Capacitive-Controlled Prussian White with a Nickel Iron Hexacyanoferrate Composite Cathode for Rapid Sodium Diffusion

Prussian blue analogues receive tremendous attention owing to their spacious three-dimensional skeleton, high theoretical specific capacity, facile synthesis procedure, and high cost-effectiveness as among the most promising candidates for cathode materials in sodium-ion batteries (SIBs). Nonetheless, the practical specific capacity, especially under high current, is particularly frail due to the sluggish ion diffusion. In this study, the strategy of Ni substitution and formation of water-coordinated Fe is applied to lower the crystal field energy and elevate the active low-spin (LS) Fe content, which leads to a capacitive sodium storage mechanism, resulting in a substantial specific capacity under high current density. The delivered specific capacity of PW-325@2NiFe-55 is 95 mAh g–1 at 50 C, which is 72.5% capacity retention of the one at 0.5 C. Also, it maintains 80.2% of its initial specific capacity after 500 cycles at 5 C. Furthermore, a hypothesis of a joint diffusion-controlled and capacitive mechanism for high-spin (HS) Fe and a mere capacitive mechanism for LS Fe is put forward and verified through potentiastatic tests, operando 57Fe Mössbauer spectroscopy, and ex situ XRD, which provides a new horizon to enhance the electrochemical performance for SIBs

High Activity of Au/γ-Fe₂O₃ for CO Oxidation: Effect of Support Crystal Phase in Catalyst Design

Au/γ-Fe₂O₃ and Au/α-Fe₂O₃ catalysts with identical size of Au nanoparticles, chemical state of Au species, and amount of surface OH^– group were prepared. The Au/γ-Fe₂O₃ catalyst exhibited exceptionally high activity, regardless of the heat treatments. The CO-TPR, sequential pulse reaction, and in situ Raman spectra demonstrate that the much higher activity of Au/γ-Fe₂O₃ originated from its higher redox property at low temperature. Systematic study shows that this higher-redox-property-based higher activity could be extended to γ-Fe₂O₃-supported Pt-group metals and to other reactions that follow Mars–Van Krevelen mechanism. This finding may provide a new avenue for catalyst improvement or development by choosing the suitable crystal phase of the oxide support

Iodine Ions Mediated Formation of Monomorphic Single-Crystalline Platinum Nanoflowers

Well-defined and strikingly monomorphic single-crystalline Pt nanoflowers were successfully synthesized through the addition of a large amount of iodine ions into polyol process (5 mM H₂PtCl₆, 30 mM KI, and 50 mM PVP in ethylene glycol solution at 160 °C). The detailed structures of the Pt nanoflowers were studied with high-resolution TEM, indicating that high-quality production of the Pt nanoflowers could be obtained when the KI concentration was increased to six times of H₂PtCl₆. The size of Pt nanoflowers could be tuned by changing the concentration of H₂PtCl₆ with the constant Pt/I ratio (1:6). The formation process of the nanoflowers was investigated by the UV–vis and EXAFS spectroscopic studies, demonstrating that the iodine ions played a key role in inducing the formation of the single-crystalline Pt nanoflowers. After the addition of iodine ions into the polyol synthesis, the Pt–I complex was formed and reduced by different kinetics compared with that of H₂PtCl₆ to induce the overgrowth of Pt nanocrystals. Additionally, a small portion of iodine element was found to be strongly adsorbed on the surfaces of Pt nanoflowers, which probably also favored the anisotropic overgrowth of Pt nanocrystals resulting in the single-crystalline Pt nanoflowers. A comprehensive set of systematic studies on the synthesis factors (the concentrations of Pt precursor, iodine ions and PVP, reaction temperature, different kinds of Pt precursors and reaction atmosphere) was also reported

Characterization of α‑Fe₂O₃/γ-Al₂O₃ Catalysts for Catalytic Wet Peroxide Oxidation of <i>m</i>‑Cresol

Fe/<b>γ-</b>Al₂O₃ catalysts calcined at different temperatures were evaluated in the catalytic wet peroxide oxidation (CWPO) of <i>m</i>-cresol. BET, XRD, and ⁵⁷Fe Mössbauer spectroscopy (MS) were used to characterize the catalysts and showed that the calcination temperature changed the crystal particles of α-Fe₂O₃ and the interactions between α-Fe₂O₃ and the <b>γ-</b>Al₂O₃ support. The reaction-condition experiments showed that changing the reaction conditions to higher reaction temperature and acidic pH promoted the degradation of <i>m</i>-cresol. <i>m</i>-Cresol was degraded completely, and TOC removal reached 51.0% after CWPO for 2 h at an initial pH of 4 and a temperature of 60 °C over an Fe/<b>γ-</b>Al₂O₃ catalyst calcined at 350 °C (Fe/<b>γ-</b>Al₂O₃-350). Both reactions for 10 consecutive reaction cycles and for 120 continuous hours in a fixed-bed reactor showed that the Fe/<b>γ-</b>Al₂O₃-350 catalyst was stable and a promising catalyst for heterogeneous CWPO. The degradation intermediates were identified by GC-MS, and the possible degradation pathway of <i>m</i>-cresol was investigated

Synthesis, Characterization, and Catalytic Applications of Core–Shell Magnetic Carbonaceous Nanocomposites

Magnetic resorcinol/formaldehyde resin (RF) and silica/RF nanocomposites with well-defined core–shell architecture and tunable structural parameters had been prepared via the extended Stöber method. The carbon counterparts with similar structure and morphology can be obtained by thermal-treating the polymer precursors under N₂ atmosphere. The prepared materials were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, Mössbauer spectroscopy, N₂ physical adsorption/desorption, and thermogravimetric analysis. The catalytic applications of the synthesized magnetic nanocomposites were also explored. It has been shown that the magnetite core was oxidized to γ-Fe₂O₃ during polymer coating process and further reduced to original Fe₃O₄ phase during carbonization. In addition, the iron oxide core can react with the shell when carbonization temperature reaches 700 °C. The structural stability of magnetic silica/RF is superior to magnetic RF because of the existence of an inner silica shell. Through a simple deposition–precipitate method, active platinum nanoparticles can be loaded in high dispersity onto the surface of the nanocomposites. The constructed magnetic catalysts are very active in hydrogenation of nitroarenes to corresponding amines and can be separated facilely with an external magnetic field

Selectivity-Switchable Conversion of Cellulose to Glycols over Ni–Sn Catalysts

The direct hydrogenolysis of cellulose represents an attractive and promising route for green polyol production. Designing a catalyst system that could control the selectivity of polyols of this process is highly desirable. In this work, we realized the selectivity-switchable production of ethylene glycol (EG) and 1,2-propylene glycol (1,2-PG) by using Sn species with different valences in combination with Ni catalysts. The combination of Ni/AC and metallic Sn powders exhibited a superior activity toward EG (57.6%) with up to 86.6% total polyol yield, while the combination of Ni/AC and SnO favored the formation of 1,2-PG (32.2%) with a 22.9% yield of EG. The Sn species in NiSn alloy in situ formed from metallic Ni and Sn powders was found to be the active sites for the high selectivity of EG as evidenced by control experiments and characterizations including X-ray diffraction, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, energy dispersive X-ray mapping, and ¹¹⁹Sn Mössbauer spectroscopy. The effects of Sn loading, reaction temperature, reaction time, and the concentration of cellulose were investigated for Ni/AC + Sn powders. Because of the formation of NiSn alloy, the Ni–Sn catalyst showed good stability during repeated use. Experimental results disclosed that the Sn species with different valence possessed distinct catalytic functions. Both SnO and the alloyed Sn species could catalyze the retro-aldol condensation of glucose to glycolaldehyde, and meanwhile, SnO was also active for the isomerization of glucose to fructose. Therefore, controlling the glycol products distribution could be realized using SnO or the alloyed Sn species as catalysts

¹¹⁹Sn Mössbauer and Ferromagnetic Studies on Hierarchical Tin- and Nitrogen-Codoped TiO₂ Microspheres with Efficient Photocatalytic Performance

Hierarchical tin-doped titania (ST) and tin- and nitrogen-codoped titania (SNT) microspheres were prepared by a hydrothermal method and nitriding treatment, in particular, SNT-enhanced visible light photocatalytic activity for the degradation of rhodamine B in aqueous solution and room-temperature ferromagnetism (RTFM). We initiated the photovoltaic study of ST and SNT microspheres to confirm the photovoltaic properties of perovskite solar cell (PSC) applications. The SNT microspheres exhibited relatively large saturation magnetization and high photocatalytic activity. To clarify the enhancement of the photoactivity, the prepared samples were characterized by ¹¹⁹Sn Mössbauer spectrometry under external magnetic fields. The broadened peaks of ST and SNT microspheres were decomposed into a doublet and a sextet under an external magnetic field because the samples showed weak ferromagnetism, although these samples are composed of nonmagnetic components. It is noteworthy that ST and SNT microspheres exhibits oxygen vacancies and defect-induced magnetism. The results signify the clear details of the RTFM and the photocatalytic activity of hierarchical ST and SNT microspheres

Highly Active and Sintering-Resistant Pt Clusters Supported on FeO_<i>x</i>–Hydroxyapatite Achieved by Tailoring Strong Metal–Support Interactions

The catalytic performance of supported metal catalysts is closely related to their structure. While Pt-based catalysts are widely used in many catalytic reactions because of their exceptional intrinsic activity, they tend to deactivate in high-temperature reactions, requiring a tedious and expensive regeneration process. The strong metal–support interaction (SMSI) is a promising strategy to improve the stability of supported metal nanoparticles, but often at the price of the activity due to either the coverage of the active sites by support overlay and/or the too-strong metal–support bonding. Herein, we newly constructed a supported Pt cluster catalyst by introducing FeOx into hydroxyapatite (HAP) support to fine-tune the SMSIs. The catalyst exhibited not only high catalytic activity but also sintering resistance, without deactivation in a 100 h test for catalytic CO oxidation. Detailed characterizations reveal that FeOx introduced into HAP weaken the strong covalent metal–support interaction (CMSI) between Pt and FeOx while simultaneously inhibiting the oxidative strong metal–support interaction (OMSI) between Pt and HAP, giving rise to both high activity and thermal stability of the supported Pt clusters

Strong Metal–Support Interactions between Gold Nanoparticles and Nonoxides

The strong metal–support interaction (SMSI) is of great importance for supported catalysts in heterogeneous catalysis. We report the first example of SMSI between Au nanoparticles (NPs) and hydroxyapatite (HAP), a nonoxide. The reversible encapsulation of Au NPs by HAP support, electron transfer, and changes in CO adsorption are identical to the classic SMSI except that the SMSI of Au/HAP occurred under oxidative condition; the opposite condition for the classical SMSI. The SMSI of Au/HAP not only enhanced the sintering resistance of Au NPs upon calcination but also improved their selectivity and reusability in liquid-phase reaction. It was found that the SMSI between Au and HAP is general and could be extended to other phosphate-supported Au systems such as Au/LaPO₄. This new discovery may open a new way to design and develop highly stable supported Au catalysts with controllable activity and selectivity

Decoration of Gold and Platinum Nanoparticle Catalysts by 1 nm Thick Metal Oxide Overlayer and Its Effect on the CO Oxidation Activity

Exfoliated M–Al layered double hydroxide (M–Al LDH; M = Mg, Co, Ni, and Zn) nanosheets were adsorbed on Au/SiO2 and calcined to transform LDH into mixed metal oxides (MMOs) and yield Au/SiO2 coated with a thin MMO overlayer. These catalysts showed a higher catalytic activity than pristine Au/SiO2. In particular, the 50% CO conversion temperature decreased by more than 250 °C for Co–Al MMO-coated Au/SiO2. In contrast, the deposition of CoAlOx on Au/SiO2 by impregnation or the deposition of Au on Co–Al MMO-coated SiO2 resulted in a worse catalytic activity. Moreover, the presence of a thick MMO overlayer decreased the catalytic activity, suggesting that the control of the overlayer thickness to less than 1 nm is a requisite for obtaining a high catalytic activity. Moreover, the thin Co–Al MMO overlayer on Au/SiO2 possessed abundant oxygen vacancies, which would play an important role in O2 activation, resulting in a highly active interface between Au and the defect-rich MMO on the Au NP surface. Finally, this can be applied to Pt/SiO2, and the obtained Co–Al MMO-coated Pt/SiO2 also exhibited a much improved catalytic activity for CO oxidation