Ultra-high thermal stability of sputtering reconstructed Cu-based catalysts

Tuning the electronic structure and SMSI by integrating trimetallic sites with defective ceria for the CO2 reduction reaction

Heterogeneous catalysts have emerged as a potential key for closing the carbon cycle by converting carbon dioxide (CO2) into value-added chemicals. In this work, we report a highly active and stable ceria (CeO2)-based electronically tuned trimetallic catalyst for CO2 to CO conversion. A unique distribution of electron density between the defective ceria support and the trimetallic nanoparticles (of Ni, Cu, Zn) was established by creating the strong metal support interaction (SMSI) between them. The catalyst showed CO productivity of 49,279 mmol g-1 h-1 at 650 °C. CO selectivity up to 99% and excellent stability (rate remained unchanged even after 100 h) stemmed from the synergistic interactions among Ni-Cu-Zn sites and their SMSI with the defective ceria support. High-energy-resolution fluorescence-detection X-ray absorption spectroscopy (HERFD-XAS) confirmed this SMSI, further corroborated by in situ electron energy loss spectroscopy (EELS) and density functional theory (DFT) simulations. The in situ studies (HERFD-XAS & EELS) indicated the key role of oxygen vacancies of defective CeO2 during catalysis. The in situ transmission electron microscopy (TEM) imaging under catalytic conditions visualized the movement and growth of active trimetallic sites, which completely stopped once SMSI was established. In situ FTIR (supported by DFT) provided a molecular-level understanding of the formation of various reaction intermediates and their conversion into products, which followed a complex coupling of direct dissociation and redox pathway assisted by hydrogen, simultaneously on different active sites. Thus, sophisticated manipulation of electronic properties of trimetallic sites and defect dynamics significantly enhanced catalytic performance during CO2 to CO conversion.

Adjustment of Molecular Sorption Equilibrium on Catalyst Surface for Boosting Catalysis

ConspectusFor chemical reactions with complex pathways, it is extremely difficult to adjust the catalytic performance. The previous strategies on this issue mainly focused on modifying the fine structures of the catalysts, including optimization of the geometric/electronic structure of the metal nanoparticles (NPs), regulation of the chemical composition/morphology of the supports, and/or adjustment of the metal-support interactions to modulate the reaction kinetics on the catalyst surface. Although significant advances have been achieved, the catalytic performance is still unsatisfactory.It is accepted that the chemical equilibrium of a reaction can be disturbed by changing the concentration of the reactants or products, and the equilibrium will shift to another side to offset the perturbation until a new equilibrium is established. This is known as Le Chatelier's principle. Following this understanding, we show that the catalytic performance can be significantly modulated by adjusting the molecular sorption equilibrium on the catalyst surface. For example, enriching the reactants and/or intermediates on the catalyst surface pushes the reaction forward, thus increasing the catalytic conversion; removing the product away from the catalyst surface improves the catalytic conversion and product selectivity; and inhibiting the side reactions enhances the product selectivity and catalyst durability. Using these strategies has successfully enhanced the catalytic performances in many challenging reactions, such as increasing H2O2 concentration around the metal active sites to enhance methane oxidation, enriching olefin on the catalyst surface to boost hydroformylation, selective combustion of H2 to shift the reaction equilibrium and improve ethane conversion in ethane dehydrogenation, and removing water from the reaction system to enhance Fischer-Tropsch synthesis. The key to these successes is effectively shifting the molecular sorption equilibrium under the working conditions.In this Account, we briefly summarize recent advances in adjusting molecular sorption equilibrium for boosting catalysis, with a focus on the equilibrium shift for a desired pathway by the unique functions of zeolites and polymers such as silanol nests on zeolite for olefin adsorption, the "molecular fence" effect of zeolite for H2O2 enrichment, MFI zeolite nanosheets for olefin diffusion, and the hydrophobic zeolite sheath and polymer for water separation/diffusion. We report the adjustment of the molecular sorption equilibrium on the catalyst surface via enriching the reactants and intermediates, removing the products, and inhibiting the side reactions to enhance the catalytic performance. As a result, high activity, excellent selectivity, and outstanding durability of the catalysts were achieved. In addition, current challenges and perspectives of applying this strategy to more important industrial reactions are discussed. Applications of advanced characterization tools, machine learning, and artificial intelligence for monitoring the dynamic structural changes of the catalyst and predicting the structural evolutions under working conditions are anticipated to continuously play important roles in catalyst design. We believe that this strategy will open a door for the development of highly efficient catalysts with potential applications in the future.

Reduction-immobilizing strategy of polymer-embedded sub-2 nm Cu nanoparticles with uniform size and distribution responsible for robust catalytic reactions

Polymer-embedded metal nanoparticles are in great demand owing to their unique features, leading to their use in various important applications, including catalysis reactions. However, particle sintering and aggregation are serious drawbacks, resulting in a drastic loss of catalytic activity and recyclability. Herein, a reduction-immobilizing strategy of polymer-embedded sub-2 nm Cu nanoparticles offered highly controlled distribution and nanoparticle size within polymer structures with high fidelity. This work sheds light on the high catalytic performance of nanoparticles that rely on their ultrasmall size and uniform distribution in polymer structures, generating more active sites that result in high efficiency reduction of organic compounds. A catalysis study was carried out for the hydrogenation of nitro compounds, achieving nearly 100% reduction in an extremely short time and remaining stable after 15 consecutive cycles. Furthermore, the catalytic mechanism was demonstrated by density functional theory (DFT) calculations. Notably, the discovery of this facile strategy may enable the remarkable cutting-edge design of catalyst materials with promising performance and stability.

Understanding and Tuning the Effects of H2O on Catalytic CO and CO2 Hydrogenation

Catalytic COx (CO and CO2) hydrogenation to valued chemicals is one of the promising approaches to address challenges in energy, environment, and climate change. H2O is an inevitable side product in these reactions, where its existence and effect are often ignored. In fact, H2O significantly influences the catalytic active centers, reaction mechanism, and catalytic performance, preventing us from a definitive and deep understanding on the structure-performance relationship of the authentic catalysts. It is necessary, although challenging, to clarify its effect and provide practical strategies to tune the concentration and distribution of H2O to optimize its influence. In this review, we focus on how H2O in COx hydrogenation induces the structural evolution of catalysts and assists in the catalytic processes, as well as efforts to understand the underlying mechanism. We summarize and discuss some representative tuning strategies for realizing the rapid removal or local enrichment of H2O around the catalysts, along with brief techno-economic analysis and life cycle assessment. These fundamental understandings and strategies are further extended to the reactions of CO and CO2 reduction under an external field (light, electricity, and plasma). We also present suggestions and prospects for deciphering and controlling the effect of H2O in practical applications.

Thermal Effect Management via Entropy Variation Strategy to Improve the Catalyst Stability in Acetylene Hydrogenation

The dynamic structure evolution of heterogeneous catalysts during reaction has gained great attention recently. However, controllably manipulating dynamic process and then feeding back catalyst design to extend the lifetime remains challenging. Herein, we proposed an entropy variation strategy to develop a dynamic CuZn-Co/HEOs catalyst, in which the non-active Co nano-islands play a crucial role in controlling thermal effect via timely capturing and utilizing reaction heat generated on the adjacent active CuZn alloys, thus solving the deactivation problem of Cu-based catalysts. Specifically, heat sensitive Co nano-islands experienced an entropy increasing process of slowly redispersion during the reaction. Under such heat dissipation effect, the CuZn-Co/HEOs catalyst exhibited 95.7 % ethylene selectivity and amazing long-term stability (>530 h) in the typical exothermic acetylene hydrogenation. Aiming at cultivating it as a catalyst with promising industrial potential, we proposed a simple regeneration approach via an entropy decreasing process.

Light-Driven Reverse Water Gas Shift Reaction with 1000-H Stability on High-Entropy Alloy Catalysts

Highly stable and active catalysts are of significant importance and a longstanding challenge for a number of industrial chemical transformations. Here, motivated by the principle of the high entropy-stabilized structure, high-entropy alloy-loaded porous TiO2 as an efficient and sintering-resistant catalyst for the light-driven reverse water gas‒shift reaction without external heating is synthesized. The optimized CoNiCuPdRu/TiO2 catalyst exhibits a long-term stability of 1000 h (1.23 mol gmetal -1 h-1 CO production rate, >99% high selectivity). In situ characterizations confirm that the slow diffusion effect of high-entropy alloys endows the catalyst with excellent structural stability. The CO adsorption measurements and theoretical calculations consolidate that the hydrogen surface coverage weakens CO adsorption on the catalyst surface. Two major problems of catalyst deactivation - sintering and poisoning, are handled in one case, which synergistically enable unparalleled stability. This work provides new guidance for the rational design of ultradurable harsh-condition operation catalysts for industrial catalysis.

Active Sites for CO2 Hydrogenation to Methanol: Mechanistic Insights and Reaction Control

Catalytic CO2 conversion to methanol is a promising way to extenuate the adverse effects of CO2 emission, global warming and energy shortage. Understanding the fundamental features of CO2 activation and hydrogenation at the molecular level is essential for carbon utilization and sustainable chemical production in the current climate crisis. This review explores the recent advances in understanding the design of catalysts with desired active sites, including single-atom, dual-atom, interface, defects/vacancies and promoters/dopants. We focused on the design of various catalytic systems to enhance their catalytic performances by stabilizing active metal in a catalyst, identifying the unique structure of active species, and engineering coordination environments of active sites. Mechanistic insights provided by advanced operando and in situ spectroscopies were also discussed. Moreover, the review highlights the key factors affecting active sites and reaction mechanisms, such as local environments, oxidation states, and metal-support interactions. By integrating recent advancements and relating knowledge gaps, this review aims to endow an inclusive overview of the field and guide future research toward more efficient and selective catalysts for CO2 hydrogenation to methanol.

The Micron-Droplet-Confined Continuous-Flow Synthesis of Freestanding High-Entropy-Alloy Nanoparticles by Flame Spray Pyrolysis

Alloying multiple immiscible elements into a nanoparticle with single-phase solid solution structure (high-entropy-alloy nanoparticles, HEA-NPs) merits great potential. To date, various kinds of synthesis techniques of HEA-NPs are developed; however, a continuous-flow synthesis of freestanding HEA-NPs remains a challenge. Here a micron-droplet-confined strategy by flame spray pyrolysis (FSP) to achieve the continuous-flow synthesis of freestanding HEA-NPs, is proposed. The continuous precursor solution undergoes gas shearing and micro-explosion to form nano droplets which act as the micron-droplet-confined reactors. The ultrafast evolution (<5 ms) from droplets to <10 nm nanoparticles of binary to septenary alloys is achieved through thermodynamic and kinetic control (high temperature and ultrafast colling). Among them, the AuPtPdRuIr HEA-NPs exhibit excellent electrocatalytic performance for alkaline hydrogen evolution reaction with 23 mV overpotential to achieve 10 mA cm-2, which is twofold better than that of the commercial Pt/C. It is anticipated that the continuous-flow synthesis by FSP can introduce a new way for the continuous synthesis of freestanding HEA-NP with a high productivity rate.

Tuning Adsorbate-Mediated Strong Metal-Support Interaction by Oxygen Vacancy: A Case Study in Ru/TiO2

The adsorbate-mediated strong metal-support interaction (A-SMSI) offers a reversible means of altering the selectivity of supported metal catalysts, thereby providing a powerful tool for facile modulation of catalytic performance. However, the fundamental understanding of A-SMSI remains inadequate and methods for tuning A-SMSI are still in their nascent stages, impeding its stabilization under reaction conditions. Here, we report that the initial concentration of oxygen vacancy in oxide supports plays a key role in tuning the A-SMSI between Ru nanoparticles and defected titania (TiO2-x). Based on this new understanding, we demonstrate the in situ formation of A-SMSI under reaction conditions, obviating the typically required CO2-rich pretreatment. The as-formed A-SMSI layer exhibits remarkable stability at various temperatures, enabling excellent activity, selectivity and long-term stability in catalyzing the reverse water gas-shift reaction. This study deepens the understanding of the A-SMSI and the ability to stabilize A-SMSI under reaction conditions represents a key step for practical catalytic applications.

Selective Upcycling of Polyethylene Terephthalate towards High-valued Oxygenated Chemical Methyl p-Methyl Benzoate using a Cu/ZrO2 Catalyst

Upgrading of polyethylene terephthalate (PET) waste into valuable oxygenated molecules is a fascinating process, yet it remains challenging. Herein, we developed a two-step strategy involving methanolysis of PET to dimethyl terephthalate (DMT), followed by hydrogenation of DMT to produce the high-valued chemical methyl p-methyl benzoate (MMB) using a fixed-bed reactor and a Cu/ZrO2 catalyst. Interestingly, we discovered the phase structure of ZrO2 significantly regulates the selectivity of products. Cu supported on monoclinic ZrO2 (5 %Cu/m-ZrO2 ) exhibits an exceptional selectivity of 86 % for conversion of DMT to MMB, while Cu supported on tetragonal ZrO2 (5 %Cu/t-ZrO2 ) predominantly produces p-xylene (PX) with selectivity of 75 %. The superior selectivity of MMB over Cu/m-ZrO2 can be attributed to the weaker acid sites present on m-ZrO2 compared to t-ZrO2 . This weak acidity of m-ZrO2 leads to a moderate adsorption capability of MMB, and facilitating its desorption. Furthermore, DFT calculations reveal Cu/m-ZrO2 catalyst shows a higher effective energy barrier for cleavage of second C-O bond compared to Cu/t-ZrO2 catalyst; this distinction ensures the high selectivity of MMB. This catalyst not only presents an approach for upgrading of PET waste into fine chemicals but also offers a strategy for controlling the primary product in a multistep hydrogenation reaction.

Temperature-driven evolution of ceria-zirconia-supported AuPd and AuRu bimetallic catalysts under different atmospheres: insights from IL-STEM studies

The evolution of the structure and composition of the system of particles in two Ce0.62Zr0.38O2-supported bimetallic catalysts based on Au and a 4d metal (Ru or Pd) under high temperature conditions and different reducing and oxidizing environments has been followed by means of Identical Location Scanning Transmission Electron Microscopy (IL-STEM). As an alternative to in situ microscopy, this technique offers valuable insights into the structural modifications occurring in chemical environments with the characteristics of a macro-scale reactor. By tracking exactly the same areas on a large number of metallic entities, it has been possible to reveal the influence of particle size and the nature of the redox environment on the temperature-driven mobilization of the different metals involved. Thus, oxidizing environments evidenced a much higher capacity to mobilize the three metals, preferentially Au. Moreover, the typical storage conditions (under air) of catalysts during the prolonged exposure time has been proved to induce significant modifications in these bimetallic systems, even at room temperature. Regardless of the type of redox environment, bimetallic systems showed better thermal resistance, which demonstrates a beneficial effect of the second metal. In summary, IL-STEM is an invaluable and complementary methodology for characterizing heterogeneous catalysts under realistic reaction conditions and is within the reach of most laboratories.

Palladium Encapsulated by an Oxygen-Saturated TiO2 Overlayer for Low-Temperature SO2 -Tolerant Catalysis during CO Oxidation

The development of oxidation catalysts that are resistant to sulfur poisoning is crucial for extending the lifespan of catalysts in real-working conditions. Herein, we describe the design and synthesis of oxide-metal interaction (OMI) catalyst under oxidative atmospheres. By using organic coated TiO2 , an oxide/metal inverse catalyst with non-classical oxygen-saturated TiO2 overlayers were obtained at relatively low temperature. These catalysts were found to incorporate ultra-small Pd metal and support particles with exceptional reactivity and stability for CO oxidation (under 21 vol % O2 and 10 vol % H2 O). In particular, the core (Pd)-shell (TiO2 ) structured OMI catalyst exhibited excellent resistance to SO2 poisoning, yielding robust CO oxidation performance at 120 °C for 240 h (at 100 ppm SO2 and 10 vol % H2 O). The stability of this new OMI catalyst was explained through density functional theory (DFT) calculations that interfacial oxygen atoms at Pd-O-Ti sites (of oxygen-saturated overlayers) serve as non-metal active sites for low-temperature CO oxidation, and change the SO2 adsorption from metal(d)-to-SO2 (π*) back-bonding to much weaker σ(Ti-S) bonding.

Designing Cu0-Cu+ dual sites for improved C-H bond fracture towards methanol steam reforming

Copper-based catalysts serve as the predominant methanol steam reforming material although several fundamental issues remain ambiguous such as the identity of active center and the aspects of reaction mechanism. Herein, we prepare Cu/Cu(Al)Ox catalysts with amorphous alumina-stabilized Cu2O adjoining Cu nanoparticle to provide Cu0-Cu+ sites. The optimized catalyst exhibits 99.5% CH3OH conversion with a corresponding H2 production rate of 110.8 μmol s-1 gcat-1 with stability over 300 h at 240 °C. A binary function correlation between the CH3OH reaction rate and surface concentrations of Cu0 and Cu+ is established based on kinetic studies. Intrinsic active sites in the catalyst are investigated with in situ spectroscopy characterization and theoretical calculations. Namely, we find that important oxygen-containing intermediates (CH3O* and HCOO*) adsorb at Cu0-Cu+ sites with a moderate adsorption strength, which promotes electron transfer from the catalyst to surface species and significantly reduces the reaction barrier of the C-H bond cleavage in CH3O* and HCOO* intermediates.

Clever Nanomaterials Fabrication Techniques Encounter Sustainable C1 Catalysis

ConspectusC1 catalysis, which refers to the conversion of molecules with a single carbon atom, such as CO, CO2, and CH4, into clean fuels and basic building blocks for chemical industries, has built a bridge between carbon resource utilization and valuable chemical supply. With respect to the goal of carbon neutrality, C1 catalysis also plays an essential role owing to its integrated functions in the green catalytic process with fewer CO2 emissions and even direct high-value-added utilization of greenhouse gases (CO2 and CH4). However, the inert nature of the C-O or C-H bond in C1 molecules as well as uncontrollable C-C coupling render C1 catalysis challenging. The rational design of highly active catalytic materials (denoted as C1 catalysts) with strong capacities for C-O or C-H bond activation and C-C coupling by convenient nanomaterials fabrication methods to boost the catalytic performance of C1 molecule conversion, including targeted product selectivity and long-term stability, is the cornerstone of C1 catalysis.Notably, the familiar concepts in heterogeneous catalysis, such as tandem catalysis and confinement catalysis, are applicable for C1 catalysis and have been successfully used to design a C1 catalyst. Regarding the tandem catalysis concept that integrates multiple reactions in a single-pass via a bi- or multifunctional catalyst, it is promising to shed new light on the oriented conversion of C1 molecules, especially for C2+ hydrocarbon or oxygenate synthesis. The confinement effect is powerful for controlling the product distribution and enhancing activation efficiency of inert chemical bonds in C1 catalysis due to the unique reactants/intermediate adsorption and evolution behaviors on the confined catalytic interface with a special electronic environment. Moreover, metal-support interactions (MSIs), electronic properties of the active site, and catalytic engineering issues are also susceptible to the C1 molecule conversion performance. Therefore, under the guidance of basic and novel rules in heterogeneous catalysis, the innovation of catalytic materials with the aid of advanced catalytic materials fabrication techniques has always been a hot research topic in C1 catalysis.In this Account, we briefly describe the challenges in thermal-catalytic C1 molecule (mainly CO, CO2, and CH4) conversion. At the same time, the synergistic functioning of the physicochemical properties of the catalytic materials on the performance in C1 molecule conversion is highlighted. More importantly, we summarize our progress in rationally designing tailor-made C1 catalysts to enhance C1 molecule activation efficiency and targeted product selectivity via powerful nanomaterials fabrication techniques, such as traditional wet-chemistry strategies, the magnetron sputtering method, and 3D printing technology. Specifically, the ingenious capsule catalyst and ammonia pools in zeolites fabricated by a wet chemistry process possess an extraordinary effect on the transformation of CO, CO2, and CH4 molecules. Also, the sputtering method is reliable in modulating the electronic properties of metallic active sites for C1 molecule conversion, thereby tailoring the final product selectivity. Furthermore, we showcase the strong capability of metal 3D printing technology in fabricating a self-catalytic reactor, by which the functions of the reaction field and nanoscale active sites are well integrated. Finally, we predict the future research opportunities in highly efficient C1 catalyst design with the assistance of clever nanomaterials fabrication techniques.

Rapid Joule Heating Synthesis of Oxide-Socketed High-Entropy Alloy Nanoparticles as CO2 Conversion Catalysts

The unorthodox surface chemistry of high-entropy alloy nanoparticles (HEA-NPs), with numerous interelemental synergies, helps catalyze a variety of essential chemical processes, such as the conversion of CO₂ to CO, as a sustainable path to environmental remediation. However, the risk of agglomeration and phase separation in HEA-NPs during high-temperature operations are lasting issues that impede their practical viability. Herein, we present HEA-NP catalysts that are tightly sunk in an oxide overlayer for promoting the catalytic conversion of CO₂ with exceptional stability and performance. We demonstrated the controlled formation of conformal oxide overlayers on carbon nanofiber surfaces via a simple sol-gel method, which facilitated a large uptake of metal precursor ions and helped to decrease the reaction temperature required for nanoparticle formation. During the rapid thermal shock synthesis process, the oxide overlayer would also impede nanoparticle growth, resulting in uniformly distributed small HEA-NPs (2.37 ± 0.78 nm). Moreover, these HEA-NPs were firmly socketed in the reducible oxide overlayer, enabling an ultrastable catalytic performance involving >50% CO₂ conversion with >97% selectivity to CO for >300 h without extensive agglomeration. Altogether, we establish the rational design principles for the thermal shock synthesis of high-entropy alloy nanoparticles and offer a helpful mechanistic perspective on how the oxide overlayer impacts the nanoparticle synthesis behavior, providing a general platform for the designed synthesis of ultrastable and high-performance catalysts that could be utilized for various industrially and environmentally relevant chemical processes.

Defects Tune the Strong Metal-Support Interactions in Copper Supported on Defected Titanium Dioxide Catalysts for CO2 Reduction

A highly active and stable Cu-based catalyst for CO₂ to CO conversion was demonstrated by creating a strong metal-support interaction (SMSI) between Cu active sites and the TiO₂-coated dendritic fibrous nano-silica (DFNS/TiO₂) support. The DFNS/TiO₂-Cu10 catalyst showed excellent catalytic performance with a CO productivity of 5350 mmol g^-1 h^-1 (i.e., 53,506 mmol g_Cu^-1 h^-1), surpassing that of almost all copper-based thermal catalysts, with 99.8% selectivity toward CO. Even after 200 h of reaction, the catalyst remained active. Moderate initial agglomeration and high dispersion of nanoparticles (NPs) due to SMSI made the catalysts stable. Electron energy loss spectroscopy confirmed the strong interactions between copper NPs and the TiO₂ surface, supported by in situ diffuse reflectance infrared Fourier transform spectroscopy and X-ray photoelectron spectroscopy. The H₂-temperature programmed reduction (TPR) study showed α, β, and γ H₂-TPR signals, further confirming the presence of SMSI between Cu and TiO₂. In situ Raman and UV-vis diffuse reflectance spectroscopy studies provided insights into the role of oxygen vacancies and Ti³⁺ centers, which were produced by hydrogen, then consumed by CO₂, and then again regenerated by hydrogen. These continuous defect generation-regeneration processes during the progress of the reaction allowed long-term high catalytic activity and stability. The in situ studies and oxygen storage complete capacity indicated the key role of oxygen vacancies during catalysis. The in situ time-resolved Fourier transform infrared study provided an understanding of the formation of various reaction intermediates and their conversion to products with reaction time. Based on these observations, we have proposed a CO₂ reduction mechanism, which follows a redox pathway assisted by hydrogen.

Ultrafast materials synthesis and manufacturing techniques for emerging energy and environmental applications

Energy and environmental issues have attracted increasing attention globally, where sustainability and low-carbon emissions are seriously considered and widely accepted by government officials. In response to this situation, the development of renewable energy and environmental technologies is urgently needed to complement the usage of traditional fossil fuels. While a big part of advancement in these technologies relies on materials innovations, new materials discovery is limited by sluggish conventional materials synthesis methods, greatly hindering the advancement of related technologies. To address this issue, this review introduces and comprehensively summarizes emerging ultrafast materials synthesis methods that could synthesize materials in times as short as nanoseconds, significantly improving research efficiency. We discuss the unique advantages of these methods, followed by how they benefit individual applications for renewable energy and the environment. We also highlight the scalability of ultrafast manufacturing towards their potential industrial utilization. Finally, we provide our perspectives on challenges and opportunities for the future development of ultrafast synthesis and manufacturing technologies. We anticipate that fertile opportunities exist not only for energy and the environment but also for many other applications.

Architecture Design and Catalytic Activity: Non-Noble Bimetallic CoFe/fe3 O4 Core-Shell Structures for CO2 Hydrogenation

Non-noble metal catalysts now play a key role in promoting efficiently and economically catalytic reduction of CO₂ into clean energy, which is an important strategy to ameliorate global warming and resource shortage issues. Here, a non-noble bimetallic catalyst of CoFe/Fe₃ O₄ nanoparticles is successfully designed with a core-shell structure that is well dispersed on the defect-rich carbon substrate for the hydrogenation of CO₂ under mild conditions. The catalysts exhibit a high CO₂ conversion activity with the rate of 30% and CO selectivity of 99%, and extremely robust stability without performance decay over 90 h in the reverse water gas shift reaction process. Notably, it is found that the reversible exsolution/dissolution of cobalt in the Fe₃ O₄ shell will lead to a dynamic and reversible deactivation/regeneration of the catalysts, accompanying by shell thickness breathing during the repeated cycles, via atomic structure study of the catalysts at different reaction stages. Combined with density functional theory calculations, the catalytic activity reversible regeneration mechanism is proposed. This work reveals the structure-property relationship for rational structure design of the advanced non-noble metallic catalyst materials with much improved performance.

Ptn-Ov synergistic sites on MoOx/γ-Mo2N heterostructure for low-temperature reverse water-gas shift reaction

In heterogeneous catalysis, the interface between active metal and support plays a key role in catalyzing various reactions. Specially, the synergistic effect between active metals and oxygen vacancies on support can greatly promote catalytic efficiency. However, the construction of high-density metal-vacancy synergistic sites on catalyst surface is very challenging. In this work, isolated Pt atoms are first deposited onto a very thin-layer of MoO₃ surface stabilized on γ-Mo₂N. Subsequently, the Pt-MoO_x/γ-Mo₂N catalyst, containing abundant Pt cluster-oxygen vacancy (Pt_n-O_v) sites, is in situ constructed. This catalyst exhibits an unmatched activity and excellent stability in the reverse water-gas shift (RWGS) reaction at low temperature (300 °C). Systematic in situ characterizations illustrate that the MoO₃ structure on the γ-Mo₂N surface can be easily reduced into MoO_x (2 < x < 3), followed by the creation of sufficient oxygen vacancies. The Pt atoms are bonded with oxygen atoms of MoO_x, and stable Pt clusters are formed. These high-density Pt_n-O_v active sites greatly promote the catalytic activity. This strategy of constructing metal-vacancy synergistic sites provides valuable insights for developing efficient supported catalysts.

Alloyed PdCu Nanoparticles within Siliceous Zeolite Crystals for Catalytic Semihydrogenation

Selective hydrogenation of acetylene to ethylene is an industrially important process to purify the raw ethylene stream for producing high-grade polyethylene. The supported Pd catalyst exhibits superior activity for acetylene hydrogenation but suffers from poor ethylene selectivity because of the easy overhydrogenation to produce ethane. Here, we report that the PdCu alloy nanoparticles within siliceous zeolite crystals effectively tuned Pd-catalyzed overhydrogenation into semihydrogenation. This catalyst displayed an ethylene selectivity of 92.9% with a full conversion of acetylene. Mechanism studies reveal that the zeolite fixation stabilized the alloyed structure, where the electron-enriched Pd surface benefits the rapid ethylene desorption to hinder the deep hydrogenation. This work provides an efficient strategy for a rational design of bimetallic metal catalysts for selective hydrogenations.