C O Bond Research Articles

Crystalline phase effects of zirconia in Ag/ZrO2 catalysts: oxygen vacancy-mediated new pathways to promote carbon–oxygen bond hydrogenation

Elucidation of the crystalline phase effect of zirconia in Ag/ZrO2 catalysts and exploration of a new way for promoting the hydrogenation of carbon–oxygen bonds with the involvement of oxygen vacancies.

The nature and degree of the cooperativity of (η5-C5H5)–metal and metal–CO bonds in half-sandwich complexes of groups 5, 7, 9, and 11 transition metals

It is shown that, the cooperativity always has the same quantitative effect on the interaction energies of two cooperated chemical bonds but may have different effects on their nature.

Mechanism of photocatalytic CO2 methanation on ultrafine Rh nanoparticles.

Selective hydrogenation of CO2 to yield CH4 relies on the appropriate catalysts that can facilitate the cleavage of CO bonds and dissociative adsorption of H2. Ultrafine Rh nanoparticles loaded on silica nanospheres were used as a class of photocatalysts to significantly improve the selectivity and reaction rate of producing CH4 from the mixture of CO2 and H2 under the illumination of a broadband visible light source. The intense light scattering resonances in the silica nanospheres generate strong electric fields near the silica surface to enhance the light absorption power in the supported ultrafine Rh nanoparticles, promoting the efficiency of hot electron generation in the Rh nanoparticles. The interaction of the hot electrons with the adsorbate species on the Rh nanoparticle surface weakens the C-O bond to facilitate the deoxygenation of CO2, favoring the production of CH4 with a unity selectivity at a faster rate in the presence of surface adsorbed hydrogen (H*). The systematic studies on reaction kinetics and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy under different conditions, including various temperatures, illumination powers, and feeding gas compositions, reveal the reaction mechanism responsible for CO2 methanation and the role of photoillumination.

Controlled degradation of chemically stable poly(aryl ethers) via directing group-assisted catalysis.

To establish a sustainable society, the development of polymer materials capable of reverting into monomers on demand is crucial. Traditional methods rely on breaking labile bonds such as esters in the main chain, which limits applicability to polymers that consist of robust covalent bonds. We found that the integration of directing groups allowed the engineering of resilient polymers with built-in recyclability. Our study showcases phenylene ether-based polymers fortified with directing groups, which can be selectively disassembled under nickel catalysts via selective cleavage of carbon-oxygen bonds. Notably, these polymers exhibit exceptional chemical stability towards acids, bases, and oxidizing agents, while being degradable to well-defined, repolymerizable molecules in the presence of a catalyst. Our findings allow for the development of next-generation polymer materials that are chemically recyclable by design.

Metal-doped M-NH4-PW catalyst with enhanced electron transfer for formaldehyde-propylene condensation to 4-methyl-1,3-dioxane

Recognizing and modifying the acid property-dependent catalytic characteristics of catalysts are of great importance for Prins condensation reaction. Herein, a series of metal-doped M-NH4-PW catalysts (M=Pt, Fe, Ir, Ru) are successfully synthesized for Prins condensation reaction of formaldehyde and propylene to produce 4-methyl-1,3-dioxane. Our findings demonstrate that the catalytic performance of M-NH4-PW catalysts is influenced by the chemical nature of metal site properties with different electron transfer abilities. Specifically, the new Lewis acid decorated by Pt metal on 4-H site is more favorable for the selective adsorption of formaldehyde and activation of its CO bond. Additionally, the synergistic effect between Pt metal sites and nearby O in [PW12O40]3− promotes the formation of CC bonds between protonated formaldehyde and propylene. Consequently, the Pt-NH4-PW catalyst exhibits high conversion (> 80 %) and simultaneous selectivity towards 4-methyl-1,3-dioxane selectivity (65 %). This strategy may provide valuable insights for developing efficient multifunctional catalysts for Prins condensation reactions.

Designed synthesis N-doped sulfonated bifunctional catalyst for efficient 5-hydroxymethylfurfural production: A pyridinic N-triggered proton-shift mechanism at basic sites

Considering the essential role of acidic/basic sites in efficient 5-hydroxymentylfurfural (5-HMF) production from cellulose, the superiority of acid-base bifunctional catalysts was unfolded. However, the lack of in-depth research on catalytic mechanism of active sites, especially the basic sites, greatly hinders its chemical utilization. Herein, N-doped sulfonated bifunctional catalysts were rationally designed. The synthesized NCS-1H catalyst exhibited outstanding activity and recyclability. Favorable 5-HMF yield of 50.0 % with 62.9 % of selectivity was obtained. Spin polarized density function theory (DFT) analysis revealed a pyridinic N-triggered proton-shift mechanism of glucose isomerization. Catalyzed by pyridinic N, the proton of glucose on C2 was shifted to O5, leading to the cleavage of C1-O1 bond. As a result, an enol intermediate was formed and converted to fructose. Compared to pyrrolic N and graphitic N, pyridinic N significantly reduced the reaction energy barrier of rate-determining step to 0.79 eV, i.e., C1-O1 bond cleavage.

Transition of characteristic explosion limits: From hydrogen to diethyl ether

In this work, the explosion limits of three different fuels: hydrogen (H2), propane (C3H8, C3), and diethyl ether (DEE, C2H5OC2H5, C4), are investigated based on detailed chemical kinetics. The results reveal that the explosion limit of H2O2 exhibits the typical Z-shape, while C3H8O2 exhibits a single-NTC response, and DEE-O2 displays a double-NTC response. Sensitivity analysis indicates that the appearance of the NTC response in both the C3 and DEE fuels is intricately linked to low-temperature reaction paths. Moreover, the extents of the NTC responses are comparable for these two fuels with similar low-temperature reaction paths, but operate under different temperature conditions. Specifically, the double-NTC response observed in DEE is attributed to its primary CH and CO bonds, generating C4 and C2 radicals. The oxygen addition and the subsequent pathways of these radicals dominate in distinct temperature ranges. In contrast, C3H8 only possesses the CH bond, resulting in a single-NTC response, as OH radicals are mainly released by C3 radicals through oxygen addition, isomerization, and decomposition reactions. The results of binary fuel mixtures with H2 addition indicate that the reactivity of H2 controls the low-pressure and high-temperature regime, while the C3 and DEE fuels dominate the high-pressure and low-temperature regime. Additionally, a triangular crossover regime is identified between these two regimes due to the switchover of the reactivity. Sensitivity analysis further reveals the transition of the dominating reactions related to different fuels at various pressure-temperature regimes. Finally, based on the explosion limits of the multi-component mixtures, a detailed explosion regime diagram is proposed for carbon-free fuel (H2), alkane fuel (C3H8), and oxygenated ether fuel (DEE). This new regime diagram provides valuable insights for the investigation and utilization of ether fuels and the mixture of different fuels.

New insights into brominated epoxy resin type WPCBs pyrolysis mechanisms: Integrated experimental and DFT simulation studies

Pyrolysis is a recycling technology for waste circuit boards (WPCBs) with a wide range of applications. In this research, the brominated epoxy resin (BER) type WPCBs were taken as the research object, and the optimal pyrolysis process parameters were determined. Combined with experiments and density functional theory (DFT) calculations, the pyrolysis gaseous generation pattern and product distribution of BER type WPCBs were analyzed, and the generation mechanism of phenol, bromide and other pyrolysis products was investigated in depth. The results of the study showed that the pyrolysis rate of WPCBs exceeded 95 % under optimal reaction conditions. In the initial phase of the pyrolysis of WPCBs, the BER's CO bonds and a portion of Ph-Br bonds will be broken, leading to the production of intermediates such propylene oxide, bisphenol A, isopropyl alcohol, tetrabromobisphenol A and HBr. Among them, propylene oxide can generate ethylene oxide through free radical reaction. In the second stage, intermediates such as bisphenol A undergo homolytic cleavage and radical addition to form phenols, bromides, alcohols, ketones and other pyrolysis products.

Synergistically catalytic regulation of surface chemistry on coal based needle coke by bimetallic interface for enhanced Li/Na storage

The oxygen functional groups (OFGs) on carbon surface are electrochemically active for rapid Li/Na storage, and always are introduced with environment-hazardous and time-consuming ways. Herein, the bimetallic synergistic effect between Fe and Ni metal nanoparticles is proved experimentally to promote the conversion from useless C–O groups to useful CO groups on the surface of needle coke (NC) greatly. In addition, the DFT calculations show that introducing second metals increase the active electrons of single metals, and the activity of transforming C–O bond to CO bond thus makes a difference in bimetallic systems. Among the modified samples, Fe/Ni-NC contains abundant CO groups, stripe like graphite domains, excellent electronic conductivity and large interlayer spacing. Therefore, Fe/Ni-NC anode shows the excellent capacities in half batteries (212/305.2 mA h g−1 after 1000/2000 cycles at 2.0/5.0 A g−1 in SIB/LIB) and full batteries (86/145 mA h g−1 in SIB/LIB at 0.05 A g−1 after 100 cycles), significantly better than other carbon materials. The work provides a practical and significant reference to regulate precisely the surface energy storage active sites of coal based carbon material, aiming at advanced SIB and LIB.

Theoretical study of the local environment of Co-NxCy structure for selective oxidation of benzene to phenol

Adjusting the local environment of single-atom catalysts (SACs) is a promising approach to enhance the catalytic performance in benzene oxidation reaction (BOR). Herein, a range of Co-based SACs with N2/3/4-coordination numbers on graphene were constructed to investigate the effect of the electronic structure of SACs on BOR via density function theory (DFT). Expectedly, the electron density and charge amount of the Co active sites in the overall reaction path on the CoNxCy catalyst can be regulated by coordination environment. In particular, the as-formed *O=CoN4=O* intermediate displays the strongest electron interaction between Co atom and O*, thus O* has the largest electron density and the most negative charge number, resulting in a lower energy barrier of 0.69 eV for the rate-determining step of CO bond formation. The methodology in this work provides a certain theory supporting and guidance for developing highly efficient SACs with controllable coordination structures to enhance hydrocarbon oxidation reactions.

Pyrolysis and combustion reaction mechanisms of methyl palmitate with ReaxFF-MD method

As a substitute for fossil fuel, methyl palmitate (C17H34O2) has important scientific and practical significance to study its pyrolysis and combustion mechanism. In this paper, the ReaxFF-MD method is used to research the reaction mechanism and main products of C17H34O2. The effects of temperature and O2 on the decomposition, main products and reaction paths of C17H34O2 are analyzed to determine its reaction mechanism. The results show that the reaction activation energies of C17H34O2 in pyrolysis and combustion are 201.76 kJ/mol and 139.07 kJ/mol, respectively. The effect of temperature on C17H34O2 is greater than O2 on C17H34O2 at higher temperature. The basic reaction paths for the initial decomposition of C17H34O2 is that the CC, CO, and CH bonds are broken into smaller intermediates. In addition, the detailed distribution and generation paths of the main products C2H4, H2, H2O, CH2O, and so on are depicted to construct the reaction mechanism of C17H34O2.

Electrochemical Reduction of C-O Bonds

Reductive activation and transformation of C-O bonds in alcohols have been a challenge for many decades, yet is still considered an important step in the process of converting biomass into biofuel and chemicals. The challenge arises from the cleavage of the carbon-oxygen bond which generally requires forcing conditions and is reflected in the high bond dissociation energy compared to other polarised sigma bonds.[1] Our project focuses on electroreductive cleavage of alcohols in the presence of a hydrogen donor in an undivided cell with up to 95% of the corresponding alkane. C-O transformation is also accomplished through carboxylation with carbon dioxide, resulting in yield up to 43%.[2][1] Villo, P.; Shatskiy, A.; Kärkäs, M. D.; Lundberg, H. Electrosynthetic C−O Bond Activation in Alcohols and Alcohol Derivatives. Angewandte Chemie International Edition 2023, 62 (4), e202211952. https://doi.org/10.1002/anie.202211952.[2] Villo, P.; Lill, M.; Alsaman, Z.; Kronberg, A. S.; Chu, V.; Ahumada, G.; Agarwala, H.; Ahlquist, M.; Lundberg, H. Electroreductive Deoxygenative C–H and C–C Bond Formation from Non-Derivatized Alcohols Fueled by Borohydride Oxidation. ChemRxiv August 2, 2023. https://doi.org/10.26434/chemrxiv-2023-tw9l1-v2. Figure 1

Insight into interactions between microplastics and fulvic acid: Mechanisms affected by microplastics type

Microplastics (MPs) can interact with dissolved organic matter (DOM), a common component found in the environment. However, the effect of MPs type on its interaction with DOM has not been systematically studied. Therefore, the binding properties of different MPs with fulvic acid (FA) were explored in this study. The results showed that polypropylene (PP) and polyethylene (PE) had higher adsorption affinity for FA than polystyrene (PS) and polyvinyl chloride (PVC). The interaction between MPs and FA conformed to the pseudo-first-order model and Freundlich model (except PS). The interaction mechanisms between various MPs tested in this paper and FA are considered to be different. PP, PE and PS interacted with the aromatic structure of FA and were entrapped in the FA polymers by the carboxyl groups and CO bonds, resulting in a highly conjugated co-polymer, suggesting that oxygen-containing functional groups played a key role. However, it was assumed that the interaction between PVC and FA was more likely to be caused by hydrophobic interaction. This research will help to enhance our comprehension of the environmental behavior of MPs and their interaction with the DOM specifically.

Identification of key microbial communities and intracellular metabolic pathways to response micro-aerobic environment for enhancing degradation of N, N-dimethylformamide in refractory membrane-making wastewater

Enhanced sludge hydrolysis in micro-aerobic environment with dissolved oxygen (DO) regulation could degrade stubborn refractory N, N-dimethylformamide (DMF) in membrane-making wastewater. However, investigations on how micro-aerobic condition affects DMF conversion and microbial metabolism in biological system are still inadequate. Herein, the responses of microbial community to micro-aerobic environment, and the consequent variations of metabolic pathways in DMF degradation were unraveled. Results indicated that low concentration of DO (0.2–0.4 mg/L) could significantly enhance the ammonification rate (from 21.8 % to 52.8 %) and COD removal efficiency (from 65.2 % to 82 %) by breaking C–N and CO bonds of amide group in macromolecular organics, which help it degraded into micromolecular organics. 16S rRNA and metagenomic analysis further revealed that low DO contents prompted the changes of microbial community structure. Specifically, toxicity-tolerant fermentation bacteria (e.g. Desulfomicrobium and unclassified_c_ Deltaproteobacteria) gradually became the dominant species in micro-aerobic environment, showing positive connections with COD removal and ammonification functions. Additionally, functional genes analysis further revealed the intracellular metabolic pathways of DMF, where the upregulation of tricarboxylic acid (TCA) cycle and oxidative phosphorylation pathway was observed in micro-aerobic environment. Such regulation led to the massive synthesis of adenosine triphosphate (ATP) and NADH, which are needful in oxidative demethylation process, and thus promoting the conversion from DMF to formamide, CH4 and NH3 in Methanolobus step-by-step. Therefore, this study provided vital insights into the responses of microbial community structure and DMF intracellular metabolic pathways to micro-aerobic environment, and profoundly discussed their contributions to the efficient treatment effect on membrane-making wastewater.

Aqueous phase selective C[dbnd]O hydrogenation of cinnamaldehyde over bimetallic RuCo catalysts with electronic and geometric modification

Aqueous phase selective hydrogenation of cinnamaldehyde (CALD), as a representative α,β-unsaturated aldehyde, into cinnamyl alcohol (CALA) has been investigated over monometallic Ru and bimetallic RuCo catalysts on pristine h-BN support. Using water as the solvent, the optimal 0.5%Ru-1.1%Co/h-BN catalyst exhibits 510 h−1 specific reaction rate and 78.9 % CALA selectivity as well as good recycling stability at 100 °C. Based on the structure characterizations of catalysts, metal nanoparticles consisting of metallic Ru0 and partially oxidized Ruδ+ sites are uniformly dispersed on h-BN thin sheets. In comparison to monometallic catalysts, additive Co metals in bimetallic RuCo/h-BN catalysts play significant geometric and electronic modification roles on Ru active sites depending on the Ru/Co ratio, and therefore remarkably enhances the preferential activation of CALD CO bond and selectivity of CALA product as well as accelerates the catalytic reaction. Furthermore, the hydrogen dissociative activation ability of various Ru and RuCo catalysts was evaluated, while the superior catalytic performance in water than other commonly used solvents was also clarified and discussed.

CeO2 crystal plane engineering to modulate CuO-CeO2 interactions and modify the CO-PROX reaction pathway

Adjustment of the CeO2 exposed planes is an effective tool for modifying the metal-support interaction, which is the basis for the excellent CO preferential oxidation (CO-PROX) performance of CuO/CeO2 catalysts. However, the relationship between the CeO2 exposed planes, CuO-CeO2 interaction and reaction performance is still unclear. Herein, we investigated the effect of interactions on the structure of CuO/CeO2 catalysts and the CO-PROX reaction by modulating the CeO2 exposed planes (CuCe-NC (nanocubes) exposed {100} planes and CuCe-NP (nanoparticles) exposed {111} planes). The results indicate that the {100} plane exhibits greater CuO dispersal capabilities due to electron transfer caused by stronger interactions produces an anchoring effect on CuO. This promotes increased contact between CO and CuO during the reaction, creating more CO adsorption sites and improving low temperature activity. Furthermore, effective electron transfer between CuO and {100} planes during reaction maintains Cu+ stability while widening the temperature window. In-situ spectroscopy and DFT calculations showed that the Cu+–CO bond strength is weakened by the enhanced interaction, which together with the excellent surface structure of CeO2-{100}, favours the direct desorption of CO2. However, forming carbonate on CuCe-NP seems to be preferable. Various CO-PROX reaction pathways are suggested for different exposed crystal planes. This insight into crystal plane effects on CO-PROX may guide the design of high-performance catalysts.

Valorization of carbon dioxide with alcohols

Utilizing CO2 for the production of bulky and valuable chemicals presents an attractive solution to address environmental and fossil energy crises. Among the various approaches, direct carboxylation of alcohols with CO2 stands out as an eco-friendly process capable of efficiently producing carboxylic acids in a sustainable manner. However, the high dissociation energy of the CO bond poses a significant challenge in this process. Over the past few decades, several strategies have been developed to activate alcohols and establish efficient catalytic systems for carboxylation with CO2. Nevertheless, the sporadic nature of reported approaches makes it difficult to determine the most effective one. This perspective aims to provide an overview of the current state-of-the-art catalytic protocols for carboxylating alcohols with CO2, encompassing esterification, halogenation, and photocatalysis, while considering their respective advantages and limitations. We aim to discern the most promising avenues for future development in this field. The insights presented in this perspective will contribute to the advancement of efficient and sustainable carboxylation methods using CO2, leading to the production of valuable chemicals in future.

Classical Gold Carbonyl Complexes in Tetrahedral and Trigonal-Planar Settings.

A unique four-coordinate, classical gold(I)-carbonyl complex with substantial backdonation from gold has been isolated by using a B-methylated and fluorinated tris(pyridyl)borate chelator. Its lighter silver(I) and copper(I) analogs enabled a study of trends in the coinage-metal family. The B-arylated ligand version also afforded a gold-carbon monoxide complex that displays a notably low C-O stretch value, but with trigonal planar geometry at the gold. A computational analysis shows that the AuI -CO bonds of these tris(pyridyl)borate ligand-supported molecules consist of electrostatic attraction, OC→Au σ-donation, and very significant Au→CO π-back-bonding components. The latter is responsible for the observed C-O stretching frequencies, which are lower than in free CO.

Ether Bond Formation in Waste Biomass–Derived, Value-Added Technical Hardwood Kraft Lignin Using Glycolic Acid

Ether bond formation in technical hardwood kraft lignin (THKL) by crosslinking using glycolic acid was investigated for bio-adhesive applications. Industrial hardwood kraft black liquor was used to extract the THKL utilized by acidification. Chemical and thermal properties of the THKL with and without crosslinking were analyzed by Fourier transform infrared (FTIR) spectroscopy, solid-state 13C cross-polarization/magic angle spinning nuclear magnetic resonance (13C CP/MAS NMR) spectroscopy, X-ray photoelectron spectroscopy (XPS), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). FTIR results revealed a new peak corresponding to the ether bond and hemiacetal formation due to crosslinking at 1075 cm-1 and 1324 cm-1. 13C CP/MAS NMR spectra revealed the presence of a higher number of ether bonds due to the reduced aromatic and aliphatic hydroxyl groups in THKL and new bonds formed at 62-64 ppm and 168-191 ppm due to crosslinking. XPS results revealed that new bonds were formed between glycolic acid and THKL, leading to increased atomic oxygen percentage and carbon–oxygen bonds in crosslinked THKL detected by peak intensity changes at 287.7 and 288.8 related to O–C–O and O–C=O. Also, the oxygen content increased from 14.88% to 31.76% due to bond formation. GPC confirmed a higher molecular weight and broader molecular-weight distribution of THKL. DSC and TGA curves of crosslinked THKL revealed exothermic behavior, high thermal stability, and low thermal degradation rate. Owing to a significant amount of kraft black liquor being generated by wood pulp industries and attractive chemical properties of THKL, THKL demonstrates promise as a raw material to produce green, sustainable bio-adhesives via the crosslinking of its different hydroxyl groups using glycolic acid.

Defect engineering enables synergistic action of hierarchical porosity and multifunctionality for efficient catalysis of diverse reactions

The limitations of embedding suitable functional groups as Brønsted and Lewis pairs in metal–organic materials hinder their application especially to promote catalysis reactions. Due to the generation abundance of unsaturated inorganic nodes upon partial ligand decarboxylation, Quasi-MOFs (Q-MOFs) are considered as a potential candidate for the installation of amino acids. Here for the first time, we demonstrated that Q-HKUST-1 possessing a Lewis acid site could be transformed into an excellent multifunctional chiral MOF (Q-HKUST-Cys), via post-synthetic modification by L-Cysteine. Applying this approach, we can fabricate a pore environment spatially decorated with multiple functional groups. The post-modified MOF has been characterized by a variety of techniques including PXRD, N2 sorption, 1HNMR, FT-IR, CD, and SEM/EDS mapping. Q-HKUST-Cys features unique properties, such as mesoporosity, high Lewis acid sites including Cu2+, Lewis base sites (NH2 group), Bronsted acid sites (COOH group), open channels, and optical activity. So, this chiral MOF exhibits excellent catalytic performance in various asymmetric reactions under mild conditions. The Q-HKUST-Cys is highly enantioselective heterogeneous and recyclable catalyst, in ring-opening of epoxide and nitroaldol reaction with up to 99 % ee, as well as 100 % and 90 % conversion, respectively. Besides, in the cycloaddition of CO2 to styrene-epoxide (STO), and production of the corresponding cyclic carbonate, this catalyst showed high performance (90 % conversion, 89 % ee) under mild conditions, at the atmospheric pressure of CO2 and in the solvent-free situation. The simultaneous presence of these properties makes Q-HKUST-Cys an attractive catalyst for the eco-friendly synthesis of fine chemicals through CC and CO bond formation. As a result, in this study, we showed that anchoring defective MOFs with multifunctional amino acids can be an effective approach for the utilization of synergistic effects in the promotion of many catalysis reactions.