Decomposition of Large Cu Crystals into Ultrasmall Particles Using Chemical Vapor Deposition and Their Application in...

In this work, we report a novel application of chemical vapor deposition (CVD) in which the calcination and reduction of Cu(thd)₂ deposited onto 4.9 wt % Cu/SiO₂ induces significant decomposition of 28 nm crystalline Cu into ultrasmall ∼2 nm particles (5.1 wt % Cu/SiO₂). The Cu loading slightly increased, but the particle size dramatically decreased. The deposition of Cu(thd)₂ onto the Cu surface can initially affect the size reduction of the metallic Cu particles due to charge transfer between Cu(thd)₂ and the Cu surface. Thermal treatments, including calcination in air and reduction in H₂, can further influence the Cu particle decomposition. The mechanism of change in the Cu particle decomposition was investigated by a variety of experiments, such as X-ray diffraction and in situ X-ray absorption spectroscopy. CVD treatment of Cu/SiO₂ can create Cu-rich sites, which effectively enhance the conversion and acrolein yield in selective propylene oxidation. The intermediate associated with propylene oxidation on the Cu catalysts was also examined by IR spectroscopy.