Transition Metal-Nitrogen-Carbon Single-Atom Catalysts Enhanced CO2 Electroreduction Reaction: A Review.

As the global energy crisis and environmental challenges worsen, CO2 conversion has emerged as a focal point in international research. CO2 electroreduction reaction (CO2ER) is a green and sustainable technology that converts CO2 into high-value chemicals, thereby achieving the recycling of carbon resources. However, the activity and selectivity are constrained by the performance of the catalyst. Although traditional N-doped carbon-based catalysts exhibit excellent performance toward CO2ER, the atomic utilization rate in these materials is far from 100%. Single atom catalysts (SACs) can attain nearly 100% atomic utilization efficiency because of the fully exposing metal atoms. Therefore, SACs have emerged as one of the hot research materials in the field of CO2ER. Recently, transition metal-nitrogen-carbon single-atom catalysts (TM-N-C SACs) have flourished because of their extraordinary catalytic activity, low cost, and excellent stability, demonstrating enormous application prospects in CO2ER. In this review, we concentrate on TM-N-C SACs that electrochemically reduce CO2 to high value products. A comprehensive and detailed discussion were conducted on the synthesis method, chemical structure, chemical characterization of TM-N-C SACs, as well as their catalytic performance, active sources, and mechanism exploration for CO2ER. Finally, challenges and prospects for commercial application of TM-N-C SACs catalysts suitable for CO2ER are proposed.

Halogen-free ionic liquids as high performance extractants for phenols separation.

As precious chemical raw materials, phenols can be applied to produce pharmaceuticals, new materials, engineering products, and so on. The separation of phenols from oil mixtures shows great economic value. In this work, five halogen-free ionic liquids (HFILs) were designed and employed to separate phenols from simulated oils, and all of them showed excellent separation performance. Among the HFILs, 1-ethyl-3-methylimidazolium acetate ([Emim][Ac]) showed the highest separation efficiency of 98.6% for phenol, and achieved a minimum ultimate content of 1.96 g dm-3. The calculated distribution coefficient of phenol reached a high value of 431.8. The separation process could be finished within 3 min, and could be performed at normal temperature. It was also found that the HFILs could separate different types of phenols effectively. During separation, toluene was entrained in the HFIL, and an n-hexane treatment was used. After treatment, the toluene entrained in the HFIL after separation was largely removed, and the purity of the phenol was greatly improved. In addition, the HFILs could be easily regenerated by diethyl ether and reused 6 times without a decrease in separation efficiency. Meanwhile, the separation mechanism was explored by using FT-IR spectroscopy, and the FT-IR results indicated the existence of hydrogen bonds.

Extraction Behavior of Indole from Simulated Wash Oil Using Halogen-Free Ionic Liquids.

Indole is an important raw material in the chemical industry, and more than 1 wt % indole is contained in wash oil. Therefore, the extraction of indole from wash oil is of much importance. The conventional separation methods generally cost much money, pollute the environment, and corrode the metallic devices due to the use of large amounts of inorganic acid and alkali solutions, and therefore, new methods should be proposed. In this work, a solvent extraction process for separating indole from simulated wash oil by five halogen-free ionic liquids (HFILs) has been designed, and the extraction behavior of indole has been evaluated. All the studied HFILs presented excellent extraction behavior for indole, and the whole separation process took no more than 5 min. For the same HFIL, the minimum residual indole contents remained the same, even if the initial indole contents changed. Among the HFILs, 1-butyl-3-methylimidazolium dimethyl phosphate ([Bmim][DMP]) has attracted more attention than other HFILs. The results showed that [Bmim][DMP] could extract over 96.9 wt % indole from the simulated wash oil, and the minimum residual indole content was as low as 2.1 g/dm3. For indole, [Bmim][DMP] presented a maximum distribution coefficient of 201, which was much improved compared to other methods. The HFILs could be regenerated by using diethyl ether with ease. The regenerated HFILs could be reused, and the extraction behavior remained the same as the original HFILs. Based on FT-IR results, a mechanism of hydrogen bonds forming between HFILs and indole was proposed. In addition, the superiorities of HFILs over other separation agents in reusability, amounts needed, distribution coefficient for indole, and chemical structure were proved by comparison.