Strong Metal–Support Interactions between Pt Single Atoms and TiO2

Strong metal–support interaction (SMSI) has gained great attention in the field of heterogeneous catalysis. However, whether single-atom catalysts can exhibit SMSI remains unknown. Here, we demonstrate that SMSI can occur on TiO₂-supported Pt single atoms but at a much higher reduction temperature than that for Pt nanoparticles (NPs). Pt single atoms involved in SMSI are not covered by the TiO₂ support nor do they sink into its subsurface. The suppression of CO adsorption on Pt single atoms stems from coordination saturation (18-electron rule) rather than the physical coverage of Pt atoms by the support. Based on the new finding it is revealed that single atoms are the true active sites in the hydrogenation of 3-nitrostyrene, while Pt NPs barely contribute to the activity since the NP sites are selectively encapsulated. The findings in this work provide a new approach to study the active sites by tuning SMSI.     

Strong Metal–Support Interactions between Pt Single Atoms and TiO2

Strong metal–support interaction (SMSI) has gained great attention in the field of heterogeneous catalysis. However, whether single‐atom catalysts can exhibit SMSI remains unknown. Here, we demonstrate that SMSI can occur on TiO₂‐supported Pt single atoms but at a much higher reduction temperature than that for Pt nanoparticles (NPs). Pt single atoms involved in SMSI are not covered by the TiO₂ support nor do they sink into its subsurface. The suppression of CO adsorption on Pt single atoms stems from coordination saturation (18‐electron rule) rather than the physical coverage of Pt atoms by the support. Based on the new finding it is revealed that single atoms are the true active sites in the hydrogenation of 3‐nitrostyrene, while Pt NPs barely contribute to the activity since the NP sites are selectively encapsulated. The findings in this work provide a new approach to study the active sites by tuning SMSI.     

Engineering Heterogeneous Catalysis with Strong Metal–Support Interactions: Characterization,Theory and Manipulation

Strong metal–support interactions (SMSI) represent a classic yet fast-growing area in catalysis research. The SMSI phenomenon results in the encapsulation and stabilization of metal nanoparticles (NPs) with the support material that significantly impacts the catalytic performance through regulation of the interfacial interactions. Engineering SMSI provides a promising approach to steer catalytic performance in various chemical processes, which serves as an effective tool to tackle energy and environmental challenges. Our Minireview covers characterization, theory, catalytic activity, dependence on the catalytic structure and inducing environment of SMSI phenomena. By providing an overview and outlook on the cutting-edge techniques in this multidisciplinary research field, we not only want to provide insights into the further exploitation of SMSI in catalysis, but we also hope to inspire rational designs and characterization in the broad field of material science and physical chemistry.     

通过g-C3N4担载MNi12 (Fe,Co, Cu,Zn)纳米团簇调节甲烷化

As a unique two-dimensional material, graphitic carbon nitride (g-C₃N₄) has received significant attention for its particular electronic structure and chemical performance. Its instinctive defect can provide a stable anchoring site for metals, potentially improving the surface reactivity. Ni-based catalysts are economical but their activity for CO₂ methanation is lower than that of noble metal catalysts. Ni nanoparticles (NPs) supported on a substrate can further enhance the stability and activity of catalysts. Based on the principles of strong metal-support interaction (SMSI) and the synergistic effect on an alloy, MNi₁₂/g-C₃N₄ composites as novel catalysts are expected to improve stability and catalytic performance of Ni-based catalysts. The configurations are established with core-shell structures of MNi₁₂ (M = Fe, Co, Cu, Zn) nanoparticles (NPs) supported on g-C₃N₄ in this work. In the CO₂ methanation reaction, the reactivity of CO on slab (E_CO) is a critical factor, which is relative to the catalytic activity. Thus, the catalytic reactivity of these complexes via CO adsorption were explored using density functional theory (DFT). The values of cohesive energy (E_coh) for MNi₁₂ NPs range from -39.90 eV to -34.82 eV, suggesting that the formation of these NPs is favored as per thermodynamics, and E_coh and partial density of state (PDOS) reveal that the central M atom with the less filled d-shell interacts more strongly with surface Ni atoms. Therefore, ZnNi₁₂ is the most unstable structure among all the studied alloy, and the synergistic effect is also the weakest among them. When MNi₁₂ NPs are supported on the g-C₃N₄ substrate, the binding energies (E_b) vary from -9.40 eV to -8.39 eV, indicating that g-C₃N₄ is indeed a good material for stabilizing these NPs. The PDOS analysis of pure g-C₃N₄ suggests the sp² dangling bonds of N atoms in g-C₃N₄ can stabilize these transition metal NPs. Furthermore, the results of CO adsorbed on MNi₁₂ NPs and MNi₁₂/g-C₃N₄ composites show that E_CO and d_CO reduced with the introduction of g-C₃N₄. According to the results of the analysis of the Hirshfeld charges and electrostatic potential (ESP), the reason is that CO obtains less electrons from MNi₁₂ NPs after deposition on the g-C₃N₄ substrate, which lowers the reactivity of CO on catalysts. Additionally, the deformation charge density is analyzed to investigate the interaction between the NPs and g-C₃N₄. With the introduction of g-C₃N₄, charge redistribution indicates the strong metal-support interaction, which further reduces the CO adsorption energy. In summary, MNi₁₂ supported on g-C₃N₄ exhibit not only high stability but also tunable reactivity in CO₂ methanation. These changes are beneficial for CO₂ methanation reaction.     

Strong Metal-Support Interactions through Sulfur-Anchoring of Metal Catalysts on Carbon Supports

In supported metal catalysts, the supports would strongly interact with the metal components instead of just acting as a carrier, which greatly affects both of their synthesis and catalytic activity, selectivity, and stability. Carbon is considered as very important but inert support and thus hard to induce strong metal-support interaction (SMSI). This mini-review highlights that sulfur—a documented poison reagent for metal catalysts—when doped in a carbon supports can induce diverse SMSI phenomenon, including electronic metal-support interaction (EMSI), classic SMSI, and reactive metal-support interaction (RMSI). These SMSI between metal and sulfur-doped carbon (S−C) supports enables the catalysts with extraordinary resistance to sintering at high temperatures of up to 1100 °C, which allows the general synthesis of single-atom, alloy cluster, and intermetallic compound catalysts with high dispersion and metal loading for a variety of applications.     

Ultrasonication-Induced Strong Metal-Support Interaction Construction in Water Towards Enhanced Catalysis

The development of facile methodologies to afford robust supported metal nanocatalysts under mild conditions is highly desirable yet challenging, particularly via strong metal-support interactions (SMSI) construction. State-of-the-art approaches capable of generating SMSI encapsulation mainly focus on high temperature annealing in reductive/oxidative atmosphere. Herein, ultra-stable metal nanocatalysts based on SMSI construction were produced by leveraging the instantaneous high-energy input from ultrasonication under ambient conditions in H₂O, which could rapidly afford abundant active intermediates, Ti³⁺ ions, and oxygen vacancies within the scaffolds to induce the SMSI overlayer formation. The encapsulation degree could be tuned and controlled via the reducibility of the solvents and the ultrasonication parameters. This facile and efficient approach could be further extended to diverse metal oxide supports and noble metal NPs leading to enhanced performance in hydrogenation reactions and CO₂ conversion.     

Stabilization of Palladium Nanoparticles on Nanodiamond–Graphene Core–Shell Supports for CO Oxidation

Nanodiamond–graphene core–shell materials have several unique properties compared with purely sp²‐bonded nanocarbons and perform remarkably well as metal‐free catalysts. In this work, we report that palladium nanoparticles supported on nanodiamond–graphene core–shell materials (Pd/ND@G) exhibit superior catalytic activity in CO oxidation compared to Pd NPs supported on an sp²‐bonded onion‐like carbon (Pd/OLC) material. Characterization revealed that the Pd NPs in Pd/ND@G have a special morphology with reduced crystallinity and are more stable towards sintering at high temperature than the Pd NPs in Pd/OLC. The electronic structure of Pd is changed in Pd/ND@G, resulting in weak CO chemisorption on the Pd NPs. Our work indicates that strong metal–support interactions can be achieved on a non‐reducible support, as exemplified for nanocarbon, by carefully tuning the surface structure of the support, thus providing a good example for designing a high‐performance nanostructured catalyst.     

Kinetics of toluene hydrogenation over platinum-titania catalysts in conditions of strong metal-support interaction

Toluene hydrogenation was investigated over different platinum-titania catalysts. It was found that the form of kinetic equation of the reaction does not depend on the modifications of titania (rutile, anatase) but the catalyst activity is different. The catalyst reduction at temperature higher than 300^oC leads to strong metal-support interaction (SMSI) which is manifested in a decrease of the reaction rate.     

三维有序大孔二氧化钛表面超细钯纳米颗粒的构筑及其增强柴油炭烟催化燃烧性能（英文）

柴油机排放颗粒物(主要成分是炭烟)是城市大气PM2.5中一次颗粒物的主要来源和二次颗粒物形成的重要组分,严重危害大气环境和人类健康.利用颗粒物捕集器与催化剂相结合的连续过滤再生技术是满足柴油车国VI炭烟颗粒物排放标准的最有效技术,目前该技术所面临的挑战是研发在排气温度的柴油炭烟颗粒物催化氧化催化剂.柴油炭烟催化燃烧反应的本质是典型的气(氧气)-固(炭烟颗粒)-固(催化剂)三相深度氧化反应,因此我们研究组提出了高活性柴油炭烟燃烧催化剂设计应该遵循优化固-固接触与强化活化分子氧能力二者相结合的研究思路.为满足此设计思路的要求,本课题组前期采用孔径大于200 nm的三维有序大孔(3DOM)结构氧化物作为载体,利用大孔效应来实现PM在催化剂内部的有效扩散,从而提高催化剂与PM的接触效率.采用具有强活化分子氧能力的负载型贵金属(Au,Pt)纳米颗粒或贵金属-氧化物复合纳米颗粒作为活性位来提高催化剂对分子氧的活化能力,进而设计了多个系列高活性催化剂,并形成了担载贵金属纳米颗粒的可控制备方法与装置.然而,Au和Pt昂贵的价格限制了其广泛应用.价格相对便宜的Pd具有与Pt相似的催化性能,是其良好替代品.但是,目前关于3DOM氧化物表面负载型Pd纳米颗粒结构和尺寸与柴油炭烟催化燃烧性能之间的相关研究仍然较少.基于此,本文采用气泡辅助膜还原法制备了3DOM二氧化钛(TiO_2)担载超细Pd纳米颗粒催化剂.利用XRD,Raman,BET,SEM,TEM,ICP,XPS和H2-TPR等技术手段对催化剂进行表征,并以模拟柴油炭烟为研究对象,利用程序升温氧化反应(TPO)对催化剂的活性进行评价,深入探讨了催化剂的制备、结构及物化性质与炭烟催化燃烧反应性能之间的关系.XRD和Raman结果表明,TiO_2载体由锐钛矿(主)和金红石(次)两种物相组成.SEM照片显示,所制催化剂为规整的有序大孔结构,球形孔互相贯通,孔径均一,大孔腔平均尺寸为280 nm,孔窗尺寸为109 nm,这种三维有序大孔TiO_2的结构能够增强炭烟颗粒与催化剂之间的接触效率.TEM表征显示,平均粒径为1.1 nm的超细半球型Pd纳米颗粒高度分散于TiO_2载体的内壁上,两者间的优化界面面积有利于增加活化O2的活性位密度,这些活性位源于Pd与TiO_2间强相互作用.H2-TPR和XPS表征印证了上述观点,具有1.1 nm超细Pd颗粒的Pd/3DOM-TiO_2催化剂表现出强的低温氧化还原特性和丰富的表面吸附氧物种.在TPO测试中,相对于担载5.0 nm Pd颗粒的催化剂,具有1.1 nm尺寸超细Pd颗粒的Pd/3DOM-TiO_2催化剂展示了高的催化炭烟燃烧活性,T10,T50和T90分别为295,370和415 oC,且在5次TPO测试过程中表现出良好的催化和结构稳定性.这种具有3DOM结构和超细Pd纳米颗粒的纳米催化剂能够有效降低Pd的使用量,在催化炭烟燃烧的实际应用中大有潜力.     

Controlling the Strong Metal-Support Interaction Overlayer Structure in Pt/TiO2 Catalysts Prevents Particle Evaporation

Platinum nanoparticles (NPs) supported by titania exhibit a strong metal-support interaction (SMSI)^[1] that can induce overlayer formation and encapsulation of the NP's with a thin layer of support material. This encapsulation modifies the catalyst's properties, such as increasing its chemoselectivity^[2] and stabilizing it against sintering.^[3] Encapsulation is typically induced during high-temperature reductive activation and can be reversed through oxidative treatments.^[1] However, recent findings indicate that the overlayer can be stable in oxygen.^{[4, 5]} Using in situ transmission electron microscopy, we investigated how the overlayer changes with varying conditions. We found that exposure to oxygen below 400 °C caused disorder and removal of the overlayer upon subsequent hydrogen treatment. In contrast, elevating the temperature to 900 °C while maintaining the oxygen atmosphere preserved the overlayer, preventing platinum evaporation when exposed to oxygen. Our findings demonstrate how different treatments can influence the stability of nanoparticles with or without titania overlayers. expanding the concept of SMSI and enabling noble metal catalysts to operate in harsh environments without evaporation associated losses during burn-off cycling.     

SMSI effect on ceria supported Cu-Pd catalysts in the hydrogenation of 1,3-butadiene

Ceria-supported copper-palladium catalysts have been tested in the hydrogenation of 1,3-butadiene. The SMSI behavior of the bimetallic catalysts depended on the temperature of reduction. They were analyzed by H₂ chemisorption and XPS.     

Light as a construction tool of metal nanoparticles: Synthesis and mechanism

The photo-induced synthesis of metal nanoparticles (NPs) was reviewed with a closer look at those based on photochemistry. Recent developments in metal NPs research, photochemistry, and photoprocessing techniques have allowed researchers to devise various photo-induced synthetic strategies to obtain metal NPs under a variety of conditions. We begin by outlining the classical method. The photochemical synthesis of metal NPs including direct photoreduction and photosensitization has been developed to achieve decent yields. We focused on stabilization and functionalization method of NPs in photochemical synthesis, which has enabled us to fabricate a variety of metal nanostructures and composite materials. In addition, we mention an alternative approach, that is, laser ablation at the solid–liquid interface. Some of the most innovative studies dealing with the three-dimensional fabrication of metal NPs are highlighted, together with new directions such as potential applications for a light-driven actuator, bioimaging, and three-dimensional processing. This review is concluded with the future perspectives for the photo-induced synthesis of metal NPs.     

Unique Possibilities of Dynamic Metal–Polymer Interactions in Selective Hydrogenation

Rationally designed polymers can function as supports or promoters for metal catalysts, imparting distinct catalytic properties in selective hydrogenation. With strongly metal–ligating functional groups, mobile polymer chains can spontaneously decorate the metal catalyst surfaces under mild conditions, forming stable metal–polymer interfaces. We have termed this phenomenon ‘dynamic metal–polymer interaction (DMPI),’ which can be roughly considered as an organic version of the strong metal–support interaction (SMSI) concept. The polymer chains that dynamically interact with the metal surface can control the adsorption of reactants and products through competitive adsorption, significantly improving selectivity and catalyst stability. One of the remarkable advantages of using polymers as catalytic materials is that their molecular structures, such as molecular weight, crystallinity, and chemical functionality, can be tailored using rich organic chemistry. This, in turn, allows us to precisely tune the metal–polymer interactions and catalytic properties. In this Concept, we will discuss how metal–polymer interfaces can be designed and utilized for selective hydrogenation, with a particular emphasis on the industrially relevant acetylene partial hydrogenation reaction.     

Strong metal-support interactions between gold nanoparticles and ZnO nanorods in CO oxidation

The catalytic performances of supported gold nanoparticles depend critically on the nature of support. Here, we report the first evidence of strong metal-support interactions (SMSI) between gold nanoparticles and ZnO nanorods based on results of structural and spectroscopic characterization. The catalyst shows encapsulation of gold nanoparticles by ZnO and the electron transfer between gold and the support. Detailed characterizations of the interaction between Au nanoparticles and ZnO were done with transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), electron paramagnetic resonance (EPR), and FTIR study of adsorbed CO. The significance of the SMSI effect is further investigated by probing the efficiency of CO oxidation over the Au/ZnO-nanorod. In contrast to the classical reductive SMSI in the TiO(2) supported group VIII metals which appears after high temperature reduction in H(2) with electron transfer from the support to metals, the oxidative SMSI in Au/ZnO-nanorod system gives oxygen-induced burial and electron transfer from gold to support. In CO oxidation, we found that the oxidative SMSI state is associated with positively charged gold nanoparticles with strong effect on its catalytic activity before and after encapsulation. The oxidative SMSI can be reversed by hydrogen treatment to induce AuZn alloy formation, de-encapsulation, and electron transfer from support to Au. Our discovery of the SMSI effects in Au/ZnO nanorods gives new understandings of the interaction between gold and support and provides new way to control the interaction between gold and the support as well as catalytic activity.     

Influence of reduction conditions on H2 adsorption in high-surface Rh/CeO2 catalysts as deduced by volumetry, calorimetry, and 1H NMR techniques

1H NMR spectra corresponding to H2 adsorption on high-surface Rh/CeO2 catalysts (S(BET) approximately 55 m2/g) are formed by two lines, attributed to hydrogen adsorbed on ceria (resonance line A) and rhodium-metal particles (upfield-shifted line B). The evolution of 1H NMR spectra as a function of temperature, time, and type of reduction (static or dynamic) allows the study of the progressive establishment of the strong metal-support interaction (SMSI) in Rh/CeO2 catalysts. As the reduction progresses, the mean adsorption heat and the amount of hydrogen adsorbed on the metal, deduced from volumetry, NMR, and calorimetry techniques, decrease considerably. As a consequence of the decrease in metal activity, the amount of hydrogen transferred to the support CeO2 is also reduced (spill-over processes). Outgassing of samples at 773 K eliminates hydrogen species retained at the metal-support surface, and oxidation treatments at 473 and 673 K eliminate the electronic effect and physical blocking of metal particles. The oxidation at 673 K recuperates the total adsorption capacity of metal particles. On the basis of these treatments, the contribution of different processes to the SMSI effect is analyzed. Electronic perturbation of rhodium particles is higher when reductions are performed in dynamic conditions; however, the importance of physical blocking of metal particles increases in static reductions. High reducibility of ceria strengthens electronic effects in Rh/CeO2 compared to those observed in Rh/TiO2 catalysts.     

Tuning the Selectivity of Catalytic Carbon Dioxide Hydrogenation over Iridium/Cerium Oxide Catalysts with a Strong Metal–Support Interaction

A one‐step ligand‐free method based on an adsorption–precipitation process was developed to fabricate iridium/cerium oxide (Ir/CeO₂) nanocatalysts. Ir species demonstrated a strong metal–support interaction (SMSI) with the CeO₂ substrate. The chemical state of Ir could be finely tuned by altering the loading of the metal. In the carbon dioxide (CO₂) hydrogenation reaction it was shown that the chemical state of Ir species—induced by a SMSI—has a major impact on the reaction selectivity. Direct evidence is provided indicating that a single‐site catalyst is not a prerequisite for inhibition of methanation and sole production of carbon monoxide (CO) in CO₂ hydrogenation. Instead, modulation of the chemical state of metal species by a strong metal–support interaction is more important for regulation of the observed selectivity (metallic Ir particles select for methane while partially oxidized Ir species select for CO production). The study provides insight into heterogeneous catalysts at nano, sub‐nano, and atomic scales.     

Physicochemical and catalytic characterizations of materials prepared from copper malonate by thermal decomposition or chemical reduction

Results of Carr and Galwey [1] concerning copper malonate (CM) decomposition in vacuo at 510 K prompted present studies on the utility of CM as a low-temperature precursor of oxide-supported copper catalysts. CM deposited upon metal oxides has been converted to copper particles by vacuum thermal decomposition or reduction with aqueous hydrazine. Using the dehydrogenation of isopropanol to acetone as a catalytic probe reaction, comparisons are made between levels of catalytic activity and selectivity induced in TiO₂, MgO and Ca(OH)₂ supports by copper deposited thereon. Effects of particle size, prereduction temperature, and support reducibility are described and evidence is given for a strong metal support interaction (SMSI)-like inhibition of activity of Cu/TiO₂ by prior high temperature reduction.     

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.     

Steering spatially separated dual sites on nano-TiO2 through SMSI and lattice matching for robust photocatalytic hydrogen evolution

Spatial isolation of different functional sites at the nanoscale in multifunctional catalysts for steering reaction sequence and paths remains a major challenge. Herein, we reported the spatial separation of dual-site Au and RuO₂ on the nanosurface of TiO₂ (Au/TiO₂/RuO₂) through the strong metal-support interaction (SMSI) and the lattice matching (LM) for robust photocatalytic hydrogen evolution. The SMSI between Au and TiO₂ induced the encapsulation of Au nanoparticles by an impermeable TiO_x overlayer, which can function as a physical separation barrier to the permeation of the second precursor. The LM between RuO₂ and rutile-TiO₂ can increase the stability of RuO₂/TiO₂ interface and thus prevent the aggregation of dual-site Au and RuO₂ in the calcination process of removing TiO_x overlayer of Au. The photocatalytic hydrogen production is used as a model reaction to evaluate the performance of spatially separated dual-site Au/TiO₂/RuO₂ catalysts. The rate of hydrogen production of the Au/TiO₂/RuO₂ is as high as 84 μmol h⁻¹ g⁻¹ under solar light irradiation without sacrificial agents, which is 2.5 times higher than the reference Au/TiO₂ and non-separated Au/RuO₂/TiO₂ samples. Systematic characterizations verify that the spatially separated dual-site Au and RuO₂ on the nanosurface of TiO₂ can effectively separate the photo-generated carriers and lower the height of the Schottky barrier, respectively, under UV and visible light irradiation. This study provides new inspiration for the precise construction of different sites in multifunctional catalysts.     

Electrocatalytic activity of Pd nanoparticles supported on poly(3,4-ethylenedioxythiophene)-graphene hybrid for ethanol electrooxidation

The support materials play a critical role for the electrocatalytic oxidation of ethanol on precious metal catalysts in fuel cells. Here, we report the poly(3,4-ethylenedioxythiophene) combined with reduced graphene oxide (PEDOT-RGO) as the support of Pd nanoparticles (NPs) for ethanol electrooxidation in alkaline medium. The as-prepared Pd/PEDOT-RGO composite catalysts are characterized by Raman spectrometer, X-ray diffraction, transmission electron microcopy, and scanning electron microcopy. PEDOT-RGO composite with the porous structure facilitates the dispersion of Pd NPs with a smaller size leading to the increase of electrochemical active surface area. The electrochemical properties and electrocatalytic activities of Pd/PEDOT-RGO hybrid are evaluated by cyclic voltammetry, chronoamperometry, CO stripping voltammetry, electrochemical impedance spectroscopy (EIS) and Tafel analysis. The results suggest that Pd/PEDOT-RGO hybrid shows a higher electrocatalytic activity, a better long-term stability, and the poisoning tolerance for the ethanol electrooxidation than Pd on carbon black. EIS and Tafel analysis indicate that PEDOT-RGO improves the kinetics of ethanol electrooxidation on the Pd NPs and is an efficient support in fuel cells.