image: It is seen the semi-hydrogenation of acetylene and propylene hydroformylation can occur smoothly on Pd/Al and Rh/Al systems, respectively with Pd or Rh atoms completely buried in the subsurface of Al substrate.
Credit: ©Science China Press
This study is led by Prof. Landong Li (College of Chemistry, Nankai University), Prof. Zhenpeng Hu (School of Physics, Nankai University) and Prof. Fan Yang (School of Physical Science and Technology, ShanghaiTech University).
Inspired by the disappearance of surface transitional metal species on aluminum substrate upon annealing, density functional theory (DFT) calculations were performed by the group of Zhenpeng Hu. Some d-block metals are found to show a self-dispersion and sinking tendency, and can be well stabilized in the subsurface region of single crystal aluminum. Meanwhile, the electronic interaction between buried single transitional metal and adjacent aluminum atoms via metallic bonding can be well demonstrated.
According to these calculation results, Landong Li and Fan Yang started to seek for solid evidence on the structure of the unique metallic system (M/Al) and the electron transfer between transitional metals and aluminum substrate through scanning tunneling microscopy (STM). Typically, it is found that both palladium and rhodium exclusively locate in the subsurface region of Al(001) and Al(111) single crystals as isolated atoms, with distinct electron transfer from palladium or rhodium to adjacent aluminum atoms.
The research team then performed DFT predictions on the catalytic properties of M/Al in several important reactions such as acetylene semi-hydrogenation and propylene hydroformylation. It is disclosed that the intrinsic catalytic properties of palladium and rhodium can be conducted to the outermost inert aluminum layer, deriving catalytically active M/Al systems although palladium and rhodium atoms are completely buried inside aluminum single crystal and inaccessible to reaction substrates.
Guided by theoretical predictions and surface science observations, the team finally built real main group metal systems containing buried transitional metal centers, showing expected catalytic performance in the reactions of alkyne semi-hydrogenation, olefin hydroformylation and Suzuki-coupling. These results further confirm that the catalytic properties of buried transitional metals can be transferred to the exposed catalytically inert main group metals, i.e., the conductive catalysis.
This concept might provide an efficient shield of the traditional active centers against poisoning or leaching by the conductive layer, in contrast to traditional supported systems. More importantly, it is proposed that the catalytic properties of buried transitional metals can be precisely regulated or completely altered when passing through the conductive layer.
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See the article:
Conductive catalysis by subsurface transition metals
https://doi.org/10.1093/nsr/nwae015
Journal
National Science Review