The particle size control of ruthenium-encapsulated hollow silica sphere catalysts for the hydrogenation of carbon dioxide into formic acid

In the present study, the control of particle size of ruthenium-encapsulated hollow silica catalysts is reported. For controlling the size, the preparation conditions of carbon sphere template particles for fabricating hollow silica sphere support materials were investigated. The particle size of templates depends on the settling temperature of glucose solutions before hydrothermal treatment for template preparation and glucose concentrations. Especially, the particle size of hollow spheres decreases with a decrease in glucose concentrations. The results of Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy indicated that the hydrolysis reaction of glucose proceeded at high settling temperatures before hydrothermal treatment and in solutions with high glucose concentrations to give carbon sphere templates, and templates with small particle size were obtained following the hydrothermal treatment. Ruthenium-encapsulated hollow silica sphere catalysts prepared using hollow silica sphere supports with small particle size contained highly dispersed active ruthenium species and exhibited high catalytic activity for the hydrogenation of carbon dioxide into formic acid.