Visible-Light Photocatalytic Reduction of CO2 to Formic Acid with a Ru Catalyst Supported by N,N'-Bis(diphenylphosphino)-2,6-diaminopyridine Ligands

Efficient Visible-Light-Driven Carbon Dioxide Reduction using a Bioinspired Nickel Molecular Catalyst

Inspired by natural enzymes, this study presents a nickel-based molecular catalyst, [Ni‖(N2S2)]Cl2 (NiN2S2, N2S2=2,11-dithia[3,3](2,6)pyridinophane), for the photochemical catalytic reduction of CO2 under visible light. The catalyst was synthesized and characterized using various techniques, including liquid chromatography-high resolution mass spectrometry (LC-HRMS), UV-Visible spectroscopy, and X-ray crystallography. The crystallographic analysis revealed a slightly distorted octahedral coordination geometry with a mononuclear Ni2+ cation, two nitrogen atoms and two sulfur atoms. Photocatalytic CO2 reduction experiments were performed in homogeneous conditions using the catalyst in combination with [Ru(bpy)3]Cl2 (bpy=2,2'-bipyridine) as a photosensitizer and 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH) as a sacrificial electron donor. The catalyst achieved a high selectivity of 89 % towards CO and a remarkable turnover number (TON) of 7991 during 8 h of visible light irradiation under CO2 in the presence of phenol as a co-substrate. The turnover frequency (TOF) in the initial 6 h was 1079 h-1, with an apparent quantum yield (AQY) of 1.08 %. Controlled experiments confirmed the dependency on the catalyst, light, and sacrificial electron donor for the CO2 reduction process. These findings demonstrate this bioinspired nickel molecular catalyst could be effective for fast and efficient photochemical catalytic reduction of CO2 to CO.

Heterogeneous Catalysis in Production and Utilization of Formic Acid for Renewable Energy

As the cleanest energy source, hydrogen has been followed with interest by researchers around the world. However, due to the internal low density of hydrogen, it cannot be stored and used efficiently which limits the hydrogen application on a huge scale. Chemical hydrogen storage is considered as a useful method for efficient handling and storage. Due to its excellent safety, formic acid stands out. It is worth noting that the matter and energy conversion is established based on formic acid, which is not referred to in the previous documentation. In this review, the latest development of research on heterogeneous catalysis via production and application of formic acid for energy application is reported. The matter and energy conversion based on formic acid are both discussed systematically. More importantly, with formic acid as the node, biomass energy shows potential to be in a dominant position in the energy conversion process. In addition, the catalytic mechanism is also mentioned. This review can provide the current state in this field and the new inspirations for developing superior catalytic systems.

Formic Acid Generation from CO2 Reduction by MOF-253 Coordinated Transition Metal Complexes: A Computational Chemistry Perspective

The inclusion of transition metal elements within metal–organic frameworks (MOFs) is considered one of the most promising approaches for enhancing the catalytic capability of MOFs. In this study, MOF-253 containing bipyridine coordination sites is investigated for possible transition metal chelation, and a consequent possible CO2 reduction mechanism in the formation of formic acid. All transition metal elements of the third, fourth and fifth periods except hafnium and the lanthanide series are considered using density functional theory calculations. Two distinct types of CO2 reduction mechanisms are identified: (1) the five-coordination Pd center, which promotes formic acid generation via an intramolecular proton transfer pathway; (2) several four-coordination metal centers, including Mn, Pd, and Pt, which generate formic acid by means of heterolytic hydrogen activation. The MOF-253 environment is found to promote beneficial steric hindrance, and to constrain metal–ligand orientation, which consequently facilitates the formation of formic acid, particularly with the tetrahedral Mn center at high-spin electronic state.

Towards Sustainable Oxalic Acid from CO2 and Biomass

To quickly and drastically reduce CO2 emissions and meet our ambitions of a circular future, we need to develop carbon capture and storage (CCS) and carbon capture and utilization (CCU) to deal with the CO2 that we produce. While we have many alternatives to replace fossil feedstocks for energy generation, for materials such as plastics we need carbon. The ultimate circular carbon feedstock would be CO2 . A promising route is the electrochemical reduction of CO2 to formic acid derivatives that can subsequently be converted into oxalic acid. Oxalic acid is a potential new platform chemical for material production as useful monomers such as glycolic acid can be derived from it. This work is part of the European Horizon 2020 project "Ocean" in which all these steps are developed. This Review aims to highlight new developments in oxalic acid production processes with a focus on CO2 -based routes. All available processes are critically assessed and compared on criteria including overall process efficiency and triple bottom line sustainability.

Tuning of Ionic Second Coordination Sphere in Evolved Rhenium Catalyst for Efficient Visible-Light-Driven CO2 Reduction

Developing an efficient and easy-to-handle strategy in designing catalysts for CO₂ reduction into CO by harnessing sunlight is a promising project. Here, a facile strategy was developed to design a Re catalyst modified with an ionic secondary coordination sphere for photoreduction of CO₂ to CO by visible light. By adding ionic liquids or tuning a different ionic secondary coordination sphere, it was discovered that an outstanding optical property, other than CO₂ absorption ability or the ability to dissociation of chloride anion, is the prerequisite for catalyst design. Accordingly, a novel Re catalyst, {Re[BpyMe(tris(2-hydroxyethyl)amine)](CO)₃ Cl}Br (Re-THEA), was designed, screened, and resulted in a relative high quantum yield (up to 34 %) for visible-light-induced CO₂ reduction with a single-molecule system. DFT calculations, combined with experimental outcomes, suggested the pendant ionic tris(2-hydroxyethyl)amino (THEA) group on Re-THEA can enhance visible-light absorption, stabilize reaction intermediates, and suppress the Re-Re dimer formation.