A New Approach to the Reduction of Carbon Dioxide: CO2 Reduction to Formate by Transfer Hydrogenation in iPrOH

Confinement Effects in Well-Defined Metal-Organic Frameworks (MOFs) for Selective CO2 Hydrogenation: A Review

Decarbonization has become an urgent affair to restrain global warming. CO₂ hydrogenation coupled with H₂ derived from water electrolysis is considered a promising route to mitigate the negative impact of carbon emission and also promote the application of hydrogen. It is of great significance to develop catalysts with excellent performance and large-scale implementation. In the past decades, metal-organic frameworks (MOFs) have been widely involved in the rational design of catalysts for CO₂ hydrogenation due to their high surface areas, tunable porosities, well-ordered pore structures, and diversities in metals and functional groups. Confinement effects in MOFs or MOF-derived materials have been reported to promote the stability of CO₂ hydrogenation catalysts, such as molecular complexes of immobilization effect, active sites in size effect, stabilization in the encapsulation effect, and electron transfer and interfacial catalysis in the synergistic effect. This review attempts to summarize the progress of MOF-based CO₂ hydrogenation catalysts up to now, and demonstrate the synthetic strategies, unique features, and enhancement mechanisms compared with traditionally supported catalysts. Great emphasis will be placed on various confinement effects in CO₂ hydrogenation. The challenges and opportunities in precise design, synthesis, and applications of MOF-confined catalysis for CO₂ hydrogenation are also summarized.

A Comprehensive Review on Graphitic Carbon Nitride for Carbon Dioxide Photoreduction

Inspired by natural photosynthesis, harnessing the wide range of natural solar energy and utilizing appropriate semiconductor-based catalysts to convert carbon dioxide into beneficial energy species, for example, CO, CH₄ , HCOOH, and CH₃ COH have been shown to be a sustainable and more environmentally friendly approach. Graphitic carbon nitride (g-C₃ N₄ ) has been regarded as a highly effective photocatalyst for the CO₂ reduction reaction, owing to its cost-effectiveness, high thermal and chemical stability, visible light absorption capability, and low toxicity. However, weaker electrical conductivity, fast recombination rate, smaller visible light absorption window, and reduced surface area make this catalytic material unsuitable for commercial photocatalytic applications. Therefore, certain procedures, including elemental doping, structural modulation, functional group adjustment of g-C₃ N₄ , the addition of metal complex motif, and others, may be used to improve its photocatalytic activity towards effective CO₂ reduction. This review has investigated the scientific community's perspectives on synthetic pathways and material optimization approaches used to increase the selectivity and efficiency of the g-C₃ N₄ -based hybrid structures, as well as their benefits and drawbacks on photocatalytic CO₂ reduction. Finally, the review concludes a comparative discussion and presents a promising picture of the future scope of the improvements.

Nitrogen–nitrogen-functionalized N-heterocyclic carbene ruthenium(ii) complexes realized efficient CO2 hydrogenation to formate

Three new Ru–CNN complexes are synthesized for the hydrogenation of CO2 to formate. The Ru–CNN complex exhibits a long lifetime of over 400 h at 170 °C with a high TON of 6.5 × 105.

Reduction of Carbon Dioxide with Ammonia-Borane under Ambient Conditions: Maneuvering a Catalytic Way

In the development of alternatives to the traditional catalytic hydrogenation of CO₂ with gaseous H₂, employing nongaseous H₂ storage compounds as potential reductants for catalytic transfer hydrogenation of CO₂ is promising. Ammonia-borane, due to its high hydrogen storage capacity (19.6 wt %), has been used for catalytic transfer hydrogenation of several organic unsaturated compounds. However, a similar protocol involving catalytic transfer hydrogenation of less reactive CO₂ with NH₃BH₃ is yet to be realized experimentally. Herein, we demonstrate the first catalytic CO₂ transfer hydrogenation process for generating formate salt with NH₃BH₃ under ambient conditions (1 atm and 30 °C) employing a cationic "Ir(III)-abnormal NHC" catalyst via an electrophilic NH₃BH₃ activation route. It exhibited an initial turnover frequency of 686 h^-1 and a high turnover number (TON) of ≈1300 in just 4 h. Most significantly, the catalyst was durable enough to maintain long-term activity, and upon only periodic recharging of NH₃BH₃, it furnished a total TON of >4200 in 10 h.

Iridium(NHC)-Catalyzed Sustainable Transfer Hydrogenation of CO2 and Inorganic Carbonates

Iridium(NHC)-catalyzed transfer hydrogenation (TH) of CO2 and inorganic carbonates with glycerol were conducted, demonstrating excellent turnover numbers (TONs) and turnover frequencies (TOFs) for the formation of formate and lactate. Regardless of carbon sources, excellent TOFs of formate were observed (CO2: 10,000 h−1 and K2CO3: 10,150 h−1). Iridium catalysts modified with the triscarbene ligand showed excellent catalytic activity at 200 °C and are a suitable choice for this transformation which requires a high temperature for high TONs of formate. On the basis of the control experiments, the transfer hydrogenation mechanism of CO2 was proposed.

Recent Progress with Pincer Transition Metal Catalysts for Sustainability

Our planet urgently needs sustainable solutions to alleviate the anthropogenic global warming and climate change. Homogeneous catalysis has the potential to play a fundamental role in this process, providing novel, efficient, and at the same time eco-friendly routes for both chemicals and energy production. In particular, pincer-type ligation shows promising properties in terms of long-term stability and selectivity, as well as allowing for mild reaction conditions and low catalyst loading. Indeed, pincer complexes have been applied to a plethora of sustainable chemical processes, such as hydrogen release, CO2 capture and conversion, N2 fixation, and biomass valorization for the synthesis of high-value chemicals and fuels. In this work, we show the main advances of the last five years in the use of pincer transition metal complexes in key catalytic processes aiming for a more sustainable chemical and energy production.

A reduced graphene oxide-supported iridium nanocatalyst for selective transformation of alcohols into carbonyl compounds via a green process

A nanocatalyst constructed from reduced graphene oxide and iridium atoms (RGOIrNc) showed high selectivity (99%-100%) and reliability for the transformation of aromatic alcohols into carbonyl compounds via ultrasonication without using harmful chemicals and solvents. Experimental data including Fourier transform infrared spectroscopy, x-ray diffraction, spherical-aberration-corrected field emission transmission electron microscopy and Raman spectra confirmed the nanostructure of the RGOIrNc. Noticeably, the structural characteristics of this catalyst remained unchanged within 25 catalytic cycles and the activity and selectivity for the transformation of benzylic alcohols showed good stability. The average turnover frequency is greater than 9000 h^-1, the total turnover number is more than 150 000 after 25 catalytic cycles and the productivity of carbonyl compounds reaches 376 048 [Formula: see text], indicating that RGOIrNc catalyst has good durability and stability and high 'greenness'.

Transfer hydrogenation of carbon dioxide via bicarbonate promoted by bifunctional C-N chelating Cp*Ir complexes

Metal-ligand cooperative Cp*Ir(iii) complexes derived from primary benzylic amines effectively promote transfer hydrogenation of atmospheric CO2 using 2-propanol at 80 °C. Isotope-labelling experiments strengthen that active Ir species can preferentially reduce bicarbonate congeners formed from CO2. The powerful transfer hydrogenation catalyst exhibits remarkable activity for the conversion of bicarbonates into formate salts with a turnover number up to 3200, even without H2 and CO2.

Catalytic hydrogenation of carbonyl and nitro compounds using an [N,O]-chelate half-sandwich ruthenium catalyst

A series of N,O-chelate half-sandwich ruthenium complexes have been synthesized, which exhibited high activity for the catalytic hydrogenation of carbonyl and nitro compounds in aqueous solution.

Transfer hydrogenation of carbon dioxide and bicarbonate from glycerol under aqueous conditions

Catalytic transfer hydrogenation of CO₂ from glycerol to afford formic and lactic acid is an attractive path to valorizing two waste streams. The process is significantly more thermodynamically favorable than direct CO₂ hydrogenation.

Flexible proton-responsive ligand-based Mn(i) complexes for CO2 hydrogenation: a DFT study

Significance of a flexible proton responsive ligand to the dihydrogen (H⋯H) bond for CO₂ hydrogenation.

New Ru(ii) N′NN′-type pincer complexes: synthesis, characterization and the catalytic hydrogenation of CO2 or bicarbonates to formate salts

A new homogeneous system based on new Ru(ii)-N′NN′ pincer complexes has been successfully applied to the hydrogenation of CO₂ to the formate, and complex 4 exhibits the best catalytic efficiency.

Aryl appended neutral and cationic half-sandwich ruthenium(ii)–NHC complexes: synthesis, characterisation and catalytic applications

Aryl appended half-sandwich Ru(ii)–NHC complexes were synthesised and their use as selective catalysts for transfer hydrogenation of aromatic ketones was demonstrated.

Recent developments in the catalytic hydrogenation of CO2 to formic acid/formate using heterogeneous catalysts

This review highlights the recent trends in the heterogeneous hydrogenation of CO₂ to formic acid/formate.

Highly efficient hydrogenation of carbon dioxide to formate catalyzed by iridium(iii) complexes of imine-diphosphine ligands

A new iridium catalyst containing an imine-diphosphine ligand has been developed, which showed high efficiency for the hydrogenation of CO₂ to formate (yield up to 99%, TON up to 450 000). A possible catalytic mechanism is proposed, in which the imine group of the catalyst plays a key role in the cleavage of H₂ and the activation of CO₂.

Mechanistic studies on the pH-controllable interconversion between hydrogen and formic acid in water: DFT insights

Our theoretical results will facilitate the mechanistic understanding of sustainable H₂ storage/delivery in homogeneous catalysis.

Utilisation of water soluble iridium catalysts for signal amplification by reversible exchange

The catalytic hyperpolarisation of pyridine, 3-hydroxypyridine and oxazol by the Signal Amplification By Reversible Exchange (SABRE) process is achieved by a series of water soluble iridium phosphine and N-heterocyclic carbene dihydride complexes.