Homogeneously Distributed Cu-ZnO(-Al2O3) Nanoparticles Encapsulated with SiO2 Shells for Superior CO2 Hydrogenation Activity to Methanol

Homogeneously distributed Cu-ZnO(-Al2O3) nanoparticles encapsulated with SiO2 shells (denoted as Cu@Si, CZ@Si, and CZA@Si) are investigated to increase their thermal resistance for stable CO2 hydrogenation activity caused by the newly formed strong metal–support interaction (SMSI) of spatially confined CZA nanoparticles. The core–shell-structured CZA nanoparticles coated with protective silica shell layers revealed a higher CO2 hydrogenation activity to methanol with an excellent catalytic stability. The uniformly distributed core–shell-structured CZA nanoparticles ∼3 nm in size were found to be thermally stable even after CO2 hydrogenation reaction without any structural collapses and insignificant aggregations of the CZA nanoparticles. The spatially confined Cu-based nanoparticles with the help of the SiO2 protective shell layers having larger strong basic sites (oxygen vacant sites) showed a higher CO2 conversion of 11.0–15.8% and selectivity to methanol of 46.3–65.4% for a 200 h reaction, which were mainly attributed to their excellent antiaggregation characteristics through SMSI contributions between CZA core nanoparticles and thermally stable protective SiO2 shell layers.