Recently, the research group of Professor Xie Yi of the University of Science and Technology of China has made new progress in the synthesis and application of atomic-thick two-dimensional ultra-thin structures. The researchers used a new ultra-thin two-dimensional structure to build an ideal model system to study the role of active centers in the catalytic process. The research results were published online in the November 27 issue of Nature Communications. As we all know, catalytic technology is the backbone of the chemical industry. More than 90% of chemical processes and more than 60% of products are related to catalytic technology. In general, only a local position in the catalyst produces activity, which is called the active center. The active center may be in various forms such as atoms, radicals, ions, surface defects, etc. The concept of active center was proposed by Taylor in 1925. He believed that those atoms located at the apex, prism or structural defect of the crystal, because of their own valence unsaturation, that is, the existence of surface free valence, so they Highly active, capable of chemically adsorbing molecules, activating them, and then reacting. However, so far, there is no unified view on the understanding of active centers, mainly because of the lack of an ideal structural model to demonstrate the relationship between active centers and catalytic activity. To understand the relationship between active centers and catalytic activity, it is urgent to construct a structural model with a large number of active centers. In response to the above challenges, Professor Xie Yi's research group first constructed an atomically thick ceria nanosheet structure. This ultrathin two-dimensional structure with three atomic layers can expose up to about 70% of the surface atoms, thus providing a large number of active centers. At the same time, in order to further understand the specific effect of the active sites with different coordination numbers on the active center on the catalytic activity, they artificially created abundant surface pits on the surface of the ultra-thin ceria nanosheets. The existence of these pits can not only provide active sites with lower coordination number, but also provide active sites with large difference in coordination number. They collaborated with Professor Wei Shiqiang of Hefei National Laboratory of Synchrotron Radiation, using synchrotron radiation X-ray absorption fine structure spectroscopy to characterize ultra-thin nanosheets, intact ultrathin nanosheets and bulk materials rich in surface pits, synchrotron radiation XAFS results show that the average coordination number of Ce atoms around the pits is 4.6, which is significantly smaller than the average coordination number of Ce atoms (6.5) on the surface of ultra-thin nanosheets and Ce atoms (8) in the bulk. At the same time, the first-principles calculations show that the 4- and 5-coordinated Ce atoms around the pit have the largest CO adsorption energy and the smallest O2 activation energy relative to the surface Ce atoms in ultra-thin nanosheets and bulk materials. This means that Ce atoms around the pit are not only conducive to CO adsorption, but also to activation, which in turn helps to improve the catalytic oxidation performance of CO. At the same time, since CO and molecules tend to adsorb on 4- and 5-coordinated Ce atoms, respectively, this avoids the poisoning of the catalyst, thereby improving the catalytic efficiency and cycle stability of the catalyst. In addition, the first-principles calculations show that the presence of pits makes the state density of ultra-thin ceria nanosheets significantly enhanced at the top of their valence band, which is conducive to the diffusion of CO and the improvement of catalytic performance. Benefiting from the above advantages, the experimental results of CO catalytic oxidation confirmed that the presence of a large number of coordinated unsaturated surface Ce atoms caused the apparent activation energy to decrease from 122.9kJmol-1 of the bulk material to 89.1kJmol- of ultra-thin nanosheets 1; At the same time, the presence of a large number of pits makes the apparent activation energy of ultra-thin CeO2 nanosheets continue to decrease to 61.7kJmol-1. Correspondingly, the 100% CO conversion temperature of CeO2 also decreased from 425 ° C in bulk to 325 ° C in ultra-thin nanosheets and 200 ° C in ultra-thin nanosheets rich in surface pits. The above theoretical calculations and experimental results confirm the semi-quantitative relationship between the active center and catalytic activity, which has important scientific significance and practical value for promoting the research progress in the field of catalysis, and is also a catalyst for the study of ultra-thin two-dimensional structures with limited scale Performance opens up new ways. Professor Xie Yi's research group has been engaged in the research of the cross-field of inorganic functional solid design and synthesis based on electrical and acoustic modulation. Since 2011, he has been regulating the fine structure, electronic structure, photoelectricity, and catalytic performance of inorganic two-dimensional ultra-thin structures. In-depth research has been carried out. Related work has been published in Nature Commun., J. Am. Chem. Soc. And Angew. Chem. Int. Ed. In three internationally renowned academic journals. Chem. Soc. Rev., a well-known review journal of the Chemical Society, has written two instructive reviews. The research group is one of several major research groups that are continuously active in this field internationally. This work was supported by the National Natural Science Foundation of China, the Ministry of Science and Technology's major research program and the Chinese Academy of Sciences pilot projects. Welcome to our Our Cellophane Bags pages. Our products include Plastic Bags , PP bags, Cellophane Gift Bags, OPP bags, shopping bags, T- shirt bags, bubble bags, zipper bags, plastic handbags, plastic film, shrink film and non woven bag. Our products are used to packing toys, garments, cards, glasses,shopping and so on.
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