Synthesis of C2+ Chemicals from CO2 and H2 via C-C Bond Formation.

Abstract

ConspectusThe severity of global warming necessitates urgent CO2 mitigation strategies. Notably, CO2 is a cheap, abundant, and renewable carbon resource, and its chemical transformation has attracted great attention from society. Because CO2 is in the highest oxidation state of the C atom, the hydrogenation of CO2 is the basic means of converting it to organic chemicals. With the rapid development of H2 generation by water splitting using electricity from renewable resources, reactions using CO2 and H2 have become increasingly important. In the past few decades, the advances of CO2 hydrogenation have mostly been focused on the synthesis of C1 products, such as CO, formic acid and its derivatives, methanol, and methane. In many cases, the chemicals with two or more carbons (C2+) are more important. However, the synthesis of C2+ chemicals from CO2 and H2 is much more difficult because it involves controlled hydrogenation and simultaneous C-C bond formation. Obviously, investigations on this topic are of great scientific and practical significance. In recent years, we have been targeting this issue and have successfully synthesized the basic C2+ chemicals including carboxylic acids, alcohols, and liquid hydrocarbons, during which we discovered several important new reactions and new reaction pathways. In this Account, we systematically present our work and insights in a broad context with other related reports.1.We discovered a reaction of acetic acid production from methanol, CO2 and H2, which is different from the well-known methanol carbonylation. We also discovered a reaction of C3+ carboxylic acids syntheses using ethers to react with CO2 and H2, which proceeds via olefins as intermediates. Following the new reaction, we realized the synthesis of acetamide by introducing various amines, which may inspire the development of further catalytic schemes for preparing a variety of special chemicals using carbon dioxide as a building block.2.We designed a series of homogeneous catalysts to accelerate the production of C2+ alcohols via CO2 hydrogenation. In the heterogeneously catalyzed CO2 hydrogenation, we discovered the role of water in enhancing the synthesis of C2+ alcohols. We also developed a series of routes for ethanol production using CO2 and H2 to react with some substrates, such as methanol, dimethyl ether, aryl methyl ether, lignin, or paraformaldehyde.3.We designed a catalyst that can directly hydrogenate CO2 to C5+ hydrocarbons at 200 °C, not via the traditional CO or methanol intermediates. We also designed a route to couple homogeneous and heterogeneous catalysis, where exceptional results are achieved at 180 °C.