As a precious metal, copper more readily oxidizes to a positive valence (Cu + or Cu 2+) than the same family element Au or Ag. In general, this chemical property is mainly determined by electron structure. Can we change the chemical properties of an element by regulating its electron structure? Can Cu act as a noble metal in catalytic reactions?
A group led by Dr. Sun Jian from the Dalian Institute of Chemical Physics (DICP) from the Chinese Academy of Sciences (CAS) gives a positive response. The team's recently published paper in Science Advances shows that the electron structure of Cu can be altered, assisted by high energy plasma, making Cu exhibit significantly different catalytic behaviors than normal Cu in selective hydrogenation reactions. Dimethyl oxalate (DMO) hydrogenation reaction was chosen as a typical multistep catalytic reaction which produces methyl glycolate (MG), ethylene glycol or ethanol, as a probe reaction for copper. In this reaction, the common product over Cu / SiO 2 catalysts is one of the latter two due to the inevitable coexistence of Cu + and CuO for deep hydrogenation. Sputtered (SP) Cu, which is bombarded by high energy argon plasma, can be "frozen" at zero valence when exposed to oxidation or reaction atmosphere at a very wide range of temperatures, which presents noble metal-like behaviors. In DMO hydrogenation, a high selectivity (87%) to the preliminary hydrogenation product, MG, a high quality chemical, was observed. The molecular level free energy surface in different reaction paths through DFT calculation also verifies that "frozen" Cu0 is crucial for preliminary hydrogenation.
Chemists turn metal catalysis on their heads for a sustainable future
"Freezing of copper as a precious metal-like catalyst for preliminary hydrogenation" Science Advances (2018). DOI: 10.1126 / sciadv.aau3275, http://advances.sciencemag.org/content/4/12/eaau3275