Yu Niu,Fuying Li,Kai Yang,Ting Qiu,Renzhang Wang,Cheng Lin
A unique Rh/TiO 2 solid acid catalyst modified with H 2 SO 4 was synthesized and evaluated in the esterification reaction of propylene glycol methyl ether and decomposition of methyl orange (MO) in aqueous phase under halogen lamp irradiation. For this purpose, rhodium (Rh) nanoparticles were loaded on SO 4 2 − /TiO 2 via the photo-deposition method. It was found that SO 4 2 − /Rh–TiO 2 exhibited stronger catalytic activity than SO 4 2 − /TiO 2 . The new catalysts were characterized by X-ray powder diffraction (XRD), Brunauer–Emmett–Teller (BET), Transmission electron microscopy (TEM) and high-resolution (HRTEM), X-ray photoelectron spectroscopy (XPS) and Fourier Transform infrared spectroscopy (FTIR). Results from XRD and BET show that SO 4 2 − /Rh–TiO 2 has higher specific surface area and smaller pore size than SO 4 2 − /TiO 2 . The distribution of loaded Rh was found to be uniform with a particle size of 2–4 nm. Data from XPS reveal that Rh primarily exists as Rh 0 and Rh 3 + in Rh–TiO 2 and SO 4 2 − /Rh–TiO 2 . These valence forms of Rh likely contribute to the enhanced catalytic activity. Furthermore, FT-IR spectra of the catalysts show an abundance of surface hydroxyl groups, which help the formation of hydroxyl radicals and the enhancement of surface acid density. The results show that more acid sites are formed on the sulfated Rh–TiO 2 , and these acidic sites are largely responsible for improving the catalytic performance. This superior SO 4 2 − /Rh–TiO 2 catalyst has potential applications in reactions requiring efficient acid catalysts, including esterification reactions and waste water treatment.
Jiaxin Zhu,Zekun Liu,Yihua Chen,Zhiqiang Chen,Hang Ma,Jian Sun,Liao Meng,Tongzhou Liu
The discharge of widely used fluorinated aromatics (FAs) leads to their notoriously high persistence and toxicity in natural environments. Defluorination is the key step for FAs pollutants detoxification. Due to its easy operation and mild reaction conditions, hydrodefluorination (HDF), especially electrochemical HDF, is a promising approach for FAs detoxification. A comprehensive and detailed investigation of the effective cathode and mechanism insights are contributable for the development of effective FAs defluorination techniques. In this study, 4-fluorophenol (4-FP) was selected as a model compound to optimize the electrochemical HDF process and understand the reaction mechanism. Cathode coating material investigation revealed that Rh outperformed Pd due to its higher reactivity towards C F bond cleavage. The Rh coating was primarily elemental and in Rh(1 1 1) crystalline form which helped store the generated atomic hydrogen (H*). Reaction conditions optimizations showed 4-FP degradation favored acidic > alkaline > neutral environment and a cell potential higher than −3 V was required for efficient 4-FP degradation. Dissolved oxygen (DO) negatively affected 4-FP degradation and the rapid 4-FP decay only occurred after DO depleted in the solution. Based on quenching experiments and ESR analysis, H* was determined as the main reactive species. In situ Raman characterization suggested that electrochemical 4-FP degradation was initiated by 4-FP adsorption through R···F···Rh bridging and H* generation/adsorption on Rh coated cathode, resulting in phenol generation. The generated phenol further experienced hydrogenation to yield cyclohexanone and cyclohexanol with lower toxicity and better biodegradation potential, demonstrating that electrochemical treatment of 4-FP simultaneously achieved defluorination along with detoxification. The outcomes of this work provide support for electrocatalyst technology development towards efficient FAs treatment while providing in-depth observation of the electrochemical HDF process.
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