Evaluation of kinetic models for the partial oxidation of methane to synthesis gas over a Pt/PrCeZrOx catalyst coated on a triangular monolith

The evaluation of kinetic models for the partial oxidation of methane to synthesis gas over a 1.4-wt% Pt/Pr0.3Ce0.35Zr0.35Ox catalyst coated on the surface of a triangular corundum channel is presented. The mathematical form of the tested models accounts for global surface steps. The formulation of reaction steps for two cases proposed in the literature contained lumped formulations to restrict reasonably the number of parameters to estimate. One mechanism considering an oxygen assisted methane activation and another considering methane dissociation without oxygen involvement were tested. In both cases a satisfying description of the experimental data was possible, suggesting that the initial activation of methane is of less importance for the overall progress of the partial oxidation than the oxidation of carbonaceous intermediates to adsorbed carbon monoxide assumed in both cases. Comparing the kinetics over unsupported platinum extensively reported in literature to the data over the 1.4-wt% Pt/Pr0.3Ce0.35Zr0.35Ox catalyst in this work reveals significantly different rates for oxygen adsorption and carbon monoxide oxidation. These differences are explained by considering the active role the ceria plays in the catalyst performance

Combining impedance and hydrodynamic methods in electrocatalysis. Characterization of Pt(pc), Pt5Gd, and nanostructured Pd for the hydrogen evolution reaction

Electrochemical hydrodynamic techniques typically involve electrodes that move relative to the solution. Historically, approaches involving rotating disc electrode (RDE) configurations have become very popular, as one can easily control the electroactive species’ mass transport in those cases. The combination of cyclic voltammetry and RDE is nowadays one of the standard characterization protocols in electrocatalysis. On the other hand, impedance spectroscopy is one of the most informative electrochemistry techniques, enabling the acquisition of information on the processes taking place simultaneously at the electrode/electrolyte interface. In this work, we investigated the hydrogen evolution reaction (HER) catalyzed by polycrystalline Pt (Pt(pc)) and Pt _5 Gd disc electrodes and characterized them using RDE and electrochemical impedance spectroscopy techniques simultaneously. Pt _5 Gd shows higher HER activities than Pt in acidic and alkaline media due to strain and ligand effects. The mechanistic study of the reaction showed that the rotation rates in acidic media do not affect the contribution of the Volmer–Heyrovsky and Volmer–Tafel pathways. However, the Volmer–Heyrovsky pathway dominates at lower rotation rates in alkaline media. Besides, the HER in acidic solutions depends more strongly on mass diffusion than in alkaline media. In addition to simple and clearly defined systems, the combined method of both techniques is applicable for systems with greater complexity, such as Pd/C nanostructured catalysts. Applying the above-presented approach, we found that the Volmer–Tafel pathway is the dominating mechanism of the HER for this catalytic system

Top-down surfactant-free electrosynthesis of magnéli phase Ti₉O₁₇ nanowires

International audienceTiO2 nanowires have proven their importance as a versatile material in numerous fields of technology due to their unique properties attributable to their high aspect ratio and large surface area. However, synthesis is an enormous challenge since state-of-the-art techniques rely on complex, multi-stage procedures with expensive, specialized equipment, employing high-temperature steps and potentially toxic precursor materials and surfactants. Hence, we elucidate a simple and facile top-down methodology for the synthesis of nanowires with non-stoichiometric Magnéli phase Ti9O17. This methodology relies on the electrochemical erosion of bulk Ti wires immersed in an aqueous electrolyte, circumventing the use of environmentally harmful precursors or surfactants, eliminating the need for high temperatures, and reducing synthesis complexity and time. Using multiple techniques, including transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction, we provide evidence of the successful synthesis of ultrathin nanowires with the crystal structure of non-stoichiometric Ti9O17 Magnéli phase. The nanowire width of ∼5 nm and the Brunauer–Emmett–Teller surface area of ∼215 m2 g−1 make the nanowires presented in this work comparable to those synthesized by state-of-the-art bottom-up techniques

Elucidation of structure–activity relations in proton electroreduction at Pd surfaces: Theoretical and experimental study

The structure–activity relationship is a cornerstone topic in catalysis, which lays the foundation for the design and functionalization of catalytic materials. Of particular interest is the catalysis of the hydrogen evolution reaction (HER) by palladium (Pd), which is envisioned to play a major role in realizing a hydrogen-based economy. Interestingly, experimentalists observed excess heat generation in such systems, which became known as the debated “cold fusion” phenomenon. Despite the considerable attention on this report, more fundamental knowledge, such as the impact of the formation of bulk Pd hydrides on the nature of active sites and the HER activity, remains largely unexplored. In this work, classical electrochemical experiments performed on model Pd(hkl) surfaces, “noise” electrochemical scanning tunneling microscopy (n-EC-STM), and density functional theory are combined to elucidate the nature of active sites for the HER. Results reveal an activity trend following Pd(111) > Pd(110) > Pd(100) and that the forma?tion of subsurface hydride layers causes morphological changes and strain, which affect the HER activity and the nature of active sites. These findings provide significant insights into the role of subsurface hydride formation on the structure–activity relations toward the design of efficient Pd-based nanocatalysts for the HER.</p