Réaction catalytique et évolution d’environnements chimiques observés par NAP-XPS sur synchrotron

La NAP-XPS est un nouvel outil révolutionnaire permettant d'utiliser les avantages d'une analyse XPS (Sensibilité aux différents éléments chimiques ainsi que leurs états) à une pression proche de l'ambiante (de l'ordre du mbar) ouvrant ainsi la voie aux études in situ en se rapprochant des conditions réels et. Deux domaines profitent de cette nouvelle machine : la chimie environnementale et la catalyse. Dans le domaine de la chimie environnementale je m'intéresse à l'étude de l'hydratation des argiles dites gonflantes. J'ai ici démontré qu'il est effectivement possible de suivre l'hydratation des contre-ions en mettant en évidence différents comportement en fonction de leurs natures. De plus j'ai pu mettre en évidence un phénomène de radiolyse sous faisceau de la pyridine en présence d'eau dans ces milieux confinés. Concernant la catalyse, j'ai étudié l'oxydation du CO sur des nanocatalyseurs composés notamment de platine un excellent catalyseur, mais sensible aux problèmes d'empoisonnement au CO. Cette réaction est pour nous une réaction prototype permettant de tester le comportement des nanocatalyseurs (Pt, Zn et PtZn). J'ai pu déterminer la température de début de la réaction d'oxidation du CO, de plus en ajoutant du zinc au platine et pour former un nanocatalyseur bimétallique, j'ai démontré qu'on améliore sa résistance à l'oxidation et il montré que le zinc seul est lui aussi capable de catalyser l'oxidation du CO sous forme de création/destruction de carbonate.The NAP-XPS is a revolutionary new tool that makes possible to use the advantages of a standard XPS analysis (sensitivity to the different chemical elements as well as their states) at a near-ambient pressure (mbar range) thus enabling in situ studies closer to real conditions. Two fields fully benefit from this new machine: environmental chemistry and catalysis. In our case for the field of environmental chemistry we are interested in studying the hydration of so-called swelling clays. I have here demonstrated that it is indeed possible to follow the hydration of counter-ions and highlighted different behavior according to their natures. Moreover, I have been able to demonstrate a beam induced pyridine photolysis phenomenon in the presence of water in these confined media. Concerning catalysis, I studied the oxidation of CO on nanocatalysts composed in particular of platinum an excellent catalyst but sensitive to the CO poisoning. This reaction is for us a prototypical reaction to test the behavior of Pt, Zn, PtZn nanocatalysts. Here, I have been able to determine the onset temperature of the CO oxidation reaction. Moreover, by adding zinc to platinum and forming a bimetallic nanocatalyst, I have improved its resistance to oxidation and proved that zinc alone is also capable of catalyzing the oxidation of CO in the form of creation / destruction of carbonate

Réaction catalytique et évolution d’environnements chimiques observés par NAP-XPS sur synchrotron

The NAP-XPS is a revolutionary new tool that makes possible to use the advantages of a standard XPS analysis (sensitivity to the different chemical elements as well as their states) at a near-ambient pressure (mbar range) thus enabling in situ studies closer to real conditions. Two fields fully benefit from this new machine: environmental chemistry and catalysis. In our case for the field of environmental chemistry we are interested in studying the hydration of so-called swelling clays. I have here demonstrated that it is indeed possible to follow the hydration of counter-ions and highlighted different behavior according to their natures. Moreover, I have been able to demonstrate a beam induced pyridine photolysis phenomenon in the presence of water in these confined media. Concerning catalysis, I studied the oxidation of CO on nanocatalysts composed in particular of platinum an excellent catalyst but sensitive to the CO poisoning. This reaction is for us a prototypical reaction to test the behavior of Pt, Zn, PtZn nanocatalysts. Here, I have been able to determine the onset temperature of the CO oxidation reaction. Moreover, by adding zinc to platinum and forming a bimetallic nanocatalyst, I have improved its resistance to oxidation and proved that zinc alone is also capable of catalyzing the oxidation of CO in the form of creation / destruction of carbonate.La NAP-XPS est un nouvel outil révolutionnaire permettant d'utiliser les avantages d'une analyse XPS (Sensibilité aux différents éléments chimiques ainsi que leurs états) à une pression proche de l'ambiante (de l'ordre du mbar) ouvrant ainsi la voie aux études in situ en se rapprochant des conditions réels et. Deux domaines profitent de cette nouvelle machine : la chimie environnementale et la catalyse. Dans le domaine de la chimie environnementale je m'intéresse à l'étude de l'hydratation des argiles dites gonflantes. J'ai ici démontré qu'il est effectivement possible de suivre l'hydratation des contre-ions en mettant en évidence différents comportement en fonction de leurs natures. De plus j'ai pu mettre en évidence un phénomène de radiolyse sous faisceau de la pyridine en présence d'eau dans ces milieux confinés. Concernant la catalyse, j'ai étudié l'oxydation du CO sur des nanocatalyseurs composés notamment de platine un excellent catalyseur, mais sensible aux problèmes d'empoisonnement au CO. Cette réaction est pour nous une réaction prototype permettant de tester le comportement des nanocatalyseurs (Pt, Zn et PtZn). J'ai pu déterminer la température de début de la réaction d'oxidation du CO, de plus en ajoutant du zinc au platine et pour former un nanocatalyseur bimétallique, j'ai démontré qu'on améliore sa résistance à l'oxidation et il montré que le zinc seul est lui aussi capable de catalyser l'oxidation du CO sous forme de création/destruction de carbonate

Orcinol and resorcinol induce local ordering of water molecules near the liquid-vapor interface

Resorcinol and orcinol are simple members of the family of phenolic compounds present in particulate matter in the atmosphere; they are amphiphilic in nature and thus surface active in aqueous solution. Here, we used X-ray photoelectron spectroscopy to probe the concentration of resorcinol (benzene-1,3-diol) and orcinol (5-methylbenzene-1,3-diol) at the liquid-vapor interface of aqueous solutions. Qualitatively consistent surface propensity and preferential orientation was obtained by molecular dynamics simulations. Auger electron yield near-edge X-ray absorption fine structure (NEXAFS) spectroscopy was used to probe the hydrogen bonding (HB) structure, indicating that the local structure of water molecules near the surface of the resorcinol and orcinol solutions tends towards a larger fraction of tetrahedrally coordinated molecules than observed at the liquid-vapor interface of pure water. The order parameter obtained from the molecular dynamics simulations confirm these observations. This effect is being discussed in terms of the formation of an ordered structure of these molecules at the surface leading to patterns of hydrated OH groups with distances among them that are relatively close to those in ice. These results suggest that the self-assembly of phenolic species at the aqueous solution-air interface could induce freezing similar to the case of fatty alcohol monolayers and, thus, be of relevance for ice nucleation in the atmosphere. We also attempted at looking at the changes of the O 1b(1), 3a(2) and 1b(2) molecular orbitals of liquid water, which are known to be sensitive to the HB structure as well, in response to the presence of resorcinol and orcinol. However, these changes remained negligible within uncertainty for both experimentally obtained valence spectra and theoretically calculated density of states.ISSN:2634-360

Palladium Catalysts for Methane Oxidation: Old Materials, New Challenges

ISSN:0001-4842ISSN:1520-489

Ordered Hydrogen Bonding Structure of Water Molecules Adsorbed on Silver Iodide Particles under Subsaturated Conditions

Silver iodide (AgI) is an efficient ice-nucleating material. This has been related to the close lattice match to hexagonal ice, which helps to nucleate ice crystals on its surface under supersaturated conditions. In turn, the structure of water molecules adsorbed on its surface, embodied in the coordination of hydrogen bonds, has not been addressed so far. We suspected that AgI may induce ice-like coordination among adsorbed water molecules already under subsaturated conditions. X-ray photoelectron spectroscopy was used to probe the structure and composition at the AgI surface. We determined the chemical properties of the surface, the thickness of adsorbed water, and the amount of contaminating carbon species. Auger electron yield near-edge X-ray absorption fine structure (NEXAFS) spectroscopy was used to assess the hydrogen bonding (HB) structure. The O K-edge NEXAFS spectra indicated that the HB structure of the adsorbed water on AgI under subsaturated conditions showed similarity to that of ice, which helps facilitate the stabilization of ice embryos at saturation. The approach used here opens up important perspectives for characterizing adsorbed water molecules on a wide variety of solids, which provides an important basis for understanding ice nucleation and other interfacial processes at the molecular level.ISSN:1932-7455ISSN:1932-744

Water inhibition and role of palladium adatoms on Pd/Al2O3 catalysts during methane oxidation

Supported palladium catalysts are the most active ones toward the complete oxidation of methane. However, the presence of relevant amounts of water hinders the catalytic activity and long-term stability, due to competition between methane and water for the active sites. Hence, understanding the inhibition effect of water on methane oxidation is mandatory to improve these catalysts. We present an in situ ambient pressure X-ray photoelectron spectroscopy study of methane oxidation on Pd/Al2O3 in presence and in absence of water. The inhibition effect of water is demonstrated by combining reactivity tests with electron microscopy and photoelectron spectroscopy measurements. In the presence of water, the redox activity of palladium decreases. Water competes with methane for the catalytically active sites, poisoning the surface with hydroxyl groups and hindering the generation of the coordinatively unsaturated palladium active sites. Multiple palladium oxide species displaying different reactivity are identified. A new cationic palladium species, assigned to adatoms, is detected, which shows higher reactivity with methane than particulate palladium oxide but also high inhibition by water.ISSN:0169-4332ISSN:1873-558

Deciphering Radiolytic Oxidation in Halide Aqueous Solutions: A Pathway Toward Improved Synchrotron NAP-XPS Analysis

International audienceSynchrotron radiation near ambient pressure X-ray photoemission spectroscopy (SR NAP-XPS) has been an invaluable tool for examining gas/liquid and liquid/solid interfaces. Despite its benefits, concerns have emerged regarding beam damage in NAP-XPS experiments, particularly involving condensed liquid water, because of the high dose rates, greater than 105 Gy·s–1. This study investigates the radiolytic effects on the chemistry of concentrated NaX sodium halide solutions (X = Cl, Br, I) and Mg–Cl solution formed over the layered double hydroxide [Mg2Al(OH)6]+[Cl–]. The formation of oxidized species XO– as the radiolytic end product under soft X-ray irradiation is discussed in detail. We examine the impact of known parameters (such as the dose rate) on the abundance of XO–. The observed scatter in the data likely arises from still unrecognized or insufficiently controlled parameters (such as solute concentration or solution hydrodynamics). Deciphering these radiolytic effects in halide solutions allows us to propose guidelines for their better identification, understanding and control, ultimately improving the reliability of synchrotron NAP-XPS analysis for interfaces relevant to environmental chemistry and electrochemistry

Improving time-resolution and sensitivity of in situ X-ray photoelectron spectroscopy of a powder catalyst by modulated excitation

Ambient pressure X-ray photoelectron spectroscopy (APXPS) is a powerful tool to characterize the surface structure of heterogeneous catalysts in situ. In order to improve the time resolution and the signal-to-noise (S/N) ratio of photoemission spectra, we collected consecutive APXP spectra during the periodic perturbation of a powder Pd/Al2O3 catalyst away from its equilibrium state according to the modulated excitation approach (ME). Averaging of the spectra along the alternate pulses of O-2 and CO improved the S/N ratio demonstrating that the time resolution of the measurement can be limited solely to the acquisition time of one spectrum. Through phase sensitive analysis of the averaged time-resolved spectra, the formation/consumption dynamics of three oxidic species, two metal species, adsorbed CO on Pd-0 as well as Pdn+ (n > 2) was followed along the gas switches. Pdn+ and 2-fold surface PdO species were recognised as most reactive to the gas switches. Our approach demonstrates that phase sensitive detection of time-resolved XPS data allows following the dynamics of reactive species at the solid-gas interface under different reaction environments with unprecedented precision.ISSN:2041-6520ISSN:2041-653

CO oxidation activity of Pt, Zn and ZnPt nanocatalysts: a comparative study by in situ near-ambient pressure X-ray photoelectron spectroscopy

International audienc

Correction: Improving time-resolution and sensitivity of in situ X-ray photoelectron spectroscopy of a powder catalyst by modulated excitation

Correction for 'Improving time-resolution and sensitivity of in situ X-ray photoelectron spectroscopy of a powder catalyst by modulated excitation' by M. Roger et al., Chem. Sci., 2023, 14, 7482-7491, https://doi.org/10.1039/D3SC01274C.ISSN:2041-6520ISSN:2041-653