Bohan Sun,Cuiyan Li,Haibo Ouyang,Ruinan Gao,Tianzhan Shen,Yanlei Li
The synthesis of hafnium carbide nanowires (HfC NWs ) on carbon fibers was successfully achieved by employing HfCl 4 and furfuryl alcohol as precursor materials, facilitated by Ni-assisted catalytic pyrolysis . In the polymerization and cross-linking processes of furfuryl alcohol, hafnium cations play a crucial role, leading to the atomic-level amalgamation and effectively enhancing the reactivity of the Hf-O-C system. The nucleation of HfC NWs takes place at 1300 °C, followed by growth through a solid-liquid-solid (SLS) mechanism. Carbon fibers were uniformly coated with tens micrometer-long HfC NWs having an approximate diameter of 500 nm. Notably, the tips of these HfC NWs exhibited clean surfaces free of Ni catalyst particles, indicating their root growth model. This novel catalyst-assisted pyrolysis method holds great potential for enabling cost-effective large-scale production of transition metal carbide nanowires.
Design catalytic materials with high Lewis acid/base sites for catalytic transfer hydrogenation (CTH) of levulinic acid (LvA) to γ-valerolactone (GVL) is highly demanded but challenging. Herein, we report a concept of metal ion-polymer hybridization to design a tea polyphenol (TP) and HfCl 4 co-doped polyacrylonitrile (PAN) nanofiber (Hf@PAN-TP) via electrospinning technique . Comprehensive characterization revealed the well coordination between hafnium ions and phenolic hydroxyl groups of TP on PAN fiber, which promoted the formation of Lewis acid and Lewis base sites. As expected, a satisfactory GVL yield of 99.1% with 100% of LvA conversion was obtained using isopropanol as a hydrogen donor at 170 °C in 5 h, and the catalytic activity remained unchanged for five cycles. The kinetic study revealed the lower activation energy for CTH of LvA to GVL (33.5 kJ/mol), demonstrating the outstanding GVL formation rate of 3383.9 μmol/g . h. Based on the systematical combine of catalyst characterization and catalytic behavior, the structure-function relationship and reaction mechanism were proposed. More gratifyingly, Hf@PAN-TP was applicable for catalytic reduction of various carbonyl compounds, demonstrating a great potential for upgrading biomass-derived aldehydes/ketones.
Zi-Yuan Wang,Jun Guo,Yu Wang,Yi-Xing Zhang,Jing Feng,Zhen-Hua Ge
Bismuth sulfide is a promising thermoelectric material because of its low cost and toxicity; however, its low electrical conductivity limits its thermoelectric properties. In this study, Bi 2 S 3 + x wt% HfCl 4 ( x = 0, 0.25, 0.5, 0.75, and 1.0) bulk samples are fabricated using a combination of melting and spark plasma sintering. The microstructures, electronic structures, and thermoelectric properties of the composites are characterized. The results of electronic structure calculations show that doping with HfCl 4 produces an impurity energy level that narrows the bandgap and allows the Fermi energy level to enter the conduction band, leading to a favorable increase in carrier concentration. By regulating the HfCl 4 doping concentration, the electrical conductivity of the 0.75 wt% doped sample reaches 253 Scm −1 at 423 K and its maximum ZT value is 0.47 at 673 K. Moreover, the sample is compounded with Bi 2 S 3 nanorods prepared by the hydrothermal method, reducing thermal conductivity by 30% due to the introduction of additional interfaces and pores. This resulted in a final ZT value of 0.61 at 673 K, which is approximately eight times higher than that of pure Bi 2 S 3 . This step-by-step optimization approach provides a valuable methodology for enhancing the performance of other thermoelectric material systems.
Mingrui Li,Yixuan Liu,Xialing Lin,Jinyu Tan,Song Yang,Hu Li
γ-Valerolactone (GVL) is an attractive biomass-derived platform molecule that plays an important role in the production of biofuels and biopolymers. The synthesis of GVL from renewable biomass and its derivatives has great application prospects but also presents challenges due to the multiple conversion steps involved. Here, a HfCl4-mediated acid–base bifunctional catalytic system was developed, which was demonstrated to be efficient for upgrading furfural (FF) to GVL in a single pot with unprecedented performance. The Lewis acidity of Hf4+ and moderate basicity of HfO(OH)2·xH2O, and strong Brønsted acidity of HCl in situ generated from HfCl4 hydrolysis were found to play a synergistic role in the cascade reaction processes, mainly contributing to the pronounced catalytic activity. The effects of the key reaction parameters, such as the catalyst dosage, reaction time, and temperature, on GVL production were optimized by response surface methodology. It is worth mentioning that the recovered catalyst after thermal treatment could be directly used for the hydrogen transfer processes, like FF-to-furfuryl alcohol conversion. This catalytic strategy opens a new avenue for the selective conversion of biomass feedstocks involving multiple steps and complex processes.
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