Modification of nanostructured palladium catalysts by p-elements and their influence on electrooxidation of glycerol

Les stocks de glycérol à travers le monde augmentent, étant une matière première secondaire, ce produit chimique doit être valorisé. La co-production d'énergie électrique ou d'hydrogène et de produits chimiques à valeur ajoutée à partir du glycérol peut être réalisée dans des réacteurs électrochimiques. L'oxydation de glycérol est une réaction complexe qui peut conduire à un grand nombre de produits chimiques et d'intermédiaires utiles pour l'industrie. Le développement de catalyseurs spécifiques pour orienter les chemins réactionnels de l'électrooxydation du glycérol vers les produits désirés est un objectif très important. Des nanoparticules non supportées de palladium à distribution de taille et de forme contrôlées ont été synthétisées par une voie colloïdale et caractérisées par microscopie électronique et des méthodes électrochimiques afin d'obtenir une corrélation entre la structure de surface et la réponse électrochimique. Ces électrolyseurs modèles ont été modifiés par dépôt d'adatomes de bismuth. Et leur activité et sélectivité vis-à-vis de l'électrooxydation du glycérol ont été respectivement évaluées par voltammétrie cyclique et spectroscopie infrarouge in situ. Des matériaux plus proches d'applications industrielles à base de palladium et d'éléments du groupe p (Bi, Sn) ont ensuite été aussi synthétisés et évalués vis-à-vis de l'électrooxydation du glycérol. Les résultats obtenus montrent clairement l'influence de la composition, de l'orientation de surface et de la nature de catalyseur sur l'activité et la sélectivité dans la réaction de l'électrooxydation du glycérol.The worldwide glycerol stocks are increasing; this chemical could be used as a secondary primary raw material. Electric energy or hydrogen and added-value-chemical cogeneration can be performed in electrochemical reactors. Glycerol oxidation is made up of complex pathway reactions that can produce a large number of useful products and valuable fine intermediates.The development of specific catalysts for electrooxidation of glycerol to obtain desired products is a very important goal.Unsupported palladium nanoparticles with controlled size and shape distribution were synthesized by a colloidal method and characterized by electron microscopy and electrochemical methods to obtain a correlation between the surface structure and the electrochemical response. These model electrocatalists have been modified by adatoms of bismuth. And their activity and selectivity towards the electrooxidation of glycerol were respectively evaluated by cyclic voltammetry and in situ infrared spectroscopy. Other materials for industrial applications based on palladium and p elements (Bi, Sn) were also synthesized and evaluated towards the electrooxidation of glycerol.The results clearly show the influence of the composition, surface orientation and the nature of the catalyst on activity and selectivity in the reaction of electrooxidation of glycerol

How do Bi-modified palladium nanoparticles work towards glycerol electrooxidation? An in situ FTIR study

International audiencePalladium nanoparticles with controlled distributions of sizes and shapes were synthesized and characterized by TEM, HRTEM and voltammetric methods. The surfaces of these nanoparticles were modified by spontaneous adsorption of bismuth. The activity and selectivity towards glycerol electrooxidation reaction were determined by coupling cyclic volatmmetry with in situ infrared spectroscopy. Higher activity were observed on pure Pd nanoparticles presenting extended (100) and/or (111) surface domains (nanocubes and nanooctahedrons, respectively), with Pd nanocubes being the most active. The modification of the surface by spontaneous adsorption of bismuth not only greatly improves the activity of Pd nanocubes but also affects the reaction pathway of glycerol electrooxidation. The study allows a better understanding of the material structure/electrocatalytic behavior relationship, which is essential on a fundamental point of view for the determination of reaction mechanisms and on a practical point of view for the rational design of catalysts active and selective towards oxidation of polyols from biomas

Bi-modified palladium nanocubes for glycerol electrooxidation

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Octahedral palladium nanoparticles as excellent hosts for electrochemically adsorbed and absorbed hydrogen

International audienceWe report new results for electrochemical H adsorption on and absorption in octahedral palladium nanoparticles (Pd-NPs) with an average tip-to-tip size of 7.8 nm and a narrow size distribution. They reveal a very high H loading of 0.90 that cannot be achieved using bulk Pd materials or larger NPs; this behavior is assigned to a combination of two factors: their small size and face morphology. Temperature-dependent cyclic voltammetry (CV) studies in the range of 296 to 333 K reveal unique features that are attributed to electrochemical H adsorption, H absorption, and H 2 generation. The CV features are used to prepare H adsorption and absorption isotherms that are then used in thermodynamic data analysis. Modeling of the experimental results demonstrates that, upon H adsorption and absorption, Pd-NPs develop a core-shell-skin structure, each with its unique H loading. The electrochemical results obtained for octahedral Pd-NPs are compared to analogous data obtained for cubic Pd-NPs with a similar size as well as for larger cubic Pd-NPs and bulk materials under gas-phase conditions

Modification of palladium surfaces by bismuth adatoms or clusters: Effect on electrochemical activity and selectivity towards polyol electrooxidation

International audienceThe syntheses of Bi-modified Pd catalysts with a controlled size distribution are presented as well as the characterizations of their structures and of their surfaces. Effects of the modification either of non-supported Pd nanospheres by spontaneous deposition of Bi or of carbon-supported Pd-based nanomaterials by decoration with bismuth clusters on the electrocatalytic activity towards glycerol electrooxidation were evaluated and compared in alkaline medium. The method of bismuth deposition has a dramatic effect on the activity of the palladium based catalysts: spontaneous deposition of Bi on non-supported Pd nanoparticles leads to relatively low activity enhancement, whereas decoration of carbon-supported Pd nanoparticles by Bi2O3 and Bi(OH)(3) clusters leads to very high activity increase at low overpotentials. In situ infrared spectroscopy indicated that the modification of Pd by Bi did not affect the selectivity of glycerol oxidation, whereas in the case of Pt containing catalyst, a dramatic change in selectivity occurred at low potentials

Electrochemical Behavior of Unsupported Shaped Palladium Nanoparticles

International audienceThe potential range in which hydrogen electro-adsorption, electro-absorption, and evolution reaction occur is examined in an acidic medium using cyclic-voltammetry (CV) and Pd nanoparticles with controlled size and shape distributions. The three processes give rise to unique features in CV profiles and are observed in distinct potential ranges. This behavior is not observed for bulk Pd materials and arises due to the nanoscopic nature of the Pd material

When cubic nanoparticles get spherical: An Identical Location Transmission Electron Microscopy case study with Pd in alkaline media

Shape-controlled nanoparticles (NPs) are viewed as electrocatalysts of choice for fuel cell applications. However, to date very few studies focus on the persistence of the controlled shape upon operation. Herein, the degradation of cubic palladium NPs is studied in alkaline media using Identical Location Transmission Electron Microscopy (ILTEM) and electrochemical measurements; this work brings evidence that the cubic shape is rapidly destroyed in certain conditions. Keywords: Shape-controlled nanoparticles, Cubic, Palladium, Identical Location Transmission Electron Microscopy, Alkaline electrolyte, Degradatio

Development of Bismuth-Modified PtPd Nanocatalysts for the Electrochemical Reforming of Polyols into Hydrogen and Value-Added Chemicals

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