Fe-Doped Zirconium Oxide Produced by Self-Sustained High-Temperature Synthesis: Evidence for an Fe−Zr Direct Bond

Advancing nitrate reduction to ammonia: insights into mechanism, activity control, and catalyst design over Pt nanoparticle-based ZrO2

The reduction of nitrogen oxides (NOx) to NH3, or N2 represents a crucial step in mitigating atmospheric NO3 and NO2 emissions, a significant contributor to air pollution. Among these reduction products, ammonia (NH3) holds particular significance due to its utility in nitrogen-based fertilizers and its versatile applications in various industrial processes. Platinum-based catalysts have exhibited promise in enhancing the rate and selectivity of these reduction reactions. In this study, we employ density functional theory (DFT) calculations to explore the catalytic potential of Pt nanoparticle (PtNP)-supported ZrO2 for the conversion of NO3 to NH3. The most favorable pathway for the NO3 reduction to NH3 follows a sequence, that is, NO3 → NO2 → NO → ONH → ONH2/HNOH → NH2/NH → NH2 → NH3, culminating in the production of valuable ammonia. The introduction of low-state Fe and Co dopants into the ZrO2 support reduces energy barriers for the most challenging rate-determining hydrogenation step in NOx reduction to NH3, demonstrating significant improvements in catalytic activity. The incorporation of dopants into the ZrO2 support results in a depletion of electron density within the Pt cocatalyst resulting in enhanced hydrogen transfer efficiency during the hydrogenation process. This study aims to provide insights into the catalytic activity of platinum-based ZrO2 catalysts and will help design new high-performance catalysts for the reduction of atmospheric pollutants and for energy applications.

Effect of Surface Dispersion of Fe Nanoparticles on the Room-Temperature Flash Sintering Behavior of 3YSZ

Arc floating in surface flashover can be controlled by reducing the interfacial charge-transfer resistance of ceramics. However, thus far, only a few studies have been conducted on methods of treating ceramic surfaces directly to reduce the interfacial charge-transfer resistance. Herein, we explore the flash sintering behavior of a ceramic surface (3 mol% yttria-stabilized zirconia (3YSZ)) onto which loose metal (iron) powder was spread prior to flash sintering at room temperature (25 °C). The iron powder acts as a conductive phase that accelerates the start of flash sintering while also doping the ceramic phase during the sintering process. Notably, the iron powder substantially reduces the transition time from the arc stage to the flash stage from 13.50 to 8.22 s. The surface temperature (~1600 °C) of the ceramic substrate is sufficiently high to melt the iron powder. The molten metal then reacts with the ceramic surface, causing iron ions to substitute Zr⁴⁺ ions and promoting rapid densification. The YSZ grains in the metal-infiltrated area grow exceptionally fast. The results demonstrate that spreading metal powder onto a ceramic surface prior to flash sintering can enable the metal to enter the ceramic pores, which will be of significance in developing and enhancing ceramic-metal powder processing techniques.

Synthesis, characterization and electrochemical properties of iron-zirconia solid solution nanoparticles prepared using a sol-gel technique

The range of compositions and temperatures at which single-phase tetragonal and monoclinic Fe-containing zirconia nanoparticles are stable is reported. Both types of iron-doped zirconia particles were synthesized by annealing dried gels FexZr1-xO2, with nominal compositions in the range 0 ≤ x ≤ 0.15, over the range of temperatures between 400 °C and 1300 °C. Monophasic crystalline specimens of Fe-ZrO2 solid solutions were characterized by different techniques including X-ray powder diffraction (XRD), infrared and Raman spectroscopies (IR and Raman), and transmission electron microscopy (TEM). Energy gaps were estimated from diffuse reflectance ultraviolet-visible spectra (DRUV-Vis) and compared with those obtained from electrochemical data. Upon increasing the amount of iron in both types of iron-containing zirconia-based structures the energy gaps slightly lowered. The electrochemical properties of those solid solutions obtained using the voltammetry of microparticles (VPM) technique indicated the presence of a small portion of iron as Fe(2+) in both types of crystalline Fe-doped ZrO2. Electrochemical data suggest that the monoclinic solid solutions provide a particularly high accessibility for promoting catalytic processes such as electrochemical oxygen reduction.