Amplified Interfacial Effect in an Atomically Dispersed RuOx -on-Pd 2D Inverse Nanocatalyst for High-Performance Oxygen Reduction

Atomically dispersed oxide-on-metal inverse nanocatalysts provide a blueprint to amplify the strong oxide-metal interactions for heterocatalysis but remain a grand challenge in fabrication. Here we report a 2D inverse nanocatalyst, RuO_x -on-Pd nanosheets, by in situ creating atomically dispersed RuO_x /Pd interfaces densely on ultrathin Pd nanosheets via a one-pot synthesis. The product displays unexpected performance toward the oxygen reduction reaction (ORR) in alkaline medium, which represents 8.0- and 22.4-fold enhancement in mass activity compared to the state-of-the-art Pt/C and Pd/C catalysts, respectively, showcasing an excellent Pt-alternative cathode electrocatalyst for fuel cells and metal-air batteries. Density functional theory calculations validate that the RuO_x /Pd interface can accumulate partial charge from the 2D Pd host and subtly change the adsorption configuration of O₂ to facilitate the O-O bond cleavage. Meanwhile, the d-band center of Pd nanosubstrates is effectively downshifted, realizing weakened oxygen binding strength.

Unique structure of active platinum-bismuth site for oxidation of carbon monoxide

As the technology development, the future advanced combustion engines must be designed to perform at a low temperature. Thus, it is a great challenge to synthesize high active and stable catalysts to resolve exhaust below 100 °C. Here, we report that bismuth as a dopant is added to form platinum-bismuth cluster on silica for CO oxidation. The highly reducible oxygen species provided by surface metal-oxide (M-O) interface could be activated by CO at low temperature (~50 °C) with a high CO2 production rate of 487 μmolCO2·gPt-1·s-1 at 110 °C. Experiment data combined with density functional calculation (DFT) results demonstrate that Pt cluster with surface Pt-O-Bi structure is the active site for CO oxidation via providing moderate CO adsorption and activating CO molecules with electron transformation between platinum atom and carbon monoxide. These findings provide a unique and general approach towards design of potential excellent performance catalysts for redox reaction.

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_x) 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_x overlayers work synergistically with surface Pt sites for enhancing CO oxidation reaction. The O-SMSI effect is also present in other h-BN-supported metal catalysts such as Au, Rh, Ru, and Ir within different oxidative atmospheres including O₂ and CO₂, which is determined by metal-boron interaction and O affinity of metals.

Synthesis of Ag-Ni-Fe-P Multielemental Nanoparticles as Bifunctional Oxygen Reduction/Evolution Reaction Electrocatalysts

Multielemental nanoparticles (MENPs) provide the possibility to integrate multiple catalytic functions from different elements into one nanoparticle. However, it is difficult to synthesize Ag-based MENPs with transition metals such as Ni and Fe because of the strong phase segregation between Ag and the other metals. Here, we show that nonmetal element P can help the amalgamation of Ag with other metals. Ag-Ni-Fe-P MENPs are successfully synthesized by a solution-phase chemistry, and they demonstrate excellent bifunctional oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) catalytic activities (the potential gap of the potential at 10 mA·cm^-2 for OER and half-wave potential for ORR is 630 mV). More important, the synergistic effect from the MENPs endows them with even higher ORR or OER activity than the Ag or NiFeP nanoparticles. A rechargeable Zn-air battery is fabricated by using the Ag-Ni-Fe-P MENPs as the air electrode. The battery has an energy efficiency of ∼60% at 10 mA cm^-2. Its performance is almost unchanged during a working period of 250 h, surpassing the Pt/C+IrO₂-based battery. These results suggest that the rationally designed MENPs can integrate multiple catalytic functions together and achieve a synergistic effect, which can be used as high-performance multifunctional catalysts.

Synergetic effect dependence on activated oxygen in the interface of NiOx-modified Pt nanoparticles for the CO oxidation from first-principles

CO oxidation on NiO_x-modified Pt nanoparticles (NPs) was investigated by first-principles calculations and microkinetic methods. The binding energies of O₂ and CO on NiO_x/Pt suggest that CO adsorption is dominant and the CO oxidation mainly follows the Mars-van Krevelen (M-vK) mechanism. It was found that the interfacial O of NiO_x/Pt played a key role in the combination of adsorbed CO to O, as well as the O₂ dissociation. With a lower O vacancy formation energy, NiO_x/Pt_edge shows about four orders higher reaction rates than NiO_x/Pt₍₁₀₀₎. Microkinetic analysis suggests that the rate-determining step also depends on the active O at the interface. The calculations highlight the synergetic effect difference of NiO_x selectively deposited on the different sites of Pt NPs on the CO oxidation from the atomic reaction mechanism, and throws light on the high activity of CO oxidation on partially covered NiO_x/Pt_edge nanoparticles.

Insights into the Interfacial Effects in Heterogeneous Metal Nanocatalysts toward Selective Hydrogenation

Heterogeneous metal catalysts are distinguished by their structure inhomogeneity and complexity. The chameleonic nature of heterogeneous metal catalysts have prevented us from deeply understanding their catalytic mechanisms at the molecular level and thus developing industrial catalysts with perfect catalytic selectivity toward desired products. This Perspective aims to summarize recent research advances in deciphering complicated interfacial effects in heterogeneous hydrogenation metal nanocatalysts toward the design of practical heterogeneous catalysts with clear catalytic mechanism and thus nearly perfect selectivity. The molecular insights on how the three key components (i.e., catalytic metal, support, and ligand modifier) of a heterogeneous metal nanocatalyst induce effective interfaces determining the hydrogenation activity and selectivity are provided. The interfaces influence not only the H₂ activation pathway but also the interaction of substrates to be hydrogenated with catalytic metal surface and thus the hydrogen transfer process. As for alloy nanocatalysts, together with the electronic and geometric ensemble effects, spillover hydrogenation occurring on catalytically "inert" metal by utilizing hydrogen atom spillover from active metal is highlighted. The metal-support interface effects are then discussed with emphasis on the molecular involvement of ligands located at the metal-support interface as well as cationic species from the support in hydrogenation. The mechanisms of how organic modifiers, with the ability to induce both 3D steric and electronic effects, on metal nanocatalysts manipulate the hydrogenation pathways are demonstrated. A brief summary is finally provided together with a perspective on the development of enzyme-like heterogeneous hydrogenation metal catalysts.

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_x nanoislands grown on Au(111) and NiO_x-Ni interfaces formed by further depositing metallic Ni layers along the edges of NiO_x nanoislands. Enhanced activity of Ni-O Lewis pairs at the NiO_x-Ni interface has been demonstrated by theoretical calculations, which are attributed to the higher Lewis acidity of metallic Ni sites and synergy of the metal and oxide components. Moreover, proton can migrate away from the NiO_x-Ni interface and refresh the O base sites, leading to further hydroxylation of the neighboring Ni acid sites.

Bimetal oxide CuO/Co3O4 derived from Cu ions partly-substituted framework of ZIF-67 for toluene catalytic oxidation

A MOF-templated method is developed to prepare bimetal oxide CuO/Co₃O₄ by in situ pyrolysis of Cu²⁺ partly-substituted ZIF-67 precursor. The physicochemical properties of CuO/Co₃O₄ are studied by various characterizations such as X-ray diffraction, Raman analysis, transmission electron microscope, scanning electron microscope, N₂ adsorption-desorption measurement, X-ray photoelectron spectroscope, O₂ temperature-programmed desorption, H₂ temperature-programmed reduction, etc. Comparison with CuO, Co₃O₄ and Mix-CuO/Co₃O₄, 90 % of both toluene conversion and mineralization over CuO/Co₃O₄ are fulfilled at around 229 °C under the condition of 1000 ppm toluene and weight hour space velocity =20,000 mL/(g h), which is promoted more than 40 °C. The better catalytic performance of CuO/Co₃O₄ attributes to high mutual dispersion of two oxides, porous structure, lower temperature reducibility, abundant lattice defects, more active oxygen species, higher Co³⁺/Co²⁺ and O_latt/O_ads molar ratios. Meanwhile, CuO/Co₃O₄ exhibits a better catalytic stability at different conversions and a good tolerance to 10 vol.% of water vapour. The investigation of temperature-dependent active oxygen species and in-situ DRIFTS results reveal that toluene oxidation on CuO/Co₃O₄ obeys Mars van Krevelen mechanism.

Interfacial sites in platinum-hydroxide-cobalt hybrid nanostructures for promoting CO oxidation activity

Metal-oxide/hydroxide hybrid nanostructures provide an excellent platform to study the interfacial effects on tailoring the catalysis of metal catalysts. Herein, a hybrid nanostructure of Pt@Co(OH)2 supported on SiO2 was synthesized by incipient wetness impregnation of Co(OH)2 with the aid of H2O2 and successive urea-assisted deposition-precipitation of platinum nanoparticles. The Fenton-like reaction between Co2+ and H2O2 during the impregnation process facilitates the formation of active interfacial sites. This hybrid nanostructure exhibits much higher catalytic activity towards CO oxidation than Pt/SiO2 nanoparticles with a similar Pt loading and particle size. In situ diffuse reflectance infrared Fourier transform spectroscopy was used to track the CO adsorption processes and to identify the reaction intermediates during CO oxidation. It shows that the OH species at the Pt-OH-Co interfacial sites could readily react with CO adsorbed on neighboring Pt to yield CO2 by forming *COOH intermediates and oxygen vacancies. Under the CO + O2 oxidation conditions, O2 molecules are activated by the oxygen vacancy and react with the CO molecules adsorbed on Pt to generate CO2, via forming the highly active *OOH intermediates as observed by DRIFTS.

Nanoscale engineering of catalytic materials for sustainable technologies

Nanostructured materials of diverse architecture are ubiquitous in industrial catalysis. They offer exciting prospects to tackle various sustainability challenges faced by society. Since the introduction of the concept a century ago, researchers aspire to control the chemical identity, local environment and electronic properties of active sites on catalytic surfaces to optimize their reactivity in given applications. Nowadays, numerous strategies exist to tailor these characteristics with varying levels of atomic precision. Making headway relies upon the existence of analytical approaches able to resolve relevant structural features and remains challenging due to the inherent complexity even of the simplest heterogeneous catalysts, and to dynamic effects often occurring under reaction conditions. Computational methods play a complementary and ever-increasing role in pushing forward the design. Here, we examine how nanoscale engineering can enhance the selectivity and stability of catalysts. We highlight breakthroughs towards their commercialization and identify directions to guide future research and innovation.

Potassium-incorporated manganese oxide enhances the activity and durability of platinum catalysts for low-temperature CO oxidation

Potassium-incorporated manganese oxide is demonstrated as an efficient support for fabricating highly active and stable Pt catalysts for low-temperature CO oxidation.

Phase junction-confined single-atom TiO2–Pt1–CeO2 for multiplying catalytic oxidation efficiency

The phase junction confinement within the TiO₂–Pt₁–CeO₂ ensemble leads to 5 times higher CO oxidation efficiency under 300 K.

Cooperative Catalysis toward Oxygen Reduction Reaction under Dual Coordination Environments on Intrinsic AMnO3 -Type Perovskites via Regulating Stacking Configurations of Coordination Units

It remains challenging for pure-phase catalysts to achieve high performance during the electrochemical oxygen reduction reaction to overcome the sluggish kinetics without the assistance of extrinsic conditions. Herein, a series of pristine perovskites, i.e., AMnO₃ (A = Ca, Sr, and Ba), are proposed with various octahedron stacking configurations to demonstrate the cooperative catalysis over SrMnO₃ jointly explored by experiments and first-principles calculations. Comparing with the unitary stacking of coordination units in CaMnO₃ or BaMnO₃ , the intrinsic SrMnO₃ with a mixture of corner-sharing and face-sharing octahedron stacking configurations demonstrates superior activity (E_half-wave  = 0.81 V), and charge-discharge stability over 400 h without the voltage gap (≈0.8 V) increasing in zinc-air batteries. The theoretical study reveals that, on the SrMnO₃ (110) surface, the active sites switch from coordinatively unsaturated atop Mn (*OO, *OOH) to Mn-Mn bridge (*O, *OH). Therefore, the intrinsic dual coordination environments of Mn-O_corner and Mn-O_face enable cooperative modulation of the interaction strength of the oxygen intermediates with the surface, inducing the decrease of the *OH desorption energy (rate-limiting step) unrestricted by scaling relationships with the overpotential of ≈0.28 V. This finding provides insights into catalyst design through screening intrinsic structures with multiple coordination unit stacking configurations.

Intrinsic electrocatalytic activity of a single IrOx nanoparticle towards oxygen evolution reaction

Identifying the intrinsic electrocatalytic activity of an individual nanoparticle is challenging as traditional ensemble measurements only provide average activity over a large number of nanoparticles and may be greatly affected by the ensemble properties, irrelevant to the nanoparticle itself. Here, single-particle collision electrochemistry is used to investigate the electrocatalytic activity of a single IrOx nanoparticle towards the oxygen evolution reaction (OER). The collision frequency is linearly proportional to the nanoparticle concentration. The mean peak current and transferred charge, extracted from current spikes of the collision, present a similar potential dependence relevant to IrOx intrinsic activity. The turnover frequency (TOF) is determined as 1.55 × 102 O2 s-1, which is orders of magnitude larger than TOFs of the reported ensemble systems. In addition, the deactivation of a single IrOx nanoparticle is also explored based on a half-width analysis of current spikes. This versatilely applicable method provides new insights into the intrinsic performance of a single nanoparticle, which is essential to reveal the structure-activity relations of nanoscale materials for the rational design of advanced catalysts.

Dynamic Surface Reconstruction of Single-Atom Bimetallic Alloy under Operando Electrochemical Conditions

The atomic-level understanding of the dynamic evolution of the surface structure of bimetallic nanoparticles under industrially relevant operando conditions provides a key guide for improving their catalytic performance. Here, we exploit operando X-ray absorption fine structure spectroscopy to determine the dynamic surface reconstruction of Cu/Au bimetallic alloy where single-atom Cu was embedded on the Au nanoparticle, under electrocatalytic conditions. We identify the migration of isolated Cu atoms from the vertex position of the Au nanoparticle to the stable (100) plane of the Au first atom layer, when the reduction potential is applied. Density functional theory calculations reveal that the surface atom migration would significantly modulate the Au electronic structure, thus serving as the real active site for the catalytic performance. These findings demonstrate the real structural change under electrochemical conditions and provide guidance for the rational design of high-activity bimetallic nanocatalysts.

Pt nanoparticles on Ti3C2Tx-based MXenes as efficient catalysts for the selective hydrogenation of nitroaromatic compounds to amines

The development of Pt nanocatalysts for the selective hydrogenation of nitroaromatic compounds to the corresponding amines is of great significance to solve the drawbacks associated with a low reserve of Pt. Herein, we develop a protocol for the preparation of a Pt/titanium carbide-based MXene heterostructure for the selective reduction of nitroaromatic compounds. In the heterostructure, well-defined and nano-sized metallic Pt crystallites are uniformly decorated on Ti3C2Tx nanosheets using a mild reducing agent of ammonia borane without additional stabilizing agents. The selective hydrogenation of p-chloronitrobenzene (p-CNB) to p-chloroaniline (p-CAN) was employed as a model reaction to investigate the catalytic performance of the as-synthesized heterostructure, denoted as Pt/Ti3C2Tx-D-AB. Notably, this catalyst can catalyze the complete conversion of p-CNB to p-CAN with 99.5% selectivity, superior to that of Pt/Ti3C2Tx-D-SB synthesized with sodium borohydride. The high performance of the present catalytic system can be ascribed to the well-dispersed Pt nanoparticles, the abundant surface electron-efficient Pt(0), and the synergistic catalysis between Pt/Ti3C2Tx-D-AB and water. This catalyst also shows generality toward the selective hydrogenation of a series of nitroaromatic compounds to the corresponding amines with high efficiency. The present study provides a strategy to synthesize efficient catalysts for catalytic applications.

Facile Top-Down Strategy for Direct Metal Atomization and Coordination Achieving a High Turnover Number in CO2 Photoreduction

Developing unique single atoms as active sites is vitally important to boosting the efficiency of photocatalytic CO₂ reduction, but directly atomizing metal particles and simultaneously adjusting the configuration of individual atoms remain challenging. Herein, we demonstrate a facile strategy at a relatively low temperature (500 °C) to access the in situ metal atomization and coordination adjustment via the thermo-driven gaseous acid. Using this strategy, the pyrolytic gaseous acid (HCl) from NH₄Cl could downsize the large metal particles into corresponding ions, which subsequently anchored onto the surface defects of a nitrogen-rich carbon (NC) matrix. Additionally, the low-temperature treatment-induced C═O motifs within the interlayer of NC could bond with the discrete Fe sites in a perpendicular direction and finally create stabilized Fe-N₄O species with high valence status (Fe³⁺) on the shallow surface of the NC matrix. It was found that the Fe-N₄O species can achieve a highly efficient CO₂ conversion when accepting energetic electrons from both homogeneous and heterogeneous photocatalysts. The optimized sample achieves a maximum turnover number (TON) of 1494 within 1 h in CO generation with a high selectivity of 86.7% as well as excellent stability. Experimental and theoretical results unravel that high valence Fe sites in Fe-N₄O species can promote the adsorption of CO₂ and lower the formation barrier of key intermediate COOH* compared with the traditional Fe-N₄ moiety with lower chemical valence. Our discovery provides new points of view in the construction of more efficient single-atom cocatalysts by considering the optimization of the atomic configuration for high-performance CO₂ photoreduction.

Metal@Zeolite Hybrid Materials for Catalysis

The fixation of metal nanoparticles into zeolite crystals has emerged as a new series of heterogeneous catalysts, giving performances that steadily outperform the generally supported catalysts in many important reactions. In this outlook, we define different noble metal-in-zeolite structures (metal@zeolite) according to the size of the nanoparticles and their relative location to the micropores. The metal species within the micropores and those larger than the micropores are denoted as encapsulated and fixed structures, respectively. The development in the strategies for the construction of metal@zeolite hybrid materials is briefly summarized in this work, where the rational preparation and improved thermal stability of the metal nanostructures are particularly mentioned. More importantly, these metal@zeolite hybrid materials as catalysts exhibit excellent shape selectivity. Finally, we review the current challenges and future perspectives for these metal@zeolite catalysts.

Ligand Stabilized Ni1 Catalyst for Efficient CO Oxidation

Supported single transition metal (TM₁ ) catalysts have attracted broad attention in academia recently. Still, their corresponding reactivity and stability under reaction conditions are critical but have not well explored at the fundamental level. Herein, we use density functional theory calculation and ab initio molecular dynamics simulation to investigate the role of reactants and ligands on the reactivity and stability of graphitic carbon nitride (g-C₃ N₄ ) supported Ni₁ for CO oxidation. We find out that supported bare Ni₁ atoms are only metastable on the surface and tend to diffuse into the interlayer of g-C₃ N₄ . Though Ni₁ is catalytically active at moderate temperatures, CO adsorption induced dimerization deactivates the catalyst. Hydroxyl groups not only are able to stabilize the supported Ni₁ atom, but also increase the reactivity by participating directly in the reaction. Our results provide valuable insights on improving the chemical stability of TM₁ by ligands without sacrificing the reactivity, which are helpful for the rational design of highly loaded atomically dispersed supported metal catalysts.

Hollow Mesoporous Carbon Sphere Loaded Ni-N4 Single-Atom: Support Structure Study for CO2 Electrocatalytic Reduction Catalyst

Single-atom catalysts have become a hot spot because of the high atom utilization efficiency and excellent activity. However, the effect of the support structure in the single-atom catalyst is often unnoticed in the catalytic process. Herein, a series of carbon spheres supported Ni-N₄ single-atom catalysts with different support structures are successfully synthesized by the fine adjustment of synthetic conditions. The hollow mesoporous carbon spheres supported Ni-N₄ catalyst (Ni/HMCS-3-800) exhibits superior catalytic activity toward the electrocatalytic CO₂ reduction reaction (CO₂ RR). The Faradaic efficiency toward CO is high to 95% at the potential range from -0.7 to -1.1 V versus reversible hydrogen electrode and the turnover frequency value is high up to 15 608 h^-1 . More importantly, the effect of the geometrical structures of carbon support on the CO₂ RR performance is studied intensively. The shell thickness and compactness of carbon spheres regulate the chemical environment of the doped-N species in the carbon skeleton effectively and promote CO₂ molecule activation. Additionally, the optimized mesopore size is beneficial to improve diffusion and overflow of the substance, which enhances the CO₂ adsorption capacity greatly. This work provides a new consideration for promoting the catalytic performance of single-atom catalysts.

Zeolite-Encaged Pd-Mn Nanocatalysts for CO2 Hydrogenation and Formic Acid Dehydrogenation

A CO₂ -mediated hydrogen storage energy cycle is a promising way to implement a hydrogen economy, but the exploration of efficient catalysts to achieve this process remains challenging. Herein, sub-nanometer Pd-Mn clusters were encaged within silicalite-1 (S-1) zeolites by a ligand-protected method under direct hydrothermal conditions. The obtained zeolite-encaged metallic nanocatalysts exhibited extraordinary catalytic activity and durability in both CO₂ hydrogenation into formate and formic acid (FA) dehydrogenation back to CO₂ and hydrogen. Thanks to the formation of ultrasmall metal clusters and the synergic effect of bimetallic components, the PdMn_0.6 @S-1 catalyst afforded a formate generation rate of 2151 mol_formate  mol_Pd ^-1  h^-1 at 353 K, and an initial turnover frequency of 6860 mol H 2  mol_Pd ^-1  h^-1 for CO-free FA decomposition at 333 K without any additive. Both values represent the top levels among state-of-the-art heterogeneous catalysts under similar conditions. This work demonstrates that zeolite-encaged metallic catalysts hold great promise to realize CO₂ -mediated hydrogen energy cycles in the future that feature fast charge and release kinetics.

Single Iron Site Nanozyme for Ultrasensitive Glucose Detection

Nanomaterials with enzyme-mimicking characteristics have engaged great awareness in various fields owing to their comparative low cost, high stability, and large-scale preparation. However, the wide application of nanozymes is seriously restricted by the relatively low catalytic activity and poor specificity, primarily because of the inhomogeneous catalytic sites and unclear catalytic mechanisms. Herein, a support-sacrificed strategy is demonstrated to prepare a single iron site nanozyme (Fe SSN) dispersed on the porous N-doped carbon. With well-defined coordination structure and high density of active sites, the Fe SSN performs prominent peroxidase-like activity by efficiently activating H₂ O₂ into hydroxyl radical (•OH) species. Furthermore, the Fe SSN is applied in colorimetric detection of glucose through a multienzyme biocatalytic cascade platform. Moreover, a low-cost integrated agarose-based hydrogel colorimetric biosensor is designed and successfully achieves the visualization evaluation and quantitative detection of glucose. This work expands the application of single-site catalysts in the fields of nanozyme-based biosensors and personal biomedical diagnosis.

Zn2+ stabilized Pd clusters with enhanced covalent metal-support interaction via the formation of Pd-Zn bonds to promote catalytic thermal stability

Pd-Based heterogeneous catalysts have been demonstrated to be efficient in numerous heterogeneous reactions. However, the effect of the support resulting in covalent metal-support interaction (CMSI) has not been researched sufficiently. In this work, a Lewis base is modulated over MgAl-LDH to investigate the support effects and it is further loaded with Pd clusters to research the metal-support interactions. MgAl-LDH with ultra-low Pd loading (0.0779%) shows CO conversion (55.0%) and dimethyl oxalate (DMO) selectivity (93.7%) for CO oxidative coupling to DMO, which was gradually deactivated after evaluation for 20 h. To promote the stability of Pd/MgAl-LDH, Zn2+ ions were introduced into the MgAl-LDH support to strengthen the CMSI by forming Pd-Zn bonds, which further increased the adsorption energy of the Pd clusters on ZnMgAl-LDH, and this was verified by X-ray absorption fine structure (XAFS) measurements and density functional theory (DFT) calculations. The stability of the Pd/ZnMgAl-LDH catalyst could be maintained for at least 100 h. This work highlights that covalent metal-support interactions can be strengthened by forming new metal-metal bonds, which could be extended to other systems for the stabilization of noble metals over supports.

Atomic-scale study of nanocatalysts by aberration-corrected electron microscopy

Aberration-corrected electron microscopy (AC-EM) including transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) has become one of the most powerful technologies in the studies of nanocatalysts. With the current spatial resolution of sub-0.5 Å and energy resolution of 10 meV, AC-EM can quantificationally articulate the connection between catalytic properties and atomic configurations of nanocatalysts. However, the restricted irradiation sensitive characteristics of specimens pose an obstacle to solve their intrinsic structure. Low-dose imaging should be applied to overcome this problem. In addition, the choice of appropriate imaging method is also crucial to tackle specific structural problems of nanocatalysts. On the basis of careful management of electron dose and selection of suitable imaging method,in situgas and liquid S/TEM are able to reveal the structure evolution of nanocatalysts in real-time. Further combination with residual gas analysis would deepen the understanding of the catalytic reaction.

Inverse iron oxide/metal catalysts from galvanic replacement

Key chemical transformations require metal and redox sites in proximity at interfaces; however, in traditional oxide-supported materials, this requirement is met only at the perimeters of metal nanoparticles. We report that galvanic replacement can produce inverse FeO_x/metal nanostructures in which the concentration of oxide species adjoining metal domains is maximal. The synthesis involves reductive deposition of rhodium or platinum and oxidation of Fe²⁺ from magnetite (Fe₃O₄). We discovered a parallel dissolution and adsorption of Fe²⁺ onto the metal, yielding inverse FeO_x-coated metal nanoparticles. This nanostructure exhibits the intrinsic activity in selective CO₂ reduction that simple metal nanoparticles have only at interfaces with the support. By enabling a simple way to control the surface functionality of metal particles, our approach is not only scalable but also enables a versatile palette for catalyst design.

While typical catalysts involve oxide-supported metals, inverse catalysts of oxides on metal supports offer an attractive alternative. Here, authors prepare FeO_x-coated Rh nanoparticles via galvanic replacement and dissolution-precipitation to form effective CO₂ reduction catalysts.

Interactions of Oxide Surfaces with Water Revealed with Solid-State NMR Spectroscopy

Hydrous materials are ubiquitous in the natural environment and efforts have previously been made to investigate the structures and dynamics of hydrated surfaces for their key roles in various chemical and physical applications, with the help of theoretical modeling and microscopy techniques. However, an overall atomic-scale understanding of the water-solid interface, including the effect of water on surface ions, is still lacking. Herein, we employ ceria nanorods with different amounts of water as an example and demonstrate a new approach to explore the water-surface interactions by using solid-state NMR in combination with density functional theory. NMR shifts and relaxation time analysis provide detailed information on the local structure of oxygen ions and the nature of water motion on the surface: the amount of molecularly adsorbed water decreases rapidly with increasing temperature (from room temperature to 150 °C), whereas hydroxyl groups are stable up to 150 °C, and dynamic water molecules are found to instantaneously coordinate to the surface oxygen ions. The applicability of dynamic nuclear polarization for selective detection of surface oxygen species is also compared to conventional NMR with surface selective isotopic-labeling: the optimal method depends on the feasibility of enrichment and the concentration of protons in the sample. These results provide new insight into the interfacial structure of hydrated oxide nanostructures, which is important to improve performance for various applications.

Highly Selective Aromatization of Octane over Pt-Zn/UZSM-5: The Effect of Pt-Zn Interaction and Pt Position

The effects of Zn-Pt interaction and Pt dispersion over a uniform compact cylindrical shape ZSM-5 (UZSM-5) on the catalytic octane aromatization performance are investigated. The comparison between different Pt- and Zn-modified ZSM-5 catalysts demonstrates the significance of ZSM-5 morphology and, more importantly, the metal distributions on it. For the UZSM-5 support, Pt atoms prefer to occupy the sites within its inner pores, resulting in high selectivity to xylenes during the octane aromatization. The Zn deposit in inner pores and higher dispersion of Pt lead to the spillover of Pt sites to the external surface, which is critical for the activation of octane to produce reaction intermediates that are further converted to aromatics over the inner pore catalytic sites. These effects are evidenced by a diffuse reflection infrared Fourier transform spectroscopy study of CO adsorbed on the catalyst surface. In situ X-ray absorption fine structure spectra are collected to probe the coordination number and the chemical environment of Pt and Zn atoms in the catalysts during the octane aromatization reaction. Pt and Zn are well dispersed and stable during the reaction, and a partial reduction of Pt during the reaction is observed. A theoretical study using the density functional theory method predicts that the reaction and transition-state intermediates upon octane activation are better stabilized by Pt(111) of Pt external surface sites with a smaller activation barrier, indicating their significance in C-H activation. This hypothesis is further evidenced by comparing the octane aromatization performance of various modified catalysts through varying Zn loading, blocking inner pores, and covering the external catalytic sites with SiO₂.

Hydro(deoxygenation) Reaction Network of Lignocellulosic Oxygenates

Hydrodeoxygenation (HDO) is a key transformation step to convert lignocellulosic oxygenates into drop-in and functional high-value hydrocarbons through controlled oxygen removal. Nevertheless, the mechanistic insights of HDO chemistry have been scarcely investigated as opposed to a significant extent of hydrodesulfurization chemistry. Current requirements emphasize certain underexplored events of HDO of oxygenates, which include 1) interactions of oxygenates of varied molecular size with active sites of the catalysts, 2) determining the conformation of oxygenates on the active site at the point of interaction, and 3) effects of oxygen contents of oxygenates on the reaction rate of HDO. It is realized that the molecular interactions of oxygenates with the surface of the catalyst dominates the degree and nature of deoxygenation to derive products with desired selectivity by overcoming complex separation processes in a biorefinery. Those oxygenates with high carbon numbers (>C10), multiple furan rings, and branched architectures are even more complex to understand. This article aims to focus on concise mechanistic analysis of biorefinery oxygenates (C_10-35 ) for their deoxygenation processes, with a special emphasis on their interactions with active sites in a complex chemical environment. This article also addresses differentiation of the mode of interactions based on the molecular size of oxygenates. Deoxygenation processes coupled with or without ring opening of furan-based oxygenates and site-substrate cooperativity dictate the formation of diverse value-added products. Oxygen removal has been the key step for microbial deoxygenation by the use of oxygen-removing decarbonylase enzymes. However, challenges to obtain branched and long-chain hydrocarbons remain, which require special attention, including the invention of newer techniques to upgrade the process for combined depolymerization-HDO from real biomass.

SO2-Tolerant Catalytic Removal of Soot Particles over 3D Ordered Macroporous Al2O3-Supported Binary Pt-Co Oxide Catalysts

The catalytic purification of soot particles is dependent on the SO₂ tolerance and activity of the catalysts in practical application. Herein, we have elaborately fabricated the nanocatalysts of three-dimensionally ordered macroporous (3DOM) Al₂O₃-supported binary Pt-cobalt oxide nanoparticles (NPs) using the method of gas bubbling-assisted membrane precipitation (GBMP), abbreviated as Pt-CoO_x/3DOM-Al₂O₃. Three-dimensionally ordered macroporous Al₂O₃ support can not only improve the contact performance between the soot and active sites but also possess surface acidity to improve the SO₂ tolerance. Supported binary Pt-CoO_x NPs over 3DOM-Al₂O₃ have high-efficient properties for activating NO and O₂. The Pt-CoO_x/3DOM-Al₂O₃ catalyst exhibits super catalytic performance and SO₂ tolerance during the removal of soot particles, whose values of turnover frequency (TOF) and T₅₀ are 0.29 h^-1 and 368 °C, respectively. The catalytic and SO₂-tolerant mechanisms of the Pt-CoO_x/3DOM-Al₂O₃ catalyst for soot purification are systematically studied by in situ diffuse reflectance infrared Fourier transform (DRIFT) spectra. The synergistic effect of binary Pt-CoO_x NPs plays a vital role in the oxidation of NO to NO₂ as a key step during catalytic soot removal, and the surface acidity of 3DOM-Al₂O₃ can not only inhibit the adsorption of SO₂ but also enhance the decomposition of surface hydrosulfate species. This work provides a novel strategy to the development of high-efficient catalysts for SO₂-tolerant catalytic removal of soot particles in both fundamental research and practical applications.

Surrounded catalysts prepared by ion-exchange inverse loading

The supported catalyst featuring highly dispersed active phase on support is the most important kind of industrial catalyst. Extensive research has demonstrated the critical role (in catalysis) of the interfacial interaction/perimeter sites between the active phase and support. However, the supported catalyst prepared by traditional methods generally presents low interface density because of limit contact area. Here, an ion-exchange inverse loading (IEIL) method has been developed, in which the precursor of support is controllably deposited onto the precursor of active phase by ion-exchange reaction, leading to an active core surrounded (by support) catalyst with various structures. The unique surrounded structure presents not only high interface density and mutually changed interface but also high stability due to the physical isolation of active phase, revealing superior catalytic performances to the traditional supported catalysts, suggesting the great potential of this new surrounded catalyst as the upgrade of supported catalyst in heterogeneous catalysis.

Deciphering atomistic mechanisms of the gas-solid interfacial reaction during alloy oxidation

Gas-solid interfacial reaction is critical to many technological applications from heterogeneous catalysis to stress corrosion cracking. A prominent question that remains unclear is how gas and solid interact beyond chemisorption to form a stable interphase for bridging subsequent gas-solid reactions. Here, we report real-time atomic-scale observations of Ni-Al alloy oxidation reaction from initial surface adsorption to interfacial reaction into the bulk. We found distinct atomistic mechanisms for oxide growth in O₂ and H₂O vapor, featuring a "step-edge" mechanism with severe interfacial strain in O₂, and a "subsurface" one in H₂O. Ab initio density functional theory simulations rationalize the H₂O dissociation to favor the formation of a disordered oxide, which promotes ion diffusion to the oxide-metal interface and leads to an eased interfacial strain, therefore enhancing inward oxidation. Our findings depict a complete pathway for the Ni-Al surface oxidation reaction and delineate the delicate coupling of chemomechanical effect on gas-solid interactions.