Isolating Single and Few Atoms for Enhanced Catalysis

Atomically dispersed metal catalysts have triggered great interest in the field of catalysis owing to their unique features. Isolated single or few metal atoms can be anchored on substrates via chemical bonding or space confinement to maximize atom utilization efficiency. The key challenge lies in precisely regulating the geometric and electronic structure of the active metal centers, thus significantly influencing the catalytic properties. Although several reviews have been published on the preparation, characterization, and application of single-atom catalysts (SACs), the comprehensive understanding of SACs, dual-atom catalysts (DACs), and atomic clusters has never been systematically summarized. Here, recent advances in the engineering of local environments of state-of-the-art SACs, DACs, and atomic clusters for enhanced catalytic performance are highlighted. Firstly, various synthesis approaches for SACs, DACs, and atomic clusters are presented. Then, special attention is focused on the elucidation of local environments in terms of electronic state and coordination structure. Furthermore, a comprehensive summary of isolated single and few atoms for the applications of thermocatalysis, electrocatalysis, and photocatalysis is provided. Finally, the potential challenges and future opportunities in this emerging field are presented. This review will pave the way to regulate the microenvironment of the active site for boosting catalytic processes.

Intermetallic Copper-Based Electride Catalyst with High Activity for C-H Oxidation and Cycloaddition of CO2 into Epoxides

Inorganic electrides have been proved to be efficient hosts for incorporating transition metals, which can effectively act as active sites giving an outstanding catalytic performance. Here, it is demonstrated that a reusable and recyclable (for more than 7 times) copper-based intermetallic electride catalyst (LaCu0.67 Si1.33 ), in which the Cu sites activated by anionic electrons with low-work function are uniformly dispersed in the lattice framework, shows vast potential for the selective C-H oxidation of industrially important hydrocarbons and cycloaddition of CO2 with epoxide. This leads to the production of value-added cyclic carbonates under mild reaction conditions. Importantly, the LaCu0.67 Si1.33 catalyst enables much higher turnover frequencies for the C-H oxidation (up to 25 276 h-1 ) and cycloaddition of CO2 into epoxide (up to 800 000 h-1 ), thus exceeding most nonnoble as well as noble metal catalysts. Density functional theory investigations have revealed that the LaCu0.67 Si1.33 catalyst is involved in the conversion of N-hydroxyphthalimide (NHPI) into the phthalimido-N-oxyl (PINO), which then triggers selective abstraction of an H atom from ethylbenzene for the generation of a radical susceptible to further oxygenation in the presence of O2 .

In Situ Engineering of the Cu+/Cu0 Interface to Boost C2+ Selectivity in CO2 Electroreduction

The Cu⁺/Cu⁰ interface in the Cu-based electrocatalyst is essential to promote the electrochemical reduction of carbon dioxide (ERCO₂) to produce multi-carbon hydrocarbons and alcohols with high selectivity. However, due to the high activity of the Cu⁺/Cu⁰ interface, it is easy to be oxidized in the air. How to control and prepare a Cu-based electrocatalyst with an abundant and stable Cu⁺/Cu⁰ interface in situ is a huge challenge. Here, combined with density functional theory (DFT) calculations and experimental studies, we found that the trace halide ions adsorbed on Cu₂O can slow the reduction kinetics of Cu⁺ → Cu⁰, which allowed us to in-situ well control the synthesis of the CuO-derived electrocatalyst with rich Cu⁺/Cu⁰ interfaces. Our Cu catalyst with a rich Cu⁺/Cu⁰ interface exhibits excellent ERCO₂ performance. Under the operation potential of -0.98 V versus RHE, the Faraday efficiency of C₂H₄ and C₂₊ products are 55.8 and 75.7%, respectively, which is about 16% higher than that of CuO-derived electrocatalysts that do not use halide ions. The high FEC2+ comes from the improvement of the coupling efficiency of reaction intermediates such as CO-CO, which is proved by DFT calculations, and the suppression of hydrogen evolution reaction. Therefore, we provide an in-situ engineering strategy, which is simple and effective for the design and preparation of high-performance ERCO₂ catalysts.

Stabilizing Oxide Nanolayer via Interface Confinement and Surface Hydroxylation

Surface hydroxylation over oxide catalysts often occurs in many catalytic processes involving H₂ and H₂O, which is considered to play an important role in elementary steps of the reactions. Here, monolayer CoO and CoOH_x nanoislands on Pt(111) are used as inverse model catalysts to study the effect of surface hydroxylation on the stability of Co oxide overlayers in O₂. Surface science experiments indicate that hydroxyl groups formed on CoO nanoislands produced by deuterium-spillover can enhance oxidation resistance of the Co oxide nanostructures. Theoretical calculation shows that the interfacial adhesion between CoO and Pt is linearly strengthened with the increasing hydroxylation degree of CoO surface. Thus, the interface confinement effect between CoO and Pt can be enhanced by the surface hydroxylation due to the more reduced Co ions and stronger Co-Pt bonding at the CoOH_x/Pt interface.

Modulating the Electronic Metal-Support Interactions in Single-Atom Pt1 -CuO Catalyst for Boosting Acetone Oxidation

The development of highly active single-atom catalysts (SACs) and identifying their intrinsic active sites in oxidizing industrial hazardous hydrocarbons are challenging prospects. Tuning the electronic metal-support interactions (EMSIs) is valid for modulating the catalytic performance of SACs. We propose that the modulation of the EMSIs in a Pt₁ -CuO SAC significantly promotes the activity of the catalyst in acetone oxidation. The EMSIs promote charge redistribution through the unified Pt-O-Cu moieties, which modulates the d-band structure of atomic Pt sites, and strengthens the adsorption and activation of reactants. The positively charged Pt atoms are superior for activating acetone at low temperatures, and the stretched Cu-O bonds facilitate the activation of lattice oxygen atoms to participate in subsequent oxidation. We believe that this work will guide researchers to engineer efficient SACs for application in hydrocarbon oxidation reactions.

Promotional Effect of H2 Pretreatment on the CO PROX Performance of Pt1/Co3O4: A First-Principles-Based Microkinetic Analysis

Atomic Pt studded on cobalt oxide is a promising catalyst for CO preferential oxidation (PROX) dependent on its surface treatment. In this work, the CO PROX reaction mechanism on Co₃O₄ supported single Pt atom is investigated by a comprehensive first-principles based microkinetic analysis. It is found that as synthesized Pt₁/Co₃O₄ interface is poisoned by CO in a wide low temperature window, leading to its low reactivity. The CO poisoning effect can be effectively mitigated by a H₂ prereduction treatment, that exposes Co ∼ Co dimer sites for a noncompetitive Langmuir-Hinshelhood mechanism. In addition, surface H atoms assist O₂ dissociation via "twisting" mechanism, avoiding the high barriers associated with direct O₂ dissociation path. Microkinetic analysis reveals that the promotion of H-assisted pathway on H₂ treated sample helps improve the activity and selectivity at low temperatures.

Optimizing the synergy between alloy and alloy-oxide interface for CO oxidation in bimetallic catalysts

Creating synergetic metal-oxide interfaces is a promising strategy to promote the catalytic performance of heterogeneous catalysts. However, this strategy has been mainly applied to monometallic catalysts, while scarcely applied to alloy catalysts. In this work, we present a comprehensive study on the synergetic alloy-oxide interfaces in the bimetallic Pt-Co/Al₂O₃ catalysts for CO oxidation. A series of Pt₁Co_x/Al₂O₃ catalysts with various Co/Pt molar ratios with x ranging from 0.5 to 3.8 was synthesized via a facile wet-chemistry strategy. Among them, the Pt₁Co_0.5/Al₂O₃ catalyst exhibits the best catalytic performance for CO oxidation, with the lowest CO complete conversion temperature of -10 °C and the highest mass specific rate of 2.61 (mol CO) h^-1 (g Pt)^-1. From in situ X-ray absorption fine structure and diffuse reflectance infrared Fourier-transform spectroscopy studies, the superior catalytic performance of Pt₁Co_0.5/Al₂O₃ originates from the optimal length of the three-dimensional alloy-oxide perimeter sites. We further extended this strategy to other bimetallic systems of Pt-Fe and Pt-Ni, which also show similar structural properties and remarkable promotional effects on the catalytic activity.

Electronic metal-support interaction constructed for preparing sinter-resistant nano-platinum catalyst with redox property

Generally, support materials with particular structural properties could effectively anchor metal nanoparticles and provide lower activation barriers in heterogeneous catalysis. To tailor the structure of stable iron oxide, NiFe₂O₄ of inverse spinel structure was obtained by combining nickel with iron element under an alkaline environment and high-temperature calcination. The p-type conductivity of NiFe₂O₄ provides the possibility of constructing electronic interfacial interaction with Pt nanoparticles by electron transfer. The constructed metal-support interaction could effectively stabilize Pt nanoparticles and be further enhanced during long-term harsh calcination (700 °C for 48 h) even under an O₂ atmosphere. Meanwhile, the abundant structural defects of NiFe₂O₄ are beneficial for constructing low-temperature redox centers with the aid of Pt nanoparticles. Pt/NiFe₂O₄ exhibited not only excellent activity in room-temperature oxidation (CO and HCHO) and reduction reactions (chemo-selective hydrogenation of nitroarenes), but also high stability even after storage for more than 6 months. A self-adjusting mechanism triggered by structural defects is disclosed by in situ characterization and systematic reaction results. This work demonstrates an alternative concept to construct sinter-resistant and highly-effective nano-platinum catalysts robust for oxidation and reduction reactions.

Enhanced Performance of Supported Ternary Metal Catalysts for the Oxidation of Toluene in the Presence of Trichloroethylene

Chlorinated volatile organic compounds (CVOCs), even in small quantities, can cause Pt-based catalyst poisoning. Improving the low-temperature chlorine resistance of catalysts is of vital importance for industrial application, although it remains challenging. Considering actual industrial production, a TiO2-supported ternary metal catalyst was prepared in this work to study the catalytic oxidation of multicomponent VOCs (toluene and trichloroethylene (TCE)). Among all of the samples, PtWRu/TiO2 and PtWCr/TiO2 exhibited the best catalytic performance for toluene oxidation. In the mixed VOC oxidation, the PtWCr/TiO2 sample showed the best catalytic activity for toluene combustion (a toluene conversion of 90% was achieved at 258 °C and a space velocity of 40,000 mL g−1 h−1, and the specific reaction rate and turnover frequency at 215 °C were 44.9 × 10−6 mol gPt−1 s−1 and 26.2 × 10−5 s−1). The PtWRu/TiO2 sample showed the best catalytic activity for TCE combustion (a TCE conversion of 90% was achieved at 305 °C and a space velocity of 40,000 mL g−1 h−1, and the specific reaction rate and turnover frequency at 270 °C were 9.0 × 10−6 mol gPt−1 s−1 and 7.3 × 10–5 s−1). We concluded that the ternary metal catalysts could greatly improve chlorine desorption by increasing the active lattice oxygen mobility and surface acidity, thus reducing chlorinated byproducts and other serious environmental pollutants. This work may serve as a reasonable design reference for solving more practical industrial production emissions of multicomponent VOCs.

Atomic overlayer of permeable microporous cuprous oxide on palladium promotes hydrogenation catalysis

The interfacial sites of metal-support interface have been considered to be limited to the atomic region of metal/support perimeter, despite their high importance in catalysis. By using single-crystal surface and nanocrystal as model catalysts, we now demonstrate that the overgrowth of atomic-thick Cu2O on metal readily creates a two-dimensional (2D) microporous interface with Pd to enhance the hydrogenation catalysis. With the hydrogenation confined within the 2D Cu2O/Pd interface, the catalyst exhibits outstanding activity and selectivity in the semi-hydrogenation of alkynes. Alloying Cu(0) with Pd under the overlayer is the major contributor to the enhanced activity due to the electronic modulation to weaken the H adsorption. Moreover, the boundary or defective sites on the Cu2O overlayer can be passivated by terminal alkynes, reinforcing the chemical stability of Cu2O and thus the catalytic stability toward hydrogenation. The deep understanding allows us to extend the interfacial sites far beyond the metal/support perimeter and provide new vectors for catalyst optimization through 2D interface interaction.

Crystal Facet-Manipulated 2D Pt Nanodendrites to Achieve an Intimate Heterointerface for Hydrogen Evolution Reactions

Despite the Pt-catalyzed alkaline hydrogen evolution reaction (HER) progressing via oxophilic metal-hydroxide surface hybridization, maximizing Pt reactivity alongside operational stability is still unsatisfactory due to the lack of well-designed and optimized interface structures. Producing atomically flat two-dimensional Pt nanodendrites (2D-PtNDs) through our 2D nanospace-confined synthesis strategy, this study tackles the insufficient interfacial contact effect during HER catalysis by realizing an area-maximized and firmly bound lateral heterointerface with NiFe-layered double hydroxide (LDH). The well-oriented {110} crystal surface exposure of Pt promotes electronic interplay that bestows strong LDH binding. The charge-relocated interfacial bond in 2D-PtND/LDH accelerates the hydrogen generation steps and achieves nearly the highest reported Pt mass activity enhancement (∼11.2 times greater than 20 wt % Pt/C) and significantly improved long-term operational stability. This work uncovers the importance of the shape and facet of Pt to create heterointerfaces that provide catalytic synergy for efficient hydrogen production.

Achieving acetone efficient deep decomposition by strengthening reactants adsorption and activation over difunctional Au(OH)Kx/hierarchical MFI catalyst

Realizing the simultaneous adsorption and activation of O₂ and reactants over supported noble metal catalysts is crucial for the oxidation of organic hydrocarbons. Herein, we report a facile one-step ethylene glycol reduction method to synthesize difunctional Au(OH)K_x sites, which were anchored on a hierarchical hollow MFI support and adopted for acetone decomposition. The alkali ion-associated adjacent surface hydroxyl groups were coordinated with Au nanoparticles, resulting in partially oxidized Au¹⁺ sites with improved dispersion. The results obtained from exclusive ex situ and in situ experiments illustrated that the proper content of K and hydroxyl groups significantly enhanced the adsorption of surface O₂ and acetone molecules around the Au sites simultaneously, whereas the excess K species inhibited the catalytic performance by blocking the pore structure and decreasing the acidity of catalysts. The Au(OH)K_0.7/h-MFI catalyst exhibited the highest efficiency for acetone oxidation, over which 1500 ppm acetone can be completely oxidized at just 280 °C with an extremely low activation energy of 32.5 kJ mol^-1. The carbonate species were detected as the main intermediates during acetone decomposition over the difunctional Au(OH)K_x sites through a Langmuir - Hinshelwood (L - H) mechanism. This finding paves the way for designing and constructing efficient functional active sites for the complete oxidation of hydrocarbons.

Efficient iron single-atom catalysts for selective ammoxidation of alcohols to nitriles

Zeolitic imidazolate frameworks derived Fe₁-N-C catalysts with isolated single iron atoms have been synthesized and applied for selective ammoxidation reactions. For the preparation of the different Fe-based materials, benzylamine as an additive proved to be essential to tune the morphology and size of ZIFs resulting in uniform and smaller particles, which allow stable atomically dispersed Fe-N₄ active sites. The optimal catalyst Fe₁-N-C achieves an efficient synthesis of various aryl, heterocyclic, allylic, and aliphatic nitriles from alcohols in water under very mild conditions. With its chemoselectivity, recyclability, high efficiency under mild conditions this new system complements the toolbox of catalysts for nitrile synthesis, which are important intermediates with many applications in life sciences and industry.

Dynamic Pt-OH-·H2O-Ag species mediate coupled electron and proton transfer for catalytic hydride reduction of 4-nitrophenol at the confined nanoscale interface

Generally, the catalytic transformation of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) at heterogeneous metal surfaces follows a Langmuir-Hinshelwood (L-H) mechanism when sodium borohydride (NaBH₄) is used as the sacrificial reductant. Herein, with Pt-Ag bimetallic nanoparticles confined in dendritic mesoporous silica nanospheres (DMSNs) as a model catalyst, we demonstrated that the conversion of 4-NP did not pass through the direct hydrogen transfer route with the hydride equivalents being supplied by borohydride via the bimolecular L-H mechanism, since Fourier transform infrared (FTIR) spectroscopy with the use of isotopically labeled reactants (NaBD₄ and D₂O) showed that the final product of 4-AP was composed of protons (or deuterons) that originated from the solvent water (or heavy water). Combined characterization by X-ray photoelectron spectroscopy (XPS), ¹H nuclear magnetic resonance (NMR) and the optical excitation and photoluminescence spectrum evidenced that the surface hydrous hydroxide complex bound to the metal surface (also called structural water molecules, SWs), due to the space overlap of p orbitals of two O atoms in SWs, could form an ensemble of dynamic interface transient states, which provided the alternative electron and proton transfer channels for selective transformation of 4-NP. The cationic Pt species in the Ag-Pt bimetallic catalyst mainly acts as a dynamic adsorption center to temporally anchor SWs and related reactants, and not as the active site for hydrogen activation.

Adjusting grain boundary within NiCo2O4rod arrays by phosphating reaction for efficient hydrogen production

In this work, the density and electronic structures of the metal active sites in NiCo₂O₄nanorod arrays were concurrently tuned by controlling the sample's exposure time in a phosphorization process. The results showed that both the density and electronic structure of the active adsorption sites played a key role towards the catalytic activity for water splitting to produce hydrogen. The optimal catalyst exhibited 81 mV overpotential for hydrogen evolution reaction (HER) at 10 mA cm^-2and 313 mV overpotential towards oxygen evolution reaction at 50 mA cm^-2. The assembled electrode delivered a current density of 50 mA cm^-2at 1.694 V in a fully functional water electrolyzer. The further results of theoretical density functional theory calculations revealed the doping of P elements lowered down the H adsorption energies involved in the water splitting process on the various active sites of P-NiCo₂O₄-10 catalyst, and thus enhanced its HER catalytic activities.

Generation of local redox potential from confined nano-bimetals in porous metal silicate materials for high-performance catalysis

Confining nano-bimetals in porous metal silicate materials could improve the stabiliy and facilitate electron and charge transfer in catalysis, demonstrating great potential to replace noble metal-based catalysts for industrial applications.

New insights into the influence mechanism of H2O and SO2 on Pt-W/Ti catalysts for CO oxidation

A series of anatase TiO2 loaded with 0.1 wt.% Pt and n% WO3 (0.1Pt-nW/Ti-A, n=0, 1, 2, 5, 10) were prepared using the step-impregnation method. Among the catalysts, 0.1Pt-5W/Ti-A showed...

Chemical Insights into Interfacial Effects in Inorganic Nanomaterials

The interfaces between inorganic functional nanomaterials and their surface modifiers play important roles in determining their chemical and physical properties. In numerous situations, interfaces created by organic ligands or secondary inorganic components on inorganic nanomaterials induce significant effects to promote their performances. However, it still remains challenging to understand those interfacial effects at the molecular level. Herein, strategies via the design of model inorganic nanomaterials with well-defined and detectable interfaces to simplify the investigation of interfacial effects in inorganic nanomaterials are summarized. While atomically precise metal nanoclusters enable "seeing" how organic ligands are coordinated on metal surface to create nanoscale metal-organic interfaces, ultrathin low-dimensional nanomaterials modified with organic ligands make it possible to extract the metal-organic interface structure from the average signal to investigate how steric and electronic effects enhance catalysis. The molecular mechanisms of the interfacial effects in supported metal catalysts are disclosed by designing two unique structures of supported catalysts. The interfacial engineering approach will be further extended to optimize the performance and stability of perovskite solar cells. Finally, a perspective on the development of operando characterization techniques is provided to track the dynamic interfacial structures during catalysis.

Design of Hepatic Targeted Drug Delivery Systems for Natural Products: Insights into Nomenclature Revision of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD), recently renamed metabolic-dysfunction-associated fatty liver disease (MAFLD), affects a quarter of the worldwide population. Natural products have been extensively utilized in treating NAFLD because of their distinctive advantages over chemotherapeutic drugs, despite the fact that there are no approved drugs for therapy. Notably, the limitations of many natural products, such as poor water solubility, low bioavailability in vivo, low hepatic distribution, and lack of targeted effects, have severely restricted their clinical application. These issues could be resolved via hepatic targeted drug delivery systems (HTDDS) that boost clinical efficacy in treating NAFLD and decrease the adverse effects on other organs. Herein an overview of natural products comprising formulas, single medicinal plants, and their crude extracts has been presented to treat NAFLD. Also, the clinical efficacy and molecular mechanism of active monomer compounds against NAFLD are systematically discussed. The targeted delivery of natural products via HTDDS has been explored to provide a different nanotechnology-based NAFLD treatment strategy and to make suggestions for natural-product-based targeted nanocarrier design. Finally, the challenges and opportunities put forth by the nomenclature update of NAFLD are outlined along with insights into how to improve the NAFLD therapy and how to design more rigorous nanocarriers for the HTDDS. In brief, we summarize the up-to-date developments of the NAFLD-HTDDS based on natural products and provide viewpoints for the establishment of more stringent anti-NAFLD natural-product-targeted nanoformulations.

Recent progresses in the synthesis of MnO2 nanowire and its application in environmental catalysis

Nanostructured MnO2 with various morphologies exhibits excellent performance in environmental catalysis owing to its large specific surface area, low density, and adjustable chemical properties. The one-dimensional MnO2 nanowire has been proved to be the dominant morphology among various nanostructures, such as nanorods, nanofibers, nanoflowers, etc. The syntheses and applications of MnO2-based nanowires also have become a research hotspot in environmental catalytic materials over the last two decades. With the continuous deepening of the research, the control of morphology and crystal facet exposure in the synthesis of MnO2 nanowire materials have gradually matured, and the catalytic performance also has been greatly improved. Differences in the crystalline phase structure, preferably exposed crystal facets, and even the length of the MnO2 nanowires will evidently affect the final catalytic performances. Besides, the modifications by doping or loading will also significantly affect their catalytic performances. This review carefully summarizes the synthesis strategies of MnO2 nanowires developed in recent years as well as the influences of the phase structure, crystal facet, morphology, dopant, and loading amount on the catalytic performance. Besides, the cutting-edge applications of MnO2 nanowires in the field of environmental catalysis, such as CO oxidation, the removal of VOCs, denitrification, etc., have been also summarized. The application of MnO2 nanowire in environmental catalysis is still in the early exploratory stage. The gigantic gap between theoretical investigation and industrial application is still a great challenge. Compared with noble metal based traditional environmental catalytic materials, the lower cost of MnO2 has injected new momentum and promising potential into this research field.

A Hydrothermally Stable Single-Atom Catalyst of Pt Supported on High-Entropy Oxide/Al2O3: Structural Optimization and Enhanced Catalytic Activity

A catalyst with high-entropy oxide (HEO)-stabilized single-atom Pt can afford low-temperature activity for catalytic oxidation and remarkable durability even under harsh conditions. However, HEO is easy to harden during sintering, which results in a few defective sites for anchoring single-atom metals. Herein, we present a sol-gel-assisted mechanical milling strategy to achieve a single-atom catalyst of Pt-HEO/Al₂O₃. The strong interaction between HEO and Al₂O₃ effectively inhibits the growth of HEO microparticles, which leads to generation of more surface defects because of the nanoscale effect. Meanwhile, another strong interaction between Pt and HEO stabilizes single-atom Pt on HEO. Temperature-programmed techniques further verify that the reactivity of surface lattice oxygen species is enhanced because of the Pt-O-M bonds on the surface of HEO. Unlike conventional single-atom Pt catalysts, Pt-HEO/Al₂O₃ as a heterogeneous catalyst not only exhibits superior stability against hydrothermal aging but also presents long-term reaction stability for CO catalytic oxidation, which exceeds 540 h. The present work opens a new door for rational design of hydrothermally stable single-atom Pt catalysts, which are highly promising in practical applications.

Atomic origins of the strong metal-support interaction in silica supported catalysts

Silica supported metal catalysts are most widely used in the modern chemical industry because of the high stability and tunable reactivity. The strong metal–support interaction (SMSI), which has been widely observed in metal oxide supported catalysts and significantly affects the catalytic behavior, has been speculated to rarely happen in silica supported catalysts since silica is hard to reduce. Here we revealed at the atomic scale the interfacial reaction induced SMSI in silica supported Co and Pt catalysts under reductive conditions at high temperature using aberration-corrected environmental transmission electron microscopy coupled with in situ electron energy loss spectroscopy. In a Co/SiO₂ system, the amorphous SiO₂ migrated onto the Co surface to form a crystallized quartz-SiO₂ overlayer, and simultaneously an interlayer of Si was generated in-between. The metastable crystalline SiO₂ overlayer subsequently underwent an order-to-disorder transition due to the continuous dissociation of SiO₂ and the interfacial alloying of Si with the underlying Co. The SMSI in the Pt–SiO₂ system was found to remarkably boost the catalytic hydrogenation. These findings demonstrate the universality of the SMSI in oxide supported catalysts, which is of general importance for designing catalysts and understanding catalytic mechanisms.

This work tracked at the atomic scale the interfacial reaction induced strong metal–support interaction between SiO₂ and metal catalysts and evolution under reactive conditions by aberration-corrected environmental transmission electron microscopy.

In Situ Raman Observation of Oxygen Activation and Reaction at Platinum-Ceria Interfaces during CO Oxidation

Understanding the fundamental insights of oxygen activation and reaction at metal-oxide interfaces is of significant importance yet remains a major challenge due to the difficulty in in situ characterization of active oxygen species. Herein, the activation and reaction of molecular oxygen during CO oxidation at platinum-ceria interfaces has been in situ explored using surface-enhanced Raman spectroscopy (SERS) via a borrowing strategy, and different active oxygen species and their evolution during CO oxidation at platinum-ceria interfaces have been directly observed. In situ Raman spectroscopic evidence with isotopic exchange experiments demonstrate that oxygen is efficiently dissociated to chemisorbed O on Pt and lattice Ce-O species simultaneously at interfacial Ce³⁺ defect sites under CO oxidation, leading to a much higher activity at platinum-ceria interfaces compared to that at Pt alone. Further in situ time-resolved SERS studies and density functional theory simulations reveal a more efficient molecular pathway through the reaction between adsorbed CO and chemisorbed Pt-O species transferred from the interfaces. This work deepens the fundamental understandings on oxygen activation and CO oxidation at metal-oxide interfaces and offers a sensitive technique for the in situ characterization of oxygen species under working conditions.

Rational Design of Single-Atom Site Electrocatalysts: From Theoretical Understandings to Practical Applications

Atomically dispersed metal-based electrocatalysts have attracted increasing attention due to their nearly 100% atomic utilization and excellent catalytic performance. However, current fundamental comprehension and summaries to reveal the underlying relationship between single-atom site electrocatalysts (SACs) and corresponding catalytic application are rarely reported. Herein, the fundamental understandings and intrinsic mechanisms underlying SACs and corresponding electrocatalytic applications are systemically summarized. Different preparation strategies are presented to reveal the synthetic strategies with engineering the well-defined SACs on the basis of theoretical principle (size effect, metal-support interactions, electronic structure effect, and coordination environment effect). Then, an overview of the electrocatalytic applications is presented, including oxygen reduction reaction, hydrogen evolution reaction, oxygen evolution reaction, oxidation of small organic molecules, carbon dioxide reduction reaction, and nitrogen reduction reaction. The underlying structure-performance relationship between SACs and electrocatalytic reactions is also discussed in depth to expound the enhancement mechanisms. Finally, a summary is provided and a perspective supplied to demonstrate the current challenges and opportunities for rational designing, synthesizing, and modulating the advanced SACs toward electrocatalytic reactions.

Rational Design of Pt-Pd-Ni Trimetallic Nanocatalysts for Room-Temperature Benzaldehyde and Styrene Hydrogenation

Nanostructures of the multimetallic catalysts offer great scope for fine tuning of heterogeneous catalysis, but clear understanding of the surface chemistry and structures is important to enhance their selectivity and efficiency. Focussing on a typical Pt-Pd-Ni trimetallic system, we comparatively examined the Ni/C, Pt/Ni/C, Pd/Ni/C and Pt-Pd/Ni/C catalysts synthesized by impregnation and galvanic replacement reaction. To clarify surface chemical/structural effect, the Pt-Pd/Ni/C catalyst was thermally treated at X=200, 400 or 600 °C in a H₂ reducing atmosphere, respectively termed as Pt-Pd/Ni/C-X. The as-prepared catalysts were characterized complementarily by XRD, XPS, TEM, HRTEM, HS-LEIS and STEM-EDS elemental mapping and line-scanning. All the catalysts were comparatively evaluated for benzaldehyde and styrene hydrogenation. It is shown that the "PtPd alloy nanoclusters on Ni nanoparticles" (PtPd/Ni) and the synergistic effect of the trimetallic Pt-Pd-Ni, lead to much improved catalytic performance, compared with the mono- or bi- metallic counterparts. However, with the increase of the treatment temperature of the Pt-Pd/Ni/C, the catalytic performance was gradually degraded, which was likely due to that the favourable nanostructure of fine "PtPd/Ni" was gradually transformed to relatively large "PtPdNi alloy on Ni" (PtPdNi/Ni) particles, thus decreasing the number of noble metal (Pt and Pd) active sites on the surface of the catalyst. The optimum trimetallic structure is thus the as synthesised Pt-Pd/Ni/C. This work provides a novel strategy for the design and development of highly efficient and low-cost multimetallic catalysts, e. g. for hydrogenation reactions.

Efficient catalytic combustion of toluene at low temperature by tailoring surficial Pt0 and interfacial Pt-Al(OH)x species

Exploring highly efficient and low-cost supported Pt catalysts is attractive for the application of volatile organic compounds (VOCs) combustion. Herein, efficient catalytic combustion of toluene at low temperature over Pt/γ-Al₂O₃ catalysts has been demonstrated by tailoring active Pt species spatially. Pt/γ-Al₂O₃ catalyst with low Pt-content (0.26 wt%) containing both interfacial Pt-Al(OH)_x and surficial metallic Pt (Pt⁰) species exhibited super activity and water-resistant stability for toluene oxidation. The strong metal-support interaction located at the Al-OH-Pt interfaces elongated the Pt-O bond and contributed to the oxidation of toluene. Meanwhile, the OH group at the Al-OH-Pt interfaces had the strongest adsorption and activation capability for toluene and the derived intermediate species were subsequently oxidized by oxygen species activated by surficial Pt⁰ to yield carbon dioxide and water. This work initiated an inspiring sight to the design of active Pt species for the VOCs combustion.

Exsolution of Iron Oxide on LaFeO3 Perovskite: A Robust Heterostructured Support for Constructing Self-Adjustable Pt-Based Room-Temperature CO Oxidation Catalysts

Constructing highly active and stable surface sites for O₂ activation is essential to lower the barrier of Pt-based catalysts for CO oxidation. Although a few active Pt-metal oxide interfaces have been reported, questions about the stability of these sites under the long-term storage and operation remain unresolved. Here, based on developing a robust FeO_x/LaFeO₃ heterostructure as a support, we constructed stable Pt-support interfaces to achieve highly active CO oxidation at room temperature. Even after it is kept in the air for more than 6 months, the catalyst (without pretreatment) still maintains the high activity like a fresh one, which is superior to metal hydroxide-Pt interfaces, and meets the requirements of long-term storage for emergency use. In situ characterizations and systematic reaction results showed that CO oxidation occurs through an alternative mechanism, which is triggered by intrinsic reactants and self-adjusted to a more active interface in the reaction process. Theoretical calculations and ⁵⁷Fe Mössbauer spectra revealed that abundant cation vacancies significantly increase the activity of surface oxygen species and should be responsible for this unique process. This work demonstrates an alternative concept to fabricate robust and highly active Pt-based catalysts for catalytic oxidation.