Selective Methanol Carbonylation to Acetic Acid on Heterogeneous Atomically Dispersed ReO4/SiO2 Catalysts

Atomically dispersed cerium on copper tailors interfacial water structure for efficient CO-to-acetate electroreduction

Electrosynthesis of acetate from carbon monoxide (CO) powered by renewable electricity offers one promising avenue to obtain valuable carbon-based products but undergoes unsatisfied selectivity because of the competing hydrogen evolution reaction. We report here a cerium single atoms (Ce-SAs) modified crystalline-amorphous dual-phase copper (Cu) catalyst, in which Ce SAs reduce the electron density of the dual-phase Cu, lowering the proportion of interfacial K+ ion hydrated water (K·H2O) and thereby decreasing the H* coverage on the catalyst surface. Meanwhile, the electron transfer from dual-phase Cu to Ce SAs yields Cu+ species, which boost the formation of active atop-adsorbed *CO (COatop), improving COatop-COatop coupling kinetics. These together lead to the preferential pathway of ketene intermediate (*CH2-C=O) formation, which then reacts with OH- enriched by pulsed electrolysis to generate acetate. Using this catalyst, we achieve a high Faradaic efficiency of 71.3 ± 2.1% toward acetate and a time-averaged acetate current density of 110.6 ± 2.0 mA cm-2 under a pulsed electrolysis mode. Furthermore, a flow-cell reactor assembled by this catalyst can produce acetate steadily for at least 138 hours with selectivity greater than 60%.

Improving the Methane Oxidation by Self-Adaptive Optimization of Liquid-Metal Catalysts

Methane (CH4), a major greenhouse gas and abundant carbon resource, presents significant challenges in catalysis due to its high symmetry and thermodynamic stability, which tend to cause over-oxidation to CO2. Traditional catalysts require high temperatures and pressures to facilitate CH4 conversion, constrained by their rigid structures which lack the flexibility needed for optimizing complex reaction steps. This study introduces a novel Cu embedded liquid metal catalyst (Cu-LMC) based on gallium alloys, characterized by dynamic, self-adaptive structures that provide enhanced catalytic performance and selectivity. Our findings reveal that Cu-LMC achieves a high methane conversion to methanol yield (5.9 mol⋅gCu -1⋅h-1) with a selectivity of 82 %. The results show that mild surface oxidation significantly boosts the catalytic performance of Cu-LMC by increasing active copper sites through the formation of a Cu-O-Ga configuration while preserving the catalyst's structural flexibility. In situ X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Fine Structure (XAFS) analyses, along with ab initio Molecular Dynamics (AIMD) simulations, demonstrate that the Cu-LMC enables self-adaptive structural adjustments that lower methanol desorption energy and increase the energy barrier for by-product formation, optimizing the overall methane conversion process. The results underscore the importance of designing catalysts with dynamic and adaptable structures to overcome traditional limitations and improve efficiency in catalytic reactions.

Stoichiometric Selective Carbonylation of Methane to Acetic Acid by Chemical Looping

The conversion of methane to valuable products is one of the main challenges of modern chemistry. Acetic acid (AcOH) is a key chemical reagent in industry, produced nowadays by the carbonylation of methanol over homogeneous Rh and Ir catalysts. Here, we propose a stepwise chemical looping approach for the highly selective stoichiometric synthesis of AcOH by carbonylation of methane with CO using single-site Pt over isolated phosphotungstic anions on a titania support (Pt-HPW-TiO2). The reaction proceeds by methane activation, which coincides with the reduction of initially oxidized Pt species in the presence of CO at 423 K and results in surface acetates attached to TiO2. Subsequent hydrolysis by water at ambient temperature results in the synthesis of AcOH in a stoichiometric amount corresponding to 1.5 Pt. Spent Pt-HPW-TiO2 is restored to the initial state by subsequent calcination in air. This approach provides an opportunity for the selective synthesis of AcOH (>99% in liquid phase) from methane, carbon monoxide, and air. A high concentration of AcOH (1.1 wt %) in an aqueous solution can be obtained at a high conversion of methane (4.5%).

MoS2-confined Rh-Zn atomic pair boosts photo-driven methane carbonylation to acetic acid

Direct carbonylation of CH4 to CH3COOH provides a promising pathway for upgrading of natural gas to transportable liquid chemicals, in which high-efficiency CH4 activation and controllable C-C coupling are both critical but challenging. Herein, we report that highly efficient photo-driven carbonylation of CH4 with CO and O2 to CH3COOH is achieved over MoS2-confined Rh-Zn atomic-pair in conjunction with TiO2. It delivers a high CH3COOH productivity of 152.0 μmol gcat.-1 h-1 and turnover frequency of 62.0 h-1 with a superior selectivity of 96.5%, outperforming previous photocatalytic CH4 carbonylation processes. Mechanistic investigations disclose the key effect of Rh-Zn synergy in combination with photo-excited electrons from TiO2 for CH3COOH formation. The active OH species produced from O2 photoreduction on the Zn site through proton-coupled electron transfer promotes CH4 dissociation to CH3 species, which then facilely couples with adsorbed CO on the adjacent Rh site forming the key CH3CO intermediate for CH3COOH formation.

Highly Selective Synthesis of Acetic Acid from Hydroxyl-Mediated Oxidation of Methane at Low Temperatures

Direct methane conversion and, in particular, the aerobic oxidation to acetic acid, remain an eminent challenge. Here, we reported a zeolite-supported Au-Fe catalyst (Au-Fe/ZSM-5) that converted methane to acetic acid with molecular oxygen as an oxidant in the presence of CO. Specifically, Au nanoparticles catalyzed the formation of hydroxyl species from the reaction of CO, O2, and H2O, meanwhile ZSM-5-supported atomically dispersed Fe species were responsible for the hydroxyl-mediated coupling of CH4 and CO to generate acetic acid. The reaction over 50 mg of Au-Fe/ZSM-5 under 62 bar (CH4 : CO : O2=14 : 14 : 3) at 120 °C for 3.0 h yielded 5.7 millimoles of acetic acid per gram of the catalyst (mmol gcat -1) with the selectivity of 92 %, outperformed most of reported catalysts. Significantly, the catalyst remained active even at 60 °C. We anticipate that this hydroxyl-mediated route may guide the design of optimized catalysts for the direct methane functionalization at low temperatures.

Heterogeneous Carbonylation of Alcohols on Charge-Density-Distinct Mo-Ni Dual Sites Localized at Edge Sulfur Vacancies

Alcohols carbonylation is of great importance in industry but remains a challenge to abandon the usage of the halide additives and noble metals. Here we report the realization of direct alcohols heterogeneous carbonylation to carbonyl-containing chemicals, especially in methanol carbonylation, with a remarkable space-time-yield (STY) of 4.74 molacetyl/kgcat./h and a durable stability as long as 100 h on Ni@MoS2 catalyst. Mechanistic analysis reveals that the Mo-Ni dual sites localized at edge sulfur vacancies of Ni@MoS2 exhibit distinct charge density, which strongly activate CH3OH to break its C-O bond and non-dissociatively activate CO. Density functional theory calculations further suggest that the low charge density in Mo-Ni, the Ni site, could significantly lower the barrier for CO migration and nucleophilic attack of methoxy species, and finally leads to the rapid formation of acetyl products. Ni@MoS2 catalyst could also effectively realize the carbonylation of ethanol, n-propanol and n-butanol to their acyl products, which may demonstrate its universal application for alcohols carbonylation.

Progress and challenges in structural, in situ and operando characterization of single-atom catalysts by X-ray based synchrotron radiation techniques

Single-atom catalysts (SACs) represent the ultimate size limit of nanoscale catalysts, combining the advantages of homogeneous and heterogeneous catalysts. SACs have isolated single-atom active sites that exhibit high atomic utilization efficiency, unique catalytic activity, and selectivity. Over the past few decades, synchrotron radiation techniques have played a crucial role in studying single-atom catalysis by identifying catalyst structures and enabling the understanding of reaction mechanisms. The profound comprehension of spectroscopic techniques and characteristics pertaining to SACs is important for exploring their catalytic activity origins and devising high-performance and stable SACs for industrial applications. In this review, we provide a comprehensive overview of the recent advances in X-ray based synchrotron radiation techniques for structural characterization and in situ/operando observation of SACs under reaction conditions. We emphasize the correlation between spectral fine features and structural characteristics of SACs, along with their analytical limitations. The development of IMST with spatial and temporal resolution is also discussed along with their significance in revealing the structural characteristics and reaction mechanisms of SACs. Additionally, this review explores the study of active center states using spectral fine characteristics combined with theoretical simulations, as well as spectroscopic analysis strategies utilizing machine learning methods to address challenges posed by atomic distribution inhomogeneity in SACs while envisaging potential applications integrating artificial intelligence seamlessly with experiments for real-time monitoring of single-atom catalytic processes.

Water-Dispersible, Magnetically Recyclable Heterogeneous Cobalt Catalyst for C-C and C-N Cross-Coupling Reactions in Aqueous Media

A cobalt catalyst supported on an iron oxide core, denoted as γ-Fe2O3@PEG@THMAM-Co, has been prepared and characterized by Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray mapping, thermogravimetry differential thermogravimetry, vibrating sample magnetometry, and inductively coupled plasma. Polyhydroxy end groups in the shell make the catalyst particles dispersible in water, allowing Hiyama, Suzuki, and C-N cross-coupling reactions of aryl iodides and bromides. The catalyst could be recovered by magnetic decantation and reused for at least five successive runs with a negligent decrease in its activity or changes in its morphology. Water as a solvent without requiring additives, surfactants, or organic co-solvents, as well as an abundant and low-cost cobalt catalyst combined with facile recovery, low leaching, and scalability, provides an environmentally and economically attractive alternative to established palladium-catalyzed C-C and C-N coupling reactions.

Water-participated mild oxidation of ethane to acetaldehyde

The direct conversion of low alkane such as ethane into high-value-added chemicals has remained a great challenge since the development of natural gas utilization. Herein, we achieve an efficient one-step conversion of ethane to C2 oxygenates on a Rh1/AC-SNI catalyst under a mild condition, which delivers a turnover frequency as high as 158.5 h-1. 18O isotope-GC-MS shows that the formation of ethanol and acetaldehyde follows two distinct pathways, where oxygen and water directly participate in the formation of ethanol and acetaldehyde, respectively. In situ formed intermediate species of oxygen radicals, hydroxyl radicals, vinyl groups, and ethyl groups are captured by laser desorption ionization/time of flight mass spectrometer. Density functional theory calculation shows that the activation barrier of the rate-determining step for acetaldehyde formation is much lower than that of ethanol, leading to the higher selectivity of acetaldehyde in all the products.

Improving Stability of CO2 Electroreduction by Incorporating Ag NPs in N-Doped Ordered Mesoporous Carbon Structures

The electroreduction of carbon dioxide (eCO2RR) to CO using Ag nanoparticles as an electrocatalyst is promising as an industrial carbon capture and utilization (CCU) technique to mitigate CO2 emissions. Nevertheless, the long-term stability of these Ag nanoparticles has been insufficient despite initial high Faradaic efficiencies and/or partial current densities. To improve the stability, we evaluated an up-scalable and easily tunable synthesis route to deposit low-weight percentages of Ag nanoparticles (NPs) on and into the framework of a nitrogen-doped ordered mesoporous carbon (NOMC) structure. By exploiting this so-called nanoparticle confinement strategy, the nanoparticle mobility under operation is strongly reduced. As a result, particle detachment and agglomeration, two of the most pronounced electrocatalytic degradation mechanisms, are (partially) blocked and catalyst durability is improved. Several synthesis parameters, such as the anchoring agent, the weight percentage of Ag NPs, and the type of carbonaceous support material, were modified in a controlled manner to evaluate their respective impact on the overall electrochemical performance, with a strong emphasis on operational stability. The resulting powders were evaluated through electrochemical and physicochemical characterization methods, including X-ray diffraction (XRD), N2-physisorption, Inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy (SEM), SEM-energy-dispersive X-ray spectroscopy (SEM-EDS), high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), STEM-EDS, electron tomography, and X-ray photoelectron spectroscopy (XPS). The optimized Ag/soft-NOMC catalysts showed both a promising selectivity (∼80%) and stability compared with commercial Ag NPs while decreasing the loading of the transition metal by more than 50%. The stability of both the 5 and 10 wt % Ag/soft-NOMC catalysts showed considerable improvements by anchoring the Ag NPs on and into a NOMC framework, resulting in a 267% improvement in CO selectivity after 72 h (despite initial losses) compared to commercial Ag NPs. These results demonstrate the promising strategy of anchoring Ag NPs to improve the CO selectivity during prolonged experiments due to the reduced mobility of the Ag NPs and thus enhanced stability.

Remotely Bonded Bridging Dioxygen Ligands Enhance Hydrogen Transfer in a Silica-Supported Tetrairidium Cluster Catalyst

A longstanding challenge in catalysis by noble metals has been to understand the origin of enhancements of rates of hydrogen transfer that result from the bonding of oxygen near metal sites. We investigated structurally well-defined catalysts consisting of supported tetrairidium carbonyl clusters with single-atom (apical iridium) catalytic sites for ethylene hydrogenation. Reaction of the clusters with ethylene and H2 followed by O2 led to the onset of catalytic activity as a terminal CO ligand at each apical Ir atom was removed and bridging dioxygen ligands replaced CO ligands at neighboring (basal-plane) sites. The presence of the dioxygen ligands caused a 6-fold increase in the catalytic reaction rate, which is explained by the electron-withdrawing capability induced by the bridging dioxygen ligands, consistent with the inference that reductive elimination is rate-determining. Electronic-structure calculations demonstrate an additional role of the dioxygen ligands, changing the mechanism of hydrogen transfer from one involving equatorial hydride ligands to that involving bridging hydride ligands. This mechanism is made evident by an inverse kinetic isotope effect observed in ethylene hydrogenation reactions with H2 and, alternatively, with D2 on the cluster incorporating the dioxygen ligands and is a consequence of quasi-equilibrated hydrogen transfer in this catalyst. The same mechanism accounts for rate enhancements induced by the bridging dioxygen ligands for the catalytic reaction of H2 with D2 to give HD. We posit that the mechanism involving bridging hydride ligands facilitated by oxygen ligands remote from the catalytic site may have some generality in catalysis by oxide-supported noble metals.

Ethylene Methoxycarbonylation over Heterogeneous Pt1/MoS2 Single-Atom Catalyst: Metal-Support Concerted Catalysis

Ethylene methoxycarbonylation (EMC) to methyl propanoate (MP) is an industrially important reaction and commercially uses a homogeneous Pd-phosphine organometallic complex as the catalyst and corrosive strong acid as the promoter. In this work, we develop a Pt1/MoS2 heterogeneous single-atom catalyst (SAC) which exhibits high activity, selectivity, and good recyclability for EMC reaction without need of any liquid acid. The production rate of MP achieves 0.35 gMP gcat-1 h-1 with MP selectivity of 91.1% at 1 MPa CO, 1 MPa C2H4, and 160 °C, which can be doubled at 2 MPa CO and corresponds to 320.1 molMP molPt-1 h-1, at least 1 order of magnitude higher than the earlier reported heterogeneous catalyst and even comparable to some of homogeneous catalyst. Advanced characterizations and DFT calculations reveal that all the Pt single atoms are located at the Mo vacancies along the Mo edge of the MoS2 nanosheets, forming pocket-like Mo-S-Pt1-S-Mo ensembles with uniform and well-defined structure. Methanol is first adsorbed and dissociated on Mo sites, and the produced H spillovers to the adjacent Pt site forming Pt-H species which then activate ethylene, forming Pt-ethyl species. Meanwhile, CO adsorbed on the other Mo site reacts with the Pt-ethyl species, yielding propionyl species, and this carbonylation is the rate-determining step. The final methoxylation step proceeds via the nucleophilic attack of propionyl species by -OCH3 affording the final product MP. Such a metal-support concerted catalysis enabled by the Mo-S-Pt1-S-Mo multisite ensemble opens a new avenue for SACs to promote the multimolecular reactions that prevail in homogeneous catalysis.

The Oxygenate-Mediated Conversion of COx to Hydrocarbons─On the Role of Zeolites in Tandem Catalysis

Decentralized chemical plants close to circular carbon sources will play an important role in shaping the postfossil society. This scenario calls for carbon technologies which valorize CO2 and CO with renewable H2 and utilize process intensification approaches. The single-reactor tandem reaction approach to convert COx to hydrocarbons via oxygenate intermediates offers clear benefits in terms of improved thermodynamics and energy efficiency. Simultaneously, challenges and complexity in terms of catalyst material and mechanism, reactor, and process gaps have to be addressed. While the separate processes, namely methanol synthesis and methanol to hydrocarbons, are commercialized and extensively discussed, this review focuses on the zeolite/zeotype function in the oxygenate-mediated conversion of COx to hydrocarbons. Use of shape-selective zeolite/zeotype catalysts enables the selective production of fuel components as well as key intermediates for the chemical industry, such as BTX, gasoline, light olefins, and C3+ alkanes. In contrast to the separate processes which use methanol as a platform, this review examines the potential of methanol, dimethyl ether, and ketene as possible oxygenate intermediates in separate chapters. We explore the connection between literature on the individual reactions for converting oxygenates and the tandem reaction, so as to identify transferable knowledge from the individual processes which could drive progress in the intensification of the tandem process. This encompasses a multiscale approach, from molecule (mechanism, oxygenate molecule), to catalyst, to reactor configuration, and finally to process level. Finally, we present our perspectives on related emerging technologies, outstanding challenges, and potential directions for future research.

CatMass: software for calculating optimal sample masses for X-ray absorption spectroscopy experiments involving complex sample compositions

This paper presents software for calculating the optimal mass of samples with complex compositions (e.g. supported metal catalysts) for X-ray absorption spectroscopy (XAS) and scattering measurements. The ability to calculate the sample mass and other relevant parameters needed for an XAS measurement allows experimentalists to be better prepared in terms of detector selection, energy range of scan and overall time needed to complete the measurement, thus increasing efficiency. CatMass builds on existing sample mass calculators allowing users to determine the optimum sample preparation, collection geometry, usable energy range for a scan and approximate edge step of the absorption event. Visualization tools present the absorption calculation results in a format familiar to XAS experimentalists, with the added ability to save calculations and plots for future reference or recalculation. CatMass is a program broadly applicable in catalysis and is helpful for users with complex samples due to composition/stoichiometry or multiple competing elements.

Catalytic utilization of converter gas – an industrial waste for the synthesis of pharmaceuticals

From waste to value. An efficient and convenient ruthenium-catalyzed reduction of aromatic nitro compounds using converter gas as a reducing agent to produce valuable pharmaceuticals has been developed.

Sustainable routes for acetic acid production: Traditional processes vs a low-carbon, biogas-based strategy

The conversion of biogas, mainly formed of CO₂ and CH₄, into high-value platform chemicals is increasing attention in a context of low-carbon societies. In this new paradigm, acetic acid (AA) is deemed as an interesting product for the chemical industry. Herein we present a fresh overview of the current manufacturing approaches, compared to potential low-carbon alternatives. The use of biogas as primary feedstock to produce acetic acid is an auspicious alternative, representing a step-ahead on carbon-neutral industrial processes. Within the spirit of a circular economy, we propose and analyse a new BIO-strategy with two noteworthy pathways to potentially lower the environmental impact. The generation of syngas via dry reforming (DRM) combined with CO₂ utilisation offers a way to produce acetic acid in a two-step approach (BIO-Indirect route), replacing the conventional, petroleum-derived steam reforming process. The most recent advances on catalyst design and technology are discussed. On the other hand, the BIO-Direct route offers a ground-breaking, atom-efficient way to directly generate acetic acid from biogas. Nevertheless, due to thermodynamic restrictions, the use of plasma technology is needed to directly produce acetic acid. This very promising approach is still in an early stage. Particularly, progress in catalyst design is mandatory to enable low-carbon routes for acetic acid production.

Bifunctional hydroformylation on heterogeneous Rh-WOx pair site catalysts

Metal-catalysed reactions are often hypothesized to proceed on bifunctional active sites, whereby colocalized reactive species facilitate distinct elementary steps in a catalytic cycle^1-8. Bifunctional active sites have been established on homogeneous binuclear organometallic catalysts^9-11. Empirical evidence exists for bifunctional active sites on supported metal catalysts, for example, at metal-oxide support interfaces^2,6,7,12. However, elucidating bifunctional reaction mechanisms on supported metal catalysts is challenging due to the distribution of potential active-site structures, their dynamic reconstruction and required non-mean-field kinetic descriptions^7,12,13. We overcome these limitations by synthesizing supported, atomically dispersed rhodium-tungsten oxide (Rh-WO_x) pair site catalysts. The relative simplicity of the pair site structure and sufficient description by mean-field modelling enable correlation of the experimental kinetics with first principles-based microkinetic simulations. The Rh-WO_x pair sites catalyse ethylene hydroformylation through a bifunctional mechanism involving Rh-assisted WO_x reduction, transfer of ethylene from WO_x to Rh and H₂ dissociation at the Rh-WO_x interface. The pair sites exhibited >95% selectivity at a product formation rate of 0.1 g_propanal cm^-3 h^-1 in gas-phase ethylene hydroformylation. Our results demonstrate that oxide-supported pair sites can enable bifunctional reaction mechanisms with high activity and selectivity for reactions that are performed in industry using homogeneous catalysts.

Rhodium promoted heteropolyacid catalysts for low temperature methanol carbonylation

Rh(OAc)2/HPW/SiO2 is an effective bifunctional catalyst for the halide-free carbonylation of methanol to methyl acetate and acetic acid.

Effectively Regulating the Microenvironment of Atomically Dispersed Rh through Co and Pi to Promote the Selectivity in Olefin Hydroformylation

In the study of heterogeneity of homogeneous processes, effective control of the microenvironment of active sites is a reliable means to improve the selectivity of products. Here, we develop a high-performance Rh-based atomically dispersed catalyst for olefin hydroformylation by controlling the electronic environment and spatial distribution of active metals on the supports, which is achieved through wet impregnation of Rh on ZnO modified with Pi and Co. Various characterizations demonstrate that Co weakens Rh-CO interactions and Pi promotes the formation of atomically dispersed Rh, which thereby improves the selectivity of linear aldehydes in hydroformylation. This strategy of rationally designing the local microenvironment of active metals is important to optimize the catalytic performance.