Catalysis research of relevance to carbon management: progress, challenges, and opportunities

Modulation of the electronic structure of nitrogen-carbon sites by sp3-hybridized carbon coupled to chloride ions improves electrochemical carbon dioxide reduction performance

The challenges remain to develop cost-effective carbon-based catalysts with high activity and selectivity. Here, we synergistically modulate carbon-based electrocatalysts through Cl doping with intrinsic defects in sp3-hybridized carbon and apply them to the electrochemical CO2 reduction reaction (CO2RR). The designed electrocatalyst achieved high selectivity over a wide potential range (-0.7 to -1.0 V), with a faraday efficiency of 96.3 % at -0.8 V for CO. In situ Fourier transform infrared spectroscopy, and analytical studies show pyrrole N to be the active site of CO2RR, and doping Cl increases the content of sp3-hybridized carbon in the carbon substrate, which synergistically accelerates the supply of hydrolysis dissociated protons and facilitates the protonation process of the intermediate products from *CO2 to *COOH. Density functional theory calculations show that Cl coupled sp3-hybridized carbon inhibits the adsorption of H* in the pyrrole N site and facilitates the desorption of *CO, thus promoting the whole process of CO2RR.

Development of SAFT-Based Coarse-Grained Models of Carbon Dioxide and Nitrogen

We develop coarse-grained models for carbon dioxide (CO2) and nitrogen (N2) that capture the vapor-liquid equilibria of both their single components and their binary mixtures over a wide range of temperatures and pressures. To achieve this, we used an equation of state (EoS), namely Statistical Associating Fluid Theory (SAFT), which utilizes a molecular-based algebraic description of the free energy of chain fluids. This significantly accelerates the exploration of the parameter space, enabling the development of coarse-grained models that provide an optimal description of the macroscopic experimental data. SAFT creates models of fluids by chaining together spheres, which represent coarse-grained parts of a molecule. The result is a series of fitted parameters, such as bead size, bond length, and interaction strengths, that seem amenable to molecular simulation. However, only a limited set of models can be directly implemented in a particle-based simulation; this is predominantly due to how SAFT handles overlap between bonded monomers with parameters that do not translate to physical features, such as bond length. To translate such parameters to bond lengths in a coarse-grained force-field, we performed Wang-Landau transition-matrix Monte Carlo (WL-TMMC) simulations in the grand canonical ensemble on homonuclear fused two-segment Mie models and evaluated the phase behavior at different bond lengths. In the spirit of the law of corresponding states, we found that a force field, which matches SAFT predictions, can be derived by rescaling length and energy scales based on ratios of critical point properties of simulations and experiments. The phase behavior of CO2 and N2 mixtures was also investigated. Overall, we found excellent agreement over a wide range of temperatures and pressures in pure components and mixtures, similar to TraPPE CO2 and N2 models. Our proposed approach is the first step to establishing a more robust bridge between SAFT and molecular simulation modeling.

Exploring CO2 Methanation Using 3D-Printed Carbon Architectures

To demonstrate for the first time the potential of stereolithography-printed, architected, bio-based carbon-supported Ni catalysts for CO2 methanation, three honeycomb carbon structures with different textural properties were prepared, impregnated with 15 wt.% of nickel metal particles, and studied to correlate their catalytic performances with their textural properties and surface chemistry. Compared with the non-activated monolith and the steam-activated monolith, the CO2-activated monolith achieved a higher CO2 conversion of 62 % with a CH4 selectivity of 73 % at 460 °C. Our comparative study demonstrated that the CO2-activated carbon support, although having fewer basic sites on the surface, exhibits greater dispersion of the Ni phase, enabling an increase in H2 chemisorption. These results are of interest for further studies related to the optimization of catalytic performance through the design of the architectural and textural properties of such macrostructures.

Unlocking CO2 Activation With a Novel Ni-Hg-Ni Trinuclear Complex

Compounds featuring bonds between mercury and transition metals are of interest for their intriguing/ambiguous bonding and scarcely explored reactivities. We report herein the synthesis and reactivities of the new compound [(POCOP)Ni]2Hg, [Ni2Hg], featuring a trinuclear Ni-Hg-Ni core (POCOP=κP,κC,κP'-2,6-(i-Pr2PO)2C6H3). [Ni2Hg] reacts with CO2 to give the carbonate-bridged complex [Ni2CO3]. Bubbling CO gas through a solution of [Ni2CO3] gave its μ-CO2 analogue [Ni2CO2], which itself reacts with CO2 to give back [Ni2CO3], indicating that these two compounds interconvert reversibly. This implies that the formation of [Ni2CO3] from [Ni2Hg] and CO2 constitutes a reductive disproportionation of two molecules of CO2 into CO3 2- and CO. Tests showed that this process proceeds through three steps, an initial CO2 insertion to give [Ni2CO2], followed by another CO2 insertion to give the second intermediate [Ni2C2O4], and the latter's decarbonylation to give [Ni2CO3]. Although the putative second intermediate could not be isolated, we have shown that it likely features a μ-carbonyl-carbonate rather than a μ-oxalate moiety, because the latter complex is thermally stable to decarbonylation. Reduction of [Ni2CO3] with excess Na/Hg regenerates [Ni2Hg], establishing that the observed deoxygenation of CO2 in this system can, in principle, be catalytic in the presence of excess reductant.

Inverse design of promising electrocatalysts for CO2 reduction via generative models and bird swarm algorithm

Directly generating material structures with optimal properties is a long-standing goal in material design. Traditional generative models often struggle to efficiently explore the global chemical space, limiting their utility to localized space. Here, we present a framework named Material Generation with Efficient Global Chemical Space Search (MAGECS) that addresses this challenge by integrating the bird swarm algorithm and supervised graph neural networks, enabling effective navigation of generative models in the immense chemical space towards materials with target properties. Applied to the design of alloy electrocatalysts for CO2 reduction (CO2RR), MAGECS generates over 250,000 structures, achieving a 2.5-fold increase in high-activity structures (35%) compared to random generation. Five predicted alloys- CuAl, AlPd, Sn2Pd5, Sn9Pd7, and CuAlSe2 are synthesized and characterized, with two showing around 90% Faraday efficiency for CO2RR. This work highlights the potential of MAGECS to revolutionize functional material development, paving the way for fully automated, artificial intelligence-driven material design.

Photoinduced formation of a platina-α-lactone - a carbon dioxide complex of platinum. Insights from femtosecond mid-infrared spectroscopy

The binding of carbon dioxide to a transition metal is a complex phenomenon that involves a major redistribution of electron density between the metal center and the triatomic ligand. The chemical reduction of the ligand reveals itself unambiguously by an angular distortion of the CO2-molecule as a result of the occupation of an anti-bonding π-orbital and a shift of its antisymmetric stretching vibration, ν3, to lower wavenumbers. Here, we generate a carbon dioxide complex of the heavier group-10 metal, platinum, by ultrafast electronic excitation and cleavage of CO2 from the photolabile oxalate precursor, oxaliplatin, and monitored the ensuing primary dynamics with ultrafast mid-infrared spectroscopy. A neutral and thermally relaxed CO2-molecule is detected in the ν3-region within 60 ps after impulsive excitation with 266 nm light. Concurrently, an induced absorption peaking at 1717 cm-1 is observed, which is distinctly up-shifted relative to the oxalate stretching bands of the precursor and which resembles the CO stretching absorption of organic ketones. Accompanying density functional theory suggests that the 1717 cm-1-absorption arises from a Pt-CO2 product complex featuring a side-on binding mode, which can indeed be regarded as a ketone; specifically, as the metalla-α-lactone, 1-oxa-3-platinacyclopropan-2-one.

Turning Solid Waste into Catalysts: A Path for Environmental Solutions

Waste, often overlooked, stands out as a prime source of valuable products, meeting the demand for natural resources. In the face of environmental challenges, this study explores the crucial role of waste-derived catalysts in sustainable practices, emphasizing the transformative potential of solid waste materials. Carbon-based catalysts sourced from agricultural, municipal, and industrial waste streams can be transformed into activated carbon, biochar, and hydrochar which are extensively used adsorbents. Furthermore, the paper also highlights the potential of transition metal-based catalysts derived from spent batteries, electronic waste, and industrial byproducts, showcasing their efficacy in environmental remediation processes. Calcium-based catalysts originating from food waste, including seashells, eggshells, bones, as well as industrial and construction waste also find an extensive application in biodiesel production, providing a comprehensive overview of their promising role in sustainable and eco-friendly practices. From mitigating pollutants to recovering valuable resources, waste-derived catalysts exhibit a versatile role in addressing waste management challenges and promoting resource sustainability. By transforming waste into valuable catalysts, this study champions a paradigm shift towards a more sustainable and resource-efficient future.

Luminescence Changeable CO2-Storage Cylinder: Triple-Stranded Helical Eu(III)/Tb(III) Fluorinated MOFs with Amide Linkers

Triple-stranded helical lanthanide MOFs with CO2 adsorption properties were investigated. Lanthanide MOFs ([Eu0.1Tb0.9(hfa)3(dpa)]n) are composed of lanthanide luminophores (Eu(III) and/or Tb(III) ions), fluorinated antenna ligands (hfa: hexafluoroacetylacetonate), and polyamide-type linker ligands (dpa: 4-(diphenylphosphoryl)-N-(4-(diphenylphosphoryl)phenyl)benzamide). The cylindrical structure was characterized by single-crystal X-ray analysis, thermogravimetric analysis, and gas adsorption measurements. The inner surfaces of the cylindrical channels were covered with the fluorine atoms of the hfa ligands. The emission intensity ratio (IEu/ITb) in [Eu0.1Tb0.9(hfa)3(dpa)]n is affected by the CO2 gas adsorption behavior. The change in IEu/ITb value was caused by the intermolecular interactions between the CO2 gas molecules and the fluorinated ligands, resulting in an electronic structural change of the lowest triplet excited state in the photosensitized hfa ligands.

Dynamics of carbene formation in the reaction of methane with the tantalum cation in the gas phase

The controlled activation of methane has drawn significant attention throughout various disciplines over the last few decades. In gas-phase experiments, the use of model systems with reduced complexity compared to condensed-phase catalytic systems allows us to investigate the intrinsic reactivity of elementary reactions down to the atomic level. Methane is rather inert in chemical reactions, as the weakening or cleavage of a C-H bond is required to make use of methane as C1-building block. The simplest model system for transition-metal-based catalysts is a mono-atomic metal ion. Only a few atomic transition-metal cations activate methane at room temperature. One of the most efficient elements is tantalum, which forms a carbene and releases molecular hydrogen in the reaction with methane: Ta+ + CH4 → TaCH2+ + H2. The reaction takes place at room temperature due to efficient intersystem crossing from the quintet to the triplet surface, i.e., from the electronic ground state of the tantalum cation to the triplet ground state of the tantalum carbene. This multi-state reactivity is often seen for reactions involving transition-metal centres, but leads to their theoretical treatment being a challenge even today. Chemical reactions, or to be precise reactive collisions, are dynamic processes making their description even more of a challenge to experiment and theory alike. Experimental energy- and angle-differential cross sections allow us to probe the rearrangement of atoms during a reactive collision. By interpreting the scattering signatures, we gain insight into the atomistic mechanisms and can move beyond stationary descriptions. Here, we present a study combining collision energy dependent experimentally measured differential cross sections with ab initio calculations of the minimum energy pathway. Product ion velocity distributions were recorded using our crossed-beam velocity map imaging experiment dedicated to studying transition-metal ion molecule reactions. TaCH2+ velocity distributions reveal a significant degree of indirect dynamics. However, the scattering distributions also show signatures of rebound dynamics. We compare the present results to the oxygen transfer reaction between Ta+ and carbon dioxide, which we recently studied.

Real-world greenhouse gas emission characteristics from in-use light-duty diesel trucks in China

The transportation sector is a significant contributor to greenhouse gas (GHG) emissions in China. However, real-world GHG emissions from in-use light-duty diesel trucks (LDDTs) are largely uncertain due to data paucity. In this study, we have conducted real driving emission (RDE) tests of real-world CO2, N2O, and CH4 emissions from 12 in-use LDDTs in China. Results reveal that China's CH4 emission rates from LDDTs are overestimated by 57.71 ± 39.15 % if using the previous ratio method of CO2:CH4. Notably, under real-world driving conditions, such as speeds exceeding 60 km/h, maximum exhaust gas temperatures are reached, potentially impacting urea decomposition catalyst temperatures and subsequently influencing N2O production, which is highly sensitive to system temperature. Moreover, uphill roads can increase CO2 emissions by 51.93 % compared to downhill roads. Despite the tightening of vehicle emission standards, CO2 and N2O emissions from the LDDTs have not decreased linearly. However, LDDTs meeting the China VI standard exhibit the lowest average CO2, N2O and CH4 emission factors (EFs) of 335.26 ± 21.72 g/km, 2.7 ± 0.69 mg/km and 3.50 ± 0.70 mg/km, respectively. At last, the uncertainties in the GHG EFs for the tested LDDTs through RDE tests were (-39 %, 82 %) in our study, while a significantly higher uncertainty (-85 %, 182 %) for GHG EFs of LDDTs were found in our study and other reported literature in China, largely due to the application of different non-native vehicle emission factor models and testing methods, as well as different vehicles of control emission standards. Our study highlights more urgent needs for direct RDE tests and the importance of considering real driving conditions, such as road grades, in special geographical regions when undertaking carbon accounting work in the transportation sector.

Oxidative and Reductive Manipulation of C1 Resources by Bio-Inspired Molecular Catalysts to Produce Value-Added Chemicals

ConspectusTo tackle the energy and environmental concerns the world faces, much attention is given to catalytic reactions converting methane (CH4) and carbon dioxide (CO2) as abundant C1 resources into value-added chemicals with high efficiency and selectivity. In the oxidative conversion of CH4 to methanol, it is necessary to solve the requirement of strong oxidants due to the large bond-dissociation energy (BDE) of the C-H bonds in methane and achieve suppression of overoxidation due to the smaller BDE of the C-H bond in methanol as the product. On the other hand, to efficiently perform CO2 reduction, proton-coupled electron transfer (PCET) processes are required since the reduction potential of CO2 becomes positive by using proton-coupled processes; however, under the acidic conditions required for PCET, hydrogen evolution by the reduction of protons becomes competitive with CO2 reduction. Thus, it is indispensable to develop efficient catalysts for selective CO2 reduction. Recently, we have developed efficient catalytic reactions toward the alleviation of the concerns mentioned above. Concerning CH4 oxidation, inspired by metalloenzymes that oxidize hydrophobic organic substrates, a hydrophobic second coordination sphere (SCS) was introduced to an FeII complex bearing a pentadentate N-heterocyclic carbene ligand, and the FeII complex was used as a catalyst for CH4 oxidation in aqueous media. Consequently, CH4 was efficiently and selectively oxidized to methanol with 83% selectivity and a turnover number of 500. In contrast, when methanol was used as a substrate for catalytic oxidation by the FeII complex, oxidation products were obtained in a negligible yield, which was comparable to that of the control experiment without the catalyst. Therefore, the hydrophobic SCS of the FeII complex can capture only hydrophobic substrates such as CH4 and release hydrophilic products such as methanol to the aqueous medium for suppressing overoxidation ("catch-and-release" mechanism). On the other hand, for photocatalytic CO2 reduction, we have developed NiII complexes with N2S2-chelating ligands as catalysts, which have been inspired by carbon monoxide dehydrogenase, and have also introduced a binding site of Lewis-acidic metal ions to the SCS of the Ni complex. When Mg2+ was applied as a moderate Lewis acid, a Mg2+-bound Ni catalyst allowed us to achieve remarkable enhancement of the photocatalytic CO2 reduction to afford CO as the product with over 99% selectivity and a quantum yield of 11.4%. Divalent metal ions besides Mg2+ also showed similar positive impacts on photocatalytic CO2 reduction, whereas monovalent metal ions exhibited almost no effects and trivalent metal ions exclusively promoted hydrogen evolution. In this Account, we highlight our recent progress in the catalytic manipulations of CH4 and CO2 as C1 resources.

Four-electron reduction of CO2: from formaldehyde and acetal synthesis to complex transformations

The expansive and dynamic field of the CO2 Reduction Reaction (CO2RR) seeks to harness CO2 as a sustainable carbon source or energy carrier. While significant progress has been made in two, six, and eight-electron reductions of CO2, the four-electron reduction remains understudied. This review fills this gap, comprehensively exploring CO2 reduction into formaldehyde (HCHO) or acetal-type compounds (EOCH2OE, with E = [Si], [B], [Zr], [U], [Y], [Nb], [Ta] or -R) using various CO2RR systems. These encompass (photo)electro-, bio-, and thermal reduction processes with diverse reductants. Formaldehyde, a versatile C1 product, is challenging to synthesize and isolate from the CO2RR. The review also discusses acetal compounds, emphasizing their significance as pathways to formaldehyde with distinct reactivity. Providing an overview of the state of four-electron CO2 reduction, this review highlights achievements, challenges, and the potential of the produced compounds - formaldehyde and acetals - as sustainable sources for valuable product synthesis, including chiral compounds.

Applications of low-valent compounds with heavy group-14 elements

Over the last two decades, the low-valent compounds of group-14 elements have received significant attention in several fields of chemistry owing to their unique electronic properties. The low-valent group-14 species include tetrylenes, tetryliumylidene, tetrylones, dimetallenes and dimetallynes. These low-valent group-14 species have shown applications in various areas such as organic transformations (hydroboration, cyanosilylation, N-functionalisation of amines, and hydroamination), small molecule activation (e.g. P4, As4, CO2, CO, H2, alkene, and alkyne) and materials. This review presents an in-depth discussion on low-valent group-14 species-catalyzed reactions, including polymerization of rac-lactide, L-lactide, DL-lactide, and caprolactone, followed by their photophysical properties (phosphorescence and fluorescence), thin film deposition (atomic layer deposition and vapor phase deposition), and medicinal applications. This review concisely summarizes current developments of low-valent heavier group-14 compounds, covering synthetic methodologies, structural aspects, and their applications in various fields of chemistry. Finally, their opportunities and challenges are examined and emphasized.

CO2 reduction using aluminum hydride: Generation of in-situ frustrated Lewis pairs and small molecule activation therein

CO2 reduction is appealing for the long-term production of high-value fuels and chemicals. Herein, using density functional theory (DFT) based calculations, we study the CO2 reduction pathway to formic acid using aluminum hydride and phosphine derivatives. Our primary focus is on aluminum hydride derivatives, aimed at improving the efficiency of the CO2 reduction process. Substituents with σ-donating properties at the aluminum center are discovered to lower the activation barriers. We demonstrate how di-tert-butylphosphine oxide (LB-O)/di-tert-butylphosphine sulfide (LB-S)/di-tert-butylphosphanimine (LB-N) work together with aluminum hydride to facilitate CO2 reduction process and generate in-situ frustrated Lewis pairs (FLPs), such as FLP-O, FLP-S, and FLP-N. The activation strain model (ASM) analysis reveals the significance of strain energy in determining activation barriers. EDA-NOCV and PIO analyses elucidate the orbital interactions at the corresponding transition states. Furthermore, the study delves into the activation of various small molecules, such as dihydrogen, acetylene, ethylene, carbon dioxide, nitrous oxide, and acetonitrile, using those in-situ generated FLPs. The study highlights the low activation barriers and emphasizes the potential for small molecule activation in this context.

Multistate Dynamics and Kinetics of CO2 Activation by Ta+ in the Gas Phase: Insights into Single-Atom Catalysis

The activation of carbon dioxide (CO2) by a transition-metal cation in the gas phase is a unique model system for understanding single-atom catalysis. The mechanism of such reactions is often attributed to a "two-state reactivity" model in which the high-energy barrier of a spin state correlating with ground-state reactants is avoided by intersystem crossing (ISC) to a different spin state with a lower barrier. However, such a "spin-forbidden" mechanism, along with the corresponding dynamics, has seldom been rigorously examined theoretically, due to the lack of global potential energy surfaces (PESs). In this work, we report full-dimensional PESs of the lowest-lying quintet, triplet, and singlet states of the TaCO2+ system, machine-learned from first-principles data. These PESs and the corresponding spin-orbit couplings enable us to provide an extensive theoretical characterization of the dynamics and kinetics of the reaction between the tantalum cation (Ta+) and CO2, which have recently been investigated experimentally at high collision energies using crossed beams and velocity map imaging, as well as at thermal energies using a selected-ion flow tube apparatus. The multistate quasi-classical trajectory simulations with surface hopping reproduce most of the measured product translational and angular distributions, shedding valuable light on the nonadiabatic reaction dynamics. The calculated rate coefficients from 200 to 600 K are also in good agreement with the latest experimental measurements. More importantly, these calculations revealed that the reaction is controlled by intersystem crossing, rather than potential barriers.

Catalytic dehydrogenative coupling and reversal of methanol-amines: advances and prospects

The development of efficient hydrogen release and storage processes to provide environmentally friendly hydrogen solutions for mobile energy storage systems (MESS) stands as one of the most challenging tasks in addressing the energy crisis and environmental degradation. The catalytic dehydrogenative coupling of methanol and amines (DCMA) and its reverse are featured by high capacity for hydrogen release and storage, enhanced capability to purify the produced hydrogen, avoidance of carbon emissions and singular product composition, offering the environmentally and operationally benign strategy of overcoming the challenges associated with MESS. Particularly, the cycle between these two processes within the same catalytic system eliminates the need for collecting and transporting spent fuel back to a central facility, significantly facilitating easy recharging. Despite the promising attributes of the above strategy for environmentally friendly hydrogen solutions, challenges persist, primarily due to the high thermodynamic barriers encountered in methanol dehydrogenation and amide hydrogenation. By systematically summarizing various reaction mechanisms and pathways involving Ru-, Mn-, Fe-, and Mo-based catalytic systems in the development of catalytic DCMA and its reverse and the cycling between the two, this review highlights the current research landscape, identifies gaps, and suggests directions for future investigations to overcome these challenges. Additionally, the critical importance of developing efficient catalytic systems that operate under milder conditions, thereby facilitating the practical application of DCMA in MESS, is also underscored.

The application prospect and challenge of the alternative methanol fuel in the internal combustion engine

In the context of global carbon neutrality, the internal combustion engines aim to further reduce the carbon emission and improve the fuel economy for the transportation sector. Methanol is treated as a renewable, reliability, and applicability energy, which also shows some superior physicochemical properties compared to the traditional fossil fuels. However, some challenges such as cold start issue, low fuel economy, high unregulated emissions need to address before the methanol widely applies in the engines. This article comprehensively reviews the physicochemical properties and production processes of the methanol, the cold start issue of the methanol engine, and emission and combustion characteristics of the methanol engine for evaluating its potential effect of emission reduction and energy saving in the transportation sector. In addition, different optimization strategies and advanced technologies are proposed and comprehensively discussed in this paper for addressing the issues of the cold start, combustion and emissions of the methanol engines in the real application. Finally, the conclusions and prospects of the methanol engine are presented for promoting its application in the transportation sector and further reducing the carbon emission in the near future, thereby achieving the carbon peak and carbon neutrality in the China.

Comparative Analysis of Nickel-Phosphine Complexes with Cumulated Double Bond Ligands: Structural Insights and Electronic Interactions via ETS-NOCV and QTAIM Approaches

This study presents a comprehensive analysis of nickel-phosphine complexes, specifically Ni(PH3)2(OCCH2), Ni(PH3)2(H2CCO), Ni(PH3)2(H2CCCH2), Ni(PH3)2(NNCH2), and Ni(PH3)2(η1-H2CNN). Utilizing ETS-NOCV analysis, we explored orbital energy decomposition and the Hirshfeld charges of the ligands, providing insights into the electronic structures and donor-acceptor interactions within these complexes. The interactions in the ketene and allene complexes exhibit similar deformation densities and NOCV orbital shapes to those calculated for Ni(PH3)2(NNCH2), indicating consistent interaction characteristics across these complexes. The total interaction energy for all η2 complexes is observed to be over 60 kcal/mol, slightly exceeding that of the analogous carbon dioxide complex reported earlier. Furthermore, the study highlights the stronger back-donation as compared to donor interactions across all η2 complexes. This is further corroborated by Hirshfeld analysis, revealing the charge distribution dynamics within the ligand fragments. The research offers new perspectives on the electron distribution and interaction energies in nickel-phosphine complexes, contributing to a deeper understanding of their catalytic and reactive behaviors.

Elucidating the structure-stability relationship of Cu single-atom catalysts using operando surface-enhanced infrared absorption spectroscopy

Understanding the structure-stability relationship of catalysts is imperative for the development of high-performance electrocatalytic devices. Herein, we utilize operando attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) to quantitatively monitor the evolution of Cu single-atom catalysts (SACs) during the electrochemical reduction of CO2 (CO2RR). Cu SACs are converted into 2-nm Cu nanoparticles through a reconstruction process during CO2RR. The evolution rate of Cu SACs is highly dependent on the substrates of the catalysts due to the coordination difference. Density functional theory calculations demonstrate that the stability of Cu SACs is highly dependent on their formation energy, which can be manipulated by controlling the affinity between Cu sites and substrates. This work highlights the use of operando ATR-SEIRAS to achieve mechanistic understanding of structure-stability relationship for long-term applications.

Advances in CO2 activation by frustrated Lewis pairs: from stoichiometric to catalytic reactions

The rise of CO2 concentrations in the environment due to anthropogenic activities results in global warming and threatens the future of humanity and biodiversity. To address excessive CO2 emissions and its effects on climate change, efforts towards CO2 capture and conversion into value adduct products such as methane, methanol, acetic acid, and carbonates have grown. Frustrated Lewis pairs (FLPs) can activate small molecules, including CO2 and convert it into value added products. This review covers recent progress and mechanistic insights into intra- and inter-molecular FLPs comprised of varying Lewis acids and bases (from groups 13, 14, 15 of the periodic table as well as transition metals) that activate CO2 in stoichiometric and catalytic fashion towards reduced products.

A Plant Dye for Photocatalytic Methane Conversion

A metal-free natural dye has been developed to selectively convert methane to methyl trifluoroacetate (CH3 TFA) using visible light, probably due to the formation of a chloride-bridged dimer undergoing fast intra-complex charge transfer.

Cascade NH3 Oxidation and N2O Decomposition via Bifunctional Co and Cu Catalysts

The selective catalytic oxidation of NH3 (NH3-SCO) to N2 is an important reaction for the treatment of diesel engine exhaust. Co3O4 has the highest activity among non-noble metals but suffers from N2O release. Such N2O emissions have recently been regulated due to having a 300× higher greenhouse gas effect than CO2. Here, we design CuO-supported Co3O4 as a cascade catalyst for the selective oxidation of NH3 to N2. The NH3-SCO reaction on CuO-Co3O4 follows a de-N2O pathway. Co3O4 activates gaseous oxygen to form N2O. The high redox property of the CuO-Co3O4 interface promotes the breaking of the N-O bond in N2O to form N2. The addition of CuO-Co3O4 to the Pt-Al2O3 catalyst reduces the full NH3 conversion temperature by 50 K and improves the N2 selectivity by 20%. These findings provide a promising strategy for reducing N2O emissions and will contribute to the rational design and development of non-noble metal catalysts.

Sequential Deoxygenation of CO2 and NO2- via Redox-Control of a Pyridinediimine Ligand with a Hemilabile Phosphine

The deoxygenation of environmental pollutants CO2 and NO2- to form value-added products is reported. CO2 reduction with subsequent CO release and NO2- conversion to NO are achieved via the starting complex Fe(PPhPDI)Cl2 (1). 1 contains the redox-active pyridinediimine (PDI) ligand with a hemilabile phosphine located in the secondary coordination sphere. 1 was reduced with SmI2 under a CO2 atmosphere to form the direduced monocarbonyl Fe(PPhPDI)(CO) (2). Subsequent CO release was achieved via oxidation of 2 using the NOx- source, NO2-. The resulting [Fe(PPhPDI)(NO)]+ (3) mononitrosyl iron complex (MNIC) is formed as the exclusive reduction product due to the hemilabile phosphine. 3 was investigated computationally to be characterized as {FeNO}7, an unusual intermediate-spin Fe(III) coupled to triplet NO- and a singly reduced PDI ligand.

Rhenium(I) Tricarbonyl Complexes of 1,10-Phenanthroline Derivatives with Unexpectedly High Cytotoxicity

Eight rhenium(I) tricarbonyl aqua complexes with the general formula fac-[Re(CO)3(N,N'-bid)(H2O)][NO3] (1-8), where N,N'-bid is (2,6-dimethoxypyridyl)imidazo[4,5-f]1,10-phenanthroline (L1), (indole)imidazo[4,5-f]1,10-phenanthroline (L2), (5-methoxyindole)-imidazo[4,5-f]1,10-phenanthroline (L3), (biphenyl)imidazo[4,5-f]1,10-phenanthroline (L4), (fluorene)imidazo[4,5-f]1,10-phenanthroline (L5), (benzo[b]thiophene)imidazo[4,5-f]1,10-phenanthroline (L6), (5-bromothiazole)imidazo[4,5-f]1,10-phenanthroline (L7), and (4,5-dimethylthiophene)imidazo[4,5-f]1,10-phenanthroline (L8), were synthesized and characterized using 1H and 13C{1H} NMR, FT-IR, UV/Vis absorption spectroscopy, and ESI-mass spectrometry, and their purity was confirmed by elemental analysis. The stability of the complexes in aqueous buffer solution (pH 7.4) was confirmed by UV/Vis spectroscopy. The cytotoxicity of the complexes (1-8) was then evaluated on prostate cancer cells (PC3), showing a low nanomolar to low micromolar in vitro cytotoxicity. Worthy of note, three of the Re(I) tricarbonyl complexes showed very low (IC50 = 30-50 nM) cytotoxic activity against PC3 cells and up to 26-fold selectivity over normal human retinal pigment epithelial-1 (RPE-1) cells. The cytotoxicity of both complexes 3 and 6 was lowered under hypoxic conditions in PC3 cells. However, the compounds were still 10 times more active than cisplatin in these conditions. Additional biological experiments were then performed on the most selective complexes (complexes 3 and 6). Cell fractioning experiments followed by ICP-MS studies revealed that 3 and 6 accumulate mostly in the mitochondria and nucleus, respectively. Despite the respective mitochondrial and nuclear localization of 3 and 6, 3 did not trigger the apoptosis pathways for cell killing, whereas 6 can trigger apoptosis but not as a major pathway. Complex 3 induced a paraptosis pathway for cell killing while 6 did not induce any of our other tested pathways, namely, necrosis, paraptosis, and autophagy. Both complexes 3 and 6 were found to be involved in mitochondrial dysfunction and downregulated the ATP production of PC3 cells. To the best of our knowledge, this report presents some of the most cytotoxic Re(I) carbonyl complexes with exceptionally low nanomolar cytotoxic activity toward prostate cancer cells, demonstrating further the future viability of utilizing rhenium in the fight against cancer.

Adaptive Design of Alloys for CO2 Activation and Methanation via Reinforcement Learning Monte Carlo Tree Search Algorithm

Data-driven machine learning (ML) has earned remarkable achievements in accelerating materials design, while it heavily relies on high-quality data acquisition. In this work, we develop an adaptive design framework for searching for optimal materials starting from zero data and with as few DFT calculations as possible. This framework integrates automatic density functional theory (DFT) calculations with an improved Monte Carlo tree search via reinforcement learning algorithm (MCTS-PG). As a successful example, we apply it to rapidly identify the desired alloy catalysts for CO₂ activation and methanation within 200 MCTS-PG steps. To this end, seven alloy surfaces with high theoretical activity and selectivity for CO₂ methanation are screened out and further validated by comprehensive free energy calculations. Our adaptive design framework enables the fast computational exploration of materials with desired properties via minimal DFT calculations.

Selective methane oxidation by molecular iron catalysts in aqueous medium

Using natural gas as chemical feedstock requires efficient oxidation of the constituent alkanes-and primarily methane1,2. The current industrial process uses steam reforming at high temperatures and pressures3,4 to generate a gas mixture that is then further converted into products such as methanol. Molecular Pt catalysts5-7 have also been used to convert methane to methanol8, but their selectivity is generally low owing to overoxidation-the initial oxidation products tend to be easier to oxidize than methane itself. Here we show that N-heterocyclic carbene-ligated FeII complexes with a hydrophobic cavity capture hydrophobic methane substrate from an aqueous solution and, after oxidation by the Fe centre, release a hydrophilic methanol product back into the solution. We find that increasing the size of the hydrophobic cavities enhances this effect, giving a turnover number of 5.0 × 102 and a methanol selectivity of 83% during a 3-h methane oxidation reaction. If the transport limitations arising from the processing of methane in an aqueous medium can be overcome, this catch-and-release strategy provides an efficient and selective approach to using naturally abundant alkane resources.

Nickel(II) Complexes of Tripodal Ligands as Catalysts for Fixation of Atmospheric CO2 as Organic Carbonates

The fixation of atmospheric CO₂ into value-added products is a promising methodology. A series of novel nickel(II) complexes of the type [Ni(L)(CH₃ CN)₂ ](BPh₄ )₂ 1-5, where L=N,N-bis(2-pyridylmethyl)-N', N'-dimethylpropane-1,3-diamine (L1), N,N-dimethyl-N'-(2-(pyridin-2-yl)ethyl)-N'-(pyridin-2-ylmethyl) propane-1,3-diamine (L2), N,N-bis((4-methoxy-3,5-dimethylpyridin-2-ylmethyl)-N',N'-dimethylpropane-1,3-diamine (L3), N-(2-(dimethylamino) benzyl)-N',N'-dimethyl-N-(pyridin-2-ylmethyl) propane-1,3-diamine (L4) and N,N-bis(2-(dimethylamino)benzyl)-N', N'-dimethylpropane-1,3-diamine (L5) have been synthesized and characterized as the catalysts for the conversion of atmospheric CO₂ into organic cyclic carbonates. The single-crystal X-ray structure of 2 was determined and exhibited distorted octahedral coordination geometry with cis-α configuration. The complexes have been used as a catalyst for converting CO₂ and epoxides into five-membered cyclic carbonates under 1 atmospheric (atm) pressure at room temperature in the presence of Bu₄ NBr. The catalyst containing electron-releasing -Me and -OMe groups afforded the maximum yield of cyclic carbonates, 34% (TON, 680) under 1 atm air. It was drastically enhanced to 89% (TON, 1780) under pure CO₂ gas at 1 atm. It is the highest catalytic efficiency known for CO₂ fixation using nickel-based catalysts at room temperature and 1 atm pressure. The electronic and steric factors of the ligands strongly influence the catalytic efficiency. Furthermore, all the catalysts can convert a wide range of epoxides (ten examples) into corresponding cyclic carbonate with excellent selectivity (>99%) under this mild condition.

NiFe(CoFe)/silica and NiFe(CoFe)/alumina nanocomposites for the catalytic hydrogenation of CO2

The fumed SiO2 and Al2O3 oxides with a specific surface area of about 80 m2 g–1 were used for the synthesis of Ni(80)Fe(20)/SiO2, Co(93)Fe(7)/SiO2, Ni(80)Fe(20)/Al2O3 and Co(93)Fe(7)/Al2O3 nanocomposites, and numbers between brackets indicate the metal content in wt%, being 10 wt% of the mass of catalysts. Catalytically active bimetallic compositions (NiFe and CoFe) that modified the fumed oxides’ surface were prepared using the solvate-stimulated method with subsequent thermal decomposition and reduction of the metal oxides to corresponding metals with hydrogen. The catalysts were characterized using the TGA in dynamic hydrogen, nitrogen physisorption, and PXRD methods. The complete conversion of carbon dioxide is observed in the temperature range of 350–425 °C at the maximum methane yield of 72–84%. The long-time catalytic test demonstrates the high stability of the catalyst during 5 weeks of exposure to the reaction mixture. The yield of methane was decreased by 3–14% after 1–2 months of long-time testing.

Copolymerization of Carbon Dioxide with 1,2-Butylene Oxide and Terpolymerization with Various Epoxides for Tailorable Properties

The copolymerization of carbon dioxide (CO₂) with epoxides demonstrates promise as a new synthetic method for low-carbon polymer materials, such as aliphatic polycarbonate materials. In this study, a binary Schiff base cobalt system was successfully used to catalyze the copolymerization of 1,2-butylene oxide (BO) and CO₂ and its terpolymerization with other epoxides such as propylene oxide (PO) and cyclohexene oxide (CHO). ¹H nuclear magnetic resonance (¹H NMR), diffusion-ordered spectroscopy (DOSY), gel permeation chromatography (GPC), and differential scanning calorimetry (DSC) confirmed the successful synthesis of the alternating terpolymer. In addition, the effects of the polymerization reaction conditions and copolymerization monomer composition on the polymer structure and properties were examined systematically. By regulating the epoxide feed ratio, polycarbonates with an adjustable glass transition temperature (T_g) (11.2-67.8 °C) and hydrophilicity (water contact angle: 85.2-95.2°) were prepared. Thus, this ternary polymerization method provides an effective method of modulating the surface hydrophobicity of CO₂-based polymers and their biodegradation properties.

CO2 Fixation and PCHC Depolymerization by a Dinuclear β-Diketiminato Zinc Complex

The production of cyclic carbonates and (or) polycarbonates from the coupling of carbon dioxide (CO₂ ) with epoxides is a practical strategy for CO₂ fixation. Chemically recycling of the polycarbonates is also urgently needed for sustainable development of plastics. Here a dinuclear β-diketiminato (BDI) methyl zinc complex((BDI-ZnMe)₂ , 1) is reported to achieve not only selective cyclic carbonates from cycloaddition of CO₂ to meso-CHO in the presence of cocatalyst, but also effective depolymerization of PCHC into trans-CHC. The trans-CHC can be further transformed into cis-CHC, thus demonstrating great application potentials of this strategy in CO₂ fixation and chemical recycling of plastics.

Oxidative Addition of Methane and Reductive Elimination of Ethane and Hydrogen on Surfaces: From Pure Metals to Single Atom Alloys

Oxidative addition of CH₄ to the catalyst surface produces CH₃ and H. If the CH₃ species generated on the surface couple with each other, reductive elimination of C₂H₆ may be achieved. Similarly, H's could couple to form H₂. This is the outline of nonoxidative coupling of methane (NOCM). It is difficult to achieve this reaction on a typical Pt catalyst surface. This is because methane is overoxidized and coking occurs. In this study, the authors approach this problem from a molecular aspect, relying on organometallic or complex chemistry concepts. Diagrams obtained by extending the concepts of the Walsh diagram to surface reactions are used extensively. C-H bond activation, i.e., oxidative addition, and C-C and H-H bond formation, i.e., reductive elimination, on metal catalyst surfaces are thoroughly discussed from the point of view of orbital theory. The density functional theory method for structural optimization and accurate energy calculations and the extended Hückel method for detailed analysis of crystal orbital changes and interactions play complementary roles. Limitations of monometallic catalysts are noted. Therefore, a rational design of single atom alloy (SAA) catalysts is attempted. As a result, the effectiveness of the Pt₁/Au(111) SAA catalyst for NOCM is theoretically proposed. On such an SAA surface, one would expect to find a single Pt monatomic site in a sea of inert Au atoms. This is desirable for both inhibiting overoxidation and promoting reductive elimination.

C2 product formation in the CO2 electroreduction on boron-doped graphene anchored copper clusters

A possible remedy for the increasing atmospheric CO₂ concentration is capturing and reducing it into valuable chemicals like methane, methanol, ethylene, and ethanol. However, a suitable catalyst for this process is still under extensive research. Small sized copper clusters have gained attention in recent years due to their catalytic activity in the CO₂ reduction reaction. Although C₂₊ products have a higher economic value, the formation of C₁ products was investigated most thoroughly. Graphene is a promising support for small copper clusters in the electrochemical reduction of CO₂. It exhibits good mechanical and electrical properties, but the weak interaction between copper and graphene is an issue. Our DFT computations reveal that small Cu clusters on the boron-doped graphene (BDG) support are promising catalysts for the electrochemical reduction of CO₂. We found facile reaction pathways towards various C₁ (carbon-monoxide, formic acid, formaldehyde, methanol or methane) and C₂ (ethanol or ethylene) products on Cu₄ and Cu₇ clusters on BDG. The reactivity is cluster-size tunable with Cu₄ being the more reactive agent, while Cu₇ shows a higher selectivity towards C₂ products.

Intramolecular frustrated Lewis pair mediated approach to the CO bond activation and cleavage of carbon dioxide

A thermally stable FLP-CO₂ adduct of pronounced nucleophilic properties that forms a range of Lewis acid-base adducts with strong Lewis acids is reported. Upon addition of Tf₂O, it generates a cationic triflate, which undergoes C-O bond cleavage to give the formal FLP adduct of the elusive dication C₂O₃²⁺.

Atmospheric-Pressure Conversion of CO2 to Cyclic Carbonates over Constrained Dinuclear Iron Catalysts

The conversion of CO₂ and epoxides to cyclic carbonates over a silica-supported di-iron(III) complex having a reduced Robson macrocycle ligand system is shown to proceed at 1 atm and 80 °C, exclusively producing the cis-cyclohexene carbonate from cyclohexene oxide. We examine the effect of immobilization configuration to show that the complex grafted in a semirigid configuration catalytically outperforms the rigid, flexible configurations and even the homogeneous counterparts. Using the semirigid catalyst, we are able to obtain a TON of up to 800 and a TOF of up to 37 h^-1 under 1 atm CO₂. The catalyst is shown to be recyclable with only minor leaching and no change to product selectivity. We further examine a range of epoxides with varying electron-withdrawing/donating properties. This work highlights the benefit arising from the constraining effect of a solid surface, akin to the role of hydrogen bonds in enzyme catalysts, and the importance of correctly balancing it.

Boosting electrocatalytic CO2-to-ethanol production via asymmetric C-C coupling

Electroreduction of carbon dioxide (CO₂) into multicarbon products provides possibility of large-scale chemicals production and is therefore of significant research and commercial interest. However, the production efficiency for ethanol (EtOH), a significant chemical feedstock, is impractically low because of limited selectivity, especially under high current operation. Here we report a new silver–modified copper–oxide catalyst (dCu₂O/Ag_2.3%) that exhibits a significant Faradaic efficiency of 40.8% and energy efficiency of 22.3% for boosted EtOH production. Importantly, it achieves CO₂–to–ethanol conversion under high current operation with partial current density of 326.4 mA cm⁻² at −0.87 V vs reversible hydrogen electrode to rank highly significantly amongst reported Cu–based catalysts. Based on in situ spectra studies we show that significantly boosted production results from tailored introduction of Ag to optimize the coordinated number and oxide state of surface Cu sites, in which the ^*CO adsorption is steered as both atop and bridge configuration to trigger asymmetric C–C coupling for stablization of EtOH intermediates.

It is of high interest to convert CO₂ into valuable ethanol product. Here the authors demonstrate the asymmetric C-C coupling triggered on Ag-modified oxide-derived Cu sites can accelerate and steer the reaction pathway for ethanol production with high faradaic efficiency and current density.

Controllable growth of Fe-doped NiS2 on NiFe-carbon nanofibers for boosting oxygen evolution reaction

The construction of high-efficiency and low-cost electrocatalysts toward oxygen evolution reaction (OER) to improve the overall water decomposition performance is a fascinating route to deal with the clean energy application. Herein, Fe-doped NiS₂ crystals grown on the surface of carbon nanofibers (CNFs) encapsulated with NiFe alloy nanoparticles ((Ni,Fe)S₂/NiFe-CNFs) are fabricated through an electrospinning-calcination-vulcanization process, which has been used as a splendid electrocatalyst for OER. Benefitting from the abundant electrochemical active sites from the incorporation of Fe element in NiS₂ and the synergistic effect between NiFe-CNFs and surface sulfides, the obtained (Ni,Fe)S₂/NiFe-CNFs catalyst exhibits highly electrochemical activities and satisfactory durability toward OER in an alkaline medium with a low overpotential of only 287 mV at a high current density of 30 mA cm^-2, and with a little decline in the current retention after 48 h, suggesting its superior OER performance even compared with some noble metal-based electrocatalysts. Additionally, a two-electrode system conducted by using the (Ni,Fe)S₂/NiFe-CNFs and commercial Pt/C as electrodes, only needs a cell voltage of 1.54 V to afford 10 mA cm^-2 for overall water splitting, which is even much better than the RuO₂||Pt/C electrolyzer. This study offers a promising approach to prepare high-efficiency OER catalysts toward overall water splitting.

Ab Initio Electronic Structure Study of the Photoinduced Reduction of Carbon Dioxide with the Heptazinyl Radical

The photocatalytic conversion of carbon dioxide to liquid fuels with electrons taken from water with solar photons is one of the grand goals of renewable energy research. Polymeric carbon nitrides recently emerged as metal-free materials with promising functionalities for hydrogen evolution from water as well as the activation of carbon dioxide. Molecular heptazine (Hz), the building block of polymeric carbon nitrides, is one the strongest known organic photo-oxidants and has been shown to be able to photo-oxidize water with near-visible light, resulting in reduced (hydrogenated) heptazine (HzH) and OH radicals. In the present work, we explored with ab initio computational methods whether the HzH chromophore is able to reduce carbon dioxide to the hydroxy-formyl (HOCO) radical in hydrogen-bonded HzH-CO₂ complexes by the absorption of a photon. In remarkable contrast to the high barrier for carbon dioxide activation in the electronic ground state, the excited-state proton-coupled electron transfer (PCET) reaction is nearly barrierless, but requires the diabatic passage of three conical intersections. The possibility of barrierless carbon dioxide activation by excited-state PCET has so far not been taken into consideration in the interpretation of photocatalytic carbon dioxide reduction on carbon nitride materials.