Abstract
Processes for the conversion of CO2 to valuable chemicals are highly desired as a result of the increasing CO2 levels in the atmosphere and the subsequent elevating global temperature. However, CO2 is thermodynamically and kinetically inert to transformation and, therefore, many efforts were made in the last few decades. Reformation/hydrogenation of CO2 is widely used as a means to access valuable products such as acetic acids, CH4, CH3OH, and CO. The electrochemical reduction of CO2 using hetero- and homogeneous catalysts recently attracted much attention. In particular, molecular CO2 reduction catalysts were widely studied using transition-metal complexes modified with various ligands to understand the relationship between various catalytic properties and the coordination spheres above the metal centers. Concurrently, the coupling of CO2 with various electrophiles under homogeneous conditions is also considered an important approach for recycling CO2 as a renewable C-1 substrate in the chemical industry. This review summarizes some recent advances in the conversion of CO2 into valuable chemicals with particular focus on the metal-catalyzed reductive conversion and functionalization of CO2.
Highlights
Many efforts were devoted in the recent decades to utilizing CO2 as a source for renewable energy and materials
The substantial energy barrier in activating CO2 is reflected by the highly negative formal reduction potential of −2.14 V vs. saturated calomel electrode (SCE) for the one-electron reduction of CO2 to CO2 − [18,19,24], where a large overpotential is required for the rapid reduction of CO2 to occur, largely as a result of the structural difference between the linear CO2 and bent CO2 – [19,20,24,25,26]
The results showed that the catalytic source (PhOH, CH3COOH, CF3CH2OH) [28]
Summary
Many efforts were devoted in the recent decades to utilizing CO2 as a source for renewable energy and materials. Direct gas-phase reactions of CO2 with other readily accessible small molecules, e.g., via the reformation with CH4 to produce syngas (CO/H2 ) and acetic acid (Equations (1) and (2)), as well as hydrogenation to produce CH4 , CH3 OH, and CO (Equations (3)–(5)), were widely studied using mainly heterogeneous or supported metal catalysts [1,2,3,4,5,6,7]. Given the wide variety of related processes, the discussion below focuses on transition-metal catalysts for the electroreduction and functionalization of CO
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