RoDSE Synthesized Fine Tailored Au Nanoparticles from Au(X)₄^– (X = Cl^–, Br^–, and OH^–) on Unsupported Vulcan XC-72R for Ethanol Oxidation Reaction in Alkaline Media

An electrosynthesis method to obtain Au nanoparticles dispersed on carbon Vulcan XC-72R support material was done using AuX4– (X = Cl–, Br–, and OH–) as molecular precursors and different electrolyte media. The Au surface structure was significantly enhanced using KOH as an electrolyte as opposed to KBr and H2SO4. Cyclic voltammetry was used as a surface sensitive technique to illustrate the Au/Vulcan XC-72R catalytic activity for the ethanol oxidation reaction (EOR). The Au electroactive surface areas obtained were 1.88, 5.83, and 13.96 m2 g–1 for Au/C–H2SO4, Au/C–KBr, and Au/C–KOH, respectively. The latter compares to chemically reduced Au/C–spheres that had an electroactive surface area of 15.0 m2 g–1. The electrochemical Au electrodeposition, in alkaline media (Au/C–KOH), exhibited the highest catalytic activity for the EOR with a 50% increase in peak current density when compared with Au nanoparticles prepared by the chemical reduction route. Raman and X-ray photoelectron spectroscopies analyses of the Au/Vulcan XC-72R nanomaterials revealed a restructuring of the carbon functionalities responsible for the metal nanoparticle anchoring. Our results strongly suggest that the enhanced EOR catalytic activity is related to the presence of oxygen functional groups on the carbon surface, particularly ketonic groups on the carbon Vulcan XC-72R substrate

Modification of CO₂ Reduction Activity of Nanostructured Silver Electrocatalysts by Surface Halide Anions

This paper describes the effect of halide anions (X = Cl, Br, I) immobilized on the surface of nanostructured silver electrocatalysts on the efficiency and the mechanism of CO2 reduction to CO in aqueous carbonate solutions. A simple oxidation–reduction cycle on Ag foil in the presence of halide anions produces high-surface-area nanostructured catalysts mainly composed of metallic Ag with a small amount of halide anions attached to the electrode surface (X–Ag) as demonstrated by XPS, XRD, and SEM studies. The activity of X–Ag electrocatalysts in 0.1 M NaHCO3 at pH 6.8 is significantly higher than that of Ag foil or Ag nanoparticles with comparable surface area and morphology. The activity enhancement is attributed to the formation of active catalytic sites, presumably Cl––Agn+ clusters on the surface of metallic Ag, as evidenced by XPS analysis. The activity of X–Ag catalysts is in the order Cl > Br > I, which is consistent with the proposed model of an active site. The Tafel analysis of electrochemical CO2 reduction points to the sensitivity of the mechanism of electrocatalysis on the nature of X

Photoelectrochemical Solar Cells Prepared From Nanoscale Zerovalent Iron Used for Aqueous Cd²⁺ Removal

Nanoscale zerovalent iron (nZVI) particles have been widely studied in the environmental sciences for wastewater treatment. These types of nanoparticles react in aqueous media producing metal oxides, which can be photoactive in the ultraviolet energy region. This prompted us to examine alternatives for the preparation of nanomaterials using nZVI in the presence of 6 and 30 ppm of Cd²⁺ in aqueous solutions. These Cd²⁺ concentrations are representative of contaminated regions of Puerto Rico such as the Las Cucharillas Marsh in Cataño. Comprehensive chemical and physical characterization of the resulting nZVI products after their exposure to Cd²⁺ was done. Further studies of the resulting nanostructures were completed using a photoelectrochemical solar cell (PSC) as the photoanode material. Incident photon-to-current efficiency (IPCE) and electrochemical impedance spectroscopy (EIS) analysis of these PSCs showed active photochemical properties in the ultraviolet range for the sample exposed to 30 ppm of Cd²⁺. Changes in the structure and chemical oxidation states of the species were observed in transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy analysis was attributed to these photochemical properties. These results show an alternative synthetic method for producing iron oxides for photocatalytic applications, and a possible strategy for reuse of nZVI after water remediation treatments

Highly Active Ceria-Supported Ru Catalyst for the Dry Reforming of Methane: In Situ Identification of Ru^δ+–Ce³⁺ Interactions for Enhanced Conversion

The metal–oxide interaction changes the surface electronic states of catalysts deployed for chemical conversion, yet details of its influence on the catalytic performance under reaction conditions remain obscure. In this work, we report the high activity/stability of a ceria-supported Ru–nanocluster (<1 nm) catalyst during the dry reforming of methane. To elucidate the structure–reactivity relationship underlying the remarkable catalytic performance, the active structure and chemical speciation of the catalyst was characterized using in situ X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS), while the surface chemistry and active intermediates were monitored by in situ ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Methane activates on the catalyst surface at temperatures as low as 150 °C. Under reaction conditions, the existence of metal–support interactions tunes the electronic properties of the Ru nanoclusters, giving rise to a partially oxidized state of ruthenium stabilized by reduced ceria (Ruδ+–CeO2–x) to sustain active chemistry, which is found to be very different from that of large Ru nanoparticles supported on ceria. The oxidation of surface carbon is also a crucial step for the completion of the catalytic cycle, and this is strongly correlated with the oxygen transfer governed by the Ruδ+–CeO2–x interactions at higher temperatures (>300 °C). The possible reaction pathways and stable surface intermediates were identified using DRIFTS including ruthenium carbonyls, carboxylate species, and surface −OH groups, while polydentate carbonates may be plain spectators at the measured reaction conditions

Identification of Highly Selective Surface Pathways for Methane Dry Reforming Using Mechanochemical Synthesis of Pd–CeO₂

The methane dry reforming (DRM) reaction mechanism was explored via mechanochemically prepared Pd/CeO2 catalysts (PdAcCeO2M), which yield unique Pd–Ce interfaces, where PdAcCeO2M has a distinct reaction mechanism and higher reactivity for DRM relative to traditionally synthesized impregnated Pd/CeO2 (PdCeO2IW). In situ characterization and density functional theory calculations revealed that the enhanced chemistry of PdAcCeO2M can be attributed to the presence of a carbon-modified Pd0 and Ce4+/3+ surface arrangement, where distinct Pd–CO intermediate species and strong Pd–CeO2 interactions are activated and sustained exclusively under reaction conditions. This unique arrangement leads to highly selective and distinct surface reaction pathways that prefer the direct oxidation of CHx to CO, identified on PdAcCeO2M using isotope labeled diffuse reflectance infrared Fourier transform spectroscopy and highlighting linear Pd–CO species bound on metallic and C-modified Pd, leading to adsorbed HCOO [1595 cm–1] species as key DRM intermediates, stemming from associative CO2 reduction. The milled materials contrast strikingly with surface processes observed on IW samples (PdCeO2IW) where the competing reverse water gas shift reaction predominates

Effects of Zr Doping into Ceria for the Dry Reforming of Methane over Ni/CeZrO₂ Catalysts: In Situ Studies with XRD, XAFS, and AP-XPS

The methane activation and methane dry reforming reactions were studied and compared over 4 wt % Ni/CeO2 and 4 wt % Ni/CeZrO2 (containing 20 wt % Zr) catalysts. Upon the incorporation of Zr into the ceria support, the catalyst exhibited a significantly improved activity and H2 selectivity. To understand the effects of the Zr dopant on Ni and CeO2 during the dry reforming of methane (DRM) reaction and to probe the structure–reactivity relationship underlying the enhanced catalytic performance of the mixed-oxide system, in situ time-resolved X-ray diffraction (TR-XRD), X-ray absorption fine structure (XAFS), and ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) were employed to characterize the catalysts under reaction conditions. TR-XRD and AP-XPS indicate that ceria–zirconia supported Ni (Ni/CeZrO2) is of higher reducibility than the pure ceria supported Ni (Ni/CeO2) upon the reaction with pure CH4 or for the methane dry reforming reaction. The active state of Ni/CeZrO2 under optimum DRM conditions (700 °C) was identified as Ni0, Ce3+/Ce4+, and Zr4+. The particle size of both nickel and the ceria support under reaction conditions was analyzed by Rietveld refinement and extended XAFS fitting. Zr in the ceria support prevents particle sintering and maintains small particle sizes for both metallic nickel and the partially reduced ceria support under reaction conditions through a stronger metal–support interaction. Additionally, Zr prevents Ni migration from the surface into ceria forming a Ce1–xNixO2–y solid solution, which is seen in Ni/CeO2, thus helping to preserve the active Ni0 on the Ni/CeZrO2 surface