Fabrication of Porous Silica-ruthenium Oxide Composite Catalysts for Hydrogenation of Carbon Dioxide Into Formic Acid

Abstract

Porous silica–ruthenium oxide composite catalysts were prepared with sol–gel-based method using a cationic surfactant, cethyltrimethylammonium bromide (CTAB), as templates to form well-ordered nanopores in the catalyst particles. The previously reported heterogeneous catalysts for hydrogenation of carbon dioxide into formic acid generally worked as metallic state, while the catalyst in the present study worked without reduction procedure for the catalyst activation to obtain the metallic states of the active ruthenium species. The textural properties of the catalysts in this work were affected by various pretreatment procedures, and washing and calcination pretreatments were identified as effective procedures to remove the surfactant micelle templates with 2–4 times higher specific surface area and pore volumes. The catalytic activity also improved with the pretreatments, and the catalyst with washing followed by calcination showed nearly three times higher activity than the catalyst without any pretreatments. The crystalline size of the active ruthenium species and the catalytic performance of porous silica–ruthenium oxide composite catalyst was influenced by amount of TEOS, the catalyst including small RuO₂ crystalline phase was obtained with high amount of TEOS and exhibited high activity for hydrogenation of carbon dioxide into formic acid with comparative TON to previously reported metallic ruthenium-based catalysts.