Oxygen-Substituted Porous C2N Frameworks as Efficient Electrocatalysts for Carbon Dioxide Electroreduction

The electrochemical carbon dioxide reduction reaction (CO2RR) provides a green avenue for decarbonizing the conventional chemical industries. Here, a structure-selectivity relationship of catalysts is pivotal for the control of a highly selective and active CO2RR pathway. We report the fabrication of an oxygen-substituted C2N as metal-free catalyst (O─C2N) for electrochemical CO2─to─CO conversion with tunable O microenvironment. Combined spectroscopic analysis reveals a fine tailored N─C─O moiety in O─C2N, where C─O─C species (e.g., ring in-plane ether) become the dominant oxygen configurations at higher pyrolysis temperatures. Based on experimental observations, a correlation between the exocyclic O-substituted N─C─O─C moieties and CO selectivity is established, giving clear chemical tools for active structure design. The optimized O─C2N electrocatalysts with the dominant appearance of C─O─C moieties exhibit an outstanding 2e- CO2RR performance with a CO selectivity up to 94.8%, which can be well maintained in a practical flow-cell reactor with an adjustable syngas feature.

Stefan-Boltzmann Water Catalyzed Propane Dehydrogenation

The traditional wisdom of utilizing water in practical olefin synthesis has been viewed as a means to reduce alkane partial pressure and assist in coke removal. However, under such harsh reaction conditions, the potential catalytic role of the water molecule remains unclear. This study explores the intriguing concept that the water molecule, through the selective excitation of molecular vibrations and collisions induced by thermal energy and thermal radiation, could act as a catalyst in homogeneous gaseous propane dehydrogenation. This occurs via the generation of the OH⋅ radicals, resulting in an olefin yield of 37.93 %, a single pass propane conversion of 51.14 %, and an excellent stability of more than 2000 hours.

Synergistical Catalysis of TiO2 and SAPO-34 for Efficient Conversion of CO2 to C2H4

The excessive emission of carbon dioxide (CO2) into the atmosphere has led to a significant global warming crisis. Utilizing bifunctional catalysts, which consist of bimetallic oxides and SAPO-34, for catalyzing the conversion of CO2 to high-value-added ethylene (C2H4) can effectively mitigate this issue. However, this process also produces a substantial number of by-products. Additionally, the use of bimetallics or precious metals increases the catalyst costs. In this study, we propose an innovative synergistic approach by integrating SAPO-34 with TiO2, enabling both efficient CO2 capture and its catalytic conversion into C2 hydrocarbons. The system achieved a C2H4 yield of 20 μmol g-1 with a selectivity of 63.5%. Comprehensive characterizations revealed that the 30% TiO2/SAPO composite exhibited a higher concentration of oxygen vacancies and a greater percentage of Ti3+ species. Moreover, the confinement effect of SAPO-34 facilitated the C-C coupling and the formation of C2H4. This work exemplifies a dual-functional strategy, providing valuable insights for carbon reduction.

One-Step Low-Temperature Synthesis of Metastable ε-Iron Carbide Nanoparticles with Unique Catalytic Properties Beyond Conventional Iron Catalysts

ε-Iron carbide has garnered increasing interest for its superior magnetic characteristics and catalytic performance compared to other iron carbides. However, its metastable nature has posed significant challenges for synthesis, often requiring ultrahigh pressure, multistep processes, complex reaction condition control, and highly toxic reagents. Consequently, the properties of ε-iron carbide remain largely unexplored. A simplified synthesis method for ε-iron carbide can accelerate the exploration of new functionalities. In this study, a novel one-step selective synthesis method for ε-iron carbide nanoparticles under mild conditions via a wet-chemical approach is presented. In this method, Fe3(CO)12, cetyltrimethylammonium bromide (CTAB), and bis(pinacolato)diboron (B2pin2) are added to hexadecylamine and reacted at 220 °C-a simple process that eliminates the need for extreme pressures and toxic substances. Detailed investigations elucidate the crucial roles of CTAB and B2pin2 in facilitating the selective formation of ε-iron carbide. This accessible and efficient synthesis process for ε-iron carbide can further enable the discovery of unprecedented catalytic properties in the reductive amination of benzaldehyde, distinct from those of conventional iron nanoparticle catalysts. Density functional theory calculations reveal insights into the electronic states responsible for the distinct activity of the ε-iron carbide nanoparticles.

Accelerated Oxide-Zeolite Catalyst Design for Syngas Conversion by Reaction Phase Diagram Analysis and Machine Learning

Oxide-zeolite (OXZEO) catalyst design concept provides an alternative approach for the direct syngas-to-olefins (STO) with superior selectivity. Enhancing the activity of oxide components remains a critical and long-pursued target in this field. However, rational design strategies for optimizing oxides and improving the catalyst performance in such complex reaction networks are still lacking. We employed energetic descriptors such as the adsorption energies of CO* and O* (GadCO* and GadO*) through reaction phase diagram (RPD) analysis to predict the catalyst performance. The prediction was initially validated by the catalytic activity trends measured by experiments. Machine learning (ML) was further utilized to accelerate the screening of new catalysts. Ultimately, Bi-doped and Sb-doped ZnCrOx were theoretically predicted as optimized oxide candidates for the OXZEO reaction, which was experimentally verified to be more active than the currently best ZnCrOx counterpart. This work demonstrated enhanced OXZEO catalysts for STO as well as a research paradigm integrating theory and experiment to optimize bifunctional catalysts for complex reaction networks.

Long-Term CO2 Hydrogenation into Liquid Fuels with a Record-High Single-Pass Yield of 31.7% over Interfacial Fe-Zn Sites

Despite extensive research efforts in CO2 hydrogenation, achieving a high yield of liquid fuels remains a significant challenge due to the limited conversion of CO2 and the considerable formation of undesired C1 byproducts. In this study, we report a record-high yield of liquid fuels from CO2 hydrogenation facilitated by an Fe-Zn catalyst enriched with interfacial sites. These interfacial sites effectively enhanced carbon chain growth through the synergistic interaction of the carbide pathway and CO insertion while simultaneously suppressing the formation of CO and CH4. Consequently, the selectivity for undesired C1 byproducts was minimized to 14.7%, while maintaining a high selectivity of 72.2% for liquid fuels. Under optimized reaction conditions including 360 °C, 4.0 MPa, 4,000 mL gcat-1 h-1, and CO2/H2 = 3, the liquid fuel yield reached 31.7% at a single-pass CO2 conversion of 48.2%.

Selectivity control by zeolites during methanol-mediated CO2 hydrogenation processes

The thermocatalytic conversion of CO2 with green or blue hydrogen into valuable energy and commodity chemicals such as alcohols, olefins, and aromatics emerges as one of the most promising strategies for mitigating global warming concerns in the future. This process can follow either a CO2-modified Fischer-Tropsch synthesis route or a methanol-mediated route, with the latter being favored for its high product selectivity beyond the Anderson-Schulz-Flory distribution. Despite the progress of the CO2-led methanol-mediated route over bifunctional metal/zeolite catalysts, challenges persist in developing catalysts with both high activity and selectivity due to the complexity of CO2 hydrogenation reaction networks and the difficulty in controlling C-O bond activation and C-C bond coupling on multiple active sites within zeolites. Moreover, the different construction and proximity modes of bifunctionality involving redox-based metallic sites and acidic zeolite sites have been explored, which have not been systematically reviewed to derive reliable structure-reactivity relationships. To bridge this "knowledge gap", in this review, we will provide a comprehensive and critical overview of contemporary research on zeolite-confined metal catalysts for alcohol synthesis and zeolite-based bifunctional tandem/cascade catalytic systems for C2+ hydrocarbons synthesis in CO2 hydrogenation via the methanol-mediated route. Accordingly, special emphasis will be placed on evaluating how confinement and proximity effects within the "redox-acid" bifunctional systems influence the reaction outcomes, particularly regarding product selectivity, which has also been analyzed from the mechanistic standpoint. This review will also examine the synergistic interactions among various catalyst components that govern catalysis, offering valuable insights for the rational design of new or improved catalyst systems. By discussing current challenges and recognizing future opportunities in CO2 hydrogenation using zeolite-based bifunctional catalysis, this review aims to contribute to the advancement of sustainable and efficient processes for CO2 valorization.

Development of hydrophobic catalysts for reducing the CO2 emission during the conversion of syngas into chemicals and fuels

Syngas conversion is a key process for the production of chemicals and fuels from non-petroleum resources, such as biomass, coal, and natural gas. Water produced during syngas conversion can not only boost the production of CO2 by-products via inducing the water-gas shift side reaction, but also inhibit the conversion of CO by occupying the active sites on the catalyst, leading to high CO2 emission and low carbon utilization efficiency. Reducing CO2 emission during syngas conversion is a main development direction of the energy chemical industry toward the goal of carbon neutrality. It has been reported that hydrophobic modification can reduce a surface's affinity to water molecules, and many breakthroughs in the development of hydrophobic catalysts for weakening the negative effect of water on syngas conversion have been made recently. A rapidly growing number of studies have demonstrated the versatility of hydrophobic catalysts. In this review, we systematically summarize and discuss the development of hydrophobic catalysts in syngas chemistry since the 2000s. These hydrophobic catalysts can be divided into three categories, i.e., catalysts with hydrophobic surfaces, catalysts with hydrophobic supports, and catalysts physically mixed with hydrophobic promoters. Different categories of hydrophobic catalysts play different roles in syngas conversion. The perspectives and challenges for the future design of hydrophobic catalysts are also discussed.

Highly efficient oxidation of methane into methanol over Ni-promoted Cu/ZSM-5

Direct functionalization of methane in natural gas is of paramount importance but faces tremendous challenges. We reported a nickel-modified copper zeolite catalyst for the selective oxidation of methane into methanol. Using H2O2 as an oxidant in the liquid phase at 80 °C, Cu1Ni0.75/ZSM-5 catalyst presented a relatively high methanol yield of 82 162 μmol gcat -1 h-1 (with a methanol selectivity of ∼74%). Combining series of designed experiments and thorough characterization analysis, including electron microscopy, X-ray photoelectric spectroscopy, Fourier transform infrared reflection as well as in situ diffuse reflectance infrared Fourier transform spectroscopy, abundant CuI active sites were found on Ni-Promoted Cu/ZSM-5, differing from the dominating CuII active sites over Cu/ZSM-5. CuI active sites had an excellent ability to promote CH4 adsorption, CH4 activation and CH3OH generation compared to CuII active sites. This work elucidates a constellation of insightful and potent perspectives for further improvement of metal-zeolite catalysts for the direct oxidation of methane to methanol.

Catalysis Enhanced by Catalyst Wettability

Heterogeneous catalysis is a surface phenomenon where the adsorption, desorption, and transfer of reactants and products are critical for catalytic performance. Recent results show that catalyst wettability is strongly related to the adsorption, desorption, and transfer of reactants and products. In this review, we briefly summarize strategies for regulating wettability to enrich reactants, accelerate the desorption of products, and promote mass transfer in heterogeneous catalysis. In addition, we explore insights into catalyst wettability for the enhancement of catalytic performance. Finally, the concerns and challenges in this subject are outlined, and practical strategies are proposed for the regulation of catalyst wettability. We hope that this review will be helpful for designing highly efficient heterogeneous catalysts in the future.

Low-temperature CO2 Hydrogenation to Olefins on Anorthic NaCoFe Alloy Carbides

The hydrogenation of carbon dioxide to olefins (CTO) represents an ideal pathway towards carbon neutrality. However, most current CTO catalysts require a high-temperature condition of 300-450 °C, resulting in high energy consumption and possible aggregation among active sites. Herein, we developed an efficient iron-based catalyst modified with high-sodium content (7 %) and low-cobalt content (2 %), achieving a CO2 conversion of 22.0 % and an olefin selectivity of 55.9 % at 240 °C and 1000 mL/g/h, and it is even active at 180 °C and 4000 mL/g/h with more than 25 % olefins in hydrocarbons. The catalyst was kept stable under continuous operating conditions of 500 hours. Numerous characterizations and calculations reveal high content of sodium as an electronic promoter enhances the stability of the active anorthic Fe5C2 phase at low temperatures. Further incorporating the above catalyst with cobalt, as a structural promoter, causes Fe species to form a FexCoy alloying phase, which in turn facilitates the formation of higher active anorthic (FexCoy)5C2 phase, different from the conventional carbides and alloy carbides. An in-depth investigation of the synergistic effects of structural and electronic promoters can improve catalyst performance, increase reaction efficiency and cost-effectiveness, and provide profound insights for understanding and optimizing CO2 hydrogenation reactions.

Surface and Interface Engineering of Electrospun Nanofibers for Heterogeneous Catalysts

Surface and interface engineering of catalysts from atomic level to macroscale exhibit good performance in regulating conversion, selectivity, and stability. Electrospinning offers such multiscale flexibility in tuning surface and interface structures and compositions for the design of fiber catalysts. This review presents an overview on the surface and interface engineering of electrospun nanofibers for heterogeneous catalysts designing. First, the building strategies for regulating catalytic performance on surface and interface at different scales are introduced. Then, typical research achievements of surface and interface regulation strategies of nanofiber catalysts in different scales are summarized, including atomic vacancy and doping at microscale, heterojunction interfaces at mesoscale, and surfaces/interfaces with special wettability at macroscale. The typical catalytic reactions are introduced that involve classical small molecule hydrogenation, oxygen evolution reaction, and pollutant photocatalytic degradation, as well as the recently emerging CO2 reduction reaction and nitrate/nitrite reduction. Finally, the challenges and future tendency on surface and interface engineering of electrospun nanofiber catalysts are highlighted.

Reactive Intermediate Confinement in Beta Zeolites for the Efficient Aerobic Epoxidation of α-Olefins

The efficient conversion of long-chain linear α-olefins (LAOs) into industrially useful epoxides is of pivotal importance. Mukaiyama epoxidation based on the use of molecular oxygen as the sole oxidant and aldehyde as the cosubstrate offers a promising route for LAOs epoxidation. However, challenges associated with epoxide forming selectivity and aldehyde coupling efficiency have long impeded the adoption of Mukaiyama epoxidation in large-scale applications. Herein, we show that confinement of key intermediates involved in the parallel epoxidation pathways within a Beta zeolite unlocks a selectivity of greater than 95 % towards the epoxides at the expense of minimal consumption of only 1.5 equivalents of the aldehyde, achieving an efficiency better than the state-of-the-art homogeneous and heterogeneous catalysts. Moreover, the incorporation of Sn sites into the Beta zeolite framework further facilitates the adsorption activation process of the aldehyde cosubstrate, thereby increasing the concentration of acylperoxy radicals and accelerating the kinetic process of the epoxidation step. Consequently, this work not only provides an efficient and green epoxidation route over zeolite catalysts with easily available O2 as the oxidant, but also systematically reveals the fundamental understanding of the zeolite confinement effects on steering the reaction pathway, which benefits the further development of valorization of LAOs.

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.

Structure-reactivity relationships in CO2 hydrogenation to C2+ chemicals on Fe-based catalysts

Catalytic conversion of carbon dioxide (CO2) to value-added products represents an important avenue towards achieving carbon neutrality. In this respect, iron (Fe)-based catalysts were recognized as the most promising for the production of C2+ chemicals via the CO2 hydrogenation reaction. However, the complex structural evolution of the Fe catalysts, especially during the reaction, presents significant challenges for establishing the structure-reactivity relationships. In this review, we provide critical analysis of recent in situ and operando studies on the transformation of Fe-based catalysts in the hydrogenation of CO2 to hydrocarbons and alcohols. In particular, the effects of composition, promoters, support, and particle size on reactivity; the role of the catalyst's activation procedure; and the catalyst's evolution under reaction conditions will be addressed.

Asymmetric Coupled Binuclear-Site Catalysts for Low-Temperature Selective Acetylene Semi-Hydrogenation

Heterogeneous metal catalysts with bifunctional active sites are widely used in chemical industries. Although their improvement process is typically based on trial-and-error, it is hindered by the lack of model catalysts. Herein, we report an effective vacancy-pair capturing strategy to fabricate 12 heterogeneous binuclear-site catalysts (HBSCs) comprising combinations of transition metals on titania. During the synthesis of these HBSCs, proton-passivation treatment and step-by-step electrostatic anchorage enabled the suppression of single-atom formation and the successive capture of two target metal cations on the titanium-oxygen vacancy-pair site. Additionally, during acetylene hydrogenation at 20 °C, the HBSCs (e.g., Pt1Pd1-TiO2) consistently generated more than two times the ethylene produced by their single-atom counterparts (e.g., Pd1-TiO2). Furthermore, the Pt1Pd1 binuclear sites in Pt1Pd1-TiO2 were demonstrated to catalyze C2H2 hydrogenation via a bifunctional active-site mechanism: initially C2H2 chemisorb on the Pt1 site, then H2 dissociates and migrates from Pd1 to Pt1, and finally hydrogenation occurs at the Pt1-Pd1 interface.

Nanocellulose encapsulated nZVI@UiO-66-NH2 aerogel for high-efficiency p-chloronitrobenzene removal with selective reduction

A poriferous nZVI aerogel (nZVI@UiO-66-NH2/TCNF) was elaborately constructed by in-situ deposition of nZVI on UiO-66-NH2 and coupling with a bio-based TEMPO oxidized cellulose nanofiber (TCNF) substrate, followed by freeze-drying process for p-chloronitrobenzene (p-CNB) degradation. With degradation efficiency of above 85 % within 3 h under a wide pH range of 3-9, the nZVI@UiO-66-NH2/TCNF aerogel presented better p-CNB removal performance than other developed aerogels. Extended to 24 h, superior p-CNB removal performance (99.83 %) and 4-chloroaniline (p-CAN) selectivity (98.84 %) were successfully achieved. This could be attributed to 1) the facilitated mass transfer via concentration-gradient driving force with buffering and drag-reducing hydrated shear layer from porous channels of hydrophilic TCNF; 2) the enhanced adhesion of p-CNB onto UiO-66-NH2 and accelerated electron transfer by Fe-O-Zr bonds, synergistically improving the nitro- reduction of p-CNB using nZVI. This work pioneered a unique paradigm, providing nZVI with both solid bio-based moldability and highly-selective removal for the treatment of chloronitrobenzene containing wastewater.

Cost-Effective Synthesis of Fe5C2 Catalyst From Nanosized Zero-Valent Iron to Achieve Efficient Photothermocatalytic CO Hydrogenation to Light Olefins

Fe-based catalysts are commonly applied in the process of Fischer-Tropsch synthesis (FTS) to olefins, with Hägg iron carbide (Fe5C2) recognized as the primary active phase. However, iron carbonyls, the raw materials for wet chemical synthesis of Fe5C2, are expensive and toxic, which limits large-scale preparation. Here, a cost-effective and versatile method is proposed for the synthesis of Fe5C2 nanoparticles (NPs) with nanosized zero-valent iron (abbreviated as NZVI, prepared by reducing iron salts or ball-milling iron powder) instead of iron carbonyls, achieving a cost reduction of 76.8%. Experimental characterizations revealed that NZVI obtained from the reduction of iron salts can catalyze the cracking of octadecylamine to form a carbonized atmosphere, thus realizing the phase transition of Fe into Fe5C2. The optimized Fe5C2 catalyst is employed in the photothermocatalytic FTS process, achieving a light olefins selectivity of 54.2% in hydrocarbons, with a CO conversion of 24.3%. Furthermore, it is proved that the particle size and surface oxide state of NZVI can impact the synthesis of Fe5C2. This study demonstrates a cost-effective method for the large-scale preparation of the Fe5C2 catalyst.

LASP to the Future of Atomic Simulation: Intelligence and Automation

Atomic simulations aim to understand and predict complex physical phenomena, the success of which relies largely on the accuracy of the potential energy surface description and the efficiency to capture important rare events. LASP software (large-scale atomic simulation with a Neural Network Potential), released in 2018, incorporates the key ingredients to fulfill the ultimate goal of atomic simulations by combining advanced neural network potentials with efficient global optimization methods. This review introduces the recent development of the software along two main streams, namely, higher intelligence and more automation, to solve complex material and reaction problems. The latest version of LASP (LASP 3.7) features the global many-body function corrected neural network (G-MBNN) to improve the PES accuracy with low cost, which achieves a linear scaling efficiency for large-scale atomic simulations. The key functionalities of LASP are updated to incorporate (i) the ASOP and ML-interface methods for finding complex surface and interface structures under grand canonic conditions; (ii) the ML-TS and MMLPS methods to identify the lowest energy reaction pathway. With these powerful functionalities, LASP now serves as an intelligent data generator to create computational databases for end users. We exemplify the recent LASP database construction in zeolite and the metal-ligand properties for a new catalyst design.

Shielding the Hägg carbide by a graphene layer for ultrahigh carbon efficiency during syngas conversion

Fischer-Tropsch synthesis represents a key endeavor aimed at converting nonpetroleum carbon resources into clean fuels and valuable chemicals. However, the current state-of-the-art industrial FTS employing Fe-based catalysts is still challenged by the low carbon efficiency (<50%), mainly attributed to the prominent formation of CO2 and CH4 resulting from the nonregulated side water gas shift reaction. Herein, we describe a shielding strategy involving the encapsulation of the active Hägg carbide (χ-Fe5C2) by a graphene layer, exhibiting excellent resilience under reaction conditions and exposure to air, thereby eliminating the need for reduction or activation before the Fischer-Tropsch synthesis reaction. The graphene layer helps to stabilize the Hägg carbide active phase, and more importantly, greatly suppresses the side water gas shift reaction. Theoretical calculations suggest that graphene shielding inhibits the water gas shift reaction by reducing the absorption strength of OHx species. Remarkably, the optimum χ-Fe5C2@Graphene catalyst demonstrates a minimized CO2 and CH4 formation of only 4.6% and 5.9%, resulting in a high carbon efficiency (ca. 90%) for value-added products. These results are expected to inspire unique designs of Fe-based nanocomposite for highly efficient FTS with regulated carbon transfer pathways.

The role of manganese in CoMnOx catalysts for selective long-chain hydrocarbon production via Fischer-Tropsch synthesis

Cobalt is an efficient catalyst for Fischer-Tropsch synthesis (FTS) of hydrocarbons from syngas (CO + H2) with enhanced selectivity for long-chain hydrocarbons when promoted by Manganese. However, the molecular scale origin of the enhancement remains unclear. Here we present an experimental and theoretical study using model catalysts consisting of crystalline CoMnOx nanoparticles and thin films, where Co and Mn are mixed at the sub-nm scale. Employing TEM and in-situ X-ray spectroscopies (XRD, APXPS, and XAS), we determine the catalyst's atomic structure, chemical state, reactive species, and their evolution under FTS conditions. We show the concentration of CHx, the key intermediates, increases rapidly on CoMnOx, while no increase occurs without Mn. DFT simulations reveal that basic O sites in CoMnOx bind hydrogen atoms resulting from H2 dissociation on Co0 sites, making them less available to react with CHx intermediates, thus hindering chain termination reactions, which promotes the formation of long-chain hydrocarbons.

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.

Technology Readiness and Emerging Prospects of Coupled Catalytic Reactions for Sustainable Chemical Value Chains

Transitioning from both the direct and indirect use of fossil fuels to the renewable and sustainable resources of the near future demands a focal shift in catalysis research - from investigating catalytic reactions in isolation to developing coupled reactions for modern chemical value chains. In this Perspective, we discuss the status and emerging prospects of coupled catalytic reactions across various scales and provide key examples. Besides being a sustainable and essential alternative to current fossil-based processes, the coupling of catalytic reactions offers novel and scalable pathways to value-added chemicals. By emphasizing the specific requirements and challenges arising from coupled reactions, we aim to identify and underscore research needs that are critical to expedite their development and to fully unlock their potential for chemical and fuel production.

Efficient conversion of syngas to linear α-olefins by phase-pure χ-Fe5C2

Oil has long been the dominant feedstock for producing fuels and chemicals, but coal, natural gas and biomass are increasingly explored alternatives1-3. Their conversion first generates syngas, a mixture of CO and H2, which is then processed further using Fischer-Tropsch (FT) chemistry. However, although commercial FT technology for fuel production is established, using it to access valuable chemicals remains challenging. A case in point is linear α-olefins (LAOs), which are important chemical intermediates obtained by ethylene oligomerization at present4-8. The commercial high-temperature FT process and the FT-to-olefin process under development at present both convert syngas directly to LAOs, but also generate much CO2 waste that leads to a low carbon utilization efficiency9-14. The efficiency is further compromised by substantially fewer of the converted carbon atoms ending up as valuable C5-C10 LAOs than are found in the C2-C4 olefins that dominate the product mixtures9-14. Here we show that the use of the original phase-pure χ-iron carbide can minimize these syngas conversion problems: tailored and optimized for the process of FT to LAOs, this catalyst exhibits an activity at 290 °C that is 1-2 orders higher than dedicated FT-to-olefin catalysts can achieve above 320 °C (refs. 12-15), is stable for 200 h, and produces desired C2-C10 LAOs and unwanted CO2 with carbon-based selectivities of 51% and 9% under industrially relevant conditions. This higher catalytic performance, persisting over a wide temperature range (250-320 °C), demonstrates the potential of the system for developing a practically relevant technology.

New Insights for High-Throughput CO2 Hydrogenation to High-Quality Fuel

In the case of CO2 thermal-catalytic hydrogenation, highly selective olefin generation and subsequent olefin secondary reactions to fuel hydrocarbons in an ultra-short residence time is a huge challenge, especially under industrially feasible conditions. Here, we report a pioneering synthetic process that achieves selective production of high-volume commercial gasoline with the assistance of fast response mechanism. In situ experiments and DFT calculations demonstrate that the designed NaFeGaZr presents exceptional carbiding prowess, and swiftly forms carbides even at extremely brief gas residence times, facilitating olefin production. The created successive hollow zeolite HZSM-5 further reinforces aromatization of olefin diffused from NaFeGaZr via optimized mass transfer in the hollow channel of zeolite. Benefiting from its rapid response mechanism within the multifunctional catalytic system, this catalyst effectively prevents the excessive hydrogenation of intermediates and controls the swift conversion of intermediates into aromatics, even in high-throughput settings. This enables a rapid one-step synthesis of high-quality gasoline-range hydrocarbons without any post-treatment, with high commercial product compatibility and space-time yield up to 0.9 kggasoline ⋅ kgcat -1 ⋅ h-1. These findings from the current work can provide a shed for the preparation of efficient catalysts and in-depth understanding of C1 catalysis in industrial level.

Breaking the activity-selectivity trade-off of CO2 hydrogenation to light olefins

Catalytic hydrogenation of CO2 to value-added fuels and chemicals is of great importance to carbon neutrality but suffers from an activity-selectivity trade-off, leading to limited catalytic performance. Herein, the ZnFeAlO4 + SAPO-34 composite catalyst was designed, which can simultaneously achieve a CO2 conversion of 42%, a CO selectivity of 50%, and a C2-C4= selectivity of 83%, resulting in a C2-C4= yield of almost 18%. This superior catalytic performance was found to be from the presence of unconventional electron-deficient tetrahedral Fe sites and electron-enriched octahedral Zn sites in the ZnFeAlO4 spinel, which were active for the CO2 deoxygenation to CO via the reverse water gas shift reaction, and CO hydrogenation to CH3OH, respectively, leading to a route for CO2 hydrogenation to C2-C4=, where the kinetics of CO2 activation can be improved, the mass transfer of CO hydrogenation can be minimized, and the C2-C4= selectivity can be enhanced via modifying the acid density of SAPO-34. Moreover, the spinel structure of ZnFeAlO4 possessed a strong ability to stabilize the active Fe and Zn sites even at elevated temperatures, resulting in long-term stability of over 450 h for this process, exhibiting great potential for large-scale applications.

Effects of surface hydrophobization on the phase evolution behavior of iron-based catalyst during Fischer-Tropsch synthesis

Iron-based Fischer-Tropsch synthesis (FTS) catalyst is widely used for syngas conversion, but its iron carbide active phase is easily oxidized into Fe3O4 by the water produced during reaction, leading to the deterioration of catalytic performance. Here, we show an efficient strategy for protecting the iron carbide active phase of FTS catalyst by surface hydrophobization. The hydrophobic surface can reduce the water concentration in the core vicinity of catalyst during syngas conversion, and thus inhibit the oxidation of iron species by water, which enhances the C - C coupling ability of catalyst and promotes the formation of long-chain olefins. More significantly, it is unraveled that appropriate shell thickness plays a crucial role in stabilizing the iron carbide active phase without Fe3O4 formation and achieving good catalytic performance.

Facet sensitivity of iron carbides in Fischer-Tropsch synthesis

Fischer-Tropsch synthesis (FTS) is a structure-sensitive reaction of which performance is strongly related to the active phase, particle size, and exposed facets. Compared with the full-pledged investigation on the active phase and particle size, the facet effect has been limited to theoretical studies or single-crystal surfaces, lacking experimental reports of practical catalysts, especially for Fe-based catalysts. Herein, we demonstrate the facet sensitivity of iron carbides in FTS. As the prerequisite, {202} and {112} facets of χ-Fe5C2 are fabricated as the outer shell through the conformal reconstruction of Fe3O4 nanocubes and octahedra, as the inner cores, respectively. During FTS, the activity and stability are highly sensitive to the exposed facet of iron carbides, whereas the facet sensitivity is not prominent for the chain growth. According to mechanistic studies, {202} χ-Fe5C2 surfaces follow hydrogen-assisted CO dissociation which lowers the activation energy compared with the direct CO dissociation over {112} surfaces, affording the high FTS activity.

Engineering ZrO2-Ru interface to boost Fischer-Tropsch synthesis to olefins

Understanding the structures and reaction mechanisms of interfacial active sites in the Fisher-Tropsch synthesis reaction is highly desirable but challenging. Herein, we show that the ZrO2-Ru interface could be engineered by loading the ZrO2 promoter onto silica-supported Ru nanoparticles (ZrRu/SiO2), achieving 7.6 times higher intrinsic activity and ~45% reduction in the apparent activation energy compared with the unpromoted Ru/SiO2 catalyst. Various characterizations and theoretical calculations reveal that the highly dispersed ZrO2 promoter strongly binds the Ru nanoparticles to form the Zr-O-Ru interfacial structure, which strengthens the hydrogen spillover effect and serves as a reservoir for active H species by forming Zr-OH* species. In particular, the formation of the Zr-O-Ru interface and presence of the hydroxyl species alter the H-assisted CO dissociation route from the formyl (HCO*) pathway to the hydroxy-methylidyne (COH*) pathway, significantly lowering the energy barrier of rate-limiting CO dissociation step and greatly increasing the reactivity. This investigation deepens our understanding of the metal-promoter interaction, and provides an effective strategy to design efficient industrial Fisher-Tropsch synthesis catalysts.

Stabilized ε-Fe2C catalyst with Mn tuning to suppress C1 byproduct selectivity for high-temperature olefin synthesis

Accurately controlling the product selectivity in syngas conversion, especially increasing the olefin selectivity while minimizing C1 byproducts, remains a significant challenge. Epsilon Fe2C is deemed a promising candidate catalyst due to its inherently low CO2 selectivity, but its use is hindered by its poor high-temperature stability. Herein, we report the successful synthesis of highly stable ε-Fe2C through a N-induced strategy utilizing pyrolysis of Prussian blue analogs (PBAs). This catalyst, with precisely controlled Mn promoter, not only achieved an olefin selectivity of up to 70.2% but also minimized the selectivity of C1 byproducts to 19.0%, including 11.9% CO2 and 7.1% CH4. The superior performance of our ε-Fe2C-xMn catalysts, particularly in minimizing CO2 formation, is largely attributed to the interface of dispersed MnO cluster and ε-Fe2C, which crucially limits CO to CO2 conversion. Here, we enhance the carbon efficiency and economic viability of the olefin production process while maintaining high catalytic activity.

Atomic/molecular layer deposition strategies for enhanced CO2 capture, utilisation and storage materials

Elevated levels of carbon dioxide (CO2) in the atmosphere and the diminishing reserves of fossil fuels have raised profound concerns regarding the resulting consequences of global climate change and the future supply of energy. Hence, the reduction and transformation of CO2 not only mitigates environmental pollution but also generates value-added chemicals, providing a dual remedy to address both energy and environmental challenges. Despite notable advancements, the low conversion efficiency of CO2 remains a major obstacle, largely attributed to its inert chemical nature. It is imperative to engineer catalysts/materials that exhibit high conversion efficiency, selectivity, and stability for CO2 transformation. With unparalleled precision at the atomic level, atomic layer deposition (ALD) and molecular layer deposition (MLD) methods utilize various strategies, including ultrathin modification, overcoating, interlayer coating, area-selective deposition, template-assisted deposition, and sacrificial-layer-assisted deposition, to synthesize numerous novel metal-based materials with diverse structures. These materials, functioning as active materials, passive materials or modifiers, have contributed to the enhancement of catalytic activity, selectivity, and stability, effectively addressing the challenges linked to CO2 transformation. Herein, this review focuses on ALD and MLD's role in fabricating materials for electro-, photo-, photoelectro-, and thermal catalytic CO2 reduction, CO2 capture and separation, and electrochemical CO2 sensing. Significant emphasis is dedicated to the ALD and MLD designed materials, their crucial role in enhancing performance, and exploring the relationship between their structures and catalytic activities for CO2 transformation. Finally, this comprehensive review presents the summary, challenges and prospects for ALD and MLD-designed materials for CO2 transformation.

CO electrolysis to multicarbon products over grain boundary-rich Cu nanoparticles in membrane electrode assembly electrolyzers

Producing valuable chemicals like ethylene via catalytic carbon monoxide conversion is an important nonpetroleum route. Here we demonstrate an electrochemical route for highly efficient synthesis of multicarbon (C2+) chemicals from CO. We achieve a C2+ partial current density as high as 4.35 ± 0.07 A cm-2 at a low cell voltage of 2.78 ± 0.01 V over a grain boundary-rich Cu nanoparticle catalyst in an alkaline membrane electrode assembly (MEA) electrolyzer, with a C2+ Faradaic efficiency of 87 ± 1% and a CO conversion of 85 ± 3%. Operando Raman spectroscopy and density functional theory calculations reveal that the grain boundaries of Cu nanoparticles facilitate CO adsorption and C - C coupling, thus rationalizing a qualitative trend between C2+ production and grain boundary density. A scale-up demonstration using an electrolyzer stack with five 100 cm2 MEAs achieves high C2+ and ethylene formation rates of 118.9 mmol min-1 and 1.2 L min-1, respectively, at a total current of 400 A (4 A cm-2) with a C2+ Faradaic efficiency of 64%.

Cu-nanocluster-loaded N-doped porous graphitic carbon for electrochemical CO2 reduction towards syngas generation

In this study, a novel electrocatalyst, namely Cu/N-pg-C derived from Cu-doped ZIF-8, was investigated for making syngas products with various H2/CO ratios. Different ratios of the electrocatalytic syngas products CO and H2 could be selected by adjusting the applied potential and hence tuning the transfer of electrons from N-doped graphitic carbon to the well-dispersed Cu nanoclusters.

Preparation of Hydrophobic Au Catalyst and Application in One-Step Oxidative Esterification of Methacrolein to Methyl Methacrylate

The water produced during the oxidative esterification reaction occupies the active sites and reduces the activity of the catalyst. In order to reduce the influence of water on the reaction system, a hydrophobic catalyst was prepared for the one-step oxidative esterification of methylacrolein (MAL) and methanol. The catalyst was synthesized by loading the active component Au onto ZnO using the deposition-precipitation method, followed by constructing the silicon shell on Au/ZnO using tetraethoxysilane (TEOS) to introduce hydrophobic groups. Trimethylchlorosilane (TMCS) was used as a hydrophobic modification reagent to prepare hydrophobic catalysts, which exhibited a water droplet contact angle of 111.2°. At a temperature of 80 °C, the hydrophobic catalyst achieved a high MMA selectivity of over 95%. The samples were characterized using XRD, N2 adsorption, ICP, SEM, TEM, UV-vis, FT-IR, XPS, and water droplet contact angle measurements. Kinetic analysis revealed an activation energy of 22.44 kJ/mol for the hydrophobic catalyst.

Upgrading CO2 to sustainable aromatics via perovskite-mediated tandem catalysis

The directional transformation of carbon dioxide (CO2) with renewable hydrogen into specific carbon-heavy products (C6+) of high value presents a sustainable route for net-zero chemical manufacture. However, it is still challenging to simultaneously achieve high activity and selectivity due to the unbalanced CO2 hydrogenation and C-C coupling rates on complementary active sites in a bifunctional catalyst, thus causing unexpected secondary reaction. Here we report LaFeO3 perovskite-mediated directional tandem conversion of CO2 towards heavy aromatics with high CO2 conversion (> 60%), exceptional aromatics selectivity among hydrocarbons (> 85%), and no obvious deactivation for 1000 hours. This is enabled by disentangling the CO2 hydrogenation domain from the C-C coupling domain in the tandem system for Iron-based catalyst. Unlike other active Fe oxides showing wide hydrocarbon product distribution due to carbide formation, LaFeO3 by design is endowed with superior resistance to carburization, therefore inhibiting uncontrolled C-C coupling on oxide and isolating aromatics formation in the zeolite. In-situ spectroscopic evidence and theoretical calculations reveal an oxygenate-rich surface chemistry of LaFeO3, that easily escape from the oxide surface for further precise C-C coupling inside zeolites, thus steering CO2-HCOOH/H2CO-Aromatics reaction pathway to enable a high yield of aromatics.

Selectivity Control by Relay Catalysis in CO and CO2 Hydrogenation to Multicarbon Compounds

ConspectusThe hydrogenative conversion of both CO and CO2 into high-value multicarbon (C2+) compounds, such as olefins, aromatic hydrocarbons, ethanol, and liquid fuels, has attracted much recent attention. The hydrogenation of CO is related to the chemical utilization of various carbon resources including shale gas, biomass, coal, and carbon-containing wastes via syngas (a mixture of H2 and CO), while the hydrogenation of CO2 by green H2 to chemicals and liquid fuels would contribute to recycling CO2 for carbon neutrality. The state-of-the-art technologies for the hydrogenation of CO/CO2 to C2+ compounds primarily rely on a direct route via Fischer-Tropsch (FT) synthesis and an indirect route via two methanol-mediated processes, i.e., methanol synthesis from CO/CO2 and methanol to C2+ compounds. The direct route would be more energy- and cost-efficient owing to the reduced operation units, but the product selectivity of the direct route via FT synthesis is limited by the Anderson-Schulz-Flory (ASF) distribution. Selectivity control for the direct hydrogenation of CO/CO2 to a high-value C2+ compound is one of the most challenging goals in the field of C1 chemistry, i.e., chemistry for the transformation of one-carbon (C1) molecules.We have developed a relay-catalysis strategy to solve the selectivity challenge arising from the complicated reaction network in the hydrogenation of CO/CO2 to C2+ compounds involving multiple intermediates and reaction channels, which inevitably lead to side reactions and byproducts over a conventional heterogeneous catalyst. The core of relay catalysis is to design a single tandem-reaction channel, which can direct the reaction to the target product controllably, by choosing appropriate intermediates (or intermediate products) and reaction steps connecting these intermediates, and arranging optimized yet matched catalysts to implement these steps like a relay. This Account showcases representative relay-catalysis systems developed by our group in the past decade for the synthesis of liquid fuels, lower (C2-C4) olefins, aromatics, and C2+ oxygenates from CO/CO2 with selectivity breaking the limitation of conventional catalysts. These relay systems are typically composed of a metal or metal oxide for CO/CO2/H2 activation and a zeolite for C-C coupling or reconstruction, as well as a third or even a fourth catalyst component with other functions if necessary. The mechanisms for the activation of H2 and CO/CO2 on metal oxides, which are distinct from that on the conventional transition or noble metal surfaces, are discussed with emphasis on the role of oxygen vacancies. Zeolites catalyze the conversion of intermediates (including hydrocracking/isomerization of heavier hydrocarbons, methanol-to-hydrocarbon reactions, and carbonylation of methanol/dimethyl ether) in the relay system, and the selectivity is mainly controlled by the Brønsted acidity and the shape-selectivity or the confinement effect of zeolites. We demonstrate that the thermodynamic/kinetic matching of the relay steps, the proximity and spatial arrangement of the catalyst components, and the transportation of intermediates/products in sequence are the key issues guiding the selection of each catalyst component and the construction of an efficient relay-catalysis system. Our methodology would also be useful for the transformation of other C1 molecules via controlled C-C coupling, inspiring more efforts toward precision catalysis.

Technological progress and coupling renewables enable substantial environmental and economic benefits from coal-to-olefins

China's growing demand for bulk chemicals and concerns regarding energy security are scaling up coal-to-olefins (CTO) production. Three generations of independent dimethyl ether/methanol-to-olefins technologies have been successively launched with greatly improved production efficiencies. However, to date, widespread concerns regarding the intensive environmental impacts and potential economic risks have not been addressed in the context of this industrialization. Here we show that, through the technological progress from the first to the third generation, life cycle energy consumption, water consumption, and carbon emissions can be reduced to 119.5 GJ/t, 27.6 t/t, and 9.1 t CO2-eq/t, respectively, and human health damage, ecosystem quality damage, and resource scarcity impacts can be decreased by 40.5 %, 50.1 %, and 16.4 %, respectively. This is accompanied by an excellent performance in terms of production cost, net present value, and internal return rate at 792.5 USD/t, 173.4 USD/t, and 19.4 %, respectively. Substantial environmental and economic benefits can be gained by coupling renewables in the form of using green hydrogen from solar and wind power to synthesize methanol. Particularly, life cycle carbon emissions and resource scarcity impacts are reduced by 23.4 % and 22.4 %, respectively, exceeding the reduction in technological progress. However, coupling renewables increases the life cycle energy consumption to 154.5 GJ/t, counteracting the benefits of technological progress. Our results highlight the importance of technological progress and coupled renewables for enhancing the sustainability of the CTO industry.

Role of H2O in Catalytic Conversion of C1 Molecules

Due to their role in controlling global climate change, the selective conversion of C1 molecules such as CH4, CO, and CO2 has attracted widespread attention. Typically, H2O competes with the reactant molecules to adsorb on the active sites and therefore inhibits the reaction or causes catalyst deactivation. However, H2O can also participate in the catalytic conversion of C1 molecules as a reactant or a promoter. Herein, we provide a perspective on recent progress in the mechanistic studies of H2O-mediated conversion of C1 molecules. We aim to provide an in-depth and systematic understanding of H2O as a promoter, a proton-transfer agent, an oxidant, a direct source of hydrogen or oxygen, and its influence on the catalytic activity, selectivity, and stability. We also summarize strategies for modifying catalysts or catalytic microenvironments by chemical or physical means to optimize the positive effects and minimize the negative effects of H2O on the reactions of C1 molecules. Finally, we discuss challenges and opportunities in catalyst design, characterization techniques, and theoretical modeling of the H2O-mediated catalytic conversion of C1 molecules.

Novel heterogeneous Fe-based catalysts for carbon dioxide hydrogenation to long chain α-olefins-A review

The thermocatalytic conversion of carbon dioxide (CO2) into high value-added chemicals provides a strategy to address the environmental problems caused by excessive carbon emissions and the sustainable production of chemicals. Significant progress has been made in the CO2 hydrogenation to long chain α-olefins, but controlling C-O activation and C-C coupling remains a great challenge. This review focuses on the recent advances in catalyst design concepts for the synthesis of long chain α-olefins from CO2 hydrogenation. We have systematically summarized and analyzed the ingenious design of catalysts, reaction mechanisms, the interaction between active sites and supports, structure-activity relationship, influence of reaction process parameters on catalyst performance, and catalyst stability, as well as the regeneration methods. Meanwhile, the challenges in the development of the long chain α-olefins synthesis from CO2 hydrogenation are proposed, and the future development opportunities are prospected. The aim of this review is to provide a comprehensive perspective on long chain α-olefins synthesis from CO2 hydrogenation to inspire the invention of novel catalysts and accelerate the development of this process.

Promoting Syngas to Olefins with Isolated Internal Silanols-Enriched Al-IDM-1 Aluminosilicate Nanosheets

Selective conversion of syngas to value-added olefins has attracted considerable research interest. Regulating product distribution remains challenging, such as achieving higher olefin selectivity, propylene/ethylene (P/E) and olefin/paraffin (O/P) ratios. A new pentasil zeolite Al-IDM-1 with recently approved -ION structure, composed of 17-membered-ring (MR) extra-large lobed pores and intersected 10-MR medium pores, shows a C2-6 = selectivity up to 85 % and a high O/P value of 14 in the conversion of syngas when being combined with Zna Alb Ox oxide. Moreover, for the high-silica Al-IDM-1 with Si/Al ratio of 400, the selectivity of propylene and butene accounts for 88 % in C2-4 = , resulting in high P/E (>4) and butene/ethylene (B/E >3) ratios. The high C3-4 = selectivity is contributed by two main reasons, that is, the relatively weak acidity of Al-IDM-1 zeolite enhances the olefin-based cycle revealed by the probe reactions of methanol-to-propylene (MTP) and 1-hexene cracking, and the rich isolated internal SiOH groups in Al-IDM-1 promote the desorption of C3-4 = , once they are formed inside zeolite pores.

Wettability Engineering of Solar Methanol Synthesis

Engineering the wettability of surfaces with hydrophobic organics has myriad applications in heterogeneous catalysis and the large-scale chemical industry; however, the mechanisms behind may surpass the proverbial hydrophobic kinetic benefits. Herein, the well-studied In2O3 methanol synthesis photocatalyst has been used as an archetype platform for a hydrophobic treatment to enhance its performance. With this strategy, the modified samples facilitated the tuning of a wide range of methanol production rates and selectivity, which were optimized at 1436 μmol gcat-1 h-1 and 61%, respectively. Based on in situ DRIFTS and temperature-programmed desorption-mass spectrometry, the surface-decorated alkylsilane coating on In2O3 not only kinetically enhanced the methanol synthesis by repelling the produced polar molecules but also donated surface active H to facilitate the subsequent hydrogenation reaction. Such a wettability design strategy seems to have universal applicability, judged by its success with other CO2 hydrogenation catalysts, including Fe2O3, CeO2, ZrO2, and Co3O4. Based on the discovered kinetic and mechanistic benefits, the enhanced hydrogenation ability enabled by hydrophobic alkyl groups unleashes the potential of the surface organic chemistry modification strategy for other important catalytic hydrogenation reactions.

3D Monolayer Silanation of Porous Structure Facilitating Multi-Phase Pollutants Removal

Activated carbon (AC) is widely used to removing hazardous pollutants from air and water, owing to its exceptional adsorption properties. However, the high affinity of water molecules with the surface oxygen-containing functional groups can adversely affect the adsorption performance of AC. In this study, a facile and efficient method is presented for fabrication of hydrophobic AC through surface monolayer silanation. Compared to initial AC, the hydrophobic AC improves the water contact angle from 29.7° to 123.5° while maintaining high specific surface area and enhances the removal capacity of multi-phase pollutants (emulsified oil and toluene). Additionally, the hydrophobic AC exhibits excellent adsorption capability to harmful algal bloom species (Chlorella) (97.56%) and algal organic matter (AOM) (96.23%) owing to electrostatic interactions and surface hydrophobicity. The study demonstrates that this method of surface monolayer silanation can effectively weaken the effect of water molecules on AC adsorption capacity, which has significant potential for practical use in air and water purification, as well as in the control of harmful algal blooms.

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.

Selective conversion of carbon dioxide into heavy olefins over Ga modified delafossite-CuFeO2

Ga-modified CuFeO2 used as an efficient catalyst for CO2 hydrogenation to heavy olefins (C=5+) can achieve a high heavy olefin selectivity of 53.5%, which lies at a high level among reported catalysts, at a single pass CO2 conversion of 41.5%. It also displays an excellent long-term stability over 100 h, exhibiting its promising potential for industrial applications.

Methyl radical chemistry in non-oxidative methane activation over metal single sites

Molybdenum supported on zeolites has been extensively studied as a catalyst for methane dehydroaromatization. Despite significant progress, the actual intermediates and particularly the first C-C bond formation have not yet been elucidated. Herein we report evolution of methyl radicals during non-oxidative methane activation over molybdenum single sites, which leads selectively to value-added chemicals. Operando X-ray absorption spectroscopy and online synchrotron vacuum ultraviolet photoionization mass spectroscopy in combination with electron microscopy and density functional theory calculations reveal the essential role of molybdenum single sites in the generation of methyl radicals and that the formation rate of methyl radicals is linearly correlated with the number of molybdenum single sites. Methyl radicals transform to ethane in the gas phase, which readily dehydrogenates to ethylene in the absence of zeolites. This is essentially similar to the reaction pathway over the previously reported SiO2 lattice-confined single site iron catalyst. However, the availability of a zeolite, either in a physical mixture or as a support, directs the subsequent reaction pathway towards aromatization within the zeolite confined pores, resulting in benzene as the dominant hydrocarbon product. The findings reveal that methyl radical chemistry could be a general feature for metal single site catalysis regardless of the support (either zeolites MCM-22 and ZSM-5 or SiO2) whereas the reaction over aggregated molybdenum carbide nanoparticles likely facilitates carbon deposition through surface C-C coupling. These findings allow furthering the fundamental insights into non-oxidative methane conversion to value-added chemicals.

An optimal Fe-C coordination ensemble for hydrocarbon chain growth: a full Fischer-Tropsch synthesis mechanism from machine learning

Fischer-Tropsch synthesis (FTS, CO + H2 → long-chain hydrocarbons) because of its great significance in industry has attracted huge attention since its discovery. For Fe-based catalysts, after decades of efforts, even the product distribution remains poorly understood due to the lack of information on the active site and the chain growth mechanism. Herein powered by a newly developed machine-learning-based transition state (ML-TS) exploration method to treat properly reaction-induced surface reconstruction, we are able to resolve where and how long-chain hydrocarbons grow on complex in situ-formed Fe-carbide (FeCx) surfaces from thousands of pathway candidates. Microkinetics simulations based on first-principles kinetics data further determine the rate-determining and the selectivity-controlling steps, and reveal the fine details of the product distribution in obeying and deviating from the Anderson-Schulz-Flory law. By showing that all FeCx phases can grow coherently upon each other, we demonstrate that the FTS active site, namely the A-P5 site present on reconstructed Fe3C(031), Fe5C2(510), Fe5C2(021), and Fe7C3(071) terrace surfaces, is not necessarily connected to any particular FeCx phase, rationalizing long-standing structure-activity puzzles. The optimal Fe-C coordination ensemble of the A-P5 site exhibits both Fe-carbide (Fe4C square) and metal Fe (Fe3 trimer) features.

Insights into the Diffusion Behaviors of Water over Hydrophilic/Hydrophobic Catalysts During the Conversion of Syngas to High-Quality Gasoline

Although considerable efforts towards directly converting syngas to liquid fuels through Fischer-Tropsch synthesis have been made, developing catalysts with low CO2 selectivity for the synthesis of high-quality gasoline remains a big challenge. Herein, we designed a bifunctional catalyst composed of hydrophobic FeNa@Si-c and HZSM-5 zeolite, which exhibited a low CO2 selectivity of 14.3 % at 49.8 % CO conversion, with a high selectivity of 62.5 % for gasoline in total products. Molecular dynamic simulations and model experiments revealed that the diffusion of water molecules through hydrophilic catalyst was bidirectional, while the diffusion through hydrophobic catalyst was unidirectional, which were crucial to tune the water-gas shift reaction and control CO2 formation. This work provides a new fundamental understanding about the function of hydrophobic modification of catalysts in syngas conversion.

Physical regulation of copper catalyst with a hydrophobic promoter for enhancing CO2 hydrogenation to methanol

The hydrogenation of CO₂ to methanol, which is restricted by water products, requires a selective removal of water from the reaction system. Here, we show that physically combining hydrophobic polydivinylbenzene with a copper catalyst supported by silica can increase methanol production and CO₂ conversion. Mechanistic investigation reveals that the hydrophobic promoter could hinder the oxidation of copper surface by water, maintaining a small fraction of metallic copper species on the copper surface with abundant Cu^δ+, resulting in high activity for the hydrogenation. Such a physically mixed catalyst survives the continuous test for 100 h owing to the thermal stability of the polydivinylbenzene promoter.

Stabilizing Co2C with H2O and K promoter for CO2 hydrogenation to C2+ hydrocarbons

The decomposition of cobalt carbide (Co₂C) to metallic cobalt in CO₂ hydrogenation results in a notable drop in the selectivity of valued C₂₊ products, and the stabilization of Co₂C remains a grand challenge. Here, we report an in situ synthesized K-Co₂C catalyst, and the selectivity of C₂₊ hydrocarbons in CO₂ hydrogenation achieves 67.3% at 300°C, 3.0 MPa. Experimental and theoretical results elucidate that CoO transforms to Co₂C in the reaction, while the stabilization of Co₂C is dependent on the reaction atmosphere and the K promoter. During the carburization, the K promoter and H₂O jointly assist in the formation of surface C^* species via the carboxylate intermediate, while the adsorption of C^* on CoO is enhanced by the K promoter. The lifetime of the K-Co₂C is further prolonged from 35 hours to over 200 hours by co-feeding H₂O. This work provides a fundamental understanding toward the role of H₂O in Co₂C chemistry, as well as the potential of extending its application in other reactions.

Disentangling the activity-selectivity trade-off in catalytic conversion of syngas to light olefins

Breaking the trade-off between activity and selectivity has been a long-standing challenge in the field of catalysis. We demonstrate the importance of disentangling the target reaction from the secondary reactions for the case of direct syngas conversion to light olefins by incorporating germanium-substituted AlPO-18 within the framework of the metal oxide-zeolite (OXZEO) catalyst concept. The attenuated strength of the catalytically active Brønsted acid sites allows enhancing the targeted carbon-carbon coupling of ketene intermediates to form olefins by increasing the active site density while inhibiting secondary reactions that consume the olefins. Thus, a light-olefins selectivity of 83% among hydrocarbons and carbon monoxide conversion of 85% were obtained simultaneously, leading to an unprecedented light-olefins yield of 48% versus current reported light-olefins yields of ≤27%.