Recent Advances in Mechanistic Understanding of Metal-Free Carbon Thermocatalysis and Electrocatalysis with Model Molecules

Metal-free carbon,as the most representative heterogeneous metal-free catalysts,have received considerable interests in electro-and thermo-catalytic reac-tions due to their impressive performance and sustainability.Over the past decade,well-designed carbon catalysts with tunable structures and heteroatom groups coupled with various characterization techniques have proposed numerous reaction mechanisms.However,active sites,key intermediate species,precise structure-activity relationships and dynamic evolution processes of carbon catalysts are still rife with controversies due to the monotony and limitation of used experimental methods.In this Review,we sum-marize the extensive efforts on model catalysts since the 2000s,particularly in the past decade,to overcome the influences of material and structure limitations in metal-free carbon catalysis.Using both nanomolecule model and bulk model,the real contribution of each alien species,defect and edge configuration to a series of fundamentally important reactions,such as thermocatalytic reactions,electrocatalytic reactions,were systematically studied.Combined with in situ techniques,isotope labeling and size control,the detailed reaction mechanisms,the precise 2D structure-activity relationships and the rate-determining steps were revealed at a molecular level.Furthermore,the outlook of model carbon catalysis has also been proposed in this work.

Metal-Free 2D/2D van der Waals Heterojunction Based on Covalent Organic Frameworks for Highly Efficient Solar Energy Catalysis

Covalent organic frameworks(COFs)have emerged as a kind of rising star materials in photocatalysis.However,their photocatalytic activities are restricted by the high photogenerated electron-hole pairs recombination rate.Herein,a novel metal-free 2D/2D van der Waals heterojunction,composed of a two-dimensional(2D)COF with ketoenamine linkage(TpPa-1-COF)and 2D defective hexagonal boron nitride(h-BN),is successfully constructed through in situ solvothermal method.Benefitting from the presence of VDW heterojunction,larger contact area and intimate electronic coupling can be formed between the interface of TpPa-1-COF and defective h-BN,which make contributions to promoting charge car-riers separation.The introduced defects can also endow the h-BN with porous structure,thus providing more reactive sites.Moreover,the TpPa-1-COF will undergo a structural transformation after being integrated with defective h-BN,which can enlarge the gap between the conduction band position of the h-BN and TpPa-1-COF,and suppress electron backflow,corroborated by experimental and density functional theory calculations results.Accordingly,the resulting porous h-BN/TpPa-1-COF metal-free VDW heterojunction displays out-standing solar energy catalytic activity for water splitting without co-catalysts,and the H_(2) evolution rate can reach up to 3.15 mmol g^(−1) h^(−1),which is about 67 times greater than that of pristine TpPa-1-COF,also surpassing that of state-of-the-art metal-free-based photocatalysts reported to date.In particular,it is the first work for constructing COFs-based heterojunctions with the help of h-BN,which may provide new avenue for designing highly efficient metal-free-based photocatalysts for H_(2) evolution.

Tetracycline removal via adsorption and metal-free catalysis with 3D macroscopic N-doped porous carbon nanosheets:Non-radical mechanism and degradation pathway

Recently,metal-based carbon materials have been verified to be an effective persulfate activator,but secondary pollution caused by metal leaching is inevitable.Hence,a green metalfree 3D macroscopic N-doped porous carbon nanosheets(NPCN)was synthesized successfully.The obtained NPCN showed high adsorption capacity of tetracycline(TC)and excellent persulfate(PS)activation ability,especially when calcined at 700℃(NPCN-700).The maximum adsorption capacity of NPCN-700 was 121.51 mg/g by H-bonds interactions.Moreover,the adsorption process followed pseudo-second-order kinetics model and Langmuir adsorption isotherm.The large specific surface area(365.27 mg/g)and hierarchical porous structure of NPCN-700 reduced the mass transfer resistance and increased the adsorption capacity.About 96.39%of TC was removed after adding PS.The effective adsorption of the catalyst greatly shortened the time for the target organic molecules to migrate to the catalyst.Moreover,the NPCN-700 demonstrated high reusability with the TC removal rate of 80.23%after 4 cycles.Quenching experiment and electron paramagnetic resonance(EPR)test confirmed the non-radical mechanism dominated by ^(1)O_(2).More importantly,the C=O groups,defects and Graphitic N acted as active sites to generate ^(1)O_(2).Correspondingly,electrochemical measurement revealed the direct electron transfer pathway of TC degradation.Finally,multiple degradation intermediates were recognized by the LC-MS measurement and three possible degradation pathways were proposed.Overall,the prepared NPCN had excellent application prospects for removal of antibiotics due to its remarkable adsorption and catalytic degradation capabilities.

Recent advances and perspectives of zinc metal-free anodes for zinc ion batteries

Zinc-ion batteries(ZIBs) are recognized as potential energy storage devices due to their advantages of low cost, high energy density, and environmental friendliness. However, zinc anodes are subject to unavoidable zinc dendrites, passivation, corrosion, and hydrogen evolution reactions during the charging and discharging of batteries, becoming obstacles to the practical application of ZIBs. Appropriate zinc metal-free anodes provide a higher working potential than metallic zinc anodes, effectively solving the problems of zinc dendrites, hydrogen evolution, and side reactions during the operation of metallic zinc anodes. The improvement in the safety and cycle life of batteries creates conditions for further commercialization of ZIBs. Therefore, this work systematically introduces the research progress of zinc metal-free anodes in “rocking chair” ZIBs. Zinc metal-free anodes are mainly discussed in four categories: transition metal oxides,transition metal sulfides, MXene(two dimensional transition metal carbide) composites, and organic compounds, with discussions on their properties and zinc storage mechanisms. Finally, the outlook for the development of zinc metal-free anodes is proposed. This paper is expected to provide a reference for the further promotion of commercial rechargeable ZIBs.

Non-Gaussian quantum states generated via quantum catalysis and their statistical properties

A new kind of non-Gaussian quantum catalyzed state is proposed via multiphoton measurements and two-mode squeezing as an input of thermal state.The characteristics of the generated multiphoton catalysis output state depends on the thermal parameter,catalyzed photon number and squeezing parameter.We then analyze the nonclassical properties by examining the photon number distribution,photocount distribution and partial negativity of the Wigner function.Our findings indicate that nonclassicality can be achieved through the implementation of multiphoton catalysis operations and modulated by the thermal parameter,catalyzed photon number and squeezing parameter.

Cobalt phthalocyanine promoted copper catalysts toward enhanced electro reduction of CO_(2)to C_(2):Synergistic catalysis or tandem catalysis?

The activity and selectivity of electrocatalytic CO_(2)reduction reaction(CO_(2)RR)to C_(2)products on metal catalysts can be regulated by molecular surfactants.However,the mechanism behind it remains elusive and debatable.Herein,copper nanowires(Cu NWs)were fabricated and decorated with cobalt phthalocyanine(CoPc).The electronic interaction between the Cu NWs,CoPc,CO_(2) and CO_(2)RR intermediates were explored by density functional theory(DFT)calculations.It was found that the selectivity and activity of CO_(2)RR towards C_(2)products on Cu NWs were considerably enhanced from 35.2%to 69.9%by surface decoration of CoPc.DFT calculations revealed that CO_(2)RR can proceed in the interphase between Cu substrate and CoPc,and the CO_(2)RR intermediates could synergistically bond with both Cu and Co metal centre in CuNWs-CoPc,which favours the adsorption of CO_(2),CO and CO_(2)RR intermediates,thus reducing the free energy for CO-COcoupling towards C_(2)products.The synergistic interaction was further extended to phthalocyanine(Pc)and other metal phthalocyanine derivatives(MPc),where a relatively weaker synergistic interaction of COintermediates with MPc and Cu substrate and only a slight enhancement of CO_(2)RR towards C_(2) products were observed.This study demonstrates a synergistic catalysis pathway for CO_(2)RR,a novel perspective in interpreting the role of CoPc in enhancing the activity and selectivity of CO_(2)RR on Cu NWs,in contrast to the conventional tandem catalysis mechanism.

Discussion of Misleading on the Interpretation of the Word “Catalysis, Catalyst”

The main idea of this paper is what the resource of the serious error of the widely popular Chemical Reaction Mode catalysis Mechanism-CRMM is. The wrong definition of “catalysis, catalyst” by the catalytic academia boss leads to the wrong interpretation of “catalysis, catalyst” by linguists (Dictionary). The interpretation of “catalysis, catalyst” in a dictionary is misleading. The most fundamental reason for this error is that catalysis experts always believe that catalysts participate in chemical reactions. The result will appear as a series of impossible events. Such as catalysis cyclic reaction, opinions vary intermedium, catalysts repeated decomposition—formation, oxidation-reduction or life and death (enzyme), Sabatier’s principle and Boudart’s principle. The wrong theory leads the research and application of catalysts to the bottomless abyss, and industrial production suffers great losses. Electron Orbital Deformation-Recovere cyclic catalysis Mechanism-EODRM or Electron Cyclic Donate-Adopt catalysis Mechanism-ECDAM shows that the catalytic phenomenon is a physical phenomenon, not a chemical phenomenon, the catalyst does not participate in chemical reactions, only contact is the electron donate-adopt cycle, is the electron orbital deformation recovery cycle Chinese and foreign scholars should change the interpretation on the “catalysis, catalyst”, or add two new words: “contact and contactor”, it is to give up “catalysis, catalyst” altogether.

Recent progress of carbon-based metal-free materials in thermal-driven catalysis

The carbon-based metal-free materials as catalysts(named as carbocatalysts) have been attracting tremendous attentions in electric-,solar-and thermal-driven reactions nowadays.Compared to electrocatalysis and photocatalysis,the thermal-driven catalysis(thermocatalysis) including liquid phase and gas phase reactions involves wider scope and is relatively easy to realize practical large-scale applications.Over the past several years,some striking achievements on the design of new carbon-based metal-free materials with well-defined structures and heteroatom groups as well as the revelation of new reaction mechanisms and active sites in thermocatalysis have been obtained.However,comparative discussions regarding these recent achievements have been rarely highlighted.In this review,we systematically summarize and discuss six kinds of carbocatalysts and their applications in thermocatalysis.These materials include typical oxygen-attached carbon,surface modified carbon(graft with certain organic compounds),mono-doped carbon,co-doped carbon,carbon nitride and materials with carbon as dopant.Some new reaction processes as well as the related reaction mechanisms,active sites and intermediates are reviewed critically.Moreover,an outlook on the in-depth investigation of the metalfree carbocatalysis in the future is provided.

Metal-free carbocatalysis for electrochemical oxygen reduction reaction: Activity origin and mechanism

Although scientists have conducted long-term and extensive studies on oxygen reduction reaction(ORR)catalyzed by metal-free carbon materials,they mainly have focused on the preparation and properties of various doped carbon materials.There is still a lack of systematic scientific guidance on the relationship between the surface structure regulation and activity of carbon-based catalysts.In this review,some of electrochemical and computational fundamental concepts about ORR are concisely summarized.The effects of edge defect and nonmetallic doping of carbon materials on ORR behavior and mechanism have been reviewed,and activity origin identification and intermediate conversion mechanism have been discussed.The outlooks for future researches on metal-free ORR electrocatalysis are suggested.

Recent advancement and future challenges of photothermal catalysis for VOCs elimination:From catalyst design to applications

Photothermal catalysis realizes the synergistic effect of solar energy and thermochemistry,which also has the potential to improve the reaction rate and optimize the selectivity.In this review,the research progress of photothermal catalytic removal of volatile organic compounds(VOCs)by nano-catalysts in recent years is systematically reviewed.First,the fundamentals of photothermal catalysis and the fabrication of catalysts are described,and the design strategy of optimizing photothermal catalysis performance is proposed.Second,the performance for VOC degradation with photothermal catalysis is evaluated and compared for the batch and continuous systems.Particularly,the catalytic mechanism of VOC oxidation is systematically introduced based on experimental and theoretical study.Finally,the future limitations and challenges have been discussed,and potential research directions and priorities are highlighted.A broad view of recent photothermal catalyst fabrication,applications,challenges,and prospects can be systemically provided by this review.

Effects of Catalysis and Separator Functionalization on High-Energy Lithium–Sulfur Batteries:A Complete Review

Lithium–sulfur(Li-S)batteries have the advantages of high theoretical specific capacity(1675 mAh g^(−1)),rich sulfur resources,low production cost,and friendly environment,which makes it one of the most promising next-generation rechargeable energy storage devices.However,the“shuttle effect”of polysulfide results in the passivation of metal lithium anode,the decrease of battery capacity and coulombic efficiency,and the deterioration of cycle stability.To realize the commercialization of Li-S batteries,its serious“shuttle effect”needs to be suppress.The commercial separators are ineffective to suppress this effect because of its large pore size.Therefore,it is an effective strategy to modify the separator surface and introduce functional modified layer.In addition to the blocking strategy,the catalysis of polysulfide conversion reaction is also an important factor hindering the migration of polysulfides.In this review,the principles of separator modification,functionalization,and catalysis in Li-S batteries are reviewed.Furthermore,the research trend of separator functionalization and polysulfide catalysis in the future is prospected.

Sustainable Ammonia Synthesis from Nitrogen and Water by One-Step Plasma Catalysis

Sustainable ammonia synthesis at ambient conditions that relies on renewable sources of energy and feedstocks is globally sought to replace the Haber-Bosch process.Here,using nitrogen and water as raw materials,a nonthermal plasma catalysis approach is demonstrated as an effective powerto-chemicals conversion strategy for ammonia production.By sustaining a highly reactive environment,successful plasma-catalytic production of NH_(3) was achieved from the dissociation of N_(2) and H_(2)O under mild conditions.Plasma-induced vibrational excitation is found to decrease the N_(2) and H_(2)O dissociation barriers,with the presence of matched catalysts in the nonthermal plasma discharge reactor contributing significantly to molecular dissociation on the catalyst surface.Density functional theory calculations for the activation energy barrier for the dissociation suggest that ruthenium catalysts supported on magnesium oxide exhibit superior performance over other catalysts in NH_(3) production by lowering the activation energy for the dissociative adsorption of N_(2) down to 1.07 eV.The highest production rate,2.67 mmol gcat.^(-1) h^(-1),was obtained using ruthenium catalyst supported on magnesium oxide.This work highlights the potential of nonthermal plasma catalysis for the activation of renewable sources to serve as a new platform for sustainable ammonia production.

Design of ZnSe-CoSe heterostructure decorated in hollow N-doped carbon nanocage with generous adsorption and catalysis sites for the reversibly fast kinetics of polysulfide conversion

Although lithium-sulfur batteries(Li SBs)are regarded as one of the most promising candidates for the next-generation energy storage system,the actual industrial application is hindered by the sluggish solid–liquid phase conversion kinetics,severe shuttle effect,and low sulfur loadings.Herein,a zeolitic imidazolate framework(ZIF)derived heterogeneous ZnSe-CoSe nanoparticles encapsulated in hollow N-doped carbon nanocage(ZnSe-CoSe-HNC)was designed by etching with tannic acid as a multifunctional electrocatalyst to boost the polysulfide conversion kinetics in LiSBs.The hollow structure in ZIF ensures large inner voids for sulfur and buffering volume expansions.Abundant exposed ZnSe-CoSe heterogeneous interfaces serve as bifunctional adsorption-catalytic centers to accelerate the conversion kinetics and alleviate the shuttle effect.Together with the highly conductive framework,the ZnSe-CoSeHNC/S cathode exhibits a high initial reversible capacity of 1305.3 m A h g-1at 0.2 C,high-rate capability,and reliable cycling stability under high sulfur loading and lean electrolyte(maintaining at 745 m A h g-1after 200 cycles with a high sulfur loading of 6.4 mg cm-2and a low electrolyte/sulfur ratio of 6μL mg^(-1)).Theoretical calculations have demonstrated the heterostructures of ZnSe-CoSe offer higher binding energy to lithium polysulfides than that of ZnSe or CoSe,facilitating the electron transfer to lithium polysulfides.This work provides a novel heterostructure with superior catalytic ability and hollow conductive architecture,paving the way for the practical application of functional sulfur electrodes.

Tandem catalysis for enhanced CO oxidation over the Bi-Au-SiO_(2)interface

Bimetallic catalysts typically exploit unique synergetic effects between two metal species to achieve their catalytic effect.Understanding the mechanism of CO oxidation using hybrid heterogeneous catalysts is important for effective catalyst design and environmental protection.Herein,we report a Bi-Au/SiO_(2)tandem bimetallic catalyst for the oxidation of CO over the Au/SiO_(2)surface,which was monitored using near-ambient-pressure X-ray photoelectron spectroscopy.The Au-decorated SiO_(2)catalyst exhibited scarce activity in the CO oxidation reaction;however,the introduction of Bi to the Au/SiO_(2)system promoted the catalytic activity.The mechanism is thought to involve the dissociation O_(2)molecules in the presence of Bi,which results in spillover of the O species to adjacent Au atoms,thereby forming Au^(δ+).Further CO adsorption,followed by thermal treatment,facilitated the oxidation of CO at the Au-Bi interface,resulting in a reversible reversion to the neutral Au valence state.Our work provides insight into the mechanism of CO oxidation on tandem surfaces and will facilitate the rational design of other Au-based catalysts.

Ti-Fe_(2)O_(3)/Ni(OH)_(x) as an efficient and durable photoanode for the photoelectrochemical catalysis of PET plastic to formic acid

Photoelectrochemical(PEC) technology provides a promising prospect for the transformation of polyethylene terephthalate(PET) plastic wastes to produce value-added chemicals.The PEC catalytic systems with high activity,selectivity and long-term durability are required for the future up-scaling industrial applications.Herein,we employed the interfacial modification strategy to develop an efficient and stable photoanode and evaluated its PEC activity for ethylene glycol(EG,derived from PET hydrolysate) oxidation to formic acid.The interfacial modification between Fe_(2)O_(3)semiconductor and Ni(OH)xcocatalyst with ultrathin TiO_(x) interlayer not only improved the photocurrent density by accelerating the kinetics of photogenerated charge carriers,but also kept the high Faradaic efficiency(over 95% in 30 h) towards the value-added formic acid product.This work proposes an effective method to promote the PEC activity and enhance the long-term stability of photoelectrodes for upcycling PET plastic wastes.

Designing high-efficiency light-to-thermal conversion materials for solar desalination and photothermal catalysis

Light-to-thermal conversion materials(LTCMs)have been of great interest to researchers due to their impressive energy conversion capacity and wide range of applications in biomedical,desalination,and synergistic catalysis.Given the limited advances in existing materials(metals,semiconductors,π-conjugates),researchers generally adopt the method of constructing complex systems and hybrid structures to optimize performance and achieve multifunctional integration.However,the development of LTCMs is still in its infancy as the physical mechanism of light-to-thermal conversion is unclear.In this review,we proposed design strategies for efficient LTCMs by analyzing the physical process of light-tothermal conversion.First,we analyze the nature of light absorption and heat generation to reveal the physical processes of light-to-thermal conversion.Then,we explain the light-to-thermal conversion mechanisms of metallic,semiconducting andπ-conjugated LCTMs,and propose new material design strategies and performance improvement methods.Finally,we summarize the challenges and prospects of LTCMs in emerging applications such as solar water evaporation and photothermal catalysis.

Is a catalyst always beneficial in plasma catalysis? Insights from the many physical and chemical interactions

Plasma-catalytic dry reforming of CH_(4)(DRM) is promising to convert the greenhouse gasses CH_(4) and CO_(2) into value-added chemicals, thus simultaneously providing an alternative to fossil resources as feedstock for the chemical industry. However, while many experiments have been dedicated to plasma-catalytic DRM, there is no consensus yet in literature on the optimal choice of catalyst for targeted products,because the underlying mechanisms are far from understood. Indeed, plasma catalysis is very complex,as it encompasses various chemical and physical interactions between plasma and catalyst, which depend on many parameters. This complexity hampers the comparison of experimental results from different studies, which, in our opinion, is an important bottleneck in the further development of this promising research field. Hence, in this perspective paper, we describe the important physical and chemical effects that should be accounted for when designing plasma-catalytic experiments in general, high-lighting the need for standardized experimental setups, as well as careful documentation of packing properties and reaction conditions, to further advance this research field. On the other hand, many parameters also create many windows of opportunity for further optimizing plasma-catalytic systems.Finally, various experiments also reveal the lack of improvement in plasma catalysis compared to plasma-only, specifically for DRM, but the underlying mechanisms are unclear. Therefore, we present our newly developed coupled plasma-surface kinetics model for DRM, to provide more insight in the underlying reasons. Our model illustrates that transition metal catalysts can adversely affect plasmacatalytic DRM, if radicals dominate the plasma-catalyst interactions. Thus, we demonstrate that a good understanding of the plasma-catalyst interactions is crucial to avoiding conditions at which these interactions negatively affect the results, and we provide some recommendations for improvement. For instance, we believe that plasma-catalytic DRM may benefit more from higher reaction temperatures,at which vibrational excitation can enhance the surface reactions.

Cooperative catalysis of Co single atoms and nanoparticles enables selective CAr-OCH_(3) cleavage for sustainable production of lignin-based cyclohexanols

In this work,a dual-size MOF-derived Co catalyst(0.2Co_(1-NPs)@NC)composed of single atoms(Co_(1))and highly dispersed nanoparticles(Co NPs)was prepared by in-situ Zn evaporation for the highperformance conversion of lignin-derived o-methoxyphenols(lignin oil)to cyclohexanols(up to 97%yield)via cascade demethoxylation and dearomatization.Theoretical calculations elaborated that the dual-size Co catalyst exhibited a cooperative effect in the selective demethoxylation process,in which the Co NPs could initially dissociate hydrogen at lower energies while Co1remarkably facilitated the cleavage of the C_(Ar)-OCH_(3)bond.Moreover,the intramolecular hydrogen bonds formed in the omethoxy-containing phenols were found to result in a decrease in the bond energy of the C_(Ar)-OCH_(3)bond,which was more prone to be activated by the dual-size Co sites.Notably,the pre-hydrogenated intermediate(e.g.,2-methoxycyclohexanol from guaiacol)is difficult to undergo demethoxylation,indicating that the selective C_(Ar)-OCH_(3)bond cleavage is a prerequisite for the synthesis of cyclohexanols.The 0.2Co_(1-NPs)@NC catalyst was highly recyclable with a neglect decline in activity during five consecutive cycles.This cooperative catalytic strategy based on the metal size effect opens new avenues for biomass upgrading via enhanced C-O bond cleavage of high selectivity.

The Nature of Active Sites for Plasmon-Mediated Photothermal Catalysis and Heat-Coupled Photocatalysis in Dry Reforming of Methane

Solar energy-induced catalysis has been attracting intensive interests and its quantum efficiencies in plasmon-mediated photothermal catalysis(P-photothermal catalysis)and external heat-coupled photocatalysis(E-photothermal catalysis)are ultimately determined by the catalyst structure for photo-induced energetic hot carriers.Herein,different catalysts of supported(TiO_(2)-P25 and Al_(2)O_(3))platinum quantum dots are employed in photo,thermal,and photothermal catalytic dry reforming of methane.Integrated experimental and computational results unveil different active sites(hot zones)on the two catalysts for photo,thermal,and photothermal catalysis.The hot zones of P-photothermal catalysis are identified to be the metal-support interface on Pt/P25 and the Pt surface on Pt/Al_(2)O_(3),respectively.However,a change of the active site to the Pt surface on Pt/P25 is for the first time observed in E-photothermal catalysis(external heating temperature of 700℃).The hot zones contribute to the significant enhancements in photothermal catalytic reactivity against thermocatalysis.This study helps to understand the reaction mechanism of photothermal catalysis to exploit efficient catalysts for solar energy utilization and fossil fuels upgrading.

Review on Metal-Acid Tandem Catalysis for Hydrogenative Rearrangement of Furfurals to C_(5) Cyclic Compounds

Hydrogenative rearrangement of biomas s-derived furfurals(furfural and 5-hydroxymethyl furfural) to C_(5) cyclic compounds(such as cyclopentanones and cyclopentanols) offers an expedient reaction route for acquiring O-containing value-added chemicals thereby replacing the traditional petroleum-based approaches.The scope for developing efficient bifunctional catalysts and establishing mild reaction conditions for upgrading furfurals to cyclic compounds has stimulated immense deliberation in recent years.Extensive efforts have been made toward developing catalysts for multiple tandem conversions,including those with various metals and supports.In this scientific review,we aim to summarize the research progress on the synergistic effect of the metal-acid sites,including simple metal-supported acidic supports,adjacent metal acid sites-supported catalysts,and in situ H_(2)-modified bifunctional catalysts.Distinctively,the catalytic performance,catalytic mechanism,and future challenges for the hydrogenative rearrangement are elaborated in detail.The methods highlighted in this review promote the development of C_(5) cyclic compound synthesis and provide insights to regulate bifunctional catalysis for other applications.