Hierarchical Cu nanoparticle-aggregated cages with high catalytic activity for reduction of 4-nitrophenol and carbon dioxide

Hierarchical similar to 10 nm Cu nanoparticle (NP)-aggregated sub -micro cage catalysts (diameter: similar to 800 rim) with a hollow interior and porous shell were prepared from SiO2 encapsulated Cu2O nanoparticle aggregates (NPAs) using a facile and scalable method. The Cu cages were analyzed by field emission-scanning electron microscopy (FE-SEM), energy-dispersed X-ray (EDX), transmission electron microscopy (TEM), high-resolution TEM, selected area electron diffraction (SAED), X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET). Owing to the small primary Cu NPs and characteristic porous shell and hollow interior, the Cu cages showed an extraordinarily high catalytic activity in the reduction of 4-nitrophenol by NaBH4 in aqueous solution. The activity factor (K = 520 s(-1) g(-1)) is approximately 2.8 times greater than the previous highest K value of unsupported Cu catalysts. In addition, the excellent catalytic activity of the Cu cages in hydrogenation of CO2 to formate, with a TON value of 58 at 200 degrees C, was comparable to that of various noble metal-supported heterogeneous catalysts and surpassed the vast majority of homogeneous first-row transition metal catalysts.