Copper nanoparticles confined in hollow silica spheres: Understanding the confinement effect and enhanced catalytic performance for the selective hydrogenation of dimethyl oxalate

Hollow silica spheres (HSS) supported Cu catalysts have been prepared by various methods and systematically characterized. The results indicated that impregnation method (IM) exhibits inferior dispersion of copper species. Compared to the deposition-precipitation (DP) and ammonia evaporation (AE) methods, the catalysts prepared by the one-pot (OP) method exhibit superior catalytic activity, evidenced by their MG yield being more than twice that achieved by the other two methods. This exceptional performance is attributed to the spatial confinement effect of HSS and the strong interaction between the Cu species and the silica support, which not only improves the dispersion of copper, reduces the size of Cu particles, but also enhances the amount of Cu⁺ species. Meanwhile, the positive correlation between the conversion of DMO and the amount of Cu⁺, and the formation of Cu⁺ species within the catalyst enhances the activation of the C-O and C=O bonds in DMO, leading to a marked enhancement in the catalytic performance during the hydrogenation.