New Progress Made in the Study of Monoatomic Catalysts of Dalian Institute of Chemicals
Recently, the Chinese Academy of Sciences Academician Zhang Tao and Researcher Wang Aiqin of the Institute of Space Chemistry and New Materials at the Dalian Institute of Chemical Physics, Chinese Academy of Sciences have made new progress in the field of monoatomic catalysts, and prepared and applied monoatomically dispersed Fe-NC catalysts. In the CH bond selective oxidation reaction, excellent activity and selectivity were obtained. In particular, using a variety of characterization techniques including X-ray absorption spectroscopy and MÃ¶ssbauer spectroscopy, it has been demonstrated for the first time that the spin-Fe-N5 structure has the highest catalytic activity. The relevant results were published in full text in the "J. Am. Chem. Soc., DOI: 10.1021/jacs.7b05130".
MNC catalysts (M stands for Fe, Co, Ni, etc.) are widely used in electrochemical reactions (such as ORR, HER, CO2RR) and organic chemical reactions, and their excellent catalytic performance is expected to be a non-precious metal alternative to Pt group metals. catalyst. However, due to the complexity of the composition of the MNC catalyst, there is much controversy over its understanding of the active center. The monoatomic dispersed catalysts provide unique advantages for the fine structure analysis of active sites due to the avoidance of interferences of nanoparticles such as M0, MOx, and MCx. Previously, the research team had synthesized a monoatomically dispersed Co-NC catalyst and determined its structure as CoN4C8-1-2O2 (Chem. Sci., 2016, 7, 5758-5764). On this basis, the team also succeeded in preparing a monoatomically dispersed Fe-NC catalyst that has the catalytic activity and selectivity comparable to the homogeneous catalyst in the selective oxidation reaction of ethylbenzene and CH bond. Universality and reaction stability. More importantly, it has been demonstrated for the first time that the Fe(III) ions in Fe-NC catalysts have a variety of coordination structures (FeNx, x = 4, 5, 6) through XAFS, MÃ¶ssbauer, EPR and poisoning tests. The -N5 structure has the highest catalytic activity, but this structure only accounts for 18% in quantity, indicating that the activity of the Fe-NC catalyst has a lot of room for improvement, which provides the following guidance for people to design a more efficient Fe-NC catalyst. New ideas.
The above research work was funded by the National Natural Science Foundation of China, the Ministry of Science and Technology, the special pilot project of the Chinese Academy of Sciences and the Collaborative Innovation Center for Energy Materials Chemistry of the Ministry of Education.
Hard Turning refers to the process of single point cutting of hardened pieces within the 2 micron range with hardness between 58 and 70 HRC.
In the grinding process, because the work piece is turning slowly, the wheel speed has to be considered in relation to the cutting speed. In the turning process, on the other hand, the work piece takes care of the cutting speed, whilst the tool performs the contouring. In consequence the high speed of the grinding wheel causes the work piece to produce a large quantity of small chips, whilst the turning process forms a continuous chip, which nearly always disintegrates into smaller pieces. Therefore one can see that grinding requires more time and energy per unit volume than turning. Another difference between turning and grinding is that with the latter it is only possible to remove an extremely small quantity of material, for instance with a thickness of only 1 Âµm. But turning is characterised by a minimal chip thickness of hundredths of a millimetre. That`s why high-precision hard turning requires a different strategy to reach exactly the dimension required.
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