Making waves: Pioneering a nanoconfinement platform with mesoporous silica for sustainable water management and environmental applications

Nanomaterials applied in industrial processes and environmental fields usually demand immobilization and recovery strategies that often result in functionality loss and added operational costs. Nanoconfinement, the spatial restriction of nano-sized particles within a larger porous substrate, not only can address critical challenges and sustainability concerns in environmental nanotechnology but also offers unique opportunities otherwise inaccessible by unconfined, bulk-phase nanomaterials. In this perspective, we propose mesoporous silica (mSiO2) as an innovative framework for spatially confining metal nanoparticles in a well-controlled manner, offering an effective nanoconfinement engineering strategy for sustainable water management and environmental applications. We first summarize the current understanding of nanoconfinement effects and briefly review previous approaches to the fabrication of engineered nanoconfinement materials. We then present a layer-by-layer engineering strategy to confine various metal nanoparticles within multi-shelled mSiO2 structures, exploring their unique nanoconfinement features and potential environmental applications, e.g. tandem catalysis, surface-enhanced Raman scattering (SERS) sensor, and visible-light-driven water treatment. Finally, we discuss challenges in studying nanoconfinement effects and outline future research directions to advance sustainable innovation. Opportunities for practical implementation exist at the intersection of fundamental studies and engineering disciplines, emphasizing the need for parallel efforts to establish system characterization standards and enable effective technological integration at scale.

Interface engineering to regulate oxidation dynamics of supported nanoparticles

Understanding the oxidation of metal nanoparticles is crucial for various applications, particularly in heterogeneous catalysis, such as catalytic oxidation reactions, where metal nanoparticles are typically dispersed on supports. However, the dynamics of interaction between nanoparticles and oxygen, especially under the influence of supporting materials, remain poorly understood, significantly hindering the precise comprehension and regulation of nanoparticle oxidation dynamics. Here, we elucidate two distinct oxidation dynamics in supported nanoparticles using aberration-corrected environmental (scanning) transmission electron microscopy (E(S)TEM), i.e., preferential self-adaptive oxidation initiating at the nanoparticle-support interface, where the support facilitates oxidation, and surface oxidation, where the support inhibits oxidation. Our systematic calculations, corroborated by experimental validations, demonstrate that the interfacial epitaxial match plays a dominant role in determining the oxidation dynamics in oxygen. It serves as a key indicator for developing a straightforward interface engineering strategy to regulate both self-adaptive and surface oxidation processes. This work highlights the diversity of interface-determined oxidation behaviors and offers a strategy for regulating the oxidation dynamics of supported nanoparticles under identical conditions.

High-efficiency Pt catalyst immobilized on hierarchical N-doped carbon nanocages for preferential oxidation of CO in H2

The N-doped carbon nanocage-supported Pt nanoparticle catalyst exhibits high activity and stability for preferential oxidation of CO in H2 over a wide temperature range of 80-180 °C, which is attributed to the modulated electronic structure of Pt and high accessibility of active sites endowed by hierarchical N-doped carbon nanocages.

'Tearing Effect' of Alloy-Support Interaction for Alloy Redispersion in NiRu/TiO2 Hydrogenation Catalysts

Supported alloy catalysts have been extensively applied to many significant industrial chemical processes due to the abundant active sites with distinguishable geometry and electron states. However, a detailed in situ investigation of the interaction between support and alloy nanoparticles is still lacking. Here, a subversive 'tearing effect' on the interface of TiO2-supported NiRu alloy nanoparticles is in situ discovered by environmental transmission electron microscopy (ETEM) with a dramatic redispersion process of alloy nanoparticles from ~25 nm to 2-3 nm under the repeated hydrogen reduction. Dual-driven by the distinct alloy-support interaction involving the restructuring of alloy nanoparticles and growth of TiOx overlayer, larger NiRu alloy nanoparticles spontaneously disintegrate into atoms migrating on support. Atoms are finally captured by the defects generated on TiO2 during the repeat reduction, which also confines the further growth of the newly alloy nanoparticles. Owing to this specific alloy-support interaction, smaller alloy nanoparticles on TiO2 support are much more stable than the bigger ones, which holds promise for industrial applications as durable catalysts. This novel metal-support interaction with the 'tearing effect' revealed on supported alloy catalysts provides new knowledge on the structure-performance relationships in all the alloy catalysts for hydrogenation reactions.

Revealing the CO Tolerance Mechanism in Acidic Hydrogen Oxidation Reactions on Platinum-Based Catalyst Surfaces

The presence of trace CO impurity gas in hydrogen fuel can rapidly deactivate platinum-based hydrogen oxidation reaction (HOR) catalysts due to poisoning effects, yet the precise CO tolerance mechanism remains debated. Our designed Au@PtX bifunctional core-shell nanocatalysts exhibit excellent performance of CO tolerance in acidic solution during HOR and possess exceptional Raman spectroscopy enhancement. Through capturing and analyzing in situ Raman spectroscopy evidences on *OH, metal-O species and *CO evolution under 0.3 V, we confirm that oxygen-containing species on PtRu and PtSn catalysts promote the oxidation and desorption of *CO. While Ru enhances *CO adsorption on Pt, the primary CO tolerance performance of PtRu arises from *CO oxidation via a bifunctional pathway. Additionally, electronic structure of Sn reduces *CO adsorption on Pt sites, complementing the bifunctional mechanism to further enhance the CO tolerance performance of PtSn. These discoveries significantly deepen our understanding of the anti-poisoning mechanism of Pt-based catalysts in the HOR process and offer valuable insights for rational catalyst design.

Nanoconfinement Effects in Electrocatalysis and Photocatalysis

Recently, the enzyme-inspired nanoconfinement effect has garnered significant attention for enhancing the efficiency of electrocatalysts and photocatalysts. Despite substantial progress in these fields, there remains a notable absence of comprehensive and insightful articles providing a clear understanding of nanoconfined catalysts. This review addresses this gap by delving into nanoconfined catalysts for electrocatalytic and photocatalytic energy conversion. Initially, the effect of nanoconfinement on the thermodynamics and kinetics of reactions is explored. Subsequently, the primary and secondary structures of nanoconfined catalysts are categorized, their properties are outlined, and typical methods for their construction are summarized. Furthermore, an overview of the state-of-the-art applications of nanoconfined catalysts is provided, focusing on reactions of hydrogen and oxygen evolution, oxygen reduction, carbon dioxide reduction, hydrogen peroxide production, and nitrogen reduction. Finally, the current challenges and future prospects in nanoconfined catalysts are discussed. This review aims to provide in-depth insights and guidelines to advance the development of electrocatalytic and photocatalytic energy conversion technology by nanoconfined catalysts.

Recent Progress in the Design and Application of Strong Metal-Support Interactions in Electrocatalysis

The strong metal-support interaction (SMSI) in supported metal catalysts represents a crucial factor in the design of highly efficient heterogeneous catalysts. This interaction can modify the surface adsorption state, electronic structure, and coordination environment of the supported metal, altering the interface structure of the catalyst. These changes serve to enhance the catalyst's activity, stability, and reaction selectivity. In recent years, a multitude of researchers have uncovered a range of novel SMSI types and induction methods including oxidized SMSI (O-SMSI), adsorbent-mediated SMSI (A-SMSI), and wet chemically induced SMSI (Wc-SMSI). Consequently, a systematic and critical review is highly desirable to illuminate the latest advancements in SMSI and to deliberate its application within heterogeneous catalysts. This article provides a review of the characteristics of various SMSI types and the most recent induction methods. It is concluded that SMSI significantly contributes to enhancing catalyst stability, altering reaction selectivity, and increasing catalytic activity. Furthermore, this paper offers a comprehensive review of the extensive application of SMSI in the electrocatalysis of hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and carbon dioxide reduction reaction (CO2RR). Finally, the opportunities and challenges that SMSI faces in the future are discussed.

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.

Interfacial Catalysis at Atomic Level

Heterogeneous catalysts are pivotal to the chemical and energy industries, which are central to a multitude of industrial processes. Large-scale industrial catalytic processes rely on special structures at the nano- or atomic level, where reactions proceed on the so-called active sites of heterogeneous catalysts. The complexity of these catalysts and active sites often lies in the interfacial regions where different components in the catalysts come into contact. Recent advances in synthetic methods, characterization technologies, and reaction kinetics studies have provided atomic-scale insights into these critical interfaces. Achieving atomic precision in interfacial engineering allows for the manipulation of electronic profiles, adsorption patterns, and surface motifs, deepening our understanding of reaction mechanisms at the atomic or molecular level. This mechanistic understanding is indispensable not only for fundamental scientific inquiry but also for the design of the next generation of highly efficient industrial catalysts. This review examines the latest developments in atomic-scale interfacial engineering, covering fundamental concepts, catalyst design, mechanistic insights, and characterization techniques, and shares our perspective on the future trajectory of this dynamic research field.

Research Progress and Perspectives on Anti-Poisoning Hydrogen Oxidation Reaction Electrocatalysts for Hydrogen Fuel Cells

As global demand for clean and sustainable energy continues to rise, fuel cell technology has seen rapid advancement. However, the presence of trace impurities like carbon monoxide (CO) and hydrogen sulfide (H₂S) in hydrogen fuel can significantly deactivate the anode by blocking its active sites, leading to reduced performance. Developing electrocatalysts that are resistant to CO and H₂S poisoning has therefore become a critical priority. This paper provides a comprehensive analysis of the poisoning mechanisms of CO and H₂S and reviews the key strategies developed over the past few decades to enhance the impurity tolerance of anode electrocatalysts. It begins by examining the differences in hydrogen oxidation reaction (HOR) mechanisms in acidic and alkaline environments, focusing on the roles of hydrogen binding energy (HBE) and hydroxide binding energy (OHBE). Next, it outlines three main approaches to mitigate CO poisoning: (I) bifunctional mechanisms, (II) direct mechanisms, and (III) constructing protective blocking layers. The review then shifts to strategies for countering H₂S poisoning, emphasizing both electrocatalyst design and structural improvements in fuel cells. Finally, the paper highlights recent advances in anti-poisoning electrocatalysts, discusses their applications and limitations, and identifies the key challenges and future opportunities for further research in this field.

Shielding Pt/γ-Mo2N by inert nano-overlays enables stable H2 production

The use of reactive supports to disperse metal species is crucial for constructing highly efficient interfacial catalysts, by tuning the competitive reactant adsorption-activation pattern in supported metal catalysts into a non-competitive mechanism1-3. However, these reactive supports are prone to deterioration during catalysis, limiting the lifespan of the catalyst and their potential practical applications4. New strategies are needed to simultaneously protect reactive supports and surface metal species without compromising the inherent catalytic performance. Here we report a new strategy to augment the structural stability of highly active interfacial catalysts by using inert nano-overlays to partially shield and partition the surface of the reactive support. Specifically, we demonstrate that atomically dispersed inert oxide nano-overlays on a highly active Pt/γ-Mo2N catalyst can block the redundant surface sites of γ-Mo2N responsible for surface oxidation of this reactive support and the resulting deactivation. This strategy yields an efficient and highly durable catalyst for hydrogen production by methanol-reforming reaction with a mere 0.26 wt% Pt loading, exhibiting a record-high turnover number, to our knowledge, of 15,300,000 and a notable apparent turnover frequency of 24,500 mol H 2 mol metal - 1 h - 1 . This innovative approach showcases the prospects of reducing noble metal consumption and boosting longevity, which could be applied to design effective and stable heterogeneous catalysts.

Low mechanical-hysteresis conductive hydrogel conferred by chitosan bridging and MXene nanoconfined mechanism

Large mechanical hysteresis, stemming from the inherent viscoelasticity of the hydrogel networks, seriously affected its service life and application scope. Herein, we introduced a synergistic approach combining MXene nanoconfinement and bridging effect to produce hydrogels with low mechanical hysteresis. The introduced MXene was able to provide an effective nanoconfined effect on the polymerization of acrylamide monomers. By synergizing with the bridging effect-facilitated by strong interactions between chitosan-grafted polyacrylamide and solvent molecules to accelerate stress transfer-we successfully developed a MXene-reinforced conductive hydrogel with mechanical hysteresis as low as 3.17 %. Additionally, the strong electrostatic interactions between the chitosan and MXene further affiliate the dispersion of MXene within the hydrogel. The resulting MXene-reinforced conductive hydrogel demonstrated remarkable temperature sensitivity (TCR = -1.42 %/°C), making it suitable to be used as a health monitoring device. These findings opened up new perspectives for the further expansion of MXene and beyond.

Enhancing Carbon Monoxide Tolerance in Low-Temperature PEM Fuel Cells through Carbon Nitride Surface Modification

Low-temperature proton exchange membrane fuel cells (PEMFCs) reuqire highly pure hydrogen gas due to their extreme sensitivity to carbon monoxide (CO) contamination, which poses a challenge for using cost-effective reformed hydrogen sources. To address this issue, we have developed a surface modification strategy by applying a 0.5-0.91 nm amorphous carbon nitride layer onto PtRu/C substrates. The electrochemical measurements indicate that the modification selectively facilitates hydrogen gas transport to a surface while inhibiting carbon monoxide diffusion. The kinetic studies of CO adsorption reveal that the surface modification significantly reduces CO adsorption, effectively halving the rate compared to conventional catalysts. Additionally, rotating disk electrode experiments show that the catalyst modified with amorphous carbon nitride layer maintains stable operation for over 20 h with 1000 ppm of CO/H2. Furthermore, it supports stable discharge at 1 A cm-2 in PEMFCs with up to 10 ppm of CO, a concentration far exceeding the widely accepted standard of 0.2 ppm.

Operando XANES Reveals the Chemical State of Iron-Oxide Monolayers During Low-Temperature CO Oxidation

We have used grazing incidence X-ray absorption near edge spectroscopy (XANES) to investigate the behavior of monolayer FeOx ${_x }$ films on Pt(111) under near ambient pressure CO oxidation conditions with a total gas pressure of 1 bar. Spectra indicate reversible changes during oxidation and reduction by O2 ${_2 }$ and CO at 150 °C, attributed to a transformation between FeO bilayer and FeO2 ${_2 }$ trilayer phases. The trilayer phase is also reduced upon heating in CO+O2 ${_2 }$ , consistent with a Mars-van-Krevelen type mechanism for CO oxidation. At higher temperatures, the monolayer film dewets the surface, resulting in a loss of the observed reducibility. A similar iron oxide film prepared on Au(111) shows little sign of reduction or oxidation under the same conditions. The results highlight the unique properties of monolayer FeO and the importance of the Pt support in this reaction. The study furthermore demonstrates the power of grazing-incidence XAFS for in situ studies of these model catalysts under realistic conditions.

Insights into the Roles of Different Iron Species on Zeolites for N2O Selective Catalytic Reduction by CO

Iron zeolites are promising candidates for mitigating nitrous oxide (N2O), a potent greenhouse gas and contributor to stratospheric ozone destruction. However, the atomic-level mechanisms by which different iron species, including isolated sites, clusters, and particles, participate in N2O decomposition in the presence of CO still remain poorly understood, which hinders the application of the reaction in practical technology. Herein, through experiments and density functional theory (DFT) calculations, we identified that isolated iron sites were active for N2O activation to generate adsorbed O* species, which readily reacted with CO following the Eley-Rideal (E-R) mechanism. In contrast, Fe2O3 particles exhibited a different reaction pathway, directly reacting with CO to generate oxygen vacancies (Ov), which could efficiently dissociate N2O following the Mars-van Krevelen (MvK) mechanism. Moreover, the transformation of iron oxide clusters into undercoordinated FeOx species by CO was also revealed through various techniques, such as CO-temperature-programmed reduction (TPR), and ab initio molecular dynamics (AIMD) simulations. Our study provides deeper insights into the roles of different iron species in N2O-SCR by CO, and is anticipated to facilitate the understanding of multicomponent catalysis and the design of efficient iron-containing catalysts for practical applications.

Confinement Effects of Two-Dimensional Surfaces on Water Adsorption and Dissociation over Pt(111)

It has been established that the confined space created by stacking a two dimensional (2D) surface atop a metal catalyst serves as a nano-reactor. According to recent research, when a graphene (Gr) overlayer encloses a catalyst from above, the activation barrier for the water dissociation reaction, a process with major industrial significance, decreases. In order to investigate how the effect of confinement varies among different two-dimensional (2D) materials, we study the adsorption and dissociation barriers of water molecule on (111) under graphene, hexagonal boron nitride (h-BN), and heptazine-based graphitic carbon nitride (g-C3N4) layers using density functional theory calculations. Our findings reveal that the strength of adsorption does not decrease consistently with a reduction in the height of the 2D overlayer. Furthermore, a smaller barrier is not always the consequence of poorer adsorption of the reactant. We also examine the effect of confinement on the shape of the reaction path, on the frequencies of vibrational modes, and on the rate constants derived using the harmonic transition state theory. Overall, all three 2D surfaces cause a decrease in barrier height and a weakening of adsorption, though to differing degrees due to a mix of mechanical, geometric and electronic variables.

Oxygen Vacancy-Enriched Alumina Stabilized Pd Nanocatalysts for Selective Hydrogenation of Phenols

The prevalence of electronic defects has not been successfully demonstrated in nonreducible oxides. This work presents a straightforward approach to the preparation of a yellow alumina rich in F-centers (oxygen vacancies containing free electrons), which is well characterized by systematic spectral methods. The surface electron density of the as-prepared F-center enriched alumina sample was estimated to be approximately 0.35 mmol·g-1. Free electrons on the surface can reduce palladium precursors in situ, leading to the deposition of fine Pd nanoparticles on alumina. The produced Pd nanocatalysts are highly effective in the selective hydrogenation of phenol to cyclohexanone, achieving a high catalytic performance under mild conditions (30 °C and 0.1 MPa of H2). Systematic mechanism investigations reveal that hydroxyl radicals generated at the catalyst interfaces facilitate the activation of phenol. The activated phenol is then sequentially hydrogenated to give the intermediate 2-cyclohexenone and then the desired cyclohexanone. The catalyst system demonstrates efficacy in selectively hydrogenating substituted phenols into a wide array of functional ketones.

Dynamic control and quantification of active sites on ceria for CO activation and hydrogenation

Ceria (CeO2) is a widely used oxide catalyst, yet the nature of its active sites remains elusive. This study combines model and powder catalyst studies to elucidate the structure-activity relationships in ceria-catalyzed CO activation and hydrogenation. Well-defined ceria clusters are synthesized on planar CeO2(111) and exhibit dynamic and tunable ranges of Ce coordination numbers, which enhance their interaction with CO. Reduced ceria clusters (e.g., Ce3O3) bind CO strongly and facilitate its dissociation, while near-stoichiometric clusters (e.g., Ce3O7) adsorb CO weakly and promote oxidation via carbonate formation. Unlike planar ceria surfaces, supported ceria clusters exhibit dynamic properties and enhanced catalytic activity, that mimic those of powder ceria catalysts. Insight from model studies provide a method to quantify active sites on powder ceria and guide further optimization of ceria catalysts for syngas conversion. This work marks a leap toward model-guided catalyst design and highlights the importance of site-specific catalysis.

Surface and interfacial sciences for future technologies

Physical science has undergone an evolutional transition in research focus from solid bulks to surfaces, culminating in numerous prominent achievements. Currently, it is experiencing a new exploratory phase-interfacial science. Many a technology with a tremendous impact is closely associated with a functional interface which delineates the boundary between disparate materials or phases, evokes complexities that surpass its pristine comprising surfaces, and thereby unveils a plethora of distinctive properties. Such an interface may generate completely new or significantly enhanced properties. These specific properties are closely related to the interfacial states formed at the interfaces. Therefore, establishing a quantitative relationship between the interfacial states and their functionalities has become a key scientific issue in interfacial science. However, interfacial science also faces several challenges such as invisibility in characterization, inaccuracy in calculation, and difficulty in precise construction. To tackle these challenges, people must develop new strategies for precise detection, accurate computation, and meticulous construction of functional interfaces. Such strategies are anticipated to provide a comprehensive toolbox tailored for future interfacial science explorations and thereby lay a solid scientific foundation for several key future technologies.

Towards bridging thermo/electrocatalytic CO oxidation: from nanoparticles to single atoms

Proton exchange membrane fuel cells (PEMFCs), as a feasible alternative to replace the traditional fossil fuel-based energy converter, contribute significantly to the global sustainability agenda. At the PEMFC anode, given the high exchange current density, Pt/C is deemed the catalyst-of-choice to ensure that the hydrogen oxidation reaction (HOR) occurs at a sufficiently fast pace. The high performance of Pt/C, however, can only be achieved under the premise that high purity hydrogen is used. For instance, in the presence of trace level carbon monoxide, a typical contaminant during H2 production, Pt is severely deactivated by CO surface blockage. Addressing the poisoning issue necessitates for either developing anti-poisoning electrocatalysts or using pre-purified H2 obtained via a thermo-catalysis route. In other words, the CO poisoning issue can be addressed by either thermal-catalysis from the H2 supply side or electrocatalysis at the user side, respectively. In spite of the distinction between thermo-catalysis and electro-catalysis, there are high similarities between the two routes. Essentially, a reduction in the kinetic barrier for the combination of CO to oxygen containing intermediates is required in both techniques. Therefore, bridging electrocatalysis and thermocatalysis might offer new insight into the development of cutting edge catalysts to solve the poisoning issue, which, however, stands as an underexplored frontier in catalysis science. This review provides a critical appraisal of the recent advancements in preferential CO oxidation (CO-PROX) thermocatalysts and anti-poisoning HOR electrocatalysts, aiming to bridge the gap in cognition between the two routes. First, we discuss the differences in thermal/electrocatalysis, CO oxidation mechanisms, and anti-CO poisoning strategies. Second, we comprehensively summarize the progress of supported and unsupported CO-tolerant catalysts based on the timeline of development (nanoparticles to clusters to single atoms), focusing on metal-support interactions and interface reactivity. Third, we elucidate the stability issue and theoretical understanding of CO-tolerant electrocatalysts, which are critical factors for the rational design of high-performance catalysts. Finally, we underscore the imminent challenges in bridging thermal/electrocatalytic CO oxidation, with theory, materials, and the mechanism as the three main weapons to gain a more in-depth understanding. We anticipate that this review will contribute to the cognition of both thermocatalysis and electrocatalysis.

Simultaneously activating molecular oxygen and surface lattice oxygen on Pt/TiO2 for low-temperature CO oxidation

Developing high-performance Pt-based catalysts with low Pt loading is crucial but challenging for CO oxidation at temperatures below 100 °C. Herein, we report a Pt-based catalyst with only a 0.15 wt% Pt loading, which consists of Pt-Ti intermetallic single-atom alloy (ISAA) and Pt nanoparticles (NP) co-supported on a defective TiO2 support, achieving a record high turnover frequency of 11.59 s-1 at 80 °C and complete conversion of CO at 120 °C. This is because the coexistence of Pt-Ti ISAA and Pt NP significantly alleviates the competitive adsorption of CO and O2, enhancing the activation of O2. Furthermore, Pt single atom sites are stabilized by Pt-Ti ISAA, resulting in distortion of the TiO2 lattice within Pt-Ti ISAA. This distortion activates the neighboring surface lattice oxygen, allowing for the simultaneous occurrence of the Mars-van Krevelen and Langmuir-Hinshelwood reaction paths at low temperatures.

DFT study of the moiré pattern of FeO monolayer on Au(111)

Metal oxides are a class of material of particular interest for catalytic purposes. Among them the iron oxide as a monolayer supported on gold, FeO/Au, stands out for its capability to promote the CO oxidation and the dissociation of O2 and H2. In this work, we use density functional theory calculations to characterize interfacial properties of this heterostructure. We consider a FeO/Au realistic model system, managing to reproduce the moiré pattern experimentally found. Specific features of the high-symmetry domains of the moiré are identified, providing a robust ground for establishing a structure-activity relationship and guessing how the surface would behave in catalytic conditions. We also describe a strategy to model smaller systems representative of each high-symmetry domains of the moiré, which will be useful in the future to model catalytic reaction mechanisms.

Recent advances in organic molecule reactions on metal surfaces

Chemical reactions of organic molecules on metal surfaces have been intensively investigated in the past decades, where metals play the role of catalysts in many cases. In this review, first, we summarize recent works on spatial molecules, small H2O, O2, CO, CO2 molecules, and the molecules carrying silicon groups as the new trends of molecular candidates for on-surface chemistry applications. Then, we introduce spectroscopy and DFT study advances in on-surface reactions. Especially, in situ spectroscopy technologies, such as electron spectroscopy, force spectroscopy, X-ray photoemission spectroscopy, STM-induced luminescence, tip-enhanced Raman spectroscopy, temperature-programmed desorption spectroscopy, and infrared reflection adsorption spectroscopy, are important to confirm the occurrence of organic reactions and analyze the products. To understand the underlying mechanism, the DFT study provides detailed information about reaction pathways, conformational evolution, and organometallic intermediates. Usually, STM/nc-AFM topological images, in situ spectroscopy data, and DFT studies are combined to describe the mechanism behind on-surface organic reactions.

Unveiling the Promoting Mechanism of H2 Activation on CuFeOx Catalyst for Low-Temperature CO Oxidation

The effect of H2 activation on the performance of CuFeOx catalyst for low-temperature CO oxidation was investigated. The characterizations of XRD, XPS, H2-TPR, O2-TPD, and in situ DRIFTS were employed to establish the relationship between physicochemical property and catalytic activity. The results showed that the CuFeOx catalyst activated with H2 at 100 °C displayed higher performance, which achieved 99.6% CO conversion at 175 °C. In addition, the H2 activation promoted the generation of Fe2+ species, and more oxygen vacancy could be formation with higher concentration of Oα species, which improved the migration rate of oxygen species in the reaction process. Furthermore, the reducibility of the catalyst was enhanced significantly, which increased the low-temperature activity. Moreover, the in situ DRIFTS experiments revealed that the reaction pathway of CO oxidation followed MvK mechanism at low temperature (<175 °C), and both MvK and L-H mechanism was involved at high temperature. The Cu+-CO and carbonate species were the main reactive intermediates, and the H2 activation increased the concentration of Cu+ species and accelerated the decomposition carbonate species, thus improving the catalytic performance effectively.

Enhanced electrocatalytic biomass oxidation at low voltage by Ni2+-O-Pd interfaces

Challenges in direct catalytic oxidation of biomass-derived aldehyde and alcohol into acid with high activity and selectivity hinder the widespread biomass application. Herein, we demonstrate that a Pd/Ni(OH)2 catalyst with abundant Ni2+-O-Pd interfaces allows electrooxidation of 5-hydroxymethylfurfural to 2, 5-furandicarboxylic acid with a selectivity near 100 % and 2, 5-furandicarboxylic acid yield of 97.3% at 0.6 volts (versus a reversible hydrogen electrode) in 1 M KOH electrolyte under ambient conditions. The rate-determining step of the intermediate oxidation of 5-hydroxymethyl-2-furancarboxylic acid is promoted by the increased OH species and low C-H activation energy barrier at Ni2+-O-Pd interfaces. Further, the Ni2+-O-Pd interfaces prevent the agglomeration of Pd nanoparticles during the reaction, greatly improving the stability of the catalyst. In this work, Pd/Ni(OH)2 catalyst can achieve 100% 5-hydroxymethylfurfural conversion and >90% 2, 5-furandicarboxylic acid selectivity in a flow-cell and work stably over 200 h under a fixed cell voltage of 0.85 V.

MOF-derived high oxygen vacancies CuO/CeO2 catalysts for low-temperature CO preferential oxidation

The CO preferential oxidation reaction (CO-PROX) is an effective strategy to remove residual poisonous CO in proton exchange membrane fuel cells, in which oxygen vacancies play a critical role in CO adsorption and activation. Herein, a series of CuO/CeO2 catalysts derived from Ce-MOFs precursors were synthesized using different organic ligands via the hydrothermal method and the CO-PROX performance was investigated. The CuO/CeO2-135 catalyst derived from homophthalic tricarboxylic acid (1,3,5-H3BTC) exhibited superior catalytic performance with 100 % CO conversion at a relatively low temperature (T100% = 100 °C), with a wide reaction temperature range and excellent stability. The superior catalytic properties were attributed to the structural improvements provided by the 1,3,5-H3BTC precursors and the promotional effects of oxygen vacancies. Additionally, in-situ Raman spectroscopy was performed to verify the dynamic roles of oxygen vacancies for CO adsorption and activation, while in-situ DRIFTS analysis revealed key intermediates in the CO-PROX reaction, shedding light on the mechanistic aspects of the catalytic process. This work not only demonstrates insights into the effective CuO/CeO2 catalysts for CO preferential oxidation, but also provides a feasible way to synthesize MOF-derived catalysts.

Nanoscale Chemical Probing of Metal-Supported Ultrathin Ferrous Oxide via Tip-Enhanced Raman Spectroscopy and Scanning Tunneling Microscopy

Metal-supported ultrathin ferrous oxide (FeO) has attracted immense interest in academia and industry due to its widespread applications in heterogeneous catalysis. However, chemical insight into the local structural characteristics of FeO, despite its critical importance in elucidating structure-property relationships, remains elusive. In this work, we report the nanoscale chemical probing of gold (Au)-supported ultrathin FeO via ultrahigh-vacuum tip-enhanced Raman spectroscopy (UHV-TERS) and scanning tunneling microscopy (STM). For comparative analysis, single-crystal Au(111) and Au(100) substrates are used to tune the interfacial properties of FeO. Although STM images show distinctly different moiré superstructures on FeO nanoislands on Au(111) and Au(100), TERS demonstrates the same chemical nature of FeO by comparable vibrational features. In addition, combined TERS and STM measurements identify a unique wrinkled FeO structure on Au(100), which is correlated to the reassembly of the intrinsic Au(100) surface reconstruction due to FeO deposition. Beyond revealing the morphologies of ultrathin FeO on Au substrates, our study provides a thorough understanding of the local interfacial properties and interactions of FeO on Au, which could shed light on the rational design of metal-supported FeO catalysts. Furthermore, this work demonstrates the promising utility of combined TERS and STM in chemically probing the structural properties of metal-supported ultrathin oxides on the nanoscale.

Site-targeted decoration of palladium nanocrystals for catalytic CH4 removal in lean-burn exhaust

Site-targeted decoration of catalytic nanocrystals is essential for maximizing performance with minimal materials use. Here, we demonstrate successful, site-targeted decoration of palladium (Pd) nanocrystals with nickel (Ni) exclusively along crystal facet edges through the thermal decomposition of nickel carbonyl (Ni(CO)4) vapor. Strong interactions between carbon monoxide and Pd facet for passivation or between Ni(CO)4 and crystal facet edges resulted in selective Ni decoration at the nanocrystal edges. The Ni-decorated Pd nanocrystals exhibit superior catalytic performance for methane (CH4) removal in an oxygen-rich lean-burn exhaust atmosphere, requiring 10 times less Ni decoration than conventional Pd-Ni composite catalysts prepared by the wet impregnation method. The site-targeted decoration of nanocrystals introduced in this work offers an efficient and resource-minimizing strategy for enhanced catalytic applications.

Hydrogen Spillover Induced PtCo/CoOx Interfaces with Enhanced Catalytic Activity for CO Oxidation at Low Temperatures in Humid Conditions

The development of catalysts with abundant active interfaces for superior low-temperature catalytic CO oxidation is critical to meet increasingly rigorous emission requirements, yet still challenging. Herein, this work reports a PtCo/CoOx/Al2O3 catalyst with PtCo clusters and enriched Pt─O─Co interfaces induced by hydrogen spillover from the Pt sites and self-oxidation process in air, exhibiting excellent performance for CO oxidation at low temperatures and humid conditions. The combination of structural characterizations and in situ Fourier transform infrared spectroscopy reveals that the PtCo cluster effectively prevents CO saturation/poisoning on the Pt surface. Additionally, the presence of Pt─O─Co interfaces in the PtCo/CoOx/Al2O3 catalyst provides a significant number of active sites for oxygen activation and ─OH formation. This facilitates efficient generation of CO2 at ambient temperature by coupling with nearby adsorbed CO molecules, resulting in superior low-temperature activity and long-term stability for CO oxidation under humid conditions. This work provides a facile route toward rationalizing the design of catalysts with more active interfaces for superior low-temperature CO oxidation under humid conditions for practical applications.

Metal-Sulfur Interfaces as the Primary Active Sites for Catalytic Hydrogenations

The determination of catalytically active sites is crucial for understanding the catalytic mechanism and providing guidelines for the design of more efficient catalysts. However, the complex structure of supported metal nanocatalysts (e.g., support, metal surface, and metal-support interface) still presents a big challenge. In particular, many studies have demonstrated that metal-support interfaces could also act as the primary active sites in catalytic reactions, which is well elucidated in oxide-supported metal nanocatalysts but is rarely reported in carbon-supported metal nanocatalysts. Here, we fill the above gap and demonstrate that metal-sulfur interfaces in sulfur-doped carbon-supported metal nanocatalysts are the primary active sites for several catalytic hydrogenation reactions. A series of metal nanocatalysts with similar sizes but different amounts of metal-sulfur interfaces were first constructed and characterized. Taking Ir for quinoline hydrogenation as an example, it was found that their catalytic activities were proportional to the amount of the Ir-S interface. Further experiments and density functional theory (DFT) calculations suggested that the adsorption and activation of quinoline occurred on the Ir atoms at the Ir-S interface. Similar phenomena were found in p-chloronitrobenzene hydrogenation over the Pt-S interface and benzoic acid hydrogenation over the Ru-S interface. All of these findings verify the predominant activity of metal-sulfur interfaces for catalytic hydrogenation reactions and contribute to the comprehensive understanding of metal-support interfaces in supported nanocatalysts.

Cyanide-Isolated Cobalt Catalyst for Ultraefficient Advanced Oxidation Treatment

Catalyst design with a "Co-N-C" structure at the atomic level has shown great interest for peroxymonosulfate (PMS) activation toward advanced oxidation water treatment. Here, we present an innovative way of producing cobalt hexacyanocobaltate (Co-HCC) with an abundance of atomically isolated CoII-NC sites at the outer surface. This material allows ultraefficient PMS activation to generate plenty of sulfate and hydroxyl radicals, with a turnover frequency much higher than those of most cobalt-based catalysts reported so far and even the homogeneous catalysis by Co2+ ions. We gained fundamental insights on its unprecedently high catalytic performance based on experimental results and computational study. Then, we controlled the growth of Co-HCC on a ceramic membrane to form a confined oxidation environment that utilizes the extended surface area and maximal exposure of short-lived radicals for a fast removal of organic pollutants that enter the pores. As a result, this catalytic membrane achieves complete disruption of micropollutants under a water flux up to 10,000 LMH (merely 0.2 s retention time) and further >90% mineralization of organic pollutants in complex industrial wastewater matrices (<100 s retention time), together with the merits of operational simplicity and great longevity (2 weeks continuous run). Our study elicits a new milestone in "Co-N-C" catalyst structure design for PMS activation and highlights the great interest of producing catalytic membranes for a confined treatment of organic pollutants from partial oxidation to complete mineralization as a new benchmark.

Confined Synthesis of Noble Metal Clusters Assisted by Liquid Film for Photocatalytic CO2 Reduction

The important concept of confined synthesis is considered a promising strategy for the design and synthesis of definable nanostructured materials with controllable compositions and specific morphology, such as highly loaded single-atom catalysts capable of providing abundant active sites for photocatalytic reactions. In recent years, researchers have been working on developing new confined reaction systems and searching for new confined spaces. Here, we present for the first time the concept of a bubble liquid film as a novel confined space. The liquid film has a typical sandwich structure consisting of a water layer, sandwiched between the upper and lower surfactant layers, with the thickness of the intermediate water layer at the micro- and nanometer scales, which can serve as a good confinement. Based on the above understanding and combined with the photodeposition method, we successfully confined synthesized Ag/TiO2, Au/TiO2, and Pd/TiO2 photocatalysts in liquid film. By HAADF-STEM, it can be seen that the noble metal morphologies are all nanoclusters of about 1 nm and are highly uniformly dispersed on the TiO2 surface. Compared with photodeposition in solution, we believe that the surfactant molecular layer restricts a limited amount of precursor to the liquid film, avoiding the accumulation of noble metals and the formation of large particle size nanoparticles. The liquid film, meanwhile, restricts the migration path of noble metal precursors, allowing for thorough in situ photodeposition and enables the complete and uniform dispersion of noble metal precursors, greatly reducing the photodeposition time. The uniform loading of the three noble metals proved the universality of the method, and the catalysts showed high activity for photocatalytic CO2 reduction. The rates of reduction of CO2 to CO over the Ag/TiO2 photocatalytic reached 230 μmol g-1 h-1.This study provides a new idea for the expansion of the confined reaction system and a reference for the study of liquid film as the confined space.

Rare-earth Element-based Electrocatalysts Designed for CO2 Electro-reduction

Electrochemical CO2 reduction presents a promising approach for synthesizing fuels and chemical feedstocks using renewable energy sources. Although significant advancements have been made in the design of catalysts for CO2 reduction reaction (CO2RR) in recent years, the linear scaling relationship of key intermediates, selectivity, stability, and economical efficiency are still required to be improved. Rare earth (RE) elements, recognized as pivotal components in various industrial applications, have been widely used in catalysis due to their unique properties such as redox characteristics, orbital structure, oxygen affinity, large ion radius, and electronic configuration. Furthermore, RE elements could effectively modulate the adsorption strength of intermediates and provide abundant metal active sites for CO2RR. Despite their potential, there is still a shortage of comprehensive and systematic analysis of RE elements employed in the design of electrocatalysts of CO2RR. Therefore, the current approaches for the design of RE element-based electrocatalysts and their applications in CO2RR are thoroughly summarized in this review. The review starts by outlining the characteristics of CO2RR and RE elements, followed by a summary of design strategies and synthetic methods for RE element-based electrocatalysts. Finally, an overview of current limitations in research and an outline of the prospects for future investigations are proposed.

Superstructure-Assisted Single-Atom Catalysis on Tungsten Carbides for Bifunctional Oxygen Reactions

Single-atom catalysis (SAC) attracts wide interest for zinc-air batteries that require high-performance bifunctional electrocatalysts for oxygen reactions. However, catalyst design is still highly challenging because of the insufficient driving force for promoting multiple-electron transfer kinetics. Herein, we report a superstructure-assisted SAC on tungsten carbides for oxygen evolution and reduction reactions. In addition to the usual single atomic sites, strikingly, we reveal the presence of highly ordered Co superstructures in the interfacial region with tungsten carbides that induce internal strain and promote bifunctional catalysis. Theoretical calculations show that the combined effects from superstructures and single atoms strongly reduce the adsorption energy of intermediates and overpotential of both oxygen reactions. The catalyst therefore presented impressive bifunctional activity with an ultralow potential gap of 0.623 V and delivered a high power density of 188.5 mW cm-2 for assembled zinc-air batteries. This work opens up new opportunities for atomic catalysis.

Probing Catalytic Sites and Adsorbate Spillover on Ultrathin FeO2-x Film on Ir(111) during CO Oxidation

The spatially resolved identification of active sites on the heterogeneous catalyst surface is an essential step toward directly visualizing a catalytic reaction with atomic scale. To date, ferrous centers on platinum group metals have shown promising potential for low-temperature CO catalytic oxidation, but the temporal and spatial distribution of active sites during the reaction and how molecular-scale structures develop at the interface are not fully understood. Here, we studied the catalytic CO oxidation and the effect of co-adsorbed hydrogen on the FeO2-x/Ir(111) surface. Combining scanning tunneling microscopy (STM), isotope-labeled pulse reaction measurements, and DFT calculations, we identified both FeO2/Ir and FeO2/FeO sites as active sites with different reactivity. The trilayer O-Fe-O structure with its Moiré pattern can be fully recovered after O2 exposure, where molecular O2 dissociates at the FeO/Ir interface. Additionally, as a competitor, dissociated hydrogen migrates onto the oxide film with the formation of surface hydroxyl and water clusters down to 150 K.

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.

Reactant-Induced Structural Evolution of Pt Catalysts Confined in Zeolite

Reactant-induced structural evolutions of heterogeneous metal catalysts are frequently observed in numerous catalytic systems, which can be associated with the formation or deactivation of active sites. In this work, we will show the structural transformation of subnanometer Pt clusters in pure-silica MFI zeolite structure in the presence of CO, O2, and/or H2O and the catalytic consequences of the Pt-zeolite materials derived from various treatment conditions. By applying the appropriate pretreatment under a reactant atmosphere, we can precisely modulate the size distribution of Pt species spanning from single Pt atoms to small Pt nanoparticles (1-5 nm) in the zeolite matrix, resulting in the desirably active and stable Pt species for CO oxidation. We also show the incorporation of Fe into the zeolite framework greatly promotes the stability of Pt species against undesired sintering under harsh conditions (up to 650 °C in the presence of CO, O2, and moisture).

Interface sites on vanadia-based catalysts are highly active for NOx removal under realistic conditions

TiO2-supported V2O5 catalysts are commonly used in NOx reduction with ammonia due to their robust catalytic performance. Over these catalysts, it is generally considered that the active species are mainly derived from the vanadia species rather than the intrinsic structure of V-O-Ti entities, namely the interface sites. To reveal the role of V-O-Ti entities in NH3-SCR, herein, we prepared TiO2/V2O5 catalysts and demonstrated that V-O-Ti entities were more active for NOx reduction under wet conditions than the V sites (V=O) working alone. On the V-O-Ti entities, kinetic measurements and first principles calculations revealed that NH3 activation exhibited a much lower energy barrier than that on V=O sites. Under wet conditions, the V-O-Ti interface significantly inhibited the transformation of V=O to V-OH sites thus benefiting NH3 activation. Under wet conditions, meanwhile, the migration of NH4+ from Ti site neighboring the V-O-Ti interface to Ti site of the V-O-Ti interface was exothermic; thus, V-O-Ti entities together with neighboring Ti sites could serve as channels linking NH3 pool and active centers for activation of NH4+. This finding reveals that the V-O-Ti interface sites on V-based catalysts play a crucial role in NOx removal under realistic conditions, providing a new perspective on NH3-SCR mechanism.

CO Oxidation Promoted by NO Adsorption on RhMn2O3- Cluster Anions

CO oxidation represents an important model reaction in the gas phase to provide a clear structure-reactivity relationship in related heterogeneous catalysis. Herein, in combination with mass spectrometry experiments and quantum-chemical calculations, we identified that the RhMn2O3- cluster cannot oxidize CO into gas-phase CO2 at room temperature, while the NO preadsorbed products RhMn2O3-[(NO)1,2] are highly reactive in CO oxidation. This discovery is helpful to get a fundamental understanding on the reaction behavior in real-world three-way catalytic conditions where different kinds of reactants coexist. Theoretical calculations were performed to rationalize the crucial roles of preadsorbed NO where the strongly attached NO on the Rh atom can greatly stabilize the products RhMn2O2-[(NO)1,2] during CO oxidation and at the same time works together with the Rh atom to store electrons that stay originally in the attached CO2- unit. The leading result is that the desorption of CO2, which is the rate-determining step of CO oxidation by RhMn2O3-, can be greatly facilitated on the reactions of RhMn2O3-[(NO)1,2] with CO.

General Synthesis of High-Entropy Oxide Nanofibers

The discovery of high-entropy oxides (HEOs) in 2015 has provided a family of potential solid catalysts, due to their tunable components, abundant defects or lattice distorts, excellent thermal stability (ΔG↓ = ΔH - TΔS↑), and so on. When facing the heterogeneous catalysis by HEOs, the micrometer bulky morphology and low surface areas (e.g., <10 m2 g-1) by traditional synthesis methods obstructed their way. In this work, an electrospinning method to fabricate HEO nanofibers with diameters of 50-100 nm was demonstrated. The key point lay in the formation of one-dimensional filamentous precursors, during which the uniform dispersion of five metal species with disordered configuration would help to crystallize into single-phase HEOs at lower temperatures: inverse spinel (Cr0.2Mn0.2Co0.2Ni0.2Fe0.2)3O4 (400 °C), perovskite La(Mn0.2Cu0.2Co0.2Ni0.2Fe0.2)O3 (500 °C), spinel Ni0.2Mg0.2Cu0.2Mn0.2Co0.2)Al2O4 (550 °C), and cubic Ni0.2Mg0.2Cu0.2Zn0.2Co0.2O (750 °C). As a proof-of-concept, (Ni3MoCoZn)Al12O24 nanofiber exhibited good activity (CH4 Conv. > 96%, CO2 Conv. > 99%, H2/CO ≈ 0.98), long-time stability (>100 h) for the dry reforming of methane (DRM) at 700 °C without coke deposition, better than control samples (Ni3MoCoZn)Al12O24-Coprecipitation-700 (CH4 Conv. < 3%, CO2 Conv. < 7%). The reaction mechanism of DRM was studied by in situ infrared spectroscopy, CO2-TPD, and CO2/CH4-TPSR. This electrospinning method provides a synthetic route for HEO nanofibers for target applications.

Conductive catalysis by subsurface transition metals

The nature of catalysis has been hotly pursued for over a century, and current research is focused on understanding active centers and their electronic structures. Herein, the concept of conductive catalysis is proposed and verified by theoretical simulations and experimental observations. Metallic systems containing buried catalytically active transitional metals and exposed catalytically inert main group metals are constructed, and the electronic interaction between them via metallic bonding is disclosed. Through the electronic interaction, the catalytic properties of subsurface transitional metals (Pd or Rh) can be transferred to outermost main group metals (Al or Mg) for several important transformations like semi-hydrogenation, Suzuki-coupling and hydroformylation. The catalytic force is conductive, in analogy with the magnetic force and electrostatic force. The traditional definition of active centers is challenged by the concept of conductive catalysis and the electronic nature of catalysis is more easily understood. It might provide new opportunities for shielding traditional active centers against poisoning or leaching and allow for precise regulation of their catalytic properties by the conductive layer.

Precise arrangement of metal atoms at the interface by a thermal printing strategy

The kinetics and pathway of most catalyzed reactions depend on the existence of interface, which makes the precise construction of highly active single-atom sites at the reaction interface a desirable goal. Herein, we propose a thermal printing strategy that not only arranges metal atoms at the silica and carbon layer interface but also stabilizes them by strong coordination. Just like the typesetting of Chinese characters on paper, this method relies on the controlled migration of movable nanoparticles between two contact substrates and the simultaneous emission of atoms from the nanoparticle surface at high temperatures. Observed by in situ transmission electron microscopy, a single Fe3O4 nanoparticle migrates from the core of a SiO2 sphere to the surface like a droplet at high temperatures, moves along the interface of SiO2 and the coated carbon layer, and releases metal atoms until it disappears completely. These detached atoms are then in situ trapped by nitrogen and sulfur defects in the carbon layer to generate Fe single-atom sites, exhibiting excellent activity for oxygen reduction reaction. Also, sites' densities can be regulated by controlling the size of Fe3O4 nanoparticle between the two surfaces. More importantly, this strategy is applicable to synthesize Mn, Co, Pt, Pd, Au single-atom sites, which provide a general route to arrange single-atom sites at the interface of different supports for various applications.

Enhanced Methanol Synthesis over Self-Limited ZnOx Overlayers on Cu Nanoparticles Formed via Gas-Phase Migration Route

Supported metal catalysts are widely used for chemical conversion, in which construction of high density metal-oxide or oxide-metal interface is an important means to improve their reaction performance. Here, Cu@ZnOx encapsulation structure has been in situ constructed through gas-phase migration of Zn species from ZnO particles onto surface of Cu nanoparticles under CO2 hydrogenation atmosphere at 450 °C. The gas-phase deposition of Zn species onto the Cu surface and growth of ZnOx overlayer is self-limited under the high temperature and redox gas (CO2 /H2 ) conditions. Accordingly, high density ZnOx -Cu interface sites can be effectively tailored to have an enhanced activity in CO2 hydrogenation to methanol. This work reveals a new route for the construction of active oxide-metal interface and classic strong metal-support interaction state through gas-phase migration of support species induced by high temperature redox reaction atmosphere.

Enhanced immobilization of Arsenic(III) and Auto-oxidation to Arsenic(V) by titanium oxide (TiO2), due to Single-Atom vacancies and oxyanion formation

Pollution control of As(III), a naturally occurring carcinogen, has recently gained a global attention, while due to the dominance of neutral H3AsO3 over a wide pH range, As(III) immobilization by most minerals is not efficient as As(V) immobilization. TiO2 shows promise for controlling As(III) pollution, and herein, a comprehensive study about As(III) adsorption by TiO2 and oxyanion formation is conducted by means of DFT + D3 methods. Both anatase and rutile are effective for As(III) adsorption, while As(III) adsorption affinities differ significantly and are -1.48 and -3.79 eV for pristine surfaces, ascend to -3.85 and -5.08 eV for O vacancies, and further to -5.37 and -5.26 eV for Ti vacancies, respectively. The bidentate binuclear complexes dominate for pristine surfaces, and O vacancies prefer OAs insertion into TiO2 lattice, while for Ti vacancies, all As(III) centers are auto-oxidized to As(V). Ti-3d, O-2p or/and As-4p rather than other orbitals contribute significantly to As adsorption, and O and Ti vacancies promote adsorption through stronger orbital hybridization. The superior adsorption for Ti vacancies originates from As(V) formation instead of bonding interactions. The formation of As oxyanions, which may occur spontaneously at pristine surfaces and is greatly promoted by O and Ti vacancies, enhances As(III) adsorption pronouncedly and becomes a viable strategy for As(III) immobilization. H2AsO3- and HAsO32- dominate for pristine surfaces and O vacancies, and for Ti vacancies, H2AsO4- and HAsO42- dominate over anatase whereas AsO43- also makes an important contribution over rutile. Results rationalize experimental observations available, and provide significantly new insights about the migration, bioavailability and fate of As(III) over TiO2 surfaces that facilitate the exploration of scavengers for As and other pollutants.

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 O2 activation and H2 adsorption on an ultrathin Mn3O4 surface enable selective oxidation of CO over H2. Theoretical calculations reveal that Mn-O pairs for H2 dissociation are separated from Mn-Mn pairs for the formation of adsorbed O2* so that H2 has to surmount much higher barriers for both H2 dissociation and H diffusion while CO can directly react with O2* following the Eley-Rideal process. Our study sheds light on the atomic-level understanding of the surface structure-dependent selective oxidation reaction on oxide catalysts.

Confined synthesis of ternary FeCoMn single-atom nanozyme in N-doped hollow mesoporous carbon nanospheres for synergistic chemotherapy and chemodynamic cancer therapy

Recently, nanozymes show increasing biological applications and promising possibilities for therapeutic intervention, while their mediated therapeutic outcomes are severely compromised due to their insufficient catalytic activity and specificity. Herein, ternary FeCoMn single atoms were incorporated into N-doped hollow mesoporous carbon nanospheres by in situ confinement pyrolysis at 800 °C as high-efficiency nanozyme. The confinement strategy endows the as-prepared nanozyme with the enhanced catalase- and oxidase-like activities. Specifically, the FeCoMn TSAs/N-HCSs nanozyme can decompose intracellular H2O2 to generate O2 and subsequently convert O2 to cytotoxic superoxide radicals (O2∙-), which can initiate cascade enzymatic reactions in tumor microenvironment (TME) for chemodynamic therapy (CDT). Moreover, the cancer therapy was largely enhanced by loading with doxorubicin (DOX). Impressively, the FeCoMn TSAs/N-HCSs nanozyme-mediated CDT and the DOX-induced chemotherapy endow the DOX@FeCoMn TSAs/N-HCSs with effective tumor inhibition, showing the superior therapeutic efficacy.

Reactant enrichment in hollow void of Pt NPs@MnOx nanoreactors for boosting hydrogenation performance

In confined mesoscopic spaces, the unraveling of a catalytic mechanism with complex mass transfer and adsorption processes such as reactant enrichment is a great challenge. In this study, a hollow nanoarchitecture of MnOx-encapsulated Pt nanoparticles was designed as a nanoreactor to investigate the reactant enrichment in a mesoscopic hollow void. By employing advanced characterization techniques, we found that the reactant-enrichment behavior is derived from directional diffusion of the reactant driven through the local concentration gradient and this increased the amount of reactant. Combining experimental results with density functional theory calculations, the superior cinnamyl alcohol (COL) selectivity originates from the selective adsorption of cinnamaldehyde (CAL) and the rapid formation and desorption of COL in the MnOx shell. The superb performance of 95% CAL conversion and 95% COL selectivity is obtained at only 0.5 MPa H2 and 40 min. Our findings showcase that a rationally designed nanoreactor could boost catalytic performance in chemoselective hydrogenation, which can be of great aid and potential in various application scenarios.

Atomic Insights into Synergistic Nitroarene Hydrogenation over Nanodiamond-Supported Pt1 -Fe1 Dual-Single-Atom Catalyst

Fundamental understanding of the synergistic effect of bimetallic catalysts is of extreme significance in heterogeneous catalysis, but a great challenge lies in the precise construction of uniform dual-metal sites. Here, we develop a novel method for constructing Pt1 -Fe1 /ND dual-single-atom catalyst, by anchoring Pt single atoms on Fe1 -N4 sites decorating a nanodiamond (ND) surface. Using this catalyst, the synergy of nitroarenes selective hydrogenation is revealed. In detail, hydrogen is activated on the Pt1 -Fe1 dual site and the nitro group is strongly adsorbed on the Fe1 site via a vertical configuration for subsequent hydrogenation. Such synergistic effect decreases the activation energy and results in an unprecedented catalytic performance (3.1 s-1 turnover frequency, ca. 100 % selectivity, 24 types of substrates). Our findings advance the applications of dual-single-atom catalysts in selective hydrogenations and open up a new way to explore the nature of synergistic catalysis at the atomic level.

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_L) or dissociate O₂ 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 via high pressure scanning tunneling microscopy. Surface science experiments indicate that oxygen intercalation under the ZnO monolayer film, termed ZnO/O/Au(111), can be achieved via a surface reaction with 1 × 10^-6 mbar O₃. Subsequent exposure of the formed ZnO/O/Au(111) surface to mbar CO at room temperature leads to the recovery of the pristine ZnO/Au(111) surface. Theoretical calculations reveal that O_L adjacent to intercalated oxygen (O_int) is activated due to the O_L-Zn-O_int bonding and surface corrugation, which can be directly involved in CO oxidation. Subsequently, O_int migrates to the formed oxygen vacancy from the subsurface resuming the pristine ZnO structure. These results thus reveal that oxygen intercalation underneath single-layer ZnO will strongly boost the oxidation reaction via activating adjacent lattice oxygen atoms.

Bimetallic Sites for Catalysis: From Binuclear Metal Sites to Bimetallic Nanoclusters and Nanoparticles

Heterogeneous bimetallic catalysts have broad applications in industrial processes, but achieving a fundamental understanding on the nature of the active sites in bimetallic catalysts at the atomic and molecular level is very challenging due to the structural complexity of the bimetallic catalysts. Comparing the structural features and the catalytic performances of different bimetallic entities will favor the formation of a unified understanding of the structure-reactivity relationships in heterogeneous bimetallic catalysts and thereby facilitate the upgrading of the current bimetallic catalysts. In this review, we will discuss the geometric and electronic structures of three representative types of bimetallic catalysts (bimetallic binuclear sites, bimetallic nanoclusters, and nanoparticles) and then summarize the synthesis methodologies and characterization techniques for different bimetallic entities, with emphasis on the recent progress made in the past decade. The catalytic applications of supported bimetallic binuclear sites, bimetallic nanoclusters, and nanoparticles for a series of important reactions are discussed. Finally, we will discuss the future research directions of catalysis based on supported bimetallic catalysts and, more generally, the prospective developments of heterogeneous catalysis in both fundamental research and practical applications.