Hydrogenation of CO 2 to formic acid on supported ruthenium catalysts

Abstract

We report on the preparation and application of novel heterogeneous supported ruthenium catalysts. The catalysts are active in the synthesis of formic acid from the hydrogenation of carbon dioxide and are characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray powder diffraction analysis and transmission electron microscopy. Abundant hydroxyl groups, which interact with the ruthenium components, play an important role in the catalytic reactions. Highly dispersed ruthenium hydroxide species enhance the hydrogenation of CO 2, while crystalline RuO 2 species, which are formed from the relatively high ruthenium content or the pH of the solution during preparation of the catalyst, restrict the production of formic acid. Optimal activity of ruthenium hydroxide as a catalyst for the hydrogenation of CO 2 to formic acid is achieved over a γ-Al 2O 3 supported 2.0 wt% ruthenium catalyst, which is prepared in a solution of pH 12.8 with NH 3·H 2O as a titration solvent. A possible hydrogenation mechanism for the hydroxide ruthenium catalyst is proposed.