Distribution Of Active Sites Research Articles

Electrochemical Imaging of Precisely‐Defined Redox and Reactive Interfaces

AbstractUnderstanding the diverse electrochemical reactions occurring at electrode‐electrolyte interfaces (EEIs) is a critical challenge to developing more efficient energy conversion and storage technologies. Establishing a predictive molecular‐level understanding of solid electrolyte interphases (SEIs) is challenging due to the presence of multiple intertwined chemical and electrochemical processes occurring at battery electrodes. Similarly, chemical conversions in reactive electrochemical systems are often influenced by the heterogeneous distribution of active sites, surface defects, and catalyst particle sizes. In this mini review, we highlight an emerging field of interfacial science that isolates the impact of specific chemical species by preparing precisely‐defined EEIs and visualizing the reactivity of their individual components using single‐entity characterization techniques. We highlight the broad applicability and versatility of these methods, along with current state‐of‐the‐art instrumentation and future opportunities for these approaches to address key scientific challenges related to batteries, chemical separations, and fuel cells. We establish that controlled preparation of well‐defined electrodes combined with single entity characterization will be crucial to filling key knowledge gaps and advancing the theories used to describe and predict chemical and physical processes occurring at EEIs and accelerating new materials discovery for energy applications.

Electrochemical Imaging of Precisely-Defined Redox and Reactive Interfaces.

Understanding the diverse electrochemical reactions occurring at electrode-electrolyte interfaces (EEIs) is a critical challenge to developing more efficient energy conversion and storage technologies. Establishing a predictive molecular-level understanding of solid electrolyte interphases (SEIs) is challenging due to the presence of multiple intertwined chemical and electrochemical processes occurring at battery electrodes. Similarly, chemical conversions in reactive electrochemical systems are often influenced by the heterogeneous distribution of active sites, surface defects, and catalyst particle sizes. In this mini review, we highlight an emerging field of interfacial science that isolates the impact of specific chemical species by preparing precisely-defined EEIs and visualizing the reactivity of their individual components using single-entity characterization techniques. We highlight the broad applicability and versatility of these methods, along with current state-of-the-art instrumentation and future opportunities for these approaches to address key scientific challenges related to batteries, chemical separations, and fuel cells. We establish that controlled preparation of well-defined electrodes combined with single entity characterization will be crucial to filling key knowledge gaps and advancing the theories used to describe and predict chemical and physical processes occurring at EEIs and accelerating new materials discovery for energy applications.

An improved coking model for simulating reactive transport phenomena and coking behavior in sucrose hydrolysis

Levulinic acid (LA) holds great significance as a biomass platform chemical in the production of bio-aviation fuel and the utilization of bioenergy. Heterogeneous acid-catalyzed polysaccharide hydrolysis has emerged as a promising method for LA production. Understanding the coupling mechanisms of the physicochemical processes are fundamentally important to optimize the reaction system. In this work, a pore-scale multicomponent reactive transport model based on lattice Boltzmann method was developed to simulate the hydrolysis of sucrose. Considering the significant effect of active sites distribution density on coking formation, an improved coking model was proposed. Systematic investigations of reactive transport and coking behavior were conducted. Simulation results demonstrated that, initial sucrose concentration had a substantial impact on the coking rate of catalyst, when sucrose concentration exceeded 250 mmol/L, the catalyst became fully deactivated before complete hydrolysis of reactant occurred. Furthermore, a marginal benefit was found for the synergistic effect of protons in solution and solid catalysts on sucrose hydrolysis, when proton concentration reached the marginal value of 0.12 mol/L, further increases in proton concentration resulted in only marginal improvements in reaction efficiency. This work underscores the importance of the catalyst morphological character engineering and processes controlled for enhancing overall performance in LA production.

Asymmetric structures to switch on the selective oxygen reduction to hydrogen peroxide

Carbon defects coupled with heteroatoms can asymmetrically rearrange the local electronic distribution and coordination environment of active sites, improving the catalytic selectivity and activity of a two-electron oxygen reduction reaction (2eORR). In this study, an asymmetry defective carbon (asy-DC) structure using wolfberry as the carbon source is employed to adjust the charge distribution of active sites with different degrees of asymmetry caused by N→S coordination bonds. The asymmetric region exhibits a considerable positive correlation between the asymmetry degree and adsorption energy for OOH*, presenting a volcano relation between the asymmetry degree and catalytic activity. The optimised asy-DC catalyst exhibits high selectivity and reliable activity after 12 h of stability testing. This study can provide a new reference into the origin of ORR activity and selectivity.

Rational design of Fe, N co-doped porous carbon derived from conjugated microporous polymer as an electrocatalytic platform for oxygen reduction reaction

Porous iron–nitrogen-doped carbons (FeNC) offer a great platform for construction of cathodic oxygen reduction reaction (ORR) catalysts in fuel cells. However, challenges still remain regarding with the collapse of carbon-skeleton during pyrolysis, uneven distribution of active sites and aggregation of metal atoms. In this work, we synthesized Fe, N co-doped conjugated microporous polymer (FeN-CMP) through a facile bottom-up strategy using 1,3,5-triethynylbenzene and iron-chelated 3,8-dibromo-1,10-phenanthroline as monomers, ensuring the uniform coordination of N with Fe element in network. Then, the resulting FeN-CMP was treated by pyrolysis without structural collapse to obtain porous FeNC electrocatalyst for ORR. The most active catalyst was fabricated under 900 °C, which exhibits remarkable ORR activity in alkaline medium with half-wave potential of 0.796 V (18 mV and 105 mV positive deviation from the commercial Pt/C catalyst and post-doping catalyst), high selectivity with nearly 4e- transfer process and excellent methanol tolerance. Our study first developed porous FeNC electrocatalysts derived from Fe, N-anchoring CMPs based on pre-functionalization of monomers, which exhibits great potential as an alternative to commercial Pt/C catalyst for ORR, and provides a feasible strategy of developing multi-atoms doping catalysts for energy storage and conversion as well as heterogeneous catalysis.

Efficient calcium sulfite oxidation treatment by a highly active iron-manganese bimetallic metal-organic frameworks (MOFs)

Calcium sulfite (CaSO3) oxidation is the key step in the resource utilization of flue gas desulfurization (FGD) ash waste. However, under natural conditions the oxidation rate of CaSO3 is very low, limiting its conversion into calcium sulfate, an acceptable product for construction material. This study was devoted to the investigation of the synthesis and performance of a bimetallic MOFs with potential catalytic activity, namely, Fe/Mn(BDC)(DMF,F) catalysts. A combination of techniques including SEM, EDS, XRD, FT-IR, etc. were used to characterize the catalysts. The excellent catalytic performance examined in a gas-liquid-solid three-phase oxidation system are due to the special flexible respiratory architecture and homogeneous distribution of active sites, which allows the reactants to fully contact with the catalyst. Mn incorporated in the backbone of the metal-organic framework significantly enriches the catalytic active species that participate in a radical chain reaction with activated SO32- as ·SO3-, which in turn generates the key radical ·SO5- that reacts with SO32- to form SO42-. In the presence of Fe/Mn(BDC)(DMF, F)-13, the oxidation ratio of CaSO3 could reach 90.71%, which is more than 30-fold compared to non-catalytic oxidation and almost 5 times the effects of the single metal Fe(BDC)(DMF, F) catalyst. In addition, the study of kinetics shows that the oxidation rate of Fe/Mn(BDC)(DMF,F)-13 can reach 0.042 mmol·L-1·s-1 with an apparent activation energy of 10.86 kJ/mol. The oxidation rate is mainly affected by reaction temperature, pH value, catalyst concentration, and air flow rate. This study provides a potentially sustainable way for utilization of CaSO3-containing desulfurization ash.

Tuning of the acid sites in the zeolite-alumina composite Ni catalysts and their impact on the palm oil hydrodeoxygenation reaction

The hydrodeoxygenation (HDO) of bio-oil is one of the potential approaches to produce green diesel. However, HDO catalyst requires the development of bifunctionality which translates to the simultaneous presence of acidic and metal sites for desired catalytic activity and selectivity. Zeolites and their composites are attractive candidates for the conversion of biomass to fuels. In the present work, a series of Ni-incorporated Al2O3-zeolite beta bifunctional composite catalysts with distinct Al2O3 (25–75 wt%) and Ni contents (5–15 wt%) were synthesized via a facile one-pot method directly from nickel acetate, nano-boehmite (γ-AlO(OH)) and the NH4+ form of beta zeolite (NH4+-BZ). The nano-boehmite particles, due to the positive charges on their surface, electrostatically attract negatively charged beta zeolite crystals, which leads to the assembly of a hierarchical pore structure upon calcination. Interestingly, the composite catalysts synthesized were quite homogeneous with uniform dispersion of Ni particles. All composite catalysts were thoroughly characterized using XRD, SEM-EDX, SEM-mapping, HR-TEM, H2-TPR, H2-TPD, NH3-TPD, XPS, 31P MAS NMR, 27Al MAS NMR and N2 sorption analysis. The synthesized composite catalysts with distinct Al2O3 contents showed diverse textural properties, distinct nature of acid sites and improved performance in hydrodeoxygenation of palm oil. Particularly, the Ni/BZ-Al50 (with BZ:Al2O3 = 50:50) composite catalyst significantly enhanced the conversion of palm oil (up to 90%) and yield of n-C15-C18 hydrocarbons (up to 69%) at moderate temperature of 375 °C as compared to 10Ni/BZ catalyst (Conv. = 75%, yield of n-C15-C18 = 52%). The higher catalytic performance realized with composite catalysts can be ascribed to its hierarchical pore structure, moderate acidity (chemisorption studies), tuned acid sites nature (solid state NMR) and homogeneous distribution of active Ni sites (H2 chemisorption) which helps to improve product selectivity by minimizing side reactions. The time-on-stream (TOS) experiments were carried out up to 20 h which clearly showed that composite catalysts are more stable suggesting the lower amount of coke deposition (TPO studies) and suppression of metal sintering.

Decoding Active Sites for Highly Efficient Semihydrogenation of Acetylene in Palladium-Copper Nanoalloys.

Accurately decoding the three-dimensional atomic structure of surface active sites is essential yet challenging for a rational catalyst design. Here, we used comprehensive techniques combining the pair distribution function and reverse Monte Carlo simulation to reveal the surficial distribution of Pd active sites and adjacent coordination environment in palladium-copper nanoalloys. After the fine-tuning of the atomic arrangement, excellent catalytic performance with 98% ethylene selectivity at complete acetylene conversion was obtained in the Pd34Cu66 nanocatalysts, outperforming most of the reported advanced catalysts. The quantitative deciphering shows a large number of active sites with a Pd-Pd coordination number of 3 distributed on the surface of Pd34Cu66 nanoalloys, which play a decisive role in highly efficient semihydrogenation. This finding not only opens the way for guiding the precise design of bimetal nanocatalysts from atomic-level insight but also provides a method to resolve the spatial structure of active sites.

Conical porous hollow g-C3N4 charge separation with high efficiency for enhancing visible-light photocatalytic activity

The performance of the photocatalysts is influenced by factors such as electron generation ability, charge separation rate, and active sites distribution. In this study, needle-shaped precursors were prepared through low-temperature supramolecular self-assembly, and conical porous hollow carbon nitride (PHCN) was obtained after high-temperature pyrolysis. The PHCN not only possesses a thin-walled porous structure but also contains nitrogen defects embedded in its structure, which synergistically enhance the efficiency of photogenerated charge separation and provide more reactive sites. The DFT calculations showed that nitrogen defects and Pt-loading synergistically optimize the intermediate reaction process of graphitic carbon nitride (g-C3N4). PHCN had excellent photocatalytic degradation of tetracycline hydrochloride (TCH) and Rhodamine B (Rh B). The photocatalytic hydrogen evolution rate of PHCN was 20.0 times higher than that of bulk g-C3N4 (BCN). This study elucidated the relationship between crystallization rate and precursor morphology, as well as the influence of their physicochemical properties on photocatalytic performance. It also lays the foundation for constructing materials with nitrogen defects and special morphology through supramolecular self-assembly.

Heterobimetallic praseodymium-nickel active sites with Pr-N4C2 and Ni-N4 moieties enabling synergistic catalysis of CO2 electroreduction

Lanthanide metals have attracted particular interest in the catalysis of electrochemical CO2 reduction. The synthesis and precise spatial distribution of active sites are fundamental important but still formidably challenging owing to the strong oxygen affinity of lanthanide. Here, heteronuclear Pr1-Ni1 single atoms are supported on the carbon matrix containing surface framework defects from lanthanide contraction. The Pr/Ni-NC catalyst exhibits a CO Faradaic efficiency of 99.1 % with a commercial-scale current density of 237 mA cm−2 and a turnover frequency as high as 18,038 h−1 at −1.1 V due to d-f coupling effect and electronic structure perturbation of Pr. Furthermore, mechanistic investigations unveil that the diatomic active sites effectively reduce the energy barrier of the crucial *COOH formation, in which the Pr site facilitates CO2 activation and the Ni site enables H2O dissociation to accelerate the proton transfer process, thereby ensuring the synergy of catalytic sites to greatly facilitate CO2-to-CO conversion.

Developing Isomeric Peptides for Mimicking the Sequence-Activity Landscapes of Enzyme Evolution.

Enzymes catalyze almost all material conversion processes within living organisms, yet their natural evolution remains unobserved. Short peptides, derived from proteins and featuring active sites, have emerged as promising building blocks for constructing bioactive supramolecular materials that mimic native proteins through self-assembly. Herein, we employ histidine-containing isomeric tetrapeptides KHFF, HKFF, KFHF, HFKF, FKHF, and FHKF to craft supramolecular self-assemblies, aiming to explore the sequence-activity landscapes of enzyme evolution. Our investigations reveal the profound impact of peptide sequence variations on both assembly behavior and catalytic activity as hydrolytic simulation enzymes. During self-assembly, a delicate balance of multiple intermolecular interactions, particularly hydrogen bonding and aromatic-aromatic interactions, influences nanostructure formation, yielding various morphologies (e.g., nanofibers, nanospheres, and nanodiscs). Furthermore, the analysis of the structure-activity relationship demonstrates a strong correlation between the distribution of the His active site on the nanostructures and the formation of the catalytic microenvironment. This investigation of the sequence-structure-activity paradigm reflects how natural enzymes enhance catalytic activity by adjusting the primary structure during evolution, promoting fundamental research related to enzyme evolutionary processes.

Rational Design and Precise Synthesis of Single-Atom Alloy Catalysts for the Selective Hydrogenation of Nitroarenes.

Single-atom alloys (SAAs) have gained increasing prominence in the field of selective hydrogenation reactions due to their uniform distribution of active sites and the unique host-guest metal interactions. Herein, 15 SAAs are constructed to comprehensively elucidate the relationship between host-guest metal interaction and catalytic performance in the selective hydrogenation of 4-nitrostyrene (4-NS) by density functional theory (DFT) calculations. The results demonstrate that the SAAs with strong host-guest metal interactions exhibit a preference for N─O bond cleavage, and the reaction energy barrier of the hydrogenation process is primarily influenced by the host metal. Among them, Ir1Ni SAA stands out as the prime catalyst candidate, showcasing exceptional activity and selectivity. Furthermore, the Ir1Ni SAA is subsequently prepared through precise synthesis techniques and evaluated in the selective hydrogenation of 4-NS to 4-aminostyrene (4-AS). As anticipated, the Ir1Ni SAA demonstrates extraordinary catalytic performance (yield>96%). In situ FT-IR experiments and DFT calculations further confirmed that the unique host-guest metal interaction at the Ir-Ni interface site of Ir1Ni SAA endows it with excellent 4-NS selective hydrogenation ability. This work provides valuable insights into enhancing the performance of SAAs catalysts in selective hydrogenation reactions by modulating the host-guest metal interactions.

Specific roles of Fe in NiFe-MOF nanosheet arrays on oxygen evolution reaction kinetics in alkaline media

Although great progress has been made in the study of the performance of NiFe-based electrocatalysts, the specific role of Fe is still under debate, largely due to the lack of desirable platforms. Metal-organic frameworks (MOFs) with uniform pore size, large specific surface area and uniform distribution of active sites are ideal platforms. Therefore, we synthesized a series of NiM-MOF (M = Fe, Co, Mn, Cu, or Zn) nanosheet arrays by solvothermal method with MOF as a platform and systematically investigated their OER properties. XRD and XPS characterizations show that the introduction of Fe into Ni-MOF not only leads to lower crystallinity, but also increases the oxidation state of Fe and modifies the electronic structure of Ni sites. This is further confirmed by DFT calculations, where the d-band center is closer to the Fermi level, enhancing the ability to adsorb/desorb oxygen-containing intermediates and thereby improving the intrinsic activity of NiFe-MOF.

Artificial Heterointerfaces with Regulated Charge Distribution of Ni Active Sites for Urea Oxidation Reaction.

In contrast to the thermodynamically unfavorable anodic oxygen evolution reaction, the electrocatalytic urea oxidation reaction (UOR) presents a more favorable thermodynamic potential. However, the practical application of UOR has been hindered by sluggish kinetics. In this study, hierarchical porous nanosheet arrays featuring abundant Ni-WO3 heterointerfaces on nickel foam (Ni-WO3/NF) is introduced as a monolith electrode, demonstrating exceptional activity and stability toward UOR. The Ni-WO3/NF catalyst exhibits unprecedentedly rapid UOR kinetics (200mAcm-2 at 1.384V vs. RHE) and a high turnover frequency (0.456s-1), surpassing most previously reported Ni-based catalysts, with negligible activity decay observed during a durability test lasting 150 h. Ex situ X-ray photoelectron spectroscopy and density functional theory calculations elucidate that the WO3 interface significantly modulates the local charge distribution of Ni species, facilitating the generation of Ni3+ with optimal affinity for interacting with urea molecules and CO2 intermediates at heterointerfaces during UOR. This mechanism accelerates the interfacial electrocatalytic kinetics. Additionally, in situ Fourier transform infrared spectroscopy provides deep insights into the substantial contribution of interfacial Ni-WO3 sites to UOR electrocatalysis, unraveling the underlying molecular-level mechanisms. Finally, the study explores the application of a direct urea fuel cell to inspire future practical implementations.

Sustainable efficient utilization of magnetic porous biochar for adsorption of orange G and tetracycline: Inherent roles of adsorption and mechanisms

Iron-doped biochar has been widely used as an adsorbent to remove contaminants due to the high adsorption performance, but it still suffers from complicated preparation methods, unstable iron loading, unsatisfactory specific surface area, and uneven distribution of active sites. Here, a novel magnetic porous biochar (FeCS800) with nanostructure on surface was synthesized by one-pot pyrolysis method of corn straw with K2FeO4, and used in orange G (OG) and tetracycline (TC) adsorption. FeCS800 exhibited outstanding adsorption capacities for OG and TC after K2FeO4 activation and the adsorption data were fitted satisfactorily to Langmuir isotherm and Pseudo-second-order kinetic model. The maximum adsorption capacities of FeCS800 for OG and TC were around 303.03 mg/g and 322.58 mg/g, respectively, at 25 °C and pH 7.0, which were 16.27 and 24.61 times higher than that before modification. Thermodynamic studies showed that the adsorption of OG/TC by FeCS800 were thermodynamically favorable and highly spontaneous. And the adsorption capacity of OG and TC by FeCS800 remained 77% and 81% after 5 cycles, respectively, indicating that FeCS800 had good stability. The outstanding adsorption properties and remarkable reusability of FeCS800 show its great potential to be an economic and environmental adsorbent in contaminants removal.

Identification of the active sites for CO2 methanation over Re/TiO2 catalysts

CO2 methanation on heterogeneous catalysts holds great significance in achieving the net-zero emission target. However, understanding the atomic-scale relationship between reactivity and active site has been a subject of debate. The study investigated CO2 methanation reaction catalyzed by Re/TiO2 catalysts and identified the active site distribution and its relationship with reactivity. The low-coordinated edge sites of Re nanoparticle were found to be the active sites where CO2 dissociated into CO via a carbide pathway and subsequently hydrogenated to form methane. Furthermore, the study revealed that the size of Re nanoparticle influenced the distribution of active edge sites and affected the reactivity and stability of the CO intermediate, which was the rate-determining step in CO2 methanation reaction. Controlling the size and structure of Re nanoparticle can, therefore, enhanced the activity and efficiency of CO2 methanation reaction. The identification of these active sites and the insights gained from this study have significant implications for the mechanistic understanding and optimization of CO2 methanation over Re/TiO2 catalysts. It provides a basis for designing more effective catalysts to facilitate the conversion of CO2 to methane, thereby contributing to the goal of achieving net-zero emissions.

Kinetic insights into reaction pathways of acrolein formation in propylene epoxidation by H2 and O2 over Au/TS-1 catalyst

Propylene epoxidation by H2 and O2 to propylene oxide (HOPO), as a novel method for PO production, has attracted widespread attention due to its economic and environmental advantages. Acrolein is a notable byproduct arising in HOPO reaction over Au/TS-1 catalyst, and is traditionally thought to be exclusively formed on Au site through propylene oxidation. However, on the intraporous and external surface Au sites of Au-Ti catalysts, the HOPO reaction have been shown to proceed by different mechanisms, yet the effect of active sites distribution on acrolein formation is far from being understood. Herein, we found that the reaction orders in acrolein formation on Au/TS-1 catalyst (H2, 0.19; O2, 0.44; C3H6, 0.44) relative to Au/TS-1 with blocked pores (Au/TS-1-B) catalyst (H2, −0.36; O2, 0.61; C3H6, 0.52) were quite different, suggesting a variation in the reaction pathway on the catalysts with different Au locations. Moreover, it is found that PO can be converted to acrolein by O2 on TS-1 zeolite, which is absent on TS-1-B zeolite without micropores. Consequently, acrolein formation on Au/TS-1 catalyst can proceed through two parallel pathways: propylene hydro-oxidation on Au site, and PO conversion by O2 inside micropores. Furthermore, by designing and preparing the Au/TS-1 catalysts with different structures, the Au locations are closely related to acrolein formation mechanism and kinetic behaviors. This work provides kinetic insights into the acrolein formation pathways in the HOPO reaction on Au/TS-1 catalyst, and is helpful to the rational design and preparation of efficient catalysts with high selectivity.

Distinct structure-activity relationship and reaction mechanism over BaCoO3/CeO2 catalysts for NO direct decomposition

The dependency on morphology is crucial for achieving highly efficient direct decomposition of NO. Herein, a BaCoO3/CeO2 catalyst is synthesized using CeO2 small particles (p), spheres (s) and rods (r) as supports. The NO conversion to N2 (NTN2) at 800 °C follows the order BaCoO3/CeO2-r (78.8 %) > BaCoO3/CeO2-s (75.9 %) > BaCoO3/CeO2-p (56.9 %) > BaCoO3 (8.6 %) at a space velocity 1 g s/cm3. BaCoO3/CeO2-r exhibts high tolerance to O2 and stability with conversion decreasing from 78.8 % to 74.6 %, 60.0 % and 50.0 % at 800 °C with 1, 5 and 10 vol% O2, respectively. The high redox activity, higher active oxygen mobility and NO adsorption capability ensures its superior performance, while the high surface area (31.29 m2/g) and uniform distribution of active sites on the surface further promote the activity. The mechanism of NO direct decomposition is elucidated by in situ Diffuse reflectance infrared Fourier transform spectroscopy, 18O2 isotopic transient exchange experiments and density functional theory (DFT) calculation.

Discovering High Entropy Alloy Electrocatalysts in Vast Composition Spaces with Multiobjective Optimization.

High entropy alloys (HEAs) are a highly promising class of materials for electrocatalysis as their unique active site distributions break the scaling relations that limit the activity of conventional transition metal catalysts. Existing Bayesian optimization (BO)-based virtual screening approaches focus on catalytic activity as the sole objective and correspondingly tend to identify promising materials that are unlikely to be entropically stabilized. Here, we overcome this limitation with a multiobjective BO framework for HEAs that simultaneously targets activity, cost-effectiveness, and entropic stabilization. With diversity-guided batch selection further boosting its data efficiency, the framework readily identifies numerous promising candidates for the oxygen reduction reaction that strike the balance between all three objectives in hitherto unchartered HEA design spaces comprising up to 10 elements.

Tailoring the Active Species Distribution of Heterogeneous Catalyst for Regulating the Chain Structure of Nascent Polyethylene

AbstractHeterogeneous catalysis is the most widely used process for ethylene polymerization in industry. Active site distribution is one of the crucial issues in the heterogeneous catalysis, which strongly influences the catalytic process and the microstructure of synthesized polyethylene. In this respect, aiming at an explicit understanding of the progress, the challenge and the possible future directions in the study of heterogeneous catalysis of ethylene polymerization, the recent strategies of designing heterogeneous catalysts are reviewed from the perspective of tailoring the active site distribution, where the regulation of chain structures, including molecular weight distribution, branch distribution and entanglement state, are highlighted. The in situ and operando characterizations are also reviewed for assisting the understanding of structural information in heterogeneous catalysts.