Selective hydrogenation of CO2 gas to formic acid over nanostructured Ru-TiO2 catalysts

Abstract

A series of ruthenium catalysts were synthesized using a well-established micro-emulsion protocol. All the catalysts were well characterized by sophisticated analytical techniques, such as XRD, BET surface area, XPS, TEM, H₂-TPR and CO-chemisorption measurements. Subsequently, the ruthenium catalysts were tested for the selective synthesis of formic acid followed by CO₂ hydrogenation reaction. The influences of the matrix nature as well as the catalyst composition were also examined in detail. Ru with only a low loading on the TiO₂ support was found to be highly active in terms of the formic acid quantity (TON/TOF) compared to a high loading of Ru over the TiO₂ support. Apart from the Ru catalysts, we also synthesized a series of functionalized ionic liquids to apply them as a reaction medium, not only for the hydrogenation reaction but also to anchor the formic acid (hydrogenation product). Such advanced applications of ionic liquids helped to run the reaction in a more optimized way to obtain maximum selectivity in terms of a high TON/TOF value of formic acid with the added benefit of catalyst recycling for at least ten cycles.