Dynamic transformation between bilayer islands and dinuclear clusters of Cr oxide on Au(111) through environment and interface effects

Revealing the key role of interfacial oxygen activation over CoMn2O4@MnO2 in the catalytic oxidation of acetone

The accumulation of intermediate products on the catalyst surface caused by insufficient oxygen activity is an important reason for the poor activity of catalysts towards oxygenated volatile organic compounds (OVOCs). CoMn2O4@MnO2 heterogeneous catalysts were fabricated to decipher the interfacial oxygen activation mechanism for efficient acetone oxidation. Experimental and theoretical explorations revealed that oxygen vacancies were easily formed at the interface. Gaseous oxygen tended to adsorb on the interfacial vacancies while bonding with adjacent Mn sites, resulting in the stretching of O-O bonds. Rapid electron transfer at the interface led to the charge accumulation on the two oxygen atoms inducing electrostatic repulsion. These factors are conducive to the O-O bond breaking and gaseous oxygen activation. The obtained CoMn2O4@0.8MnO2 exhibited excellent catalytic performance with 90 % of acetone conversion at 159 °C, better than CoMn2O4 and MnO2. The acetone oxidation on CoMn2O4@0.8MnO2 not only avoided the accumulation of aldehydes, but also realized the rapid degradation of acetate into formate, achieving the shortest degradation pathway due to the rapid interfacial oxygen activation. CoMn2O4@0.8MnO2 also exhibited better catalytic activity for other OVOCs (ethyl acetate, ethylene oxide, methanol). This work provides new insights for the mechanism of interfacial oxygen activation and the design of heterogeneous catalyst for efficient OVOC oxidation.

OH Regulator of Amorphous CrOx on Defect-Rich Ultrafine Pd Nanowires Boosts Electrocatalytic Ethanol Oxidation

Reasonable construction of high activity and selectivity electrocatalysts is crucial to achieve efficient ethanol oxidation reaction (EOR). However, the oxidation of ethanol tends to produce CO species that poison the active centers of the EOR electrocatalysts. Herein, a unique amorphous CrOx-protected defect-rich ultrafine Pd nanowires (CrOx-Pd NWs) is developed. On the one hand, the CrOx layer can act as a protective layer to maintain the structure of the nanowire. On the other hand, it can play the role of OH regulator to optimize the adsorption energy barrier of intermediate species in Pd nanowire, thereby enhancing the ability of the catalyst to resist CO poisoning. The CrOx-Pd NWs exhibit excellent EOR performance with 3.64 times higher mass activity and 50 mV lower CO electro-oxidation potential than commercial Pd black. The results show that the CrOx layer promotes the dissociation of H2O into OHads, while the CrOx transfers electrons to neighboring Pd atoms optimizing the electronic configuration of Pd, thus selectively oxidizing ethanol to acetate and preventing the formation of toxic *CO. This work provides an effective strategy for the synthesis of nanowire materials with oxide/metal interfaces and offers new ideas for the design of catalysts that can efficiently drive EOR.

Atomic Scale Responses of High Entropy Oxides to Redox Environments

The potential of high entropy oxides (HEOs) as high-performance energy storage materials and catalysts has been mainly understood through their bulk structures. However, the importance of their surfaces, which may play an even more critical role, remains largely unknown. In this study, we employed advanced scanning transmission electron microscopy to investigate the atomic-scale structural and chemical responses of CeYLaHfTiZrOx HEOs to high-temperature redox environments. Our observations reveal dynamic elemental and structural reconstructions in the surface of HEOs under different gas environments, contrasting with the high stability of the bulk structure. Notably, the surfaces of HEO particles consistently exhibit abundant oxygen vacancies, regardless of the redox environment. These findings indicate that HEOs offer distinct advantages in facilitating chemical and electrochemical reactions, relying on oxygen vacancies. Our results also suggest that the exceptional performance of HEOs in energy storage applications arises from surface structural and chemical adaptability.

Confinement-Induced Indium Oxide Nanolayers Formed on Oxide Support for Enhanced CO2 Hydrogenation Reaction

An enclosed nanospace often shows a significant confinement effect on chemistry within its inner cavity, while whether an open space can have this effect remains elusive. Here, we show that the open surface of TiO2 creates a confined environment for In2O3 which drives spontaneous transformation of free In2O3 nanoparticles in physical contact with TiO2 nanoparticles into In oxide (InOx) nanolayers covering onto the TiO2 surface during CO2 hydrogenation to CO. The formed InOx nanolayers are easy to create surface oxygen vacancies but are against over-reduction to metallic In in the H2-rich atmospheres, which thus show significantly enhanced activity and stability in comparison with the pure In2O3 catalyst. The formation of interfacial In-O-Ti bonding is identified to drive the In2O3 dispersion and stabilize the metastable InOx layers. The InOx overlayers with distinct chemistry from their free counterpart can be confined on various oxide surfaces, demonstrating the important confinement effect at oxide/oxide interfaces.

Disentangling Local Interfacial Confinement and Remote Spillover Effects in Oxide-Oxide Interactions

Supported oxides are widely used in many important catalytic reactions, in which the interaction between the oxide catalyst and oxide support is critical but still remains elusive. Here, we construct a chemically bonded oxide-oxide interface by chemical deposition of Co3O4 onto ZnO powder (Co3O4/ZnO), in which complete reduction of Co3O4 to Co0 has been strongly impeded. It was revealed that the local interfacial confinement effect between Co oxide and the ZnO support helps to maintain a metastable CoOx state in CO2 hydrogenation reaction, producing 93% CO. In contrast, a physically contacted oxide-oxide interface was formed by mechanically mixing Co3O4 and ZnO powders (Co3O4-ZnO), in which reduction of Co3O4 to Co0 was significantly promoted, demonstrating a quick increase of CO2 conversion to 45% and a high selectivity toward CH4 (92%) in the CO2 hydrogenation reaction. This interface effect is ascribed to unusual remote spillover of dissociated hydrogen species from ZnO nanoparticles to the neighboring Co oxide nanoparticles. This work clearly illustrates the equally important but opposite local and remote effects at the oxide-oxide interfaces. The distinct oxide-oxide interactions contribute to many diverse interface phenomena in oxide-oxide catalytic systems.

Nonclassical Strong Metal-Support Interactions for Enhanced Catalysis

Strong metal-support interaction (SMSI), which encompasses reversible encapsulation and de-encapsulation and modulation of surface adsorption properties, imposes great impacts on the performance of heterogeneous catalysts. Recent development of SMSI has surpassed the prototypical encapsulated Pt-TiO₂ catalyst, affording a series of conceptually novel and practically advantageous catalytic systems. Here we provide our perspective on recent progress in nonclassical SMSIs for enhanced catalysis. Unravelling the structural complexity of SMSI necessitates the combination of multiple characterization techniques at different scales. Synthesis strategies leveraging chemical, photonic, and mechanochemical driving forces further expand the definition and application scope of SMSI. Exquisite structure engineering permits elucidation of the interface, entropy, and size effect on the geometric and electronic characteristics. Materials innovation places the atomically thin two-dimensional materials at the forefront of interfacial active site control. A broader space is awaiting exploration, where exploitation of metal-support interactions brings compelling catalytic activity, selectivity, and stability.

Oxide-Metal Interaction Probed by Scanning Tunneling Microscope Manipulation of Cr2O7 Clusters on Au(111)

Interfacial interaction plays a crucial rule in catalysis over supported catalysts, and the catalyst-support interaction needs to be explored at microscopic scale. Here, we use the scanning tunneling microscope (STM) tip to manipulate Cr₂O₇ dinuclear clusters on Au(111) and find that the Cr₂O₇-Au interaction can be weakened by an electric field in the STM junction, facilitating rotation and translation of the individual clusters at the imaging temperature (78 K). Surface alloying with Cu makes the manipulation of the Cr₂O₇ clusters hard due to the enhanced Cr₂O₇-substrate interaction. Density functional theory calculations reveal that barrier for translation of a Cr₂O₇ cluster on the surface can be increased by surface alloying, influencing the tip manipulation. Our study demonstrates that the oxide-metal interfacial interaction can be probed by STM tip manipulation of supported oxide clusters, which provides a new method to investigate the interfacial interaction.

Periodic Arrays of Metal Nanoclusters on Ultrathin Fe-Oxide Films Modulated by Metal-Oxide Interactions

Rational design of highly stable and active metal catalysts requires a deep understanding of metal-support interactions at the atomic scale. Here, ultrathin films of FeO and FeO2-x grown on Pt(111) are used as templates for the construction of well-defined metal nanoclusters. Periodic arrays of Cu clusters in the form of monomers and trimers are preferentially located at FCC domains of FeO/Pt(111) surface, while the selective location of Cu clusters at FeO2 domains is observed on FeO2-x /Pt(111) surface. The preferential nucleation and formation of well-ordered Cu clusters are driven by different interactions of Cu with the Fe oxide domains in the sequence of FeO2-FCC > FeO-FCC > FeO-HCP > FeO-TOP, which is further validated by density functional theory calculations. It has been revealed that the p-band center as a reactivity descriptor of surface O atoms determines the interaction between metal adatoms and Fe oxides. The modulated metal-oxide interaction provides guidance for the rational design of supported single-atom and nanocluster catalysts.