Rational Catalyst Design Research Articles

Hydrogenation Reaction Mechanisms on Ni-Doped MoS2 Catalysts: A Density Functional Theory Study of Sulfur Edge Engineering and Coregulated Electronic Effects.

Precise modulation of local interatomic interactions affecting the electronic structure is an important method to control the catalytic activity and reaction pathways. In this study, we focused on the hydrogenation reaction of naphthalene and employed density functional theory calculations to investigate the specific influence of electronic effects triggered by the coregulation of Ni and sulfur edge engineering on the hydrogenation performance of Ni-doped MoS2 at different edge sulfur coverages (Ni-MoS2-X-θs). Our findings reveal that the interaction between Ni and S in the catalyst matrix material modifies the local electronic structure surrounding the sulfur atoms in the active site. Notably, Ni doping facilitates significant electron transfer, altering the charge and the electronic states at the catalyst edge. This, in turn, affects the adsorption capacity and reactivity of the catalyst, thereby reducing the energy barrier of the hydrogenation reaction. Furthermore, we paid particular attention to the modulation of catalytic activity and reaction pathways under the Eley-Rideal (E-R) mechanism. Interestingly, the sulfur coverage exhibited a nonlinear relationship with the adsorption and activation properties of the probe molecule. Typically, changes in the Mo edge sulfur coverage probability of Ni-MoS2-X-θs have a greater impact on the activation properties. Through comprehensive studies, we demonstrated that both compositional and structural factors must be considered when tailoring the catalytic performance. Importantly, adjusting the ratio of marginal sulfur atoms to metal atoms to 1:1 can effectively enhance the catalytic activity. This study provides valuable insights into the electronic effects regulating the hydrogenation reaction activity of MoS2-based catalysts. It also opens the way for the rational design of novel hydrogenation catalysts, offering a new strategy for optimizing the catalytic performance.

Manipulating C-C coupling pathway in electrochemical CO2 reduction for selective ethylene and ethanol production over single-atom alloy catalyst.

Manipulation C-C coupling pathway is of great importance for selective CO2 electroreduction but remain challenging. Herein, two model Cu-based catalysts, by modifying Cu nanowires with Ag nanoparticles (AgCu NW) and Ag single atoms (Ag1Cu NW), respectively, are rationally designed for exploring the C-C coupling mechanisms in electrochemical CO2 reduction reaction (CO2RR). Compared to AgCu NW, the Ag1Cu NW exhibits a more than 10-fold increase of C2 selectivity in CO2 reduction to ethanol, with ethanol-to-ethylene ratio increased from 0.41 over AgCu NW to 4.26 over Ag1Cu NW. Via a variety of operando/in-situ techniques and theoretical calculation, the enhanced ethanol selectivity over Ag1Cu NW is attributed to the promoted H2O dissociation over the atomically dispersed Ag sites, which effectively accelerated *CO hydrogenation to form *CHO intermediate and facilitated asymmetric *CO-*CHO coupling over paired Cu atoms adjacent to single Ag atoms. Results of this work provide deep insight into the C-C coupling pathways towards target C2+ product and shed light on the rational design of efficient CO2RR catalysts with paired active sites.

Cation‐Vacancy Engineering Modulated Perovskite Oxide for Boosting Electrocatalytic Conversion of Polysulfides

AbstractLithium‐sulfur batteries face challenges like polysulfide shuttle and slow conversion kinetics, hindering their practical applications in renewable energy storage and electric vehicles. Herein, a solution to solve this issue is reported by using a cation vacancy engineering strategy with rational synthesis of La‐deficient LaCoO3 (LCO‐VLa). The introduction of cation vacancies in LCO‐VLa modifies the geometric structure of coordinating atoms, exposing Co‐rich surface with more catalytically active surfaces. Meanwhile, the d‐band center of LCO‐VLa shifts toward the Fermi level, enhancing polysulfide adsorption. Furthermore, multivalent cobalt ions (Co3+/Co4+) induced by charge compensation enhance the electrical conductivity of LCO‐VLa, accelerating electron transfer processes and improving catalytic performance. Theoretical calculations and experimental characterizations demonstrate that La‐deficient LCO‐VLa effectively suppresses the polysulfide shuttle, reduces the energy barrier for polysulfide conversion, and accelerates redox reaction kinetics. LCO‐VLa‐based batteries demonstrate exceptional rate performance and cycling stability, retaining 70% capacity after nearly 500 cycles at 1.0 C, with a minimal decay rate of 0.055% per cycle. These findings highlight the significance of cation vacancy engineering for exploring precise structure‐activity relationships during polysulfides conversion, facilitating the rational design of catalysts at the atomic level for lithium‐sulfur batteries.

Transient Kinetic Investigation of Chain Growth and the Accumulation of Surface Carbon during CO Hydrogenation on Cobalt Catalysts

CO hydrogenation is a promising approach for the storage of renewable energy in the form of hydrocarbons via the Fischer‐Tropsch synthesis (FTS). Since transient operation of FTS reactors might be necessary and even be beneficial, transient kinetics for a rational catalyst and reactor design are essential. In order to advance the development of such transient kinetics, the periodic transient kinetics (PTK) method was applied to the CO hydrogenation on a Co/TiO2 catalyst under FT‐like conditions. It was revealed that there are two carbon species of different reactivity, Cα and Cβ, present on the catalyst surface during the reaction. Cα forms fast within a few seconds and is highly reactive, while Cβ forms slowly, is accumulating on the surface over a longer time and imposes an inhibiting effect. The results indicate an important role of the Cβ species to chain growth and the formation of C2+ products. Finally, the transient experimental results are evaluated based on a material balance and the amounts of Cα and Cβ present on the catalyst surface during the reaction were determined.

Surface restructuring and predictive design of heterogeneous catalysts.

Heterogeneous catalysts, which often consist of metal nanoparticles loaded on supports such as metal oxides, can undergo several types of restructuring under reaction and catalytic conditions. Advanced characterizations now allow the surface structure of a catalyst in a gas phase to be determined to some extent. Metal nanoparticles may experience changes in shape, surface structure and composition, and atomic packing in response to the pressure of a reactant or product gas, temperature, and reaction between the catalyst surface and gas. Metal oxide supports can partially or fully encapsulate metal nanoparticles, altering their electronic structure and reactivity. Restructuring is a main approach to creating active catalytic sites. The rational design of catalysts must anticipate that such restructurings can occur under reaction or catalytic conditions and gain knowledge of how they occur. It is expected that computational studies can predict such restructurings and that advanced synthesis may be used to prepare pristine catalysts with enhanced resistance to restructurings.

State of the Art and Challenges in Complete Benzene Oxidation: A Review.

Increased levels and detrimental effects of volatile organic compounds (VOCs) on air quality and human health have become an important issue in the environmental field. Benzene is classified as one of the most hazardous air pollutants among non-halogenated aromatic hydrocarbons with toxic, carcinogenic, and mutagenic effects. Various technologies have been applied to decrease harmful emissions from various sources such as petrochemistry, steel manufacturing, organic chemical, paint, adhesive, and pharmaceutical production, vehicle exhausts, etc. Catalytic oxidation to CO2 and water is an attractive approach to VOC removal due to high efficiency, low energy consumption, and the absence of secondary pollution. However, catalytic oxidation of the benzene molecule is a great challenge because of the extraordinary stability of its six-membered ring structure. Developing highly efficient catalysts is of primary importance for effective elimination of benzene at low temperatures. This review aims to summarize and discuss some recent advances in catalyst composition and preparation strategies. Advantages and disadvantages of using noble metal-based catalysts and transition metal oxide-based catalysts are addressed. Effects of some crucial factors such as catalyst support nature, metal particle size, electronic state of active metal, redox properties, reactivity of lattice oxygen and surface adsorbed oxygen on benzene removal are explored. Thorough elucidation of reaction mechanisms in benzene oxidation is a prerequisite to develop efficient catalysts. Benzene oxidation mechanisms are analyzed based on in situ catalyst characterization, reaction kinetics, and theoretical simulation calculations. Considering the role of oxygen vacancies in improving catalytic performance, attention is given to oxygen defect engineering. Catalyst deactivation due to coexistence of water vapor and other pollutants, e.g., sulfur compounds, is discussed. Future research directions for rational design of catalysts for complete benzene oxidation are provided.

Dual Near-Infrared-Response S-Scheme Heterojunction with Asymmetric Adsorption Sites for Enhanced Nitrogen Photoreduction.

Photocatalytic nitrogen reduction reaction (PNRR) holds immense promise for sustainable ammonia (NH3) synthesis. However, few photocatalysts can utilize NIR light that carries over 50% of the solar energy for NH3 production with high performance. Herein, a dual NIR-responsive S-scheme ZnCoSx/Fe3S4 heterojunction photocatalyst is designed with asymmetric adsorption sites and excellent PNRR performance. The heterojunction possesses a hollow-on-hollow superstructure: Fe3S4 nanocrystal-modified ZnCoSx nanocages as building blocks assemble into spindle-shaped particles with a spindle-like cavity. Both Fe3S4 and ZnCoSx are NIR active, allowing efficient utilization of full-spectrum light. Moreover, an S-scheme heterojunction is constructed that promotes charge separation. In addition, the Fe/Co dual-metal sites at the interface enable an asymmetric side-on adsorption mode of N2, favoring the polarization and activation of N2 molecules. In combination with the promoted mass transfer and active site exposure of hollow superstructure, a superior PNRR performance is achieved, with a high NH3 evolution rate of 2523.4 µmolg-1h-1, an apparent quantum yield of 9.4% at 400nm and 8% at 1000nm, and a solar-to-chemical conversion efficiency of 0.32%. The work paves the way for the rational design of advanced heterojunction catalysts for PNRR.

NMR Relaxation to Probe Zeolites: Mobility of Adsorbed Molecules, Surface Acidity, Pore Size Distribution and Connectivity.

Unique structural and chemical properties, such as ion exchange, developed inner surface, etc., as well as the wide possibilities and flexibility of regulating these properties, cause a keen interest in zeolites. They are widely used in industry as molecular sieves, ion exchangers and catalysts. Current trends in the development of zeolite-based catalysts include the adaptation of their cationic composition, acidity and porosity for a specific catalytic process. Recent studies have shown that mesoporosity is beneficial to the rational design of catalysts with controlled product selectivity and an improved catalyst lifetime due to its efficient mass-transport properties. Nuclear magnetic resonance (NMR) has proven to be a reliable method for studying zeolites. Solid-state NMR spectroscopy allows for the quantification of both Lewis and Brønsted acidity in zeolite catalysts and, nowadays, 27Al and 29Si magic angle spinning NMR spectroscopy has become firmly established in the set of approved methods for characterizing zeolites. The use of probe molecules opens up the possibility for the indirect measurement of the characteristics of acid sites. NMR relaxation is less common, although it is especially informative and enlightening for studying the mobility of guest molecules in the porous matrix. Moreover, the NMR relaxation of guest molecules and NMR cryoporometry can quantify pore size distribution on a broader scale (compared to traditional methods), which is especially important for systems with complex pore organization. Over the last few years, there has been a growing interest in the use of 2D NMR relaxation techniques to probe porous catalysts, such as 2D T1-T2 correlation to study the acidity of the surface of catalysts and 2D T2-T2 exchange to study pore connectivity. This contribution provides a comprehensive review of various NMR relaxation techniques for studying porous media and recent results of their applications in probing micro- and mesoporous zeolites, mainly focused on the mobility of adsorbed molecules, the acidity of the zeolite surface and the pore size distribution and connectivity of zeolites with hierarchical porosity.

Nature-Inspired N, O Co-Coordinated Manganese Single-Atom Catalyst for Efficient Hydrogen Peroxide Electrosynthesis.

The two-electron oxygen reduction reaction (2e- ORR) is a pivotal pathway for the distributed production of hydrogen peroxide (H2O2). In nature, enzymes containing manganese (Mn) centers can convert reactive oxygen species into H2O2. However, Mn-based heterogeneous catalysts for 2e- ORR are scarcely reported. Herein, we developed a nature-inspired single-atom electrocatalyst comprising N, O co-coordinated Mn sites, utilizing carbon dots as the modulation platform (Mn CD/C). As-synthesized Mn CD/C exhibited exceptional 2e- ORR activity with an onset potential of 0.786 V and a maximum H2O2 selectivity of 95.8 %. Impressively, Mn CD/C continuously produced 0.1 M H2O2 solution at 200 mA/cm2 for 50 h in the flow cell, with negligible loss in activity and H2O2 faradaic efficiency, demonstrating practical application potential. The enhanced activity was attributed to the incorporation of Mn atomic sites into the carbon dots. Theoretical calculations revealed that the N, O co-coordinated structure, combined with abundant oxygen-containing functional groups on the carbon dots, optimized the binding strength of intermediate *OOH at the Mn sites to the apex of the catalytic activity volcano. This work illustrates that carbon dots can serve as a versatile platform for modulating the microenvironment of single-atom catalysts and for the rational design of nature-inspired catalysts.

Efficient Hydrodeoxygenation of Lignin-Derived Phenolic Compounds Over Ru-Based Catalyst with Biochar and Al2O3 as Composite Support.

Hydrodeoxygenation (HDO) is a common strategy for upgrading lignin-derived phenolic compounds into high-quality liquid fuels, and the support rational design of HDO catalysts is critical to achieve a good reaction performance. This work proposed a novel Ru-based catalyst with biochar and Al2O3 as composite support. The addition of biochar can enlarge the porous structure, and the addition of Al2O3 can enhance the acid property of the support. By regulating the content of biochar and Al2O3 components, Ru/CA-2 catalyst achieved the best HDO performance of lignin-derived phenolic compounds, with the optimal component balance of 50 %C and 50 %Al2O3. This catalyst possesses the high Ru metal dispersion (1.38 nm particle size) to activate the hydrogen source, the moderate acid property to suppress carbon deposition and the abundant oxygen vacancy to promote substrate adsorption at the same time. 99.9 % conversion of guaiacol is obtained at 230 °C, with 99.9 % selectivity towards cyclohexane. Ru/CA-2 catalyst also has a good recyclability, with no obvious activity loss after five runs. Furthermore, in the application of catalytic lignin-oil HDO, the content of hydrocarbons increase from 10.7 % to 95.7 %, showing great potential on the industrial usage.

High‐Throughput Screening of Dual‐Atom Catalysts for Methane Combustion: A Combined Density Functional Theory and Machine‐Learning Study

AbstractCeria‐supported precious metal catalysts have undergone extensive investigation for the catalytic methane combustion. However, it remains a significant challenge to achieve both highly synergistic oxidation activity and efficient atom utilization remains a challenge for commonly used supported nanoparticles and single‐atom catalysts. Dual‐atom catalysts (DACs) emerges as a frontier of advanced catalysts, presenting unique catalytic properties that benefit from the synergy of neighboring metal sites. In this study, 361 ceria‐supported DACs (M1M2/CeO2) encompassing combinations of 19 transition metals are systematically explored. Using high‐throughput density functional theory calculations, the structures, stability as well as activity of M1M2/CeO2 are assessed. Notably, Au1Ga1/CeO2 is identified as a promising DAC exhibiting high activity for methane total oxidation, substantiated by comprehensive DFT‐calculated reaction pathways. Furthermore, employing six machine‐learning algorithms, the structure‐properties relationship is explored within ceria‐based DACs and highlight the importance of oxidation states and atomic radii of doped metals as the descriptors. The trained model by computational dataset exhibits high accuracy and predict a more active Mn1Au1/CeO2 than those screened using only DFT datasets. The high‐throughput strategy demonstrated in this work not only provides insights into the rational design of methane oxidation catalysts, but also paves the way for exploring DACs for diverse applications.

Regulating the Microenvironment of Zn‐Based Metal‐Organic Framework for Enhanced CO2 Electroreduction to Formate

Electrocatalytic CO2 reduction (ECR) has emerged as one of the most promising strategies to alleviate the energy crisis and CO2 pollution, for which a wide variety of catalysts are under development. Metal‐organic frameworks (MOFs) with clear and designable structures are an excellent platform for ECR. Here, two isostructural N, O‐coordinated Zn‐MOFs, FJU‐126‐4F and FJU‐126‐CH3, based on terephthalic acid ligand with different groups (one is ‐4F, the other is ‐CH3) on the benzene ring, have been constructed for ECR catalysts. Significantly, the different functional groups make the performance difference of ECR. The maximum Faraday efficiency of formate (FEformate) for FJU‐126‐4F is 60.5% with the partial current density of formate (jformate) of ‐19.35 mA cm‐2 at ‐1.47 V, while the optimum FEformate of FJU‐126‐CH3 is 50.2% with the jformate of ‐10.04 mA cm‐2 at ‐1.57 V. The work provides insight into the rational design of MOF catalysts for ECR.

Nanoscale Identification of Local Strain Effect on TMD Catalysis.

Strain engineering plays a crucial role in activating the basal plane of the TMD catalysts. However, experimental evidence linking strain strength to activity and distinguishing effects of compressive and tensile strain remains elusive due to the absence of high-resolution in situ correlation techniques. Here, we utilize nanobubble imaging by on-chip total-internal reflection microscopy to visualize active sites on the basal plane of strained MoS2 during hydrogen evolution reaction and atomic force microscopy to correlatively capture the nanoscale morphology and strain maps. By integrating the activity, morphology, and strain maps into comprehensive statistical analyses, we elucidate the strain effect on local activity at both multiprotrusion and (sub)single-protrusion levels. Our findings demonstrate that strain effectively activates sulfur vacancies on the basal plane, with tensile strain significantly enhancing local activity compared to compressive strain. Furthermore, we observe a time-dependent propagation of activity from high-activity to low-activity regions within single protrusions. This work clarifies the interplay between structural morphology and catalytic activity and provides new guidelines for the rational design of optimal TMD catalysts.

Reductive Coupling of N-Heteroarenes and 1,2-Dicarbonyls for Direct Access to γ-Amino Acids, Esters, and Ketones Using a Heterogeneous Single-Atom Iridium Catalyst.

Despite their significant importance, the challenges in direct and diverse synthesis of N-heterocyclic γ-amino acids/esters/ketones hamper exploration of their applications. Herein, by developing a multifunctional heterogeneous iridium single-atom catalyst composed of silica-confined iridium species and a boron-doped ZrO2 support (Ir-SAs@B-ZrO2/SiO2), we describe its utility in establishing a new reductive coupling reaction of N-heteroarenes and 1,2-dicarbonyls for selective and diverse construction of the as-described compounds in a straightforward manner. The striking features, including good substrate and functionality tolerance, high step and atom economy, exceptional catalyst reusability, and diversified product post-transformations, highlight the practicality of the developed chemistry. Mechanistic studies reveal that the synergy between the active Ir sites and acidic support favors a chemoselective reduction of the more inert N-heteroarenes and affords requisite enamine intermediates. In this work, the concept on precise transformation of reductive intermediates will open a door to further develop useful tandem reactions by rational catalyst design.

Rational Design of Diatomic Active Sites for Elucidating Oxygen Evolution Reaction Performance Trends.

Diatomic catalysts, especially those with heteronuclear active sites, have recently attracted significant attention for their advantages over single-atom catalysts in reactions with relatively high energy barrier, e.g. oxygen evolution reaction. Rational design and synthesis of heteronuclear diatomic catalysts are of immense significance but have so far been plagued by the lack of a definitive correlation between structure and catalytic properties. Here, we report macrocyclic precursor constrained strategy to fabricate series of transition metal (MT, Ni, Co, Fe, Mn, or Cu)-noble (MN, Ir or Ru) centers in carbon material. One notable performance trend is observed in the order of Cu-MN<Mn-MN<Fe-MN<MN<Co-MN<Ni-MN. Meanwhile, the pathway has been not altered, still following the traditional adsorption reaction mechanism. The effect of the MT atoms on the performances could possibly originate from the distinct adsorption/desorption behaviors of key intermediates (i.e. *OH, *O and/or *OOH), strongly implying that ΔG*OOH-ΔG*OH could be used as the performance descriptor. We believe that our work provides useful strategy for synthesis of diatomic active sites with sole coordination configuration and varied composition, and in-depth insight to their catalytic mechanism, which could be used for further optimization of diatomic catalysts towards oxygen electrocatalysis.

Rational Design of Diatomic Active Sites for Elucidating Oxygen Evolution Reaction Performance Trends

AbstractDiatomic catalysts, especially those with heteronuclear active sites, have recently attracted significant attention for their advantages over single‐atom catalysts in reactions with relatively high energy barrier, e.g. oxygen evolution reaction. Rational design and synthesis of heteronuclear diatomic catalysts are of immense significance but have so far been plagued by the lack of a definitive correlation between structure and catalytic properties. Here, we report macrocyclic precursor constrained strategy to fabricate series of transition metal (MT, Ni, Co, Fe, Mn, or Cu)‐noble (MN, Ir or Ru) centers in carbon material. One notable performance trend is observed in the order of Cu−MN&lt;Mn−MN&lt;Fe−MN&lt;MN&lt;Co−MN&lt;Ni−MN. Meanwhile, the pathway has been not altered, still following the traditional adsorption reaction mechanism. The effect of the MT atoms on the performances could possibly originate from the distinct adsorption/desorption behaviors of key intermediates (i.e. *OH, *O and/or *OOH), strongly implying that ΔG*OOH–ΔG*OH could be used as the performance descriptor. We believe that our work provides useful strategy for synthesis of diatomic active sites with sole coordination configuration and varied composition, and in‐depth insight to their catalytic mechanism, which could be used for further optimization of diatomic catalysts towards oxygen electrocatalysis.

Fluorine-regulated Cu catalyst boosts electrochemical reduction of CO2 towards ethylene production

Electrochemical reduction of carbon dioxide (CO2RR) into value-added multi-carbon (C2) products utilizing renewable energy is a promising way to reduce carbon emission and achieve carbon neutrality. However, rational design of catalysts towards high C2 products selectivity remains a formidable task. Herein, fluorine modified copper catalyst was synthesised by thermal anneal in the presence of ammonium fluoride and sequential annealing in argon atmosphere. The charge distribution and coordination environment on copper surface were adjusted by doped fluorine atoms, which enables the formation of key intermediates and their sequential evolution into ethylene. The catalyst achieves a remarkable Faradaic efficiency (FE) of 40.6 % for eCO2RR to ethylene and remains stable over 13 h. Density functional theory calculations indicates that the excellent CO2RR performance can be attributed to the suppressed hydrogen evolution on fluorine-doped copper catalyst. Our work brings a potential modification strategy of Cu-based catalyst for electrolytic CO2-to-C2 pathway.

Progressive Fabrication of a Pt‐Based High‐Entropy‐Alloy Catalyst toward Highly Efficient Propane Dehydrogenation

High‐entropy alloys (HEAs) have emerged as burgeoning heterogeneous catalysts due to their vast material space, unique structure, and superior stability. However, the dominant trial‐and‐error approaches hamper the exploration of efficient catalysts, necessitating the development of rational design strategies. Here, we report a progressive approach to the design and fabrication of HEA catalysts guided by alloying effects toward propane dehydrogenation. Cu, Sn, Au, and Pd are selected and demonstrated to induce dilution, encapsulation, surface enrichment, and inhomogeneity effects on Pt. The fabricated HEA, PtCuSnAuPd/SiO2, exhibits excellent activity, selectivity, and stability. The propylene formation rates reach 256 and 390 molC3H6 gPt−1 h−1 at 550 and 600 °C, respectively. Systematic characterizations reveal that the random elemental mixing, structural stability, and high Pt exposure promote the exposure of abundant stable isolated Pt sites. This work comprehensively explores the rational design and fabrication of HEA catalysts from a unique perspective, offering opportunities for developing advanced catalysts.

Progressive Fabrication of a Pt-Based High-Entropy-Alloy Catalyst toward Highly Efficient Propane Dehydrogenation.

High-entropy alloys (HEAs) have emerged as burgeoning heterogeneous catalysts due to their vast material space, unique structure, and superior stability. However, the dominant trial-and-error approaches hamper the exploration of efficient catalysts, necessitating the development of rational design strategies. Here, we report a progressive approach to the design and fabrication of HEA catalysts guided by alloying effects toward propane dehydrogenation. Cu, Sn, Au, and Pd are selected and demonstrated to induce dilution, encapsulation, surface enrichment, and inhomogeneity effects on Pt. The fabricated HEA, PtCuSnAuPd/SiO2, exhibits excellent activity, selectivity, and stability. The propylene formation rates reach 256 and 390 molC3H6 gPt-1 h-1 at 550 and 600 °C, respectively. Systematic characterizations reveal that the random elemental mixing, structural stability, and high Pt exposure promote the exposure of abundant stable isolated Pt sites. This work comprehensively explores the rational design and fabrication of HEA catalysts from a unique perspective, offering opportunities for developing advanced catalysts.

Water-promoted oxidative coupling of aromatics with subnanometer palladium clusters confined in zeolites

A fundamental understanding of the active sites in working catalysts can guide the rational design of new catalysts with improved performances. In this work, we have followed the evolution of homogeneous and heterogeneous Pd catalysts under the reaction conditions for aerobic oxidative coupling of toluene for the production of 4,4′-bitolyl. We have found that subnanometer Pd clusters made with a few Pd atoms are the working active sites in both homogeneous and heterogeneous catalytic systems. Moreover, water can promote the activity of Pd clusters by nearly one-order magnitude for oxidative coupling reaction by facilitating the activation of O2. These new insights lead to the preparation of a catalyst made with Pd clusters supported on a two-dimensional zeolite, which expands the scope of the oxidative coupling of aromatics to larger substrates.