Wu Kai Group, School of chemistry and molecular engineering, Peking University has made new progress in the study of supported metal monoatomic model catalysts

The dispersion limit of the supported metal catalyst is that the metal is uniformly distributed on the support in the form of single atom, which is the ideal state of the supported metal catalyst and pushes the catalytic chemistry to the single atom scale Single atom catalyst has the characteristics of "isolated active site" and "stable and easy separation" of homogeneous catalyst In recent years, Professor Wu Kai's research group and collaborators in the school of chemistry and molecular engineering of Peking University have realized the preparation of metal monatoms by regulating the surface free energy of oxides and investigated their reaction performance Generally, the surface free energy of bulk metal is much higher than that of oxide, which is the reason why metal atoms tend to agglomerate on oxide surface If the oxide is thinned to a single layer, its surface free energy will be close to the metal surface free energy (the mixing of chemical potential) by the modulation of the base metal At this time, the metal deposited on the thin layer oxide may be in a highly dispersed state The single-layer CuO film was grown on the surface of Cu (110) single crystal, and then platinum (PT) metal atoms were deposited The PT single atom model catalyst with thermal stability over 400 K was obtained If the thickness of oxide layer is increased, Pt atoms with the same deposition amount will agglomerate and form metal clusters at room temperature The preparation method of the supported metal monoatomic model catalyst system is simple and easy, and it does not need adsorption molecules or embedded lattice to stabilize the metal monoatom, which provides a new idea for the preparation of the supported metal monoatomic model catalyst (J Phys Chem C, 2016, 120 (3), PP 1709 – 1715; http://pubs.acs.org/doi/abs/10.1021/acs.jpcc.5b11362) Recently, Wu Kai's group and collaborators have prepared gold (AU) single atom model catalyst by using the above-mentioned developed surface free energy regulation method In the case of high dispersion, the chemically inert metal Au shows high activity of specific reaction How to explain the highly active sources of highly dispersed AU has been a controversial scientific issue, especially the charge state of Au in the reaction process Wu Kai's group and collaborators investigated the evolution of charge state and the change of corresponding activity of Au model catalyst in the oxidation of carbon monoxide (CO) It is found that the single atom of Au is in a negative electric state before the reaction The main way is that the nearest oxygen (o) ions in CuO transfer electrons to Au, thus activating the nearest o ions At the same time, the negative Au single atom is conducive to the D - π * feedback between the metal and Co, which is conducive to the activation of the adsorbed CO molecules The activated CO molecule reacts with the nearest o ion at room temperature to form CO 2 molecule and O hole After the reaction, the single atom of Au becomes electrically neutral, and the reaction activity is lost When O 2 is used to repair the lattice O defect, the single atom of Au becomes negative again and the reaction activity is restored Thus a complete reaction cycle is formed, which follows the MVK reaction mechanism (see the figure below) In this study, the ultra-high spatial resolution of STM and the chemical resolution of X-ray photoelectron spectroscopy (XPS) are used to clearly characterize the evolution of charge state and the change of reaction activity of Au single atom in the process of reaction on the atomic scale, which provides an important basis for understanding the catalytic activity of Au single atom The work was recently published online in Journal of the American Chemical Society (J am Chem SOC., 2018, 140 (2), PP 554 – 557; http://pubs.acs.org/doi/10.1021/jacs.7b10394) (a) STM diagram of Au single atom prepared on single-layer CuO film (b) STM diagram of oxygen hole formed by CO molecule and oxygen in the lattice near Au single atom at room temperature (c) The changes of Au 4f and O 1s XPS signals during CO oxidation (d) Mechanism diagram of CO oxidation reaction activated by Au single atom Source: the first author of this series of papers in the school of molecular chemistry and molecular engineering of Peking University is Dr Zhou Xiong, a graduate student of Wu Kai Group The series of research was completed in collaboration with Yang Xueming, researcher of Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Chen Wei and Xu Guoqin, Professor of Department of chemistry, National University of Singapore, and Shaoxiang, Professor of University of science and technology of China The research was jointly supported by the National Natural Science Foundation of China, the Ministry of science and technology, the National Research Center of Molecular Science in Beijing and the spring program of NRF in Singapore Profile of Professor Wu Kai: http://www.chem.pku.edu.cn/szll/zzjs/wlhxyjs1/55882.htm Professor Wu Kai