. The electronic structure and chemical composition of surfaces become heavily influenced by the surrounding environment. However, the lack of surface sensitive techniques that are able to monitor these modifications under high pressure conditions hinders the understanding of such processes. This limitation is known throughout the community as the "pressure gap." We have developed a novel experimental setup that provides chemical information on a molecular level under atmospheric pressure and in presence of reactive gases and at elevated temperatures. This approach is based on separating the vacuum environment from the high-pressure environment by a silicon nitride grid-that contains an array of micrometer-sized holes-coated with a bilayer of graphene. Using this configuration, we have investigated the local electronic structure of catalysts by means of photoelectron spectroscopy and in presence of gases at 1 atm. The reaction products were monitored online by mass spectrometry and gas chromatography. The successful operation of this setup was demonstrated with three different examples: the oxidation/reduction reaction of iridium (noble metal) and copper (transition metal) nanoparticles and with the hydrogenation of propyne on Pd black catalyst (powder).