Ruthenium-hydrotalcite (Ru-HT) as an effective heterogeneous catalyst for the selective hydrogenation of CO2 to formic acid

Abstract

The reaction containing CO2 and H2 has been investigated for the hydrogenation of CO2 to formic acid using ruthenium hydrotalcite (Ru-HT) catalyst. Ruthenium salt was introduced to the synthesis of hydrotalcite as an active metal center to develop ruthenium based heterogeneous catalyst. Hydrotalcite not only acted as a support for the active metal but also acted as a soft solid base avoiding the use of the liquid base, which is normally required under homogeneous conditions for the formation of formic acid from the hydrogenation of CO2. Reaction temperatures were in the range of 40–100 °C, total pressure 10–100 bar with an ideal 1:1 ratio of pCO2:pH2. The maximum Turnover Number (TON) of 11389 was obtained for the formic acid formation under the optimized conditions at 60 °C temperature and 60 bar total pressure, using a mixture of methanol:water as a solvent (5:1, v/v). Ru-HT catalyst was synthesised and thorougly characterized by FT-IR, PXRD, SEM-EDX and surface area analysis. The catalyst was effectively recycled up to 7 times without any loss in catalytic activity.