Dynamically Confined Active Silver Nanoclusters with Ultrawide Operating Temperature Window in CO oxidation.

Supported metal nanoclusters are often highly active in many catalytic reactions but less stable particularly under harsh reaction conditions. Here, we demonstrate that this activity-stability trade-off can be efficiently broken through rational design of surrounding microenvironment of the supported nanocatalyst including gas adsorbate overlayer and underneath support surface chemistry. Our studies reveal that chemisorbed oxygen species on Ag surface and surface hydroxyl groups on oxide support, which are dynamically consumed during reaction but sustained by reaction environment (O and HO vapor), drive spontaneous redispersion of Ag particles and stabilization of highly active Ag nanoclusters.

Oxygen Vacancy Activates the Second-Nearest-Neighbor Lattice Oxygen for Oxidation Reaction.

Oxygen vacancies on the oxide surface are regarded to play critical roles in catalytic oxidation reactions because they can alter the electronic and geometric properties of oxide catalysts. However, the effects of the oxygen vacancy on the CO oxidation activity of the surrounding lattice oxygen have remained elusive. In this work, using high-pressure scanning tunneling microscopy we identify that oxygen vacancy can activate surface lattice oxygen on the MnO thin layer.

Visualizing Surface-Subsurface Cu Atom Exchange at the FeO/Pt(111) Surface Induced by CO Adsorption at 150 K.

Structural evolution of solid catalyst surfaces induced by direct exposure to reaction gas has been extensively studied and is well understood. However, whether and how subsurface atomic structures are affected by the reaction atmosphere require further exploration. In this work, our results confirm that Cu clusters supported on FeO/Pt(111) (Cu/FeO/Pt) transform into surface CuCO complexes (CuCO/FeO/Pt) with exposure to CO at 78 K.

Reverse water gas-shift reaction product driven dynamic activation of molybdenum nitride catalyst surface.

In heterogeneous catalysis catalyst activation is often observed during the reaction process, which is mostly attributed to the induction by reactants. In this work we report that surface structure of molybdenum nitride (MoN) catalyst exhibits a high dependency on the partial pressure or concentration of reaction products i.e.

Water-assisted oxidative redispersion of Cu particles through formation of Cu hydroxide at room temperature.

Sintering of active metal species often happens during catalytic reactions, which requires redispersion in a reactive atmosphere at elevated temperatures to recover the activity. Herein, we report a simple method to redisperse sintered Cu catalysts via O-HO treatment at room temperature. In-situ spectroscopic characterizations reveal that HO induces the formation of hydroxylated Cu species in humid O, pushing surface diffusion of Cu atoms at room temperature.

Confinement-Induced Indium Oxide Nanolayers Formed on Oxide Support for Enhanced CO 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 TiO creates a confined environment for InO which drives spontaneous transformation of free InO nanoparticles in physical contact with TiO nanoparticles into In oxide (InO) nanolayers covering onto the TiO surface during CO hydrogenation to CO. The formed InO nanolayers are easy to create surface oxygen vacancies but are against over-reduction to metallic In in the H-rich atmospheres, which thus show significantly enhanced activity and stability in comparison with the pure InO catalyst.

Spatially Separated Active Sites Enable Selective CO Oxidation Reaction on Oxide Catalyst.

The search for efficient non-noble-metal catalysts able to perform selective oxidation reactions is of great importance, with relevance to many catalytic processes. However, this is often hampered because the origin of the selectivity remains controversial, particularly for reactions catalyzed by oxides. Here, combining high-pressure surface imaging techniques and theoretical calculations, we identify that spatially separated active sites for O activation and H adsorption on an ultrathin MnO surface enable selective oxidation of CO over H.

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 CoO onto ZnO powder (CoO/ZnO), in which complete reduction of CoO to Co 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 CoO state in CO hydrogenation reaction, producing 93% CO.

Activating lattice oxygen of single-layer ZnO for the catalytic oxidation reaction.

Tuning an oxide/metal interface is of critical importance for the performance enhancement of many heterogeneous catalytic reactions. However, catalytic oxidation occurring at the interface between non-reducible oxide and metal has been challenging, since non-reducible oxides hardly lose their lattice oxygen (O) or dissociate O from the gas phase. In this work, a ZnO monolayer film on Au(111) is used as an inverse catalyst to investigate CO oxidation occurring at the ZnO/Au(111) interface high pressure scanning tunneling microscopy.

Stabilizing Oxide Nanolayer via Interface Confinement and Surface Hydroxylation.

Surface hydroxylation over oxide catalysts often occurs in many catalytic processes involving H and HO, which is considered to play an important role in elementary steps of the reactions. Here, monolayer CoO and CoOH 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 O. Surface science experiments indicate that hydroxyl groups formed on CoO nanoislands produced by deuterium-spillover can enhance oxidation resistance of the Co oxide nanostructures.

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

SignificanceFor oxide catalysts, it is important to elucidate and further control their atomic structures. In this work, well-defined CrO bilayer islands and CrO dinuclear clusters have been grown on Au(111) and unambiguously identified by scanning tunneling microscopy and theoretical calculations. Upon cycled redox treatments, the two kinds of oxide nanostructures can be reversibly transformed.

Overturning CO Hydrogenation Selectivity with High Activity via Reaction-Induced Strong Metal-Support Interactions.

Encapsulation of metal nanoparticles by support-derived materials known as the classical strong metal-support interaction (SMSI) often happens upon thermal treatment of supported metal catalysts at high temperatures (≥500 °C) and consequently lowers the catalytic performance due to blockage of metal active sites. Here, we show that this SMSI state can be constructed in a Ru-MoO catalyst using CO hydrogenation reaction gas and at a low temperature of 250 °C, which favors the selective CO hydrogenation to CO. During the reaction, Ru nanoparticles facilitate reduction of MoO to generate active MoO overlayers with oxygen vacancies, which migrate onto Ru nanoparticles' surface and form the encapsulated structure, that is, Ru@MoO.

Oxidative Strong Metal-Support Interactions between Metals and Inert Boron Nitride.

The strong metal-support interaction (SMSI) is one of the most important concepts in heterogeneous catalysis, which has been widely investigated between metals and active oxides triggered by reductive atmospheres. Here, we report the oxidative strong metal-support interaction (O-SMSI) effect between Pt nanoparticles (NPs) and inert hexagonal boron nitride (h-BN) sheets, in which Pt NPs are encapsulated by oxidized boron (BO) overlayers derived from the h-BN support under oxidative conditions. De-encapsulation of Pt NPs has been achieved by washing in water, and the residual ultrathin BO overlayers work synergistically with surface Pt sites for enhancing CO oxidation reaction.

In situ identification of the metallic state of Ag nanoclusters in oxidative dispersion.

Oxidative dispersion has been widely used in regeneration of sintered metal catalysts and fabrication of single atom catalysts, which is attributed to an oxidation-induced dispersion mechanism. However, the interplay of gas-metal-support interaction in the dispersion processes, especially the gas-metal interaction has not been well illustrated. Here, we show dynamic dispersion of silver nanostructures on silicon nitride surface under reducing/oxidizing conditions and during carbon monoxide oxidation reaction.

Design of Lewis Pairs via Interface Engineering of Oxide-Metal Composite Catalyst for Water Activation.

The rational design and controlled construction of active centers remain grand challenges in heterogeneous catalysis, in particular for oxide catalysts with complex surface and interface structures. This work describes a facile way in the design of highly active Ni-O Lewis pairs for water activation where Ni and O sites act as Lewis acid and base, respectively. Surface science experiments indicate that dissociative adsorption of water occurs at edges of NiO nanoislands grown on Au(111) and NiO-Ni interfaces formed by further depositing metallic Ni layers along the edges of NiO nanoislands.

Coverage-Dependent Behaviors of Vanadium Oxides for Chemical Looping Oxidative Dehydrogenation.

Chemical looping provides an energy- and cost-effective route for alkane utilization. However, there is considerable CO co-production caused by kinetically mismatched O bulk diffusion and surface reaction in current chemical looping oxidative dehydrogenation systems, rendering a decreased olefin productivity. Sub-monolayer or monolayer vanadia nanostructures are successfully constructed to suppress CO production in oxidative dehydrogenation of propane by evading the interference of O bulk diffusion (monolayer versus multi-layers).

FeO Octahedral Distortion Activates Lattice Oxygen in Perovskite Ferrite for Methane Partial Oxidation Coupled with CO Splitting.

Modulating lattice oxygen in metal oxides that conducts partial oxidation of methane in balancing C-H activation and syngas selectivity remains challenging. This paper describes the discovery of distorting FeO octahedra in LaCeFeO ( = 0, 0.25 0.

Facilitating the reduction of V-O bonds on VO /ZrO catalysts for non-oxidative propane dehydrogenation.

Supported vanadium oxide is a promising catalyst in propane dehydrogenation due to its competitive performance and low cost. Nevertheless, it remains a grand challenge to understand the structure-performance correlation due to the structural complexity of VO -based catalysts in a reduced state. This paper describes the structure and catalytic properties of the VO /ZrO catalyst.

Modulating the surface defects of titanium oxides and consequent reactivity of Pt catalysts.

In heterogeneous catalysis, it is widely believed that the surface states of catalyst supports can strongly influence the catalytic performance, because active components are generally anchored on supports. This paper describes a detailed understanding of the influence of surface defects of TiO supports on the catalytic properties of Pt catalysts. Pt was deposited on reduced (r-), hydroxylated (h-), and oxidized (o-) TiO surfaces, respectively, and the different surface states of TiO not only lead to differences in metal dispersion, but also distinct electronic interactions between the metal and the support.

Modulating Lattice Oxygen in Dual-Functional Mo-V-O Mixed Oxides for Chemical Looping Oxidative Dehydrogenation.

Oxygen chemistry plays a pivotal role in numerous chemical reactions. In particular, selective cleavage of C-H bonds by metal oxo species is highly desirable in dehydrogenation of light alkanes. However, high selectivity of alkene is usually hampered through consecutive oxygenation reactions in a conventional oxidative dehydrogenation (ODH) scheme.

The Interplay between Structure and Product Selectivity of CO Hydrogenation.

Identification of the active structure under reaction conditions is of great importance for the rational design of heterogeneous catalysts. However, this is often hampered by their structural complexity. The interplay between the surface structure of Co O and the CO hydrogenation is described.