Sustaining metal–organic frameworks for water–gas shift catalysis by non-thermal plasma

Research progress on elemental mercury (Hg0) removal in flue gas using non-thermal plasma technology

Elemental mercury (Hg0) removal is a crucial target for mercury pollution control in flue gas. This article focuses on Hg0 removal in flue gas using corona discharge (CD) and dielectric barrier discharge (DBD) technologies, and provides a mechanistic perspective on the development and influencing factors of non-thermal plasma (NTP) technology for Hg0 removal. The influence factors include reactor configurations, power supplies, energy density, residence time, oxidation methods, gas composition, and the synergy between NTP and catalysis/adsorption, etc. This study reveals that the use of a pulsating electrical power supply significantly increases electron densities in both CD and DBD systems, thereby ensuring high energy efficiency and economic viability. Cl2 proves to be more effective than HCl as a chlorine source for Hg0 removal. NO significantly reduces Hg0 oxidation efficiency, while the effects of SO2 and H2O remain unclear. Energy density distribution is closely related to plasma devices, power supplies, and overall reactor configurations. Direct oxidation proves to be more effective than indirect oxidation for Hg0 removal. The combination of NTP with adsorption/catalysis technologies shows significantly better Hg0 removal efficiency compared to using NTP alone. This study can provide theoretical support for enhancing Hg0 removal mechanisms and optimizing process control parameters in industrial applications of NTP technology.

Angstrom-Level Tuning in Confined Space of Metal-Organic Framework for Ultra-High Resolution in Gas Chromatographic Separation

Optimizing the balance between thermodynamic interaction and kinetic diffusion is pivotal to obtaining high-performance gas chromatographic stationary phases. Here, three aluminum-based metal-organic frameworks featuring fym topology were chosen to achieve such balance by refined controlling the thermodynamic interactions toward analytes at angstrom level in a confined space. The CAU-10-H with the middle-sized channels (5.4 Å) provided weak interactions with xylenes because of the benzene ring around the channel, leading to the fastest diffusion. While the MIL-160 provided stronger interactions toward the analytes due to the abundance of O-heterocyclic sites of 2,5-furandicarboxylic acid ligands, resulting in slightly higher diffusion barriers. Thereby, although MIL-160 had a larger channel (5.9 Å) than CAU-10-H, the xylenes still diffused more slowly in MIL-160 than in CAU-10-H. The CAU-10-NH2 with the channel of 4.7 Å provided overstrong thermodynamic interactions and significant stereospecific blockade to the analytes because of the NH2 sites in the confined channels. These factors collectively contributed to achieving the lowest diffusion kinetics. The confined interactions were also proved by molecular dynamics simulation. Furthermore, the application indicated that MIL-160 exhibited the highest separation ability as a GC stationary phase among all reported materials. This strategy offers an approach for developing high-performance MOF stationary phases.

Highly Efficient Nitrogen Reduction to Ammonia through the Cooperation of Plasma and Porous Metal-Organic Framework Reactors with Confined Water

While the ambient N2 reduction to ammonia (NH3) using H2O as hydrogen source (2N2+6H2O=4NH3+3O2) is known as a promising alternative to the Haber-Bosch process, the high bond energy of N≡N bond leads to the extremely low NH3 yield. Herein, we report a highly efficient catalytic system for ammonia synthesis using the low-temperature dielectric barrier discharge plasma to activate inert N2 molecules into the excited nitrogen species, which can efficiently react with the confined and concentrated H2O molecules in porous metal-organic framework (MOF) reactors with V3+, Cr3+, Mn3+, Fe3+, Co2+, Ni2+ and Cu2+ ions. Specially, the Fe-based catalyst MIL-100(Fe) causes a superhigh NH3 yield of 22.4 mmol g-1 h-1. The investigation of catalytic performance and systematic characterizations of MIL-100(Fe) during the plasma-driven catalytic reaction unveils that the in situ generated defective Fe-O clusters are the highly active sites and NH3 molecules indeed form inside the MIL-100(Fe) reactor. The theoretical calculation reveals that the porous MOF catalysts have different adsorption capacity for nitrogen species on different catalytic metal sites, where the optimal MIL-100(Fe) has the lowest energy barrier for the rate-limiting *NNH formation step, significantly enhancing efficiency of nitrogen fixation.

Nonthermal Plasma Activation of Adsorbates: The Case of CO on Pt

Nonthermal plasmas provide a unique approach to electrically driven heterogeneous catalytic processes. Despite much interest from the community, fundamental activation pathways in these processes remain poorly understood. Here, we investigate how exposure to a nonthermal plasma sustained in an argon nonreactive atmosphere affects the desorption of carbon monoxide (CO) from platinum nanoparticles. Temperature-programmed desorption measurements indicate that the plasma reduces the effective binding energy (BE) of CO to Pt surfaces by as much as ∼0.3 eV, with the reduction in the BE scaling linearly with the plasma density. We find that the effective CO BE is most strongly reduced for under-coordinated sites (steps and edges) compared to well-coordinated sites (terraces). Density functional theory calculations suggest that this is due to plasma-induced charging and electric fields at the catalyst surface, which preferentially affect under-coordinated sites. This study provides direct experimental evidence of plasma-induced nonthermal activation of the adsorbate-catalyst couple.

Unveiling the Mechanism of Plasma-Catalytic Low-Temperature Water-Gas Shift Reaction over Cu/γ-Al2O3 Catalysts

The water-gas shift (WGS) reaction is a crucial process for hydrogen production. Unfortunately, achieving high reaction rates and yields for the WGS reaction at low temperatures remains a challenge due to kinetic limitations. Here, nonthermal plasma coupled to Cu/γ-Al2O3 catalysts was employed to enable the WGS reaction at considerably lower temperatures (up to 140 °C). For comparison, thermal-catalytic WGS reactions using the same catalysts were conducted at 140-300 °C. The best performance (72.1% CO conversion and 67.4% H2 yield) was achieved using an 8 wt % Cu/γ-Al2O3 catalyst in plasma catalysis at ∼140 °C, with 8.74 MJ mol-1 energy consumption and 8.5% H2 fuel production efficiency. Notably, conventional thermal catalysis proved to be ineffective at such low temperatures. Density functional theory calculations, coupled with in situ diffuse reflectance infrared Fourier transform spectroscopy, revealed that the plasma-generated OH radicals significantly enhanced the WGS reaction by influencing both the redox and carboxyl reaction pathways.

Synergistic Etching and Hydrogen Bonding-Induced Self-Assembly of MXene/MOF Hybrid Aerogel for Flexible Room-Temperature Gas Sensing

Limited by insufficient active sites and restricted mechanical strength, designing reliable and wearable gas sensors with high activity and ductility remains a challenge for detecting hazardous gases. In this work, a thermally induced and solvent-assisted oxyanion etching strategy was implemented for selective pore opening in a rigid microporous Cu-based metal-organic framework (referred to as CuM). A conductive CuM/MXene aerogel was then self-assembled through cooperative hydrogen bonding interactions between the carbonyl oxygen atom in PVP grafted on the surface of defect-rich Cu-BTC and the surface functional hydroxyl group on MXene. A flexible NO2 sensing performance using the CuM/MXene aerogel hybridized sodium alginate hydrogel is finally achieved, demonstrating extraordinary sensitivity (S = 52.47 toward 50 ppm of NO2), good selectivity, and rapid response/recovery time (0.9/4.5 s) at room temperature. Compared with commercial sensors, the relative error is less than 7.7%, thereby exhibiting significant potential for application in monitoring toxic and harmful gases. This work not only provides insights for guiding rational synthesis of ideal structure models from MOF composites but also inspires the development of high-performance flexible gas sensors for potential multiscenario applications.

Turning copper into an efficient and stable CO evolution catalyst beyond noble metals

Using renewable electricity to convert CO2 into CO offers a sustainable route to produce a versatile intermediate to synthesize various chemicals and fuels. For economic CO2-to-CO conversion at scale, however, there exists a trade-off between selectivity and activity, necessitating the delicate design of efficient catalysts to hit the sweet spot. We demonstrate here that copper co-alloyed with isolated antimony and palladium atoms can efficiently activate and convert CO2 molecules into CO. This trimetallic single-atom alloy catalyst (Cu92Sb5Pd3) achieves an outstanding CO selectivity of 100% (±1.5%) at -402 mA cm-2 and a high activity up to -1 A cm-2 in a neutral electrolyte, surpassing numerous state-of-the-art noble metal catalysts. Moreover, it exhibits long-term stability over 528 h at -100 mA cm-2 with an FECO above 95%. Operando spectroscopy and theoretical simulation provide explicit evidence for the charge redistribution between Sb/Pd additions and Cu base, demonstrating that Sb and Pd single atoms synergistically shift the electronic structure of Cu for CO production and suppress hydrogen evolution. Additionally, the collaborative interactions enhance the overall stability of the catalyst. These results showcase that Sb/Pd-doped Cu can steadily carry out efficient CO2 electrolysis under mild conditions, challenging the monopoly of noble metals in large-scale CO2-to-CO conversion.

Plasma-Driven Efficient Conversion of CO2 and H2O into Pure Syngas with Controllable Wide H2/CO Ratios over Metal-Organic Frameworks Featuring In Situ Evolved Ligand Defects

While the mild production of syngas (a mixture of H2 and CO) from CO2 and H2O is a promising alternative to the coal-based chemical engineering technologies, the inert nature of CO2 molecules, unfavorable splitting pathways of H2O and unsatisfactory catalysts lead to the challenge in the difficult integration of high CO2 conversion efficiency with produced syngas with controllable H2/CO ratios in a wide range. Herein, we report an efficient plasma-driven catalytic system for mild production of pure syngas over porous metal-organic framework (MOF) catalysts with rich confined H2O molecules, where their syngas production capacity is regulated by the in situ evolved ligand defects and the plasma-activated intermediate species of CO2 molecules. Specially, the Cu-based catalyst system achieves 61.9 % of CO2 conversion and the production of pure syngas with wide H2/CO ratios of 0.05 : 1-4.3 : 1. As revealed by the experimental and theoretical calculation results, the in situ dynamic structure evolution of Cu-containing MOF catalysts favors the generation of coordinatively unsaturated metal active sites with optimized geometric and electronic characteristics, the adsorption of reactants, and the reduced energy barriers of syngas-production potential-determining steps of the hydrogenation of CO2 to *COOH and the protonation of H2O to *H.

Unveiling the Potential of Covalent Organic Framework Electrocatalyst for Enhanced Oxygen Evolution

The potential for sustainable energy and carbon neutrality has expanded with the development of a highly active electrocatalyst for the oxygen evolution reaction (OER). Covalent Organic Frameworks (COF) have recently garnered attention because of their enormous potential in a number of cutting-edge application sectors, such as gas storage, sensors, fuel cells, and active catalytic supports. A simple and effective COF constructed and integrated by post-alteration plasma modification facilitates high electrocatalytic OER activity under alkaline conditions. Variations in parameters such as voltage and treatment duration have been employed to enhance the factor that demonstrates high OER performance. The overpotential and Tafel slope are the lowest of all when using an optimized parameter, such as plasma treatment for 30 min utilizing 6 kV of voltage, PT-30 COF, measuring 390 mV at a current density of 10 mA.cm-2 and 69 mV.dec-1, respectively, as compared to 652 mV and 235 mV.dec-1 for the Pristine-COF. Our findings provide a method for broadening the scope by post-functionalizing the parent framework for effective water splitting.

Enhancements of electric field and afterglow of non-equilibrium plasma by Pb(ZrxTi1-x)O3 ferroelectric electrode

Manipulating surface charge, electric field, and plasma afterglow in a non-equilibrium plasma is critical to control plasma-surface interaction for plasma catalysis and manufacturing. Here, we show enhancements of surface charge, electric field during breakdown, and afterglow by ferroelectric barrier discharge. The results show that the ferroelectrics manifest spontaneous electric polarization to increase the surface charge by two orders of magnitude compared to discharge with an alumina barrier. Time-resolved in-situ electric field measurements reveal that the fast polarization of ferroelectrics enhances the electric field during the breakdown in streamer discharge and doubles the electric field compared to the dielectric barrier discharge. Moreover, due to the existence of surface charge, the ferroelectric electrode extends the afterglow time and makes discharge sustained longer when alternating the external electric field polarity. The present results show that ferroelectric barrier discharge offers a promising technique to tune plasma properties for efficient plasma catalysis and electrified manufacturing.

Customizing catalyst surface/interface structures for electrochemical CO2 reduction

Electrochemical CO2 reduction reaction (CO2RR) provides a promising route to converting CO2 into value-added chemicals and to neutralizing the greenhouse gas emission. For the industrial application of CO2RR, high-performance electrocatalysts featuring high activities and selectivities are essential. It has been demonstrated that customizing the catalyst surface/interface structures allows for high-precision control over the microenvironment for catalysis as well as the adsorption/desorption behaviors of key reaction intermediates in CO2RR, thereby elevating the activity, selectivity and stability of the electrocatalysts. In this paper, we review the progress in customizing the surface/interface structures for CO2RR electrocatalysts (including atomic-site catalysts, metal catalysts, and metal/oxide catalysts). From the perspectives of coordination engineering, atomic interface design, surface modification, and hetero-interface construction, we delineate the resulting specific alterations in surface/interface structures, and their effect on the CO2RR process. At the end of this review, we present a brief discussion and outlook on the current challenges and future directions for achieving high-efficiency CO2RR via surface/interface engineering.

Asymmetric Fe-O2-Ti structures accelerate reduced-layer-FeII "electron" conversion: Facilitating photocatalytic nitrogen fixation

As a green and sustainable method for ammonia production, solar photocatalytic nitrogen fixation (PNRR) provides a new approach to slowing down the consumption of non-renewable energy resources. Given the extremely huge energy required to activate inert nitrogen, a rational design of efficient nitrogen fixation catalytic materials is essential. This study constructs defective Ti3+-Ti3C2Ox to regulate the NH2-MIL-101(Fe) reduced layer-FeII 'electron' transition; meanwhile, the heterojunction interface electronic structure formed by coupling promotes catalytic charges' transfer/separation, while the interface-asymmetric Fe-O2-Ti structure accelerates the response with nitrogen. It is shown that the heterojunction NM-101(FeII/FeIII)-1.5 exhibits a 75.1 % FeII enrichment (FeII:FeIII), which successfully impedes the fouling relationship between the two (FeII/FeIII). Mössbauer spectroscopy analysis demonstrates that the presence of D1-high spin state FeIII and D2-low/medium spin state FeII structures in the heterojunction boosts the PNRR activity. Furthermore, it is found that the defective state Ti3+-Ti3C2Ox modulation enhances the reduced nitrogen fixation capacity of the heterojunction (CB = -0.84 eV) and decreases the interfacial charge transfer resistance, yielding 450 umol·g-1·h-1 ammonia. Furthermore, this study modulates the charge ration of the catalyst reduction layer by constructing a charge-asymmetric structure with Ti3+-deficient carriers; this method provides a potential opportunity for enhancing photocatalytic nitrogen fixation in the future.

Probing the stability of metal-organic frameworks by structure-responsive mass spectrometry imaging

The widespread application of metal-organic frameworks (MOFs) is seriously hindered by their structural instability and it is still very challenging to probe the stability of MOFs during application by current techniques. Here, we report a novel structure-responsive mass spectrometry (SRMS) imaging technique to probe the stability of MOFs. We discovered that intact CuBTC (as a model of MOFs) could generate the characteristic peaks of organic ligands and carbon cluster anions in laser desorption/ionization mass spectrometry, but these peaks were significantly changed when the structure of CuBTC was dissociated, thus enabling a label-free probing of the stability. Furthermore, SRMS can be performed in imaging mode to visualize the degradation kinetics and reveal the spatial heterogeneity of the stability of CuBTC. This technique was successfully applied in different application scenarios (in water, moist air, and CO2) and also validated with different MOFs. It thus provides a versatile new tool for better design and application of environment-sensitive materials.

Boosting a practical Li-CO2 battery through dimerization reaction based on solid redox mediator

Li-CO2 batteries offer a promising avenue for converting greenhouse gases into electricity. However, the inherent challenge of direct electrocatalytic reduction of inert CO2 often results in the formation of Li2CO3, causing a dip in output voltage and energy efficiency. Our innovative approach involves solid redox mediators, affixed to the cathode via a Cu(II) coordination compound of benzene-1,3,5-tricarboxylic acid. This technique effectively circumvents the shuttle effect and sluggish kinetics associated with soluble redox mediators. Results show that the electrochemically reduced Cu(I) solid redox mediator efficiently captures CO2, facilitating Li2C2O4 formation through a dimerization reaction involving a dimeric oxalate intermediate. The Li-CO2 battery employing the Cu(II) solid redox mediator boasts a higher discharge voltage of 2.8 V, a lower charge potential of 3.7 V, and superior cycling performance over 400 cycles. Simultaneously, the successful development of a Li-CO2 pouch battery propels metal-CO2 batteries closer to practical application.

Amorphous-crystalline phase transition and intrinsic magnetic property of nickel organic framework for easy immobilization and recycling of β-Galactosidase

This work describes the synthesis of fibrous nickel-based metal organic framework (Ni-ZIF) via simple solvothermal method. The material formed was calcinated at 400, 600, 800 °C to improve its surface area, porosity and enzyme binding capacity. Changes in X-ray diffraction pattern after calcination revealed the Ni-ZIF transitioned from amorphous to crystalline structure. The surface area, pore volume and pore size for Ni-ZIF@600 were found to be 312.15 m2/g, 0.88 cm3/g and 10.28 nm, with an enzyme loading capacity of 593.85 mg/g after 30 h The free (β-Gal-LEH) and immobilized β-Galactosidase were stable at pH 7.5, temperature 50 °C, and yielded 70.70 and 63.95 mM glucose after milk lactose hydrolysis, respectively. The Ni-ZIF@600@β-Gal-LEH exhibited high enzyme retention capacity, maintaining 59.44 % of its original activity after 6-cycles. The enhanced magnetic property, enzyme binding capacity and easy recoverability of the calcinated Ni-ZIF could guarantee its industrial significance as immobilization module for enzyme-mediated catalysis.

Direct OC-CHO coupling towards highly C2+ products selective electroreduction over stable Cu0/Cu2+ interface

Electroreduction of CO2 to valuable multicarbon (C2+) products is a highly attractive way to utilize and divert emitted CO2. However, a major fraction of C2+ selectivity is confined to less than 90% by the difficulty of coupling C-C bonds efficiently. Herein, we identify the stable Cu0/Cu2+ interfaces derived from copper phosphate-based (CuPO) electrocatalysts, which can facilitate C2+ production with a low-energy pathway of OC-CHO coupling verified by in situ spectra studies and theoretical calculations. The CuPO precatalyst shows a high Faradaic efficiency (FE) of 69.7% towards C2H4 in an H-cell, and exhibits a significant FEC2+ of 90.9% under industrially relevant current density (j = -350 mA cm-2) in a flow cell configuration. The stable Cu0/Cu2+ interface breaks new ground for the structural design of electrocatalysts and the construction of synergistic active sites to improve the activity and selectivity of valuable C2+ products.

Laser-Assisted Design of MOF-Derivative Platforms from Nano- to Centimeter Scales for Photonic and Catalytic Applications

Laser conversion of metal-organic frameworks (MOFs) has recently emerged as a fast and low-energy consumptive approach to create scalable MOF derivatives for catalysis, energy, and optics. However, due to the virtually unlimited MOF structures and tunable laser parameters, the results of their interaction are unpredictable and poorly controlled. Here, we experimentally base a general approach to create nano- to centimeter-scale MOF derivatives with the desired nonlinear optical and catalytic properties. Five three- and two-dimensional MOFs, differing in chemical composition, topology, and thermal resistance, have been selected as precursors. Tuning the laser parameters (i.e., pulse duration from fs to ns and repetition rate from kHz to MHz), we switch between ultrafast nonthermal destruction and thermal decomposition of MOFs. We have established that regardless of the chemical composition and MOF topology, the tuning of the laser parameters allows obtaining a series of structurally different derivatives, and the transition from femtosecond to nanosecond laser regimes ensures the scaling of the derivatives from nano- to centimeter scales. Herein, the thermal resistance of MOFs affects the structure and chemical composition of the resulting derivatives. Finally, we outline the "laser parameters versus MOF structure" space, in which one can create the desired and scalable platforms with nonlinear optical properties from photoluminescence to light control and enhanced catalytic activity.

Direct Conversion of Methane to Ethylene and Acetylene over an Iron-Based Metal-Organic Framework

Conversion of methane (CH4) to ethylene (C2H4) and/or acetylene (C2H2) enables routes to a wide range of products directly from natural gas. However, high reaction temperatures and pressures are often required to activate and convert CH4 controllably, and separating C2+ products from unreacted CH4 can be challenging. Here, we report the direct conversion of CH4 to C2H4 and C2H2 driven by non-thermal plasma under ambient (25 °C and 1 atm) and flow conditions over a metal-organic framework material, MFM-300(Fe). The selectivity for the formation of C2H4 and C2H2 reaches 96% with a high time yield of 334 μmol gcat-1 h-1. At a conversion of 10%, the selectivity to C2+ hydrocarbons and time yield exceed 98% and 2056 μmol gcat-1 h-1, respectively, representing a new benchmark for conversion of CH4. In situ neutron powder diffraction, inelastic neutron scattering and solid-state nuclear magnetic resonance, electron paramagnetic resonance (EPR), and diffuse reflectance infrared Fourier transform spectroscopies, coupled with modeling studies, reveal the crucial role of Fe-O(H)-Fe sites in activating CH4 and stabilizing reaction intermediates via the formation of an Fe-O(CH3)-Fe adduct. In addition, a cascade fixed-bed system has been developed to achieve online separation of C2H4 and C2H2 from unreacted CH4 for direct use. Integrating the processes of CH4 activation, conversion, and product separation within one system opens a new avenue for natural gas utility, bridging the gap between fundamental studies and practical applications in this area.

Cold plasma synthesis of phosphorus-doped CoFe2O4 with oxygen vacancies for enhanced OER activity

Spinel-type metal oxides are promising electrocatalysts for the oxygen evolution reaction (OER) due to their unique electronic structure and low cost. Herein, we induced oxygen vacancies and doped phosphorus into CoFe2O4 using cold plasma. The abundant oxygen vacancies enhanced hydrophilicity and modified the electronic structure of CoFe2O4, while the phosphorus doping formed numerous new active centers. The doped P and formed FeP promoted the charge transfer and improved the conductivity of the catalyst. The phosphorus-doped CoFe2O4 exhibited exceptional OER activity with an overpotential of 180 mV at 10 mA cm-2 and a Tafel slope of 65.8 mV dec-1 in an alkaline electrolyte. DFT calculations confirmed that phosphorus doping can improve the charge distribution near the Fermi level and optimize the d-band center position.

Enabling Ultrahigh Surface Area of Covalently-linked Organic Framework for Boosted CO2 Capture: An Air Liquid Interfacial Plasma as Post-furnishing Protocol

The cognitive intent of a highly ordered and robust adsorbent is extremely sensible and, in this context, Covalent Organic Framework (COF) materials have significantly burgeoned their scope in diverse applications. Herein, we present a simple time-competent hydrothermal procedure to construct a covalent framework with an ultrahigh surface area of 1428 m2/g that shows active adsorption of carbon dioxide (CO2) at variable temperature ranges. Moreover, we substantiate a facile scalably controlled post-synthetic air-liquid interfacial plasma (ALIP) induced protocol that explicitly amplifies the surface area of the pristine framework even to a higher value of 2051 m2/g. The post-synthetic plasma approach presented here led to the rapid enhancement of the surface area of the pristine COF by 43%, which concurrently advances the CO2 uptake up to 67%. Hence, the current study may open up a new frontier in the design as well as fine-tune the properties of the covalent framework that unfolds the advanced outlook in addressing the challenges of CO2 capture.

Nanomaterials as catalysts for CO2 transformation into value-added products: A review

Carbon dioxide (CO₂₎ is the most important greenhouse gas (GHG), accounting for 76% of all GHG emissions. The atmospheric CO₂ concentration has increased from 280 ppm in the pre-industrial era to about 418 ppm, and is projected to reach 570 ppm by the end of the 21^st century. In addition to reducing CO₂ emissions from anthropogenic activities, strategies to adequately address climate change must include CO₂ capture. To promote circular economy, captured CO₂ should be converted to value-added materials such as fuels and other chemical feedstock. Due to their tunable chemistry (which allows them to be selective) and high surface area (which allows them to be efficient), engineered nanomaterials are promising for CO₂ capturing and/or transformation. This work critically reviewed the application of nanomaterials for the transformation of CO₂ into various fuels, like formic acid, carbon monoxide, methanol, and ethanol. We discussed the literature on the use of metal-based nanomaterials, inorganic/organic nanocomposites, as well as other routes suitable for CO₂ conversion such as the electrochemical, non-thermal plasma, and hydrogenation routes. The characteristics, steps, mechanisms, and challenges associated with the different transformation technologies were also discussed. Finally, we presented a section on the outlook of the field, which includes recommendations for how to continue to advance the use of nanotechnology for conversion of CO₂ to fuels.

Plasmonic Cu Nanoparticles for the Low-temperature Photo-driven Water-gas Shift Reaction

The activation of water molecules in thermal catalysis typically requires high temperatures, representing an obstacle to catalyst development for the low-temperature water-gas shift reaction (WGSR). Plasmonic photocatalysis allows activation of water at low temperatures through the generation of light-induced hot electrons. Herein, we report a layered double hydroxide-derived copper catalyst (LD-Cu) with outstanding performance for the low-temperature photo-driven WGSR. LD-Cu offered a lower activation energy for WGSR to H₂ under UV/Vis irradiation (1.4 W cm^-2 ) compared to under dark conditions. Detailed experimental studies revealed that highly dispersed Cu nanoparticles created an abundance of hot electrons during light absorption, which promoted *H₂ O dissociation and *H combination via a carboxyl pathway, leading to the efficient production of H₂ . Results demonstrate the benefits of exploiting plasmonic phenomena in the development of photo-driven low-temperature WGSR catalysts.

Atomic Plasma Grafting: Precise Control of Functional Groups on Ti3C2Tx MXene for Room Temperature Gas Sensors

Gas sensing properties of two-dimensional (2D) materials are derived from charge transfer between the analyte and surface functional groups. However, for sensing films consisting of 2D Ti₃C₂T_x MXene nanosheets, the precise control of surface functional groups for achieving optimal gas sensing performance and the associate mechanism are still far from well understood. Herein, we present a functional group engineering strategy based on plasma exposure for optimizing the gas sensing performance of Ti₃C₂T_x MXene. For performance assessment and sensing mechanism elucidation, we synthesize few-layered Ti₃C₂T_x MXene through liquid exfoliation and then graft functional groups via in situ plasma treatment. Functionalized Ti₃C₂T_x MXene with large amounts of -O functional groups shows NO₂ sensing properties that are unprecedented among MXene-based gas sensors. Density functional theory (DFT) calculations reveal that -O functional groups are associated with increased NO₂ adsorption energy, thereby enhancing charge transport. The -O functionalized Ti₃C₂T_x sensor shows a record-breaking response of 13.8% toward 10 ppm NO₂, good selectivity, and long-term stability at room temperature. The proposed technique is also capable of improving selectivity, a well-known challenge in chemoresistive gas sensing. This work paves the way to the possibility of using plasma grafting for precise functionalization of MXene surfaces toward practical realization of electronic devices.

Synergistic promotions between CO2 capture and in-situ conversion on Ni-CaO composite catalyst

The integrated CO₂ capture and conversion (iCCC) technology has been booming as a promising cost-effective approach for Carbon Neutrality. However, the lack of the long-sought molecular consensus about the synergistic effect between the adsorption and in-situ catalytic reaction hinders its development. Herein, we illustrate the synergistic promotions between CO₂ capture and in-situ conversion through constructing the consecutive high-temperature Calcium-looping and dry reforming of methane processes. With systematic experimental measurements and density functional theory calculations, we reveal that the pathways of the reduction of carbonate and the dehydrogenation of CH₄ can be interactively facilitated by the participation of the intermediates produced in each process on the supported Ni-CaO composite catalyst. Specifically, the adsorptive/catalytic interface, which is controlled by balancing the loading density and size of Ni nanoparticles on porous CaO, plays an essential role in the ultra-high CO₂ and CH₄ conversions of 96.5% and 96.0% at 650 °C, respectively.

Plasma Meets MOFs: Synthesis, Modifications, and Functionalities

As a porous and network materials consisting of metals and organic ligands, metal-organic frameworks (MOFs) have become one of excellent crystalline porous materials and play an important role in the era about materials science. Plasma, as a useful tool for stimulating efficient reactions under many conditions, and the plasma-assisted technology gets more attractions and endows MOFs more properties. Based on its feature, the research about the modifications and functionalities of MOFs have been developing a certain extent. This review contains a description of the methods for plasma-assisted modification and synthesis of MOFs, with specifically focusing on the plasma-assisted potential for modifications and functionalities of MOFs. The different applications of plasma-assisted MOFs were also presented.

Space-confined growth of nanoscale metal-organic frameworks/Pd in hollow mesoporous silica for highly efficient catalytic reduction of 4-nitrophenol

The development of confined growth of metal-organic frameworks (MOFs) in a nano-space remains a challenge mainly due to the spatial size randomness and inhomogeneity of host materials and the limitation of MOF species. In this study, we developed a general "stepwise vacuum evaporation" strategy, which allows the nano-confined growth of MOFs in hollow mesoporous silica nanospheres (HMSN) by the vacuum forces and the capillary effect. A series of nanoscale MOFs including ZIF-8, ZIF-90, HKUST-1, MIL-53(Cr) and UiO-66-NH2 were confinely synthesized inside the cavities of HMSN, resulting in hierarchically porous composites with core-shell structures. Further functionalization was studied by anchoring Pd to obtain UiO-66-NH2/Pd@HMSN catalyst, which exhibited excellent activity in the catalytic reduction of 4-nitrophenol to 4-aminophenol under ambient condition.

Cooperative Catalysis of Vibrationally Excited CO2 and Alloy Catalyst Breaks the Thermodynamic Equilibrium Limitation

Using nonthermal plasma (NTP) to promote CO₂ hydrogenation is one of the most promising approaches that overcome the limitations of conventional thermal catalysis. However, the catalytic surface reaction dynamics of NTP-activated species are still under debate. The NTP-activated CO₂ hydrogenation was investigated in Pd₂Ga/SiO₂ alloy catalysts and compared to thermal conditions. Although both thermal and NTP conditions showed close to 100% CO selectivity, it is worth emphasizing that when activated by NTP, CO₂ conversion not only improves more than 2-fold under thermal conditions but also breaks the thermodynamic equilibrium limitation. Mechanistic insights into NTP-activated species and alloy catalyst surface were investigated by using in situ transmission infrared spectroscopy, where catalyst surface species were identified during NTP irradiation. Moreover, in in situ X-ray absorption fine-structure analysis under reaction conditions, the catalyst under NTP conditions not only did not undergo restructuring affecting CO₂ hydrogenation but also could clearly rule out catalyst activation by heating. In situ characterizations of the catalysts during CO₂ hydrogenation depict that vibrationally excited CO₂ significantly enhances the catalytic reaction. The agreement of approaches combining experimental studies and density functional theory (DFT) calculations substantiates that vibrationally excited CO₂ reacts directly with hydrogen adsorbed on Pd sites while accelerating formate formation due to neighboring Ga sites. Moreover, DFT analysis deduces the key reaction pathway that the decomposition of monodentate formate is promoted by plasma-activated hydrogen species. This work enables the high designability of CO₂ hydrogenation catalysts toward value-added chemicals based on the electrification of chemical processes via NTP.

Shielding Protection by Mesoporous Catalysts for Improving Plasma-Catalytic Ambient Ammonia Synthesis

Plasma catalysis is a promising technology for decentralized small-scale ammonia (NH3) synthesis under mild conditions using renewable energy, and it shows great potential as an alternative to the conventional Haber-Bosch process. To date, this emerging process still suffers from a low NH3 yield due to a lack of knowledge in the design of highly efficient catalysts and the in situ plasma-induced reverse reaction (i.e., NH3 decomposition). Here, we demonstrate that a bespoke design of supported Ni catalysts using mesoporous MCM-41 could enable efficient plasma-catalytic NH3 production at 35 °C and 1 bar with >5% NH3 yield at 60 kJ/L. Specifically, the Ni active sites were deliberately deposited on the external surface of MCM-41 to enhance plasma-catalyst interactions and thus NH3 production. The desorbed NH3 could then diffuse into the ordered mesopores of MCM-41 to be shielded from decomposition due to the absence of plasma discharge in the mesopores of MCM-41, that is, "shielding protection", thus driving the reaction forward effectively. This promising strategy sheds light on the importance of a rational design of catalysts specifically for improving plasma-catalytic processes.

Reversible and Irreversible Laser Interference Patterning of MOF Thin Films

Laser interference patterning on top of a thin film and inside a crystal is a powerful tool today to create the desired patterns for optical data processing. Here, we demonstrate reversible and irreversible laser interference patterning on a metal-organic framework (MOF) thin film through the water desorption and thermal decomposition processes, respectively. The irreversible interference pattern with a period of the strips of up to 5 µm has been realized, and its morphology has been characterized using confocal Raman and reflection spectroscopy as well as atomic force microscopy. We revealed that reducing the distance between the interference maxima from 10.5 to a record of 5 µm for MOFs yields a 10-fold increase in the surface roughness of the irreversible pattern; on the other hand, the reversible laser pattern provides a completely non-destructive effect of variable optical contrast. The experimental results obtained open up prospects for the use of MOF crystals as photosensitive materials in the template drawing of the desired patterns for different application scopes.

Tuning the local electronic structure of SrTiO3 catalysts to boost plasma-catalytic interfacial synergy

Boosting plasma-catalyst synergy to enhance volatile organic compounds (VOCs) decomposition remains a challenge. Herein, rich oxygen vacancies (V_O) were engineered into the SrTiO₃ catalysts through a facile nitrogen incorporation strategy for the plasma-catalytic decomposition of toluene and ethyl acetate. 100% toluene conversion with 81% CO₂ selectivity at a competitive energy efficiency was achieved under ambient conditions. The characterization results and theoretical calculations evidenced that the partial substitution of oxygen by nitrogen triggered the electronic reconstruction and local disorder, thus modulating the electronic properties and coordination structures contributed to the formation of V_O-Ti³⁺ pairs. Quasi in-situ EPR, operando OES, and operando DRIFTS originally demonstrated that the V_O-Ti³⁺ pairs as active sites promoted the plasma-catalytic synergy instead of isolated V_O. Importantly, the V_O-Ti³⁺ pairs with favorable electron transfer characteristics energetically preferred to capture and utilize vibrationally excited oxygen species. And the lattice oxygen supplied by the V_O-Ti³⁺ pairs were more vigorously activated by the plasma to participate in the surface/interface reaction. This work advances our understanding of the real active sites in plasma-catalytic interfacial synergy and thus paving the way for the rational design of efficiently heterogeneous catalysts.

Construction of Confined Bifunctional 2D Material for Efficient Sulfur Resource Recovery and Hg2+ Adsorption in Desulfurization

Substantial energy penalty of valuable sulfate recovery restricts the efficiency of wet desulfurization and increases the risk of Hg⁰ reemission. Although the enhanced sulfite oxidation rate with cobalt-based materials can increase the energy efficiency, inactivation and poisoning of catalyst due to the competition of reactant must be addressed. Here we obtained a superwetting two-dimensional cobalt-nitrogen-doped carbon (2D Co-N-C) nanosheet featuring confined catalysis/adsorption sites for the energy-efficient sulfite oxidation and Hg²⁺ adsorption. The designed structure exhibits enhanced surface polarity, availability and short reactant diffusion path, thus enabling the significant catalytic TOF value of 0.085 s^-1 and simultaneous mercury removal ability of 143.26 mg·g^-1. The catalyst nanosheets present regenerating stabilities to improve cost-efficiency. By deployment of the Co-N-C catalysts, a marked reduction of heat penalty up to 69% can be achieved, which makes this catalytic pathway for sulfur resource recovery economically feasible in real industry scenario.

Engineering Bimodal Oxygen Vacancies and Pt to Boost the Activity Toward Water Dissociation

Water dissociation is the rate-limiting step of several energy-related reactions due to the high energy barrier required for breaking the oxygen-hydrogen bond. In this work, a bimodal oxygen vacancy (V_O ) catalysis strategy is adopted to boost the efficient water dissociation on Pt nanoparticles. The single facet-exposed TiO₂ surface and NiO_x nanocluster possess two modes of V_O different from each other. In ammonia borane hydrolysis, the highest catalytic activity among Pt-based materials is achieved with the turnover frequency of 618 min^-1 under alkaline-free conditions at 298 K. Theoretical simulation and characterization analyses reveal that the bimodal V_O significantly promotes the water dissociation in two ways. First, an ensemble-inducing effect of Pt and V_O in TiO₂ drives the activation of water molecules. Second, an electron promoter effect induced by the electron transfer from V_O in NiO_x to Pt further enhances the ability of Pt to dissociate water and ammonia borane. This insight into bimodal V_O catalysis establishes a new avenue to rationally design heterogeneous catalytic materials in the energy chemistry field.

Stabilizing Cu2+ Ions by Solid Solutions to Promote CO2 Electroreduction to Methane

Copper is the only metal catalyst that can perform the electrocatalytic CO₂ reduction reaction (CRR) to produce hydrocarbons and oxygenates. Its surface oxidation state determines the reaction pathway to various products. However, under the cathodic potential of CRR conditions, the chemical composition of most Cu-based catalysts inevitably undergoes electroreduction from Cu²⁺ to Cu⁰ or Cu¹⁺ species, which is generally coupled with phase reconstruction and the formation of new active sites. Since the initial Cu²⁺ active sites are hard to retain, there have been few studies about Cu²⁺ catalysts for CRR. Herein we propose a solid-solution strategy to stabilize Cu²⁺ ions by incorporating them into a CeO₂ matrix, which works as a self-sacrificing ingredient to protect Cu²⁺ active species. In situ spectroscopic characterization and density functional theory calculations reveal that compared with the conventionally derived Cu catalysts with Cu⁰ or Cu¹⁺ active sites, the Cu²⁺ species in the solid solution (Cu-Ce-O_x) can significantly strengthen adsorption of the *CO intermediate, facilitating its further hydrogenation to produce CH₄ instead of dimerization to give C₂ products. As a result, different from most of the other Cu-based catalysts, Cu-Ce-O_x delivered a high Faradaic efficiency of 67.8% for CH₄ and a low value of 3.6% for C₂H₄.

Dielectric Barrier Discharge Plasma-Assisted Catalytic CO2 Hydrogenation: Synergy of Catalyst and Plasma

CO2 hydrogenation is an effective way to convert CO2 to value-added chemicals (e.g., CH4 and CH3OH). As a thermal catalytic process, it suffers from dissatisfactory catalytic performances (low conversion/selectivity and poor stability) and high energy input. By utilizing the dielectric barrier discharge (DBD) technology, the catalyst and plasma could generate a synergy, activating the whole process in a mild condition, and enhancing the conversion efficiency of CO2 and selectivity of targeted product. In this review, a comprehensive summary of the applications of DBD plasma in catalytic CO2 hydrogenation is provided in detail. Moreover, the state-of-the-art design of the reactor and optimization of reaction parameters are discussed. Furthermore, several mechanisms based on simulations and experiments are provided. In the end, the existing challenges of this hybrid system and corresponding solutions are proposed.

Conductive metal and covalent organic frameworks for electrocatalysis: design principles, recent progress and perspective

Metal and covalent organic frameworks (MOFs/COFs) are emerging promising candidates in the field of catalysts due to their porous nature, chemically well-defined active sites and structural diversity. However, they are typically provided with poor electrical conductivity, which is insufficient for them to work as satisfying electrocatalysts. Designing and fabricating MOFs/COFs with high conductivity presents a new avenue towards special electrochemical reactions. This minireview firstly highlighted the origin and design principles of conductive MOFs/COFs for electrocatalysis on the basis of typical charge transfer mechanisms, that is "through space", "extended conjugation" and "through bond". An overview of conductive MOFs/COFs used in the electrocatalytic carbon dioxide reduction reaction (CO₂RR), water splitting and the oxygen reduction reaction (ORR) was then made to track the very recent progress. In the final remarks, the present challenges and perspectives for the use of conductive MOFs/COFs as electrocatalysts including their structural optimization, feasible applications and structure-activity correlation are proposed.

Recent Progress and Prospects in Catalytic Water Treatment

Presently, conventional technologies in water treatment are not efficient enough to completely mineralize refractory water contaminants. In this context, the implementation of catalytic processes could be an alternative. Despite the advantages provided in terms of kinetics of transformation, selectivity, and energy saving, numerous attempts have not yet led to implementation at an industrial scale. This review examines investigations at different scales for which controversies and limitations must be solved to bridge the gap between fundamentals and practical developments. Particular attention has been paid to the development of solar-driven catalytic technologies and some other emerging processes, such as microwave assisted catalysis, plasma-catalytic processes, or biocatalytic remediation, taking into account their specific advantages and the drawbacks. Challenges for which a better understanding related to the complexity of the systems and the coexistence of various solid-liquid-gas interfaces have been identified.

Harnessing Plasma Environments for Ammonia Catalysis: Mechanistic Insights from Experiments and Large-Scale Ab Initio Molecular Dynamics

By combining experimental measurements with ab initio molecular dynamics simulations, we provide the first microscopic description of the interaction between metal surfaces and a low-temperature nitrogen-hydrogen plasma. Our study focuses on the dissociation of hydrogen and nitrogen as the main activation route. We find that ammonia forms via an Eley-Rideal mechanism where atomic nitrogen abstracts hydrogen from the catalyst surface to form ammonia on an extremely short time scale (a few picoseconds). On copper, ammonia formation occurs via the interaction between plasma-produced atomic nitrogen and the H-terminated surface. On platinum, however, we find that surface saturation with NH groups is necessary for ammonia production to occur. Regardless of the metal surface, the reaction is limited by the mass transport of atomic nitrogen, consistent with the weak dependence on catalyst material that we observe and has been reported by several other groups. This study represents a significant step toward achieving a mechanistic, microscopic-scale understanding of catalytic processes activated in low-temperature plasma environments.

Enhanced moisture resistance of Cu/Ce catalysts for CO oxidation via Plasma-Catalyst interactions

Copper/cerium bimetallic catalyst is an efficient material for the removal of carbon monoxide, while the rapid deactivation under moisture-rich conditions in the conventional thermal-catalysis limited its wide application. Here, we investigated the plasma-assisted catalytic oxidation of CO over Cu/Ce oxides supported on γ-Alumina in comparison with the conventional thermal catalytic oxidation. The TOF values of the Cu/Ce catalysts showed that the plasma catalysis was the better catalytic system for CO oxidation (2.96 s^-1 for thermal catalysis, 5.13 s^-1 for plasma catalysis). Importantly, the energy barriers for plasma catalysis were much lower than that for thermal catalysis, especially under moisture-rich conditions (e.g. 130.3 kJ/mol versus 246.1 kJ/mol under 9.8 vol% water vapor). The loss of activity caused by water was reversible for the plasma process, but not for the thermal process. The Cu/Ce catalyst remained good stability within 60 h in the presence of 6.1% water for plasma oxidation, while the thermal catalytic activity declines gradually. Also, water could inhibit the formation of gas byproducts (O₃ and NO_x). The promoting role of plasma could be mainly ascribed to the enhanced strength of oxygen mobility and plasma-assisted decomposition of surface carbonate in the presence of water, as revealed by the in-situ NTP-TPR, XPS, and the ex-situ DRIFTS analyses.