Low Temperature Oxidation of Ethane to Oxygenates by Oxygen over Iridium-Cluster Catalysts

Rutile TiO2-Supported Pt Nanoparticle Catalysts for the Low-Temperature Oxidation of Ethane to Ethanol

Structure-function relationships of supported metal nanoparticle catalysts in the CO-assisted oxidation of ethane to ethanol were investigated. A rutile TiO2-supported Pt nanoparticle catalyst exhibited the highest ethanol production rate and selectivity. During the reaction, sequential changes in the geometric/electronic states and the particle size of the Pt nanoparticles were observed. The comparison of the catalytic performances of model catalysts with controlled metal-support interactions revealed that Pt0 nanoparticles of 2-3 nm with a high fraction of the surface Ptδ+ species are highly active for the oxidation of ethane to ethanol. The coadded CO plays a pivotal role not only in tuning the oxidation state of the surface Pt but also in producing H2O2, which is the true oxidant for the reaction. The supported Pt nanoparticle uses in situ-generated H2O2 to activate ethane, where the C2H5OOH intermediate is formed through a nonradical mechanism and subsequently converted to C2H5OH. This reaction occurs even at 50 °C with an apparent activation energy of 32 kJ mol-1. The present study sheds light on the usefulness of surface-engineered Pt nanoparticles for the low-temperature oxidation of ethane to ethanol.

High-Rate and Selective C2H6-to-C2H4 Photodehydrogenation Enabled by Partially Oxidized Pdδ+ Species Anchored on ZnO Nanosheets under Mild Conditions

Photocatalytic C2H6-to-C2H4 conversion is very promising, yet it remains a long-lasting challenge due to the high C-H bond dissociation energy of 420 kJ mol-1. Herein, partially oxidized Pdδ+ species anchored on ZnO nanosheets are designed to weaken the C-H bond by the electron interaction between Pdδ+ species and H atoms, with efforts to achieve high-rate and selective C2H6-to-C2H4 conversion. X-ray photoelectron spectra, Bader charge calculations, and electronic localization function demonstrate the presence of partially oxidized Pdδ+ sites, while quasi-in situ X-ray photoelectron spectra disclose the Pdδ+ sites initially adopt and then donate the photoexcited electrons for C2H6 dehydrogenation. In situ electron paramagnetic resonance spectra, in situ Fourier transform infrared spectra, and trapping agent experiments verify C2H6 initially converts to CH3CH2OH via ·OH radicals, then dehydroxylates to CH3CH2· and finally to C2H4, accompanied by H2 production. Density-functional theory calculations elucidate that loading Pd site can lengthen the C-H bond of C2H6 from 1.10 to 1.12 Å, which favors the C-H bond breakage, affirmed by a lowered energy barrier of 0.04 eV. As a result, the optimized 5.87% Pd-ZnO nanosheets achieve a high C2H4 yield of 16.32 mmol g-1 with a 94.83% selectivity as well as a H2 yield of 14.49 mmol g-1 from C2H6 dehydrogenation in 4 h, outperforming all the previously reported photocatalysts under similar conditions.

Enabling direct oxidation of ethane to acetaldehyde with oxygen using supported PdO nanoparticles

Industrial-scale production of acetaldehyde relies heavily on homogeneous catalysts. Here, we used ethane as the feedstock and developed ZSM-5-supported PdO nanoparticles for the direct oxidation of ethane to acetaldehyde by utilizing O2 and CO. PdO nanoparticles clearly demonstrate effective activity and prevent the further deep oxidation of acetaldehyde.

Facilitating the dry reforming of methane with interfacial synergistic catalysis in an Ir@CeO2-x catalyst

The dry reforming of methane provides an attractive route to convert greenhouse gases (CH4 and CO2) into valuable syngas, so as to resolve the carbon cycle and environmental issues. However, the development of high-performance catalysts remains a huge challenge. Herein, we report a 0.6% Ir/CeO2-x catalyst with a metal-support interface structure which exhibits high CH4 (~72%) and CO2 (~82%) conversion and a CH4 reaction rate of ~973 μmolCH4 gcat-1 s-1 which is stable over 100 h at 700 °C. The performance of the catalyst is close to the state-of-the-art in this area of research. A combination of in situ spectroscopic characterization and theoretical calculations highlight the importance of the interfacial structure as an intrinsic active center to facilitate the CH4 dissociation (the rate-determining step) and the CH2* oxidation to CH2O* without coke formation, which accounts for the long-term stability. The catalyst in this work has a potential application prospect in the field of high-value utilization of carbon resources.

Ultrafine Pt Nanoparticles on Defective Tungsten Oxide for Photocatalytic Ethylene Synthesis

The selective conversion of ethane (C2H6) to ethylene (C2H4) under mild conditions is highly wanted, yet very challenging. Herein, it is demonstrated that a Pt/WO3-x catalyst, constructed by supporting ultrafine Pt nanoparticles on the surface of oxygen-deficient tungsten oxide (WO3-x) nanoplates, is efficient and reusable for photocatalytic C2H6 dehydrogenation to produce C2H4 with high selectivity. Specifically, under pure light irradiation, the optimized Pt/WO3-x photocatalyst exhibits C2H4 and H2 yield rates of 291.8 and 373.4 µmol g-1 h-1, respectively, coupled with a small formation of CO (85.2 µmol g-1 h-1) and CH4 (19.0 µmol g-1 h-1), corresponding to a high C2H4 selectivity of 84.9%. Experimental and theoretical studies reveal that the vacancy-rich WO3-x catalyst enables broad optical harvesting to generate charge carriers by light for working the redox reactions. Meanwhile, the Pt cocatalyst reinforces adsorption of C2H6, desorption of key reaction species, and separation and migration of light-induced charges to promote the dehydrogenation reaction with high productivity and selectivity. In situ diffuse reflectance infrared Fourier transform spectroscopy and density functional theory calculation expose the key intermediates formed on the Pt/WO3-x catalyst during the reaction, which permits the construction of the possible C2H6 dehydrogenation mechanism.

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.

Highly Selective Hydrogenation of Unsaturated Aldehydes in Aqueous Phase

Chemoselective hydrogenation of carbonyl in unsaturated aldehydes is a significant process in the chemical industry, in which the development of aqueous-phase reaction systems as a substitution to organic ones is challenging. Herein, we report Ir atomic cluster catalysts anchored onto WO3-x nanorods via a reduction treatment at various temperatures (denoted as Ir/WOx-T, T = 200, 300, 400, and 500 °C), which accelerates the chemoselective hydrogenation of carbonyl groups in aqueous solutions. The optimal catalyst Ir/WOx-300 exhibits exceptional activity (TOF value: 1313.7 min-1) and chemoselectivity toward cinnamaldehyde (CAL) hydrogenation to cinnamyl alcohol (COL) (yield: ∼98.0%) in water medium, which is, to the best of our knowledge, the highest level compared with previously reported heterogeneous catalysts in liquid-phase reaction. Ac-HAADF-STEM, XAFS, and XPS verify the formation of interface structure (Irδ+-Ov-W5+ (0 ≤ δ ≤ 4); Ov denotes oxygen vacancy) induced by metal-support interaction and the largest concentration of interfacial Ir (Irδ+) in Ir/WOx-300. In situ studies (Raman, FT-IR), isotopic labeling measurements combined with DFT calculations substantiate that the hydrogenation of the C=O group consists of two pathways: water-mediated hydrogenation (predominant) and direct hydrogenation via H2 dissociation (secondary). In the former case, W5+-Ov site accelerates the activation adsorption of H2O, while Ir0 site facilitates the H-H bond cleavage of H2 and Irδ+ promotes the CAL adsorption. H2O molecule, as the source of hydrogen species, participates directly in the hydrogenation of the carbonyl group through a hydrogen-bonded network, with a largely reduced energy barrier relative to the H2 dissociation path. This work demonstrates a green catalytic route that breaks the activity-selectivity trade-off toward the selective hydrogenation of unsaturated aldehydes, which shows great potential in heterogeneous catalysis.

Efficient propane mineralization over unsaturated Pd cluster/CeO2 with prominent C-C cleavage capacity driven by inherent oxygen activation ability

Light alkanes extensively presented in industrial exhausts have led tremendous harm to the atmospheric environment and human health. However, the catalytic destruction of light alkanes generally operates at elevated temperatures and the consequent reaction by-products are inevitably produced. It is therefore of great significance to engineer catalysts with superior thermal stability, internal activity and selectivity. Herein, we developed a Pd cluster/CeO2 catalyst (Pdn/CeO2) by a scalable deposition precipitation strategy, which demonstrates unexpected activity and thermal stability in the presence of 5% H2O attributing to abundant unsaturated Pd metal sites and excellent oxygen dissociation performance. Pdn/CeO2 possesses a highly efficient C-C cleavage capability due to the persistent formation of a large number of oxygen vacancies. In comparison, the Pd1/CeO2 catalyst, which is preferential for C-H bond cleavage and inactive for C-C bond cracking, produces remarkable hazardous organic by-products such as propyne and propylene, inhibiting the continuous decomposition of propane. The present study sheds critical insights into engineering efficient and stable catalysts for light alkane destruction.

Scalable Synthesis of Ir Cluster Anchored on Porous Hollow Carbon Nanobowls for Enhancing pH-Universal Hydrogen Evolution

Design high-loading with superior activity and high atomic efficiency has consistently been a new frontier of heterogeneous catalysis while challenging in synthetic technology. In this work, a universal solid-state strategy is proposed for large scalable production of high-loading Ir clusters on porous hollow carbon nanobowls (Ir CSs/PHCNBs). The strong electronic interaction between metallic Ir cluster and C on PHCNBs leads to electron redistribution, which significantly improves the electron transfer rate on the interface. The obtained Ir CSs/PHCNBs only require overpotentials of 35, 34, and 37 mV for the hydrogen evolution reaction (HER) with stable outputting of 10 mA cm-2 under acidic, alkaline, and neutral conditions, respectively, which exceeds the state-of-the-art HER electrocatalysts. Meanwhile, the Tafel slopes of Ir CSs/PHCNBs for the HER process are 23.07, 48.76, and 28.95 mV dec-1 , greatly lower than that of PHCNBs (152.73, 227.96, and 140.29 mV dec-1 ) and commercial Pt/C (20%) (36.33, 66.10, and 36.61 mV dec-1 ). These results provide a new strategy for the universal synthesis of clusters catalysts and insight into understanding the interface effects between clusters and carbon substrate, facilitating the industrial application of hydrogen production.

Selective Oxidation of Methane to Methanol over Au/H-MOR

Selective oxidation of methane to methanol by dioxygen (O₂) is an appealing route for upgrading abundant methane resource and represents one of the most challenging reactions in chemistry due to the overwhelmingly higher reactivity of the product (methanol) versus the reactant (methane). Here, we report that gold nanoparticles dispersed on mordenite efficiently catalyze the selective oxidation of methane to methanol by molecular oxygen in aqueous medium in the presence of carbon monoxide. The methanol productivity reaches 1300 μmol g_cat^-1 h^-1 or 280 mmol g_Au^-1 h^-1 with 75% selectivity at 150 °C, outperforming most catalysts reported under comparable conditions. Both hydroxyl radicals and hydroperoxide species participate in the activation and conversion of methane, while it is shown that the lower affinity of methanol on gold mainly accounts for higher methanol selectivity.

Structure-dependence and metal-dependence on atomically dispersed Ir catalysts for efficient n-butane dehydrogenation

Single-site pincer-ligated iridium complexes exhibit the ability for C-H activation in homogeneous catalysis. However, instability and difficulty in catalyst recycling are inherent disadvantages of the homogeneous catalyst, limiting its development. Here, we report an atomically dispersed Ir catalyst as the bridge between homogeneous and heterogeneous catalysis, which displays an outstanding catalytic performance for n-butane dehydrogenation, with a remarkable n-butane reaction rate (8.8 mol·g_Ir^-1·h^-1) and high butene selectivity (95.6%) at low temperature (450 °C). Significantly, we correlate the BDH activity with the Ir species from nanoscale to sub-nanoscale, to reveal the nature of structure-dependence of catalyst. Moreover, we compare Ir single atoms with Pt single atoms and Pd single atoms for in-depth understanding the nature of metal-dependence at the atomic level. From experimental and theoretical calculations results, the isolated Ir site is suitable for both reactant adsorption/activation and product desorption. Its remarkable dehydrogenation capacity and moderate adsorption behavior are the key to the outstanding catalytic activity and selectivity.

Enabling Specific Photocatalytic Methane Oxidation by Controlling Free Radical Type

Selective CH₄ oxidation to CH₃OH or HCHO with O₂ in H₂O under mild conditions provides a desired sustainable pathway for synthesis of commodity chemicals. However, manipulating reaction selectivity while maintaining high productivity remains a huge challenge due to the difficulty in the kinetic control of the formation of a desired oxygenate against its overoxidation. Here, we propose a highly efficient strategy, based on the precise control of the type of as-formed radicals by rational design on photocatalysts, to achieve both high selectivity and high productivity of CH₃OH and HCHO in CH₄ photooxidation for the first time. Through tuning the band structure and the size of active sites (i.e., single atoms or nanoparticles) in our Au/In₂O₃ catalyst, we show alternative formation of two important radicals, ^•OOH and ^•OH, which leads to distinctly different reaction paths to the formation of CH₃OH and HCHO, respectively. This approach gives rise to a remarkable HCHO selectivity and yield of 97.62% and 6.09 mmol g^-1 on In₂O₃-supported Au single atoms (Au₁/In₂O₃) and an exceptional CH₃OH selectivity and yield of 89.42% and 5.95 mmol g^-1 on In₂O₃-supported Au nanoparticles (Au_NPs/In₂O₃), respectively, upon photocatalytic CH₄ oxidation for 3 h at room temperature. This work opens a new avenue toward efficient and selective CH₄ oxidation by delicate design of composite photocatalysts.

Study of the Kinetics of Reduction of IrO2 on TiO2 (Anatase) by Temperature-Programmed Reduction

The interaction between IrO2 and TiO2 (anatase) in non-isothermal reduction conditions has been studied by the temperature programmed reduction technique. IrO2 clusters are of sizes between 0.5 and 0.9 nm as determined from High Resolution Transmission Electron Microscopy (HRTEM). Largely, two main regions for reduction were found and modeled at ca. 100 and 230 °C. The first region is attributed to the partial reduction of IrO2 clusters, while the second one is due to reduction of the formed crystalline (rutile IrO2), during TPR, to Ir metal. Two methods for calculating kinetic parameters were tested. First, by applying different ramping rates on a 3.5 wt.% IrO2/TiO2 using Kissinger’s method. The apparent activation energy values for the first and second reduction regions were found to be ca. 35 and 100 kJ/mol, respectively. The second method was based on fitting different kinetic models for the experimental results in order to extract qualitative information on the nature of interaction during the reduction process. It was found that the first reduction is largely due to the amount of IrO2 (reactant concentration) while the second one involved phase boundary effect as well as nucleation.

General Synergistic Hybrid Catalyst Synthesis Method Using a Natural Enzyme Scaffold-Confined Metal Nanocluster

Due to differences in the chemical properties or optimal reaction conditions of the catalysts, the challenge in the design of bio-chemical hybrid catalysts is that the bio-catalysts or chemical catalysts usually cannot maintain the initial catalytic performance. Herein, we report a general bio-chemical hybrid catalyst synthesis method using a natural enzyme scaffold-confined metal nanocluster. A redox-active enzyme is a nanoreactor that allows access to and reduces metal ions into metal nanoclusters in situ, resulting in the enzyme-confined metal nanocluster hybrid catalyst with a synergistic effect to boost catalytic performance. Specifically, bilirubin oxidase-Ir nanoclusters (BOD-Ir NCs) with catalytic properties for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are designed. The BOD-Ir NCs exhibit an approximately 2-fold ORR activity compared with pure BOD and a 4-fold OER activity compared with pure Ir NCs. BOD-Ir NCs exhibit stability for over 50,000 s, exceeding that of pure Ir NCs (22,000 s). The synergistic catalytic performance is attributed to the following: the mild preparation condition and matched sizes of BOD and the Ir NCs maintain the natural activity of BOD; the highly conductive Ir NCs improve the ORR activity of BOD; and the confining effect of BOD, which improves the stability and activity of the Ir NCs during the OER. In particular, BOD-Ir NCs exhibit a high half-wave potential of 0.97 V for the ORR and a low overpotential of 319 mV at 10 mA cm^-2 for the OER, surpassing most of reported catalysts under neutral conditions. Furthermore, laccase-Ir NCs and glucose oxidase-Pd NCs with synergistic catalytic performances are fabricated, proving the universality of this synthetic method. This facile strategy for designing synergistic hybrid catalysts is expected to be applied to more complex chemical transformations.

Methane Oxidation to Methanol

The direct transformation of methane to methanol remains a significant challenge for operation at a larger scale. Central to this challenge is the low reactivity of methane at conditions that can facilitate product recovery. This review discusses the issue through examination of several promising routes to methanol and an evaluation of performance targets that are required to develop the process at scale. We explore the methods currently used, the emergence of active heterogeneous catalysts and their design and reaction mechanisms and provide a critical perspective on future operation. Initial experiments are discussed where identification of gas phase radical chemistry limited further development by this approach. Subsequently, a new class of catalytic materials based on natural systems such as iron or copper containing zeolites were explored at milder conditions. The key issues of these technologies are low methane conversion and often significant overoxidation of products. Despite this, interest remains high in this reaction and the wider appeal of an effective route to key products from C-H activation, particularly with the need to transition to net carbon zero with new routes from renewable methane sources is exciting.

Catalytic Synthesis of Formamides by Integrating CO2 Capture and Morpholine Formylation on Supported Iridium Catalyst

Herein we report an efficient and recyclable catalytic system for tandem CO₂ capture and N-formylation to value-added chemicals. CO₂ is apt to be captured by morpholine solution, while a highly efficient heterogeneous catalyst, isolated iridium atoms supported over nanadiamond/graphene, is discovered to be highly reactive for the formylation of morpholine, leading to the formation of N-formylmorpholine with excellent productivity (with a turnover number of 5 120 000 in a single batch reaction) and selectivity (>99 %). In addition, the CO₂ captured by morpholine under atmospheric conditions can be converted to N-formylmorpholine with decent conversion (51 %), which realizes the integration of CO₂ capture and conversion to value-added chemicals.

Selective Catalytic Oxidation of Methane to Methanol in Aqueous Medium over Copper Cations Promoted by Atomically Dispersed Rhodium on TiO2

Direct conversion of methane into value-added chemicals, such as methanol under mild conditions, is a promising route for industrial applications. In this work, atomically dispersed Rh on TiO₂ suspended in an aqueous solution was used for the oxidation of methane to methanol. Promoted by copper cations (as co-catalyst) in solution, the catalysts exhibited high activity and selectivity for the production of methanol using molecular oxygen with the presence of carbon monoxide at 150 °C with a reaction pressure of 31 bar. Millimole level yields of methanol were reached with the selectivity higher than 99 % using the Rh/TiO₂ catalysts with the promotion of the copper cation. CO was the reductive agent to generate H₂ from H₂ O, which led to the formation of H₂ O₂ through the reaction of H₂ and O₂ . Atomically dispersed Rh activated the C-H bond in CH₄ and catalyzed the oxidation using H₂ O₂ . Copper cations maintained the low-valence state of Rh. Moreover, copper acted as a scavenger for suppressing the overoxidation, thus leading to the high selectivity of methanol.

Catalytic Kinetics Regulation for Enhanced Electrochemical Nitrogen Oxidation by Ru-Nanoclusters-Coupled Mn3 O4 Catalysts Decorated with Atomically Dispersed Ru Atoms

Electrochemical N₂ oxidation reaction (NOR), using water and N₂ in the atmosphere, represents a sustainable approach for nitric production to replace the conventional industrial synthesis with high energy consumption and greenhouse gas emission. Meanwhile, owing to chemical inertness of N₂ and sluggish kinetics for 10-electron transfer, emerging electrocatalysts remain largely underexplored. Herein, Ru-nanoclusters-coupled Mn₃ O₄ catalysts decorated with atomically dispersed Ru atoms (Ru-Mn₃ O₄ ) are designed and explored as an advanced electrocatalyst for ambient N₂ oxidation, with an excellent Faraday efficiency (28.87%) and a remarkable NO₃ ^- yield (35.34 µg h^-1 mg^-1 _cat. ), respectively. Experiments and density functional theory calculations reveal that the outstanding activity is ascribed to the coexistence of Ru clusters and single-atom Ru. The synergistic effect between the Ru clusters and Mn₃ O₄ can effectively activate the chemically inert N₂ , lowering the kinetic barrier for the vital breakage of N≡N. The intensive *OH supply and enhanced conductivity are used to regulate the catalytic kinetics for optimized performance. This work provides brand-new ideas for the rational design of electrocatalysts in complicated electrocatalytic reactions with multiple dynamics-different steps.

Atomically dispersed and oxygen deficient CuO clusters as an extremely efficient heterogeneous catalyst

Preparation of high-density and atomically-dispersed clusters is of great importance yet remains a formidable challenge, which precludes rational design of high-performance, ultrasmall heterogeneous catalysts for alleviating the energy and environmental crises. In this study, we demonstrated an appealing non-equilibrium growth model to give sub-2 nm CuO clusters not from the growth of nuclei but from the top-down growth of metastable bulk crystals. These CuO clusters have high density and intriguingly uniform orientation, and are atomically scattered on an inactive ultrathin AlOOH substrate, which has been driven by the lattice matching between the CuO clusters and the utlrathin AlOOH substrate. The catalytic activity of CuO clusters, with the hydrogenation of 4-nitrophenol as a model reaction, proved to be extremely efficient and showed a rate constant of 130.0 s^-1 g^-1, outperforming the commercial Pd/C catalysts and reported state-of-the-art noble-metal catalysts (1.89-117.2 s^-1 g^-1). These clusters have abundant interfacial oxygen vacancies (OVs) whose concentration can be regulated, and the OVs are found to be essential, according to density functional theory (DFT) calculations, in reducing the energy barrier of catalytic reduction and significantly boosting the catalytic reaction. These findings could add to the library of crystals downsized to the atomic level and demonstrate how engineering point defects on the sub-nanometer materials help design high-efficient catalysts.

Commercial Gold Complexes Supported on Functionalised Carbon Materials as Efficient Catalysts for the Direct Oxidation of Ethane to Acetic Acid

The single-pot efficient oxidation of ethane to acetic acid catalysed by Au(I) or Au(III) compounds, chlorotriphenylphosphinegold(I) (1), chlorotrimethylphosphinegold(I) (2), 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidenegold(I) chloride (3), dichloro(2-pyridinecarboxylato)gold(III) (4), homogenous and supported on different carbon materials: activated carbon (AC), multi-walled carbon nanotubes (CNT) and carbon xerogel (CX), oxidised with nitric acid followed by treatment with NaOH (-ox-Na), is reported. The reactions were performed in water/acetonitrile. The materials were selective for the production of acetic acid, with no trace of by-products being detected. The best homogenous catalysts were complexes 2 and 3 which showed the highest ethane conversion and an acetic acid yield of ca. 21%, followed by 4 and 1. The heterogenised materials showed much better activity than the homogenous counterparts, with acetic acid yields up to 41.4% for 4@CNT-ox-Na, and remarkable selectivity (with acetic acid being the only product detected). The heterogenised catalysts with the best results were reused up to five cycles, with no significant loss of activity, and maintaining high selectivity for acetic acid. 4@CNT-ox-Na showed not only the best catalytic activity but also the best stability during the recycling runs.

Interactions between atomically dispersed copper and phosphorous species are key for the hydrochlorination of acetylene

Vinyl chloride, the monomer of polyvinyl chloride (PVC), is industrially synthesized via acetylene hydrochlorination. Thereby, easy to sublimate but toxic mercury chloride catalysts are widely used. It is imperative to find environmentally friendly non-mercury catalysts to promote the green production of PVC. Low-cost copper-based catalysts are promising candidates. In this study, phosphorus-doped Cu-based catalysts are prepared. It is shown that the type of phosphorus configuration and the distribution on the surface of the carrier can be adjusted by changing the calcination temperature. Among the different phosphorus species, the formed P-C bond plays a key role. The coordination structure formed by the interaction between P-C bonds and atomically dispersed Cu²⁺ species results in effective and stable active sites. Insights on how P-C bonds activate the substrate may provide ideas for the design and optimization of phosphorus-doped catalysts for acetylene hydrochlorination.

Binary Au-Cu Reaction Sites Decorated ZnO for Selective Methane Oxidation to C1 Oxygenates with Nearly 100% Selectivity at Room Temperature

Direct and efficient oxidation of methane to methanol and the related liquid oxygenates provides a promising pathway for sustainable chemical industry, while still remaining an ongoing challenge owing to the dilemma between methane activation and overoxidation. Here, ZnO with highly dispersed dual Au and Cu species as cocatalysts enables efficient and selective photocatalytic conversion of methane to methanol and one-carbon (C1) oxygenates using O₂ as the oxidant operated at ambient temperature. The optimized AuCu-ZnO photocatalyst achieves up to 11225 μmol·g^-1·h^-1 of primary products (CH₃OH and CH₃OOH) and HCHO with a nearly 100% selectivity, resulting in a 14.1% apparent quantum yield at 365 nm, much higher than the previous best photocatalysts reported for methane conversion to oxygenates. In situ EPR and XPS disclose that Cu species serve as photoinduced electron mediators to promote O₂ activation to ^•OOH, and simultaneously that Au is an efficient hole acceptor to enhance H₂O oxidation to ^•OH, thus synergistically promoting charge separation and methane transformation. This work highlights the significances of co-modification with suitable dual cocatalysts on simultaneous regulation of activity and selectivity.

Heterogeneous Catalysis in Water

Heterogeneous catalytic processes produce the majority of the fuels and chemicals in the chemical industry and have kept improving the welfare of human beings for centuries. Although most of the heterogeneous catalytic reactions occur at the gas-solid interface, numerous cases have demonstrated that the condensed water near the active site and/or the aqueous phase merging the catalysts play positive roles in enhancing the performance of heterogeneous catalysts and creating novel catalytic conversion routes. We enumerate the traditional heterogeneous catalytic reactions that enable significant rate/selectivity promotion in the aqueous phase or adsorbed micro water environment and discuss the role of water in specific systems. Some of the novel heterogeneous reactions achieved with only the assistance of the aqueous phase have been summarized. The development of reactions with the participation of the aqueous phase/water and the investigation of the role of water in the heterogeneous catalytic reactions will open new horizons for catalysts with better activity, improved selectivity, and novel processes.

Atomically dispersed metal catalysts on nanodiamond and its derivatives: synthesis and catalytic application

Atomically dispersed metal catalysts (ADMCs) have attracted increasing interest in the field of heterogeneous catalysis. As sub-nanometric catalysts, ADMCs have exhibited remarkable catalytic performance in many reactions. ADMCs are classified into two categories: single atom catalysts (SACs) and atomically dispersed clusters with a few atoms. To stabilize the highly active ADMCs, nanodiamond (ND) and its derivatives (NDDs) are promising supports. In this Feature Article, we have introduced the advantages of NDDs with a highly curved surface and tunable surface properties. The controllable defective sites and oxygen functional groups are known as the anchoring sites for ADMCs. Tunable surface acid-base properties enable ADMCs supported on NDDs to exhibit unique selectivity towards target products and an extended lifetime in many reactions. In addition, we have firstly overviewed the recent advances in the synthesis strategies for effectively fabricating ADMCs on NDDs, and further discussed how to achieve the atomic dispersion of metal precursors and stabilize the as-formed metal atoms against migration and agglomeration based on NDDs. And then, we have also systematically summarized the advantages of ADMCs supported on NDDs in reactions, including hydrogenation, dehydrogenation, aerobic oxidation and electrochemical reaction. These reactions can also effectively guide the design of ADMCs. The recent progress in understanding the effect of structure of active centers and metal-support interactions (MSIs) on the catalytic performance of ADMCs is particularly highlighted. At last, the possible research directions in ADMCs are forecasted.

Reductive electrophilic C-H alkylation of quinolines by a reusable iridium nanocatalyst

The incorporation of a coupling step into the reduction of unsaturated systems offers a desirable way for diverse synthesis of functional molecules, but it remains to date a challenge due to the difficulty in controlling the chemoselectivity. Herein, by developing a new heterogeneous iridium catalyst composed of Ir-species (Ir^δ+) and N-doped SiO₂/TiO₂ support (Ir/N-SiO₂/TiO₂), we describe its application in reductive electrophilic mono and dialkylations of quinolines with various 2- or 4-functionalized aryl carbonyls or benzyl alcohols by utilizing renewable formic acid as the reductant. This catalytic transformation offers a practical platform for direct access to a vast range of alkyl THQs, proceeding with excellent step and atom-efficiency, good substrate scope and functional group tolerance, a reusable catalyst and abundantly available feedstocks, and generation of water and carbon dioxide as by-products. The work opens a door to further develop more useful organic transformations under heterogeneous reductive catalysis.

By developing a heterogeneous iridium catalyst composed of a N-doped SiO₂/TiO₂ support and Ir-species (Ir/N-SiO₂/TiO₂), its application in reductive electrophilic alkylation of quinolines with various aryl carbonyls or benzyl alcohols is presented.

In-situ spectroscopic observation of dynamic-coupling oxygen on atomically dispersed iridium electrocatalyst for acidic water oxidation

Uncovering the dynamics of active sites in the working conditions is crucial to realizing increased activity, enhanced stability and reduced cost of oxygen evolution reaction (OER) electrocatalysts in proton exchange membrane electrolytes. Herein, we identify at the atomic level potential-driven dynamic-coupling oxygen on atomically dispersed hetero-nitrogen-configured Ir sites (AD-HN-Ir) in the OER working conditions to successfully provide the atomically dispersed Ir electrocatalyst with ultrahigh electrochemical acidic OER activity. Using in-situ synchrotron radiation infrared and X-ray absorption spectroscopies, we directly observe that one oxygen atom is formed at the Ir active site with an O-hetero-Ir-N₄ structure as a more electrophilic active centre in the experiment, which effectively promotes the generation of key *OOH intermediates under working potentials; this process is favourable for the dissociation of H₂O over Ir active sites and resistance to over-oxidation and dissolution of the active sites. The optimal AD-HN-Ir electrocatalyst delivers a large mass activity of 2860 A g_metal^-1 and a large turnover frequency of 5110 h^-1 at a low overpotential of 216 mV (10 mA cm^-2), 480-510 times larger than those of the commercial IrO₂. More importantly, the AD-HN-Ir electrocatalyst shows no evident deactivation after continuous 100 h OER operation in an acidic medium.

Unprecedented Use of NHC Gold (I) Complexes as Catalysts for the Selective Oxidation of Ethane to Acetic Acid

The highly efficient eco-friendly synthesis of acetic acid (40% yield) directly from ethane is achieved by the unprecedented use of N-heterocyclic carbene (NHC) and N-heterocyclic oxo-carbene (NHOC) gold(I) catalysts in mild conditions. This is a selective and promising protocol to generate directly acetic acid from ethane, in comparison with the two most used methods: (i) the three-step, capital- and energy-intensive process based on the high-temperature conversion of methane to acetic acid; (ii) the current industrial methanol carbonylation processes, based in iridium and expensive rhodium catalysts. Green metrics determinations highlight the environmental advantages of the new ethane oxidation procedure. Comparison with previous reported published catalysts is performed to highlight the features of this remarkable protocol.

Identification of Kinetic and Spectroscopic Signatures of Copper Sites for Direct Oxidation of Methane to Methanol

Copper-exchanged zeolites of different topologies possess high activity in the direct conversion of methane to methanol via the chemical looping approach. Despite a large number of studies, identification of the active sites, and especially their intrinsic kinetic characteristics remain incomplete and ambiguous. In the present work, we collate the kinetic behavior of different copper species with their spectroscopic identities and track the evolution of various copper motifs during the reaction. Using time-resolved UV/Vis and in situ EPR, XAS, and FTIR spectroscopies, two types of copper monomers were identified, one of which is active in the reaction with methane, in addition to a copper dimeric species with the mono-μ-oxo structure. Kinetic measurements showed that the reaction rate of the copper monomers is somewhat slower than that of the dicopper mono-μ-oxo species, while the activation energy is two times lower.

Methane Oxidation to Methanol in Water

Methane represents one of the most abundant carbon sources for fuel or chemical production. However, remote geographical locations and high transportation costs result in a substantial proportion being flared at the source. The selective oxidation of methane to methanol remains a grand challenge for catalytic chemistry due to the large energy barrier for the initial C-H activation and prevention of overoxidation to CO₂. Indirect methods such as steam reforming produce CO and H₂ chemical building blocks, but they consume large amounts of energy over multistage processes. This makes the development of the low-temperature selective oxidation of methane to methanol highly desirable and explains why it has remained an active area of research over the last 50 years.The thermodynamically favorable oxidation of methane to methanol would ideally use only molecular oxygen. Nature effects this transformation with the enzyme methane monooxygenase (MMO) in aqueous solution at ambient temperature with the addition of 2 equiv of a reducing cofactor. MMO active sites are Fe and Cu oxoclusters, and the incorporation of these metals into zeolitic frameworks can result in biomimetic activity. Most approaches to methane oxidation using metal-doped zeolites use high temperature with oxygen or N₂O; however, demonstrations of catalytic cycles without catalyst regeneration cycles are limited. Over the last 10 years, we have developed Fe-Cu-ZSM-5 materials for the selective oxidation of methane to methanol under aqueous conditions at 50 °C using H₂O₂ as an oxidant (effectively O₂ + 2 reducing equiv), which compete with MMO in terms of activity. To date, these materials are among the most active and selective catalysts for methane oxidation under this mild condition, but industrially, H₂O₂ is an expensive oxidant to use in the production of methanol.This observation of activity under mild conditions led to new approaches to utilize O₂ as the oxidant. Supported precious metal nanoparticles have been shown to be active for a range of C-H activation reactions using O₂ and H₂O₂, but the rapid decomposition of H₂O₂ over metal surfaces limits efficiency. We identified that this decomposition could be minimized by removing the support material and carrying out the reaction with colloidal AuPd nanoparticles. The efficiency of methanol production with H₂O₂ consumption was increased by 4 orders of magnitude, and crucially it was demonstrated for the first time that molecular O₂ could be incorporated into the methanol produced with 91% selectivity. The understanding gained from these two approaches provides valuable insight into possible new routes to selective methane oxidation which will be presented here in the context of our own research in this area.

Regulating coordination number in atomically dispersed Pt species on defect-rich graphene for n-butane dehydrogenation reaction

Metal nanoparticle (NP), cluster and isolated metal atom (or single atom, SA) exhibit different catalytic performance in heterogeneous catalysis originating from their distinct nanostructures. To maximize atom efficiency and boost activity for catalysis, the construction of structure-performance relationship provides an effective way at the atomic level. Here, we successfully fabricate fully exposed Pt3 clusters on the defective nanodiamond@graphene (ND@G) by the assistance of atomically dispersed Sn promoters, and correlated the n-butane direct dehydrogenation (DDH) activity with the average coordination number (CN) of Pt-Pt bond in Pt NP, Pt3 cluster and Pt SA for fundamentally understanding structure (especially the sub-nano structure) effects on n-butane DDH reaction at the atomic level. The as-prepared fully exposed Pt3 cluster catalyst shows higher conversion (35.4%) and remarkable alkene selectivity (99.0%) for n-butane direct DDH reaction at 450 °C, compared to typical Pt NP and Pt SA catalysts supported on ND@G. Density functional theory calculation (DFT) reveal that the fully exposed Pt3 clusters possess favorable dehydrogenation activation barrier of n-butane and reasonable desorption barrier of butene in the DDH reaction.

Highly efficient visible-light photocatalytic ethane oxidation into ethyl hydroperoxide as a radical reservoir

Photocatalytic ethane conversion into value-added chemicals is a great challenge especially under visible light irradiation. The production of ethyl hydroperoxide (CH₃CH₂OOH), which is a promising radical reservoir for regulating the oxidative stress in cells, is even more challenging due to its facile decomposition. Here, we demonstrated a design of a highly efficient visible-light-responsive photocatalyst, Au/WO₃, for ethane oxidation into CH₃CH₂OOH, achieving an impressive yield of 1887 μmol g_cat ^-1 in two hours under visible light irradiation at room temperature for the first time. Furthermore, thermal energy was introduced into the photocatalytic system to increase the driving force for ethane oxidation, enhancing CH₃CH₂OOH production by six times to 11 233 μmol g_cat ^-1 at 100 °C and achieving a significant apparent quantum efficiency of 17.9% at 450 nm. In addition, trapping active species and isotope-labeling reactants revealed the reaction pathway. These findings pave the way for scalable ethane conversion into CH₃CH₂OOH as a potential anticancer drug.

Active site engineering of atomically dispersed transition metal-heteroatom-carbon catalysts for oxygen reduction

Owing to the advantage of atomic utilization, the single-atom catalyst has attracted much attention and been employed in multifarious catalytic reactions. Its definite site configuration is favorable for exploring the actual active centers and corresponding reaction mechanism. At the atomic scale, the tunable site configuration, from central metal atoms, coordinated heteroatoms, peripheral dopants, and feasible polymetallic centers to the synergetic intrinsic carbon defects, can effectively augment the intrinsic activity for oxygen reduction reaction (ORR). From a practical viewpoint, the propagation strategies of single-atom sites, the loading-activity relation and the structural retention during practical tests are crucial for the industrial applications. Furthermore, the activity contribution of multiple additional active centers including the active carbon sites and the pony-size well-wrapped metal species should be acknowledged. From the perspective mentioned above, this paper thoroughly analyses the consensuses, controversies, challenges and possible solutions based on the current research progress, thereby providing inspiration and guidance for the active center engineering of single-atom catalysts.

Boosting the sintering resistance of platinum–alumina catalyst via a morphology-confined phosphate-doping strategy

The size-dependent metal–support interaction, high surface area, and, above all, the support morphology-confined effect contribute to a good sintering-resistant catalyst.

Direct electrochemical synthesis of oxygenates from ethane using phosphate-based electrolysis cells

Ethane was converted directly to acetaldehyde and ethanol by partial oxidation at 220 °C and ambient pressure using an electrolysis cell with a proton-conducting electrolyte, CsH2PO4/SiP2O7, and Pt/C electrodes. The ethane conversion and the selectivity to the products increased with the voltage applied to the cell. It was found that O species generated by water electrolysis functioned as a favorable oxidant for partial oxidation of ethane on the Pt/C anode at intermediate temperatures. The production rates of acetaldehyde and ethanol recorded in this study were significantly higher than those in preceding reports.