Silica nanowires encapsulated Ru nanoparticles as stable nanocatalysts for selective hydrogenation of CO2 to CO

• Ru@mSiO 2 has been designed by encapsulating Ru nanoparticles with size of 1–3 nm inside mesoporous channels of silica nanowires. • Pretreatment of Ru@mSiO 2 catalyst in nitrogen or air leads to generation of 1–3 nm Ru@mSiO 2 and 5–20 nm Ru@mSiO 2 catalyst, respectively. • Up to 100% selectivity of CO is achieved on 1–3nm Ru@mSiO 2 catalyst, while 95.4% selectivity of CH 4 is achieved on 5–20nm Ru@mSiO 2 catalyst. • DRIFTS study identifies different reaction intermediates formed: CO-Ru n+ on 1–3nm Ru@mSiO 2 and formate on 5–20nm Ru@mSiO 2 . • Stable production of CO with high selectivity has been demonstrated during extended reaction of 50 h. Hydrogenation of carbon dioxide (CO 2 ) to produce useful chemicals has been identified as a promising strategy for mitigation of greenhouse gas emission. Ruthenium (Ru) based catalysts have been reported to be the most active catalysts for the hydrogenation of CO 2 to methane (CH 4 ) which unfortunately is also a greenhouse gas and is difficult to activate. Controlling the hydrogenation selectivity to produce carbon monoxide (CO), a direct precursor for enormous important chemicals, thus becomes desirable. However, achieving high CO selectivity with supported Ru catalysts has remained a challenging task. In this work, we report the synthesis of highly selective and stable Ru@ m SiO 2 nanocatalysts via encapsulation of 1–3 nm Ru nanoparticles within mesoporous silica nanowires for hydrogenation of CO 2 to CO. Calcination of the catalyst in nitrogen prevented sintering of the encapsulated Ru nanoparticles , making high CO selectivity of up to 100% possible, while larger (5–20 nm) Ru particles resulting from calcination in air favored formation of CH 4 . DRIFTS study of 1–3 nm Ru@ m SiO 2 and 5–20 nm Ru@ m SiO 2 catalysts after adsorption of reaction mixture of H 2 and CO 2 reveals that different reaction intermediates form on catalyst surface: CO-Ru n+ on 1–3 nm Ru@ m SiO 2 and formate species on 5–20 nm Ru@ m SiO 2 , which are responsible for the distinctively different selectivity observed on 1–3 nm Ru@ m SiO 2 and 5–20 nm Ru@ m SiO 2 catalysts. Plausible reaction pathways have been proposed for selective hydrogenation of CO 2 on the two types of catalysts, respectively. In addition, high CO selectivity of 1–3 nm Ru@ m SiO 2 catalyst has been demonstrated to be stable.