The increase in atmospheric carbon dioxide is linked to climate changes; hence there is an urgent need to reduce the accumulation of CO2 in the atmosphere. The utilization of CO2 as a raw material in the synthesis of chemicals and liquid energy carriers offers a way to mitigate the increasing CO2 buildup. This review covers six important CO2 transformations namely: chemical transformations, photochemical reductions, chemical and electrochemical reductions, biological conversions, reforming and inorganic transformations. Furthermore, the vast research area of carbon capture and storage is reviewed briefly. This review is intended as an introduction to CO2, its synthetic reactions and their possible role in future CO2 mitigation schemes that has to match the scale of man-made CO2 in the atmosphere, which rapidly approaches 1 teraton.

The teraton challenge. A review of fixation and transformation of carbon dioxide

Two major energy-related problems confront the world in the
next 50 years. First, increased worldwide competition for
gradually depleting fossil fuel reserves (derived from past
photosynthesis) will lead to higher costs, both monetarily and politically. Second, atmospheric CO_2 levels are at their highest recorded level since records began. Further increases are predicted to produce large and uncontrollable impacts on the world climate. These projected impacts extend beyond climate to ocean acidification, because the ocean is a major sink for atmospheric CO2.1 Providing a future energy supply that is secure and CO_2-neutral will require switching to nonfossil energy sources such as wind, solar, nuclear, and geothermal energy and developing methods for transforming the energy produced by these new sources into forms that can be stored, transported, and used upon demand.

Frontiers, Opportunities, and Challenges in Biochemical and Chemical Catalysis of CO2 Fixation

There is increased recognition by the world’s scientific, industrial, and political communities that the concentrations of greenhouse gases in the earth’s
atmosphere, particularly CO_2, are increasing. For
example, recent studies of Antarctic ice cores to
depths of over 3600 m, spanning over 420 000 years,
indicate an 80 ppm increase in atmospheric CO_2 in
the past 200 years (with most of this increase
occurring in the past 50 years) compared to the
previous 80 ppm increase that required 10 000 years.2
The 160 nation Framework Convention for Climate
Change (FCCC) in Kyoto focused world attention on
possible links between CO2 and future climate change
and active discussion of these issues continues.3 In
the United States, the PCAST report4 “Federal
Energy Research and Development for the Challenges
of the Twenty First Century” focused attention
on the growing worldwide demand for energy and the
need to move away from current fossil fuel utilization.
According to the U.S. DOE Energy Information
Administration,5 carbon emission from the transportation
(air, ground, sea), industrial (heavy manufacturing,
agriculture, construction, mining, chemicals,
petroleum), buildings (internal heating, cooling, lighting),
and electrical (power generation) sectors of the
World economy amounted to ca. 1823 million metric
tons (MMT) in 1990, with an estimated increase to
2466 MMT in 2008-2012 (Table 1).

Catalysis Research of Relevance to Carbon Management: Progress, Challenges, and Opportunities

The recent literature on photochemical and photoelectrochemical reductions of CO(2) is reviewed. The different methods of achieving light absorption, electron-hole separation, and electrochemical reduction of CO(2) are considered. Energy gap matching for reduction of CO(2) to different products, including CO, formic acid, and methanol, is used to identify the most promising systems. Different approaches to lowering overpotentials and achieving high chemical selectivities by employing catalysts are described and compared.

https://www.annualreviews.org/doi/pdf/10.1146/annurev-physchem-032511-143759

Photochemical and Photoelectrochemical Reduction of CO2

Ruthenium-Catalyzed Reactions for Organic Synthesis.

A series of copper(II) complexes with tripodal polypyridylmethylamine ligands, such as tris(2-pyridylmethyl)amine (tpa), ((6-methyl-2-pyridyl)methyl)bis(2-pyridylmethyl)amine (Me1tpa), bis((6-methyl-2-pyridyl)methyl)(2-pyridylmethyl)amine (Me2tpa), and tris((6-methyl-2-pyridyl)methyl)amine (Me3tpa), have been synthesized and characterized by X-ray crystallography. [Cu(H2O)(tpa)](ClO4)2 (1) crystallized in the monoclinic system, space group P21/a, with a = 15.029(7) A, b = 9.268(2) A, c = 17.948(5) A, β = 113.80(3)°, and Z = 4 (R = 0.061, Rw = 0.059). [CuCl(Me1tpa)]ClO4 (2) crystallized in the triclinic system, space group P1, with a = 13.617(4) A, b = 14.532(4) A, c = 12.357(4) A, α = 106.01(3)°, β = 111.96(2)°, γ = 71.61(2)°, and Z = 4 (R = 0.054, Rw = 0.037). [CuCl(Me2tpa)]ClO4 (3) crystallized in the monoclinic system, space group P21/n, with a = 19.650(4) A, b = 13.528(4) A, c = 8.55(1) A, β = 101.51(5)°, and Z = 4 (R = 0.071, Rw = 0.050). [CuCl(Me3tpa)][CuCl2(Me3tpa)]ClO4 (4) crystallized in the mon...

Structural and Electrochemical Comparison of Copper(II) Complexes with Tripodal Ligands

Chemical reactions of [Ru(bpy){sub 2}(CO){sub 2}](PF{sub 6}){sub 2} (1) of [Ru(bpy)(trpy)(CO)](PF{sub 6}){sub 2} (2) with OH{sub -} lead to formation of hydroxycarbonyls, such as [Ru(bpy){sub 2}(CO)(CH{sub 2}OH)]PF{sub 6} (3). Crystal structures are reported for 1, 2, and 3. The organic oxygen compound products for the electrochemical reduction of 1 and 2 were identified.

Carbon-Carbon Bond Formation in the Electrochemical Reduction of Carbon Dioxide Catalyzed by a Ruthenium Complex

The molecular structures of [Ru(bpy)[sub 2](CO)[sub 2]](PF[sub 6])[sub 2], [Ru(bpy)[sub 2](CO)(C(O)OCH[sub 3])]B(C[sub 6]H[sub 5])[sub 4][center dot]CH[sub 3]CN as a model complex of [Ru(bpy)[sub 2](CO)(C(O)OH)][sup +], and [Ru(bpy)[sub 2](CO)([eta][sup 1]-CO[sub 2])][center dot]3H[sub 2]O have been determined by X-ray analysis. The observation that the Ru-C(O)OCH[sub 3] bond distance of [Ru(bpy)[sub 2](CO)(C(O)OCH[sub 3])][sup +] i shorter than the Ru-CO[sub 2] one of [Ru(bpy)[sub 2](CO)(CO[sub 2])] suggests that the multibond character of the Ru-CO[sub 2] bond is not larger than that for Ru-C(O)OCH[sub 3]. One extra electron pair involved in [Ru(bpy)[sub 2](CO)(CO[sub 2])] resulting from dissociation of a terminal proton of [Ru(bpy)[sub 2](CO)(C(O)OH)][sup +] may be mainly localized in the CO[sub 2] ligand rather than delocalized over the RuCO[sub 2] moiety, and the extended three-dimensional network of hydrogen bonding between the CO[sub 2] ligand and three hydrated water molecules compensates the increase in the electron density of the CO[sub 2] moiety of [Ru(bpy)[sub 2](CO)(CO[sub 2])][center dot]3H[sub 2]O. 19 refs., 7 figs.

Comparative study on crystal structures of ruthenium bipyridine carbonyl complexes [Ru(bpy)2(CO)2](PF6)2, [Ru(bpy)2(CO)(C(O)OCH3)]B(C6H5)4.cntdot.CH3CN, and [Ru(bpy)2(CO)(.eta.1-CO2)].cntdot.3H2O (bpy = 2,2'-bipyridyl)

Hirotaka Nagao

Papers

Structural and Electrochemical Comparison of Copper(II) Complexes with Tripodal Ligands

Carbon-Carbon Bond Formation in the Electrochemical Reduction of Carbon Dioxide Catalyzed by a Ruthenium Complex

Comparative study on crystal structures of ruthenium bipyridine carbonyl complexes [Ru(bpy)2(CO)2](PF6)2, [Ru(bpy)2(CO)(C(O)OCH3)]B(C6H5)4.cntdot.CH3CN, and [Ru(bpy)2(CO)(.eta.1-CO2)].cntdot.3H2O (bpy = 2,2'-bipyridyl)

Ruthenium Formyl Complexes as the Branch Point in Two- and Multi-Electron Reductions of CO2

Redox- and Thermally-Induced Nitro-Nitrito Linkage Isomerizations of Ruthenium(II) Complexes Having Nitrosyl as a Spectator Ligand