A Facile Strategy for Constructing a Carbon‐Particle‐Modified Metal–Organic Framework for Enhancing the Efficiency of CO 2 Electroreduction into Formate

Direct Conversion of CO2 in Lime Kiln Waste Gas Catalyzed by a Copper-Based N-heterocyclic Carbene Porous Polymer

Industrial waste gas is one of the major sources of atmospheric CO₂ , yet the direct conversion of the low concentrations of CO₂ in waste gases into high value-added chemicals have been a great challenge. Herein, a copper-based N-heterocyclic carbene porous polymer catalyst (Cu@NHC-1) for the direct conversion of low concentration CO₂ into oxazolidinones was successfully fabricated via a facile copolymerization process followed by the complexation with Cu(OAc)₂ . A continuous flow device was designed to deliver a continuous and stable carbon source for the reaction. Due to the triple synergistic effect of its porous structure, nitrogen activation sites and catalytic Cu center, Cu@NHC-1 shows highly efficient and selective adsorption, activation, and conversion of the low concentration CO₂ (30 vol%). Its practical application potential is demonstrated by the ability to successfully convert the CO₂ in lime kiln waste gas into oxazolidinones in satisfactory yields under mild conditions.

Metal-Organic Frameworks as Electrocatalysts

Transition metal complexes are well-known homogeneous electrocatalysts. In this regard, metal-organic frameworks (MOFs) can be considered as an ensemble of transition metal complexes ordered in a periodic arrangement. In addition, MOFs have several additional positive structural features that make them suitable for electrocatalysis, including large surface area, high porosity, and high content of accessible transition metal with exchangeable coordination positions. The present review describes the current state in the use of MOFs as electrocatalysts, both as host of electroactive guests and their direct electrocatalytic activity, particularly in the case of bimetallic MOFs. The field of MOF-derived materials is purposely not covered, focusing on the direct use of MOFs or its composites as electrocatalysts. Special attention has been paid to present strategies to overcome their poor electrical conductivity and limited stability.

Single-ion chelation strategy for synthesis of monodisperse Pd nanoparticles anchored in MOF-808 for highly efficient hydrogenation and cascade reactions

Ultrafine Pd nanoparticles are prepared using a single-ion precursor on a MOF-808 carrier. The ligand 2,3-pyrazinedicarboxylic acid (Pza) is dispersed in porous MOF-808 via grafting on formic acid sites, and thus Pd²⁺ ions are chelated by Pza to form a new single-ion precursor Pd@MOF-808-Pza. Then a Pd-nano@MOF-808-Pza catalyst is prepared by direct reduction of this precursor using NaBH₄. Material characterization reveals the homogeneous dispersion of 3-6 nm Pd nanoparticles within the MOF-808 matrix. Pd-nano@MOF-808-Pza exhibits excellent catalytic activity in the hydrogenation of unsaturated nitrogen-containing compounds, and other typical reactions, such as the Knoevenagel condensation, Suzuki/Heck cross-coupling, and hydrogen tandem reactions. In addition, density functional theory (DFT) calculations are carried out to elucidate the chelation of Pd²⁺ ions by Pza on MOF-808 and propose mechanisms of hydrogenation reactions. This work provides an effective reduction catalyst, and more importantly, a single-ion chelation strategy for design and synthesis of metal supported catalysts.

Carbon-Confined Indium Oxides for Efficient Carbon Dioxide Reduction in a Solid-State Electrolyte Flow Cell

Developing robust electrocatalysts and advanced devices is important for electrochemical carbon dioxide (CO₂ ) reduction toward the generation of valuable chemicals. We present herein a carbon-confined indium oxide electrocatalyst for stable and efficient CO₂ reduction. The reductive corrosion of oxidative indium to the metallic state during electrolysis could be prevented by carbon protection, and the applied carbon layer also optimizes the reaction intermediate adsorption, which enables both high selectivity and activity for CO₂ reduction. In a liquid-phase flow cell, the formate selectivity exceeds 90 % in a wide potential window from -0.8 V to -1.3 V vs. RHE. The continuous production of ca. 0.12 M pure formic acid solution is further demonstrated at a current density of 30 mA cm^-2 in a solid-state electrolyte mediated reactor. This work provides significant concepts in the parallel development of electrocatalysts and devices for carbon-neutral technologies.

Selectively Regulating Lewis Acid-Base Sites in Metal-Organic Frameworks for Achieving Turn-On/Off of the Catalytic Activity in Different CO2 Reactions

Regulating Lewis acid-base sites in catalysts to investigate their influence in the chemical fixation of CO₂ is significant but challenging. A metal-organic framework (MOF) with open metal Co sites, {(NH₂ Me₂ )[Co₃ (μ₃ -OH)(BTB)₂ (H₂ O)]⋅9 H₂ O⋅5 DMF}_n (1), was obtained and the results of the catalytic investigation show that 1 can catalyze cycloaddition of CO₂ and aziridines to give 99 % yield. The efficiency of the cyclization of CO₂ with propargyl amines is only 32 %. To improve the catalytic ability of 1, ligand XN with Lewis base sites was introduced into 1 and coordinated with the open Co sites, resulting in a decrease of the Lewis acid sites and an increase in the Lewis base sites in a related MOF 2 ({(NH₂ Me₂ )[Co₃ (μ₃ -OH)(NHMe₂ )(BTB)₂ (XN)]⋅8 H₂ O⋅4 DMF}_n ). Selective regulation of the type of active centers causes the yield of oxazolidinones to be enhanced by about 2.4 times, suggesting that this strategy can turn on/off the catalytic activity for different reactions. The catalytic results from 2 treated with acid solution support this conclusion. This work illuminates a MOF-construction strategy that produces efficient catalysts for CO₂ conversion.