Heterogeneous Hydrogenation Of Carbon Dioxide To Formic Acid Over The Supported Ruthenium Catalyst

As the development of society and economy, a large quantity of Carbon dioxide (CO₂) was produced from many industrial processes and it becomes a major contributor to the greenhouse effect. Formic acid is an important organic industrial chemical, and the traditional methods of formic acid synthesis consume a lot of energy and cause environmental pollution. Synthesis of formic acid from hydrogenation of carbon dioxide is an atom-economic reaction which consistent with the'green chemistry'concept. Therefore, the development of clean synthesis of formic acid from carbon dioxide as raw material is of great significance and potential for both economy and environment.The heterogeneous hydrogenation of supercritical carbon dioxide to formic acid over the supported hydroxide ruthenium catalyst was investigated in this paper. Evaluation results showed that ruthenium supported onγ-Al₂O₃ catalyst has an favourable catalytic performance in the hydrogenation. 139 mol/h·molRu TON of formic acid was obtained over supported Ru catalyst with Ru content 2.0 wt.%, catalyst preparation solution pH=12.8 and NH3·H₂O precipitator when T 80℃, stirring rate 300 r/min and PH₂=5.0 MPa/13.5 MPa.The physicochemical properties of the ruthenium catalysts were investigated via FT-IR, XRD, XPS and TEM. By means of FT-IR and XPS, it is indicated that the presence of abundant hydroxyl groups on the support plays an important role in the catalytic reactions, and the interaction between active ruthenium components with hydroxyl groups through formation of Ru?OH species as the active species is crucial for the reaction. Characterization results of XRD and TEM showed that the highly dispersed ruthenium hydroxide species enhance the hydrogenation of CO₂, while crystalline RuO₂ species, which are formed from the relatively high ruthenium content or the pH of the solution during the preparation of catalysts, restrict the production of formic acid. Moreover, a possible hydrogenation mechanism for the hydroxide ruthenium catalyst is proposed.