Taming the stability of Pd active phases through a compartmentalizing strategy toward nanostructured catalyst supports

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.

Enhancing Oxygen Reduction Reaction of Single-Atom Catalysts by Structure Tuning

Deciphering the fine structure has always been a crucial approach to unlocking the distinct advantages of high activity, selectivity, and stability in single-atom catalysts (SACs). However, the complex system and unclear catalytic mechanism have obscured the significance of exploring the fine structure. Therefore, we endeavored to develop a three-component strategy to enhance oxygen reduction reaction (ORR), delving deep into the profound implications of the fine structure, focusing on central atoms, coordinating atoms, and environmental atoms. Firstly, the mechanism by which the chemical state and element type of central atoms influence catalytic performance is discussed. Secondly, the significance of coordinating atoms in SACs is analyzed, considering both the number and type. Lastly, the impact of environmental atoms in SACs is reviewed, encompassing existence state and atomic structure. Thorough analysis and summarization of how the fine structure of SACs influences the ORR have the potential to offer valuable insights for the accurate design and construction of SACs.

Regulating socketed geometry of nanoparticles on perovskite oxide supports for enhanced stability in oxidation reactions

Heterogeneous catalysts with highly dispersed active particles on supports often face stability challenges during high-temperature industrial applications. The ex-solution strategy, which involves in situ extrusion of metals to form socketed particles, shows potential for addressing this stability issue. However, a deeper understanding of the relationship between the socketed geometry of these partially embedded nanoparticles and their catalytic performance is still lacking. Here, in situ transmission electron microscopy and theoretical calculations are utilized to investigate the oxygen-induced ex-solution process of Pd-doped LaAlO3 with varying concentrations of La vacancies (LaxAl0.9Pd0.1O3-δ). We find that the socketed geometry of Pd-based particles can be tuned by manipulating the levels of La deficiencies in the oxide support, which in turn influences the catalytic performance in high-temperature oxidation reactions. As for the socketed particles, the balance between particle size and outcrop height is crucial for determining the oxidation activity and sinter-resistance behavior. Consequently, the optimized catalyst, La0.8Al0.9Pd0.1O3-δ, exhibits superior catalytic performances, particularly high stability (still working after aging at 1000 °C for 50 h) and water resistance in various combustion reactions (e.g., CH4 oxidation and C3H8 oxidation).

Real-Time Simulation of the Reaction Kinetics of Supported Metal Nanoparticles

A common issue with supported metal catalysts is the sintering of metal nanoparticles, resulting in catalyst deactivation. In this study, we propose a theoretical framework for realizing a real-time simulation of the reactivity of supported metal nanoparticles during the sintering process, combining density functional theory calculations, microkinetic modeling, Wulff-Kaichew construction, and sintering kinetic simulations. To validate our approach, we demonstrate its feasibility on α-Al2O3(0001)-supported Ag nanoparticles, where the simulated sintering behavior and ethylene epoxidation reaction rate as a function of time show qualitative agreement with experimental observation. Our proposed theoretical approach can be employed to screen out the promising microstructure feature of α-Al2O3 for stable supported Ag NPs, including the surface orientation and promoter species modified on it. The outlined approach of this work may be applied to a range of different thermocatalytic reactions other than ethylene epoxidation and provide guidance for the development of supported metal catalysts with long-term stability.

Construction of Molecularly Dispersed Polyoxometalate-Alumina Hybrid Hollow Nanoflowers via Water-Induced Kirkendall Effect

Hybrid nanomaterials with controllable structures and diverting components have attracted significant interest in the functional materials field. Here, we develop a solvent evaporation-induced self-assembly (EISA) strategy to synthesize nanosheet-assembled phosphomolybdic acid (H3PMo)-alumina hybrid hollow spheres. The resulting nanoflowers display a high surface area (up to 697 m2 g-1), adjustable diameter, high chemical/thermal stability, and especially molecularly dispersed H3PMo species. By employing various microscopic and spectroscopic techniques, the formation mechanism is elucidated, revealing the simultaneous control of the morphology by heteropoly acids and water through the water-induced Kirkendall effect. The versatility of the synthesis method is demonstrated by varying surfactants, heteropoly acids, and metal oxide precursors for the facile synthesis of hybrid metal oxides. Spherical hybrid alumina serves as an attractive support material for constructing metal-acid bifunctional catalysts owing to its advantageous surface area, acidity, and mesoporous microenvironment. Pt-loaded hollow flowers exhibit excellent catalytic performance and exceptional stability in the hydrodeoxygenation of vanillin with recyclability for up to 10 cycles. This research presents an innovative strategy for the controllable synthesis of hybrid metal oxide nanospheres and hollow nanoflowers, providing a multifunctional platform for diverse applications.

Unveiling the Stability of Encapsulated Pt Catalysts Using Nanocrystals and Atomic Layer Deposition

Platinum exhibits desirable catalytic properties, but it is scarce and expensive. Optimizing its use in key applications such as emission control catalysis is important to reduce our reliance on such a rare element. Supported Pt nanoparticles (NPs) used in emission control systems deactivate over time because of particle growth in sintering processes. In this work, we shed light on the stability against sintering of Pt NPs supported on and encapsulated in Al2O3 using a combination of nanocrystal catalysts and atomic layer deposition (ALD) techniques. We find that small amounts of alumina overlayers created by ALD on preformed Pt NPs can stabilize supported Pt catalysts, significantly reducing deactivation caused by sintering, as previously observed by others. Combining theoretical and experimental insights, we correlate this behavior to the decreased propensity of oxidized Pt species to undergo Ostwald ripening phenomena because of the physical barrier imposed by the alumina overlayers. Furthermore, we find that highly stable catalysts can present an abundance of under-coordinated Pt sites after restructuring of both Pt particles and alumina overlayers at a high temperature (800 °C) in C3H6 oxidation conditions. The enhanced stability significantly improves the Pt utilization efficiency after accelerated aging treatments, with encapsulated Pt catalysts reaching reaction rates more than two times greater than those of a control supported Pt catalyst.

Creating Atomically Iridium-Doped PdOx Nanoparticles for Efficient and Durable Methane Abatement

The urgent environmental concern of methane abatement, attributed to its high global warming potential, necessitates the development of methane oxidation catalysts (MOC) with enhanced low-temperature activity and durability. Herein, an iridium-doped PdOx nanoparticle supported on silicalite-1 zeolite (PdIr/S-1) catalyst was synthesized and applied for methane catalytic combustion. Comprehensive characterizations confirmed the atomically dispersed nature of iridium on the surface of PdOx nanoparticles, creating an Ir4f-O-Pdcus microstructure. The atomically doped Ir transferred more electrons to adjacent oxygen atoms, modifying the electronic structure of PdOx and thus enhancing the redox ability of the PdIr/S-1 catalysts. This electronic modulation facilitated methane adsorption on the Pd site of Ir4f-O-Pdcus, reducing the energy barrier for C-H bond cleavage and thereby increasing the reaction rate for methane oxidation. Consequently, the optimized PdIr0.1/S-1 showed outstanding low-temperature activity for methane combustion (T50 = 276 °C) after aging and maintained long-term stability over 100 h under simulated exhaust conditions. Remarkably, the novel PdIr0.1/S-1 catalyst demonstrated significantly enhanced activity even after undergoing harsh hydrothermal aging at 750 °C for 16 h, significantly outperforming the conventional Pd/Al2O3 catalyst. This work provides valuable insights for designing efficient and durable MOC catalysts, addressing the critical issue of methane abatement.

Crystal-Phase Engineering in Heterogeneous Catalysis

The performance of a chemical reaction is critically dependent on the electronic and/or geometric structures of a material in heterogeneous catalysis. Over the past century, the Sabatier principle has already provided a conceptual framework for optimal catalyst design by adjusting the electronic structure of the catalytic material via a change in composition. Beyond composition, it is essential to recognize that the geometric atomic structures of a catalyst, encompassing terraces, edges, steps, kinks, and corners, have a substantial impact on the activity and selectivity of a chemical reaction. Crystal-phase engineering has the capacity to bring about substantial alterations in the electronic and geometric configurations of a catalyst, enabling control over coordination numbers, morphological features, and the arrangement of surface atoms. Modulating the crystallographic phase is therefore an important strategy for improving the stability, activity, and selectivity of catalytic materials. Nonetheless, a complete understanding of how the performance depends on the crystal phase of a catalyst remains elusive, primarily due to the absence of a molecular-level view of active sites across various crystal phases. In this review, we primarily focus on assessing the dependence of catalytic performance on crystal phases to elucidate the challenges and complexities inherent in heterogeneous catalysis, ultimately aiming for improved catalyst design.

In Situ Synthesis of Encapsulated Pd@silicalite-2 for Highly Stable Methane Catalytic Combustion

Methane emissions from vehicles have made a significant contribution to the greenhouse effect, primarily due to its high global warming potential. Supported noble metal catalysts are widely employed in catalytic combustion of methane in vehicles, but they still face challenges such as inadequate low-temperature activity and deactivation due to sintering under harsh operating conditions. In the present work, a series of encapsulated structured catalysts with palladium nanoparticles confined in hydrophobic silicalite-2 were prepared by an in situ synthesis method. Based on various characterization methods, including XRD, HR-TEM, XPS, H2-TPR, O2-TPD, H2O-TPD, CH4-TPR, Raman, and in situ DRIFTS-MS, it was confirmed that PdOx nanoparticles were mainly encapsulated inside the silicalite-2 zeolite, which further maintained the stability of the nanoparticles under harsh conditions. Specifically, the 3Pd@S-2 sample exhibited high catalytic activity for methane oxidation even after harsh hydrothermal aging at 750 °C for 16 h and maintained long-term stability at 400 °C for 130 h during wet methane combustion. In situ Raman spectroscopy has confirmed that PdOx species act as active species for methane oxidation. During this reaction, methane reacts with PdOx to produce CO2 and H2O, while simultaneously reducing PdOx to metallic Pd species, which is further reoxidized by oxygen to replenish the PdOx catalyst.

Insight into the Promotion Effect of Trace Pd Doping on the Catalytic Performance of Ag/Al2O3 for C3H6-SCR of NOx

The mechanistic cause of the enhancement of the C3H6-SCR activity of Ag/Al2O3 by trace Pd doping and the corresponding structure-property relationship were investigated. Pd doping enhanced the water resistance of Ag/Al2O3 for C3H6-SCR by changing the reaction pathway. Under wet conditions, a series of in situ DRIFT studies indicated that the production of an active acetate intermediate on Ag/Al2O3 was suppressed during the partial oxidation of C3H6, while trace Pd doping promoted the formation of another active intermediate, an enolic species. Furthermore, a pathway for the formation of enolic species by the reaction of acrylate with hydroxyl species was proposed. DFT calculations revealed that the surface of Ag clusters was easily covered by hydroxyl in the presence of water vapor, which could inhibit the formation of acetates. Doping with Pd facilitated the activation of acrylate which might further react with hydroxyl species to form enolic species. These findings can be helpful for the future design of efficient HC-SCR catalysts.

Differential thermal analysis techniques as a tool for preliminary examination of catalyst for combustion

The need for more economical catalysts for various combustion reactions is continuously driving catalyst development. We present Differential Thermal Analysis (DTA) and Differential Scanning Calorimetry (DSC) as suitable techniques for fast examination of catalyst activity for combustion reactions. The heat of reaction ΔH_r generated at the catalyst in a combustible atmosphere is the measure for estimating the capability of the catalyst. Present investigations verify the reliability of both methods for the pre-selection of catalysts for further extensive investigations. To simplify the measurements and the result evaluation, a new measurement routine is introduced which is more suitable for rapid catalyst investigation than the conventional approach. For initial investigations, oxidation of 1% methane on a cobalt oxide catalyst was used. First, DTA measurements were performed. The vessel size and the amount of catalyst are considered as factors influencing the thermal signal. Simultaneous mass spectrometry measurements were used to better understand the formation of the DTA response. Comparable DSC investigations were then conducted. Finally, the behavior of catalyst was compared with two commercial palladium/alumina catalysts using DTA and DSC. Our investigations show that DTA and DSC are powerful methods to identify potential catalysts in a fast and reproducible manner, provided that all parameters influencing the thermal signal are kept constant.

Boosting Ozone Catalytic Oxidation of Toluene at Room Temperature by Using Hydroxyl-Mediated MnOx/Al2O3 Catalysts

Ozone catalytic oxidation (OZCO) has gained great interest in environmental remediation while it still faces a big challenge during the deep degradation of refractory volatile organic compounds (VOCs) at room temperature. Hydroxylation of the catalytic surface provides a new strategy for regulating the catalytic activity to boost VOC degradation. Herein, OZCO of toluene at room temperature over hydroxyl-mediated MnO_x/Al₂O₃ catalysts was originally demonstrated. Specifically, a novel hydroxyl-mediated MnO_x/Al₂O₃ catalyst was developed via the in situ AlOOH reconstruction method and used for toluene OZCO. The toluene degradation performance of MnO_x/Al₂O₃ was significantly superior to those of most of the state-of-the-art catalysts, and 100% toluene was removed with an excellent mineralization rate (82.3%) and catalytic stability during OZCO. ESR and in situ DRIFTs results demonstrated that surface hydroxyl groups (HGs) greatly improved the reactive oxygen species generation, thus dramatically accelerating the benzene ring breakage and deep mineralization. Furthermore, HGs provided anchoring sites for uniformly dispersing MnO_x and greatly enhanced toluene adsorption and ozone activation. This work paves a way for deep decomposition of aromatic VOCs at room temperature.

Tunable Interfacial Electronic Pd-Si Interaction Boosts Catalysis via Accelerating O2 and H2O Activation

Engineering the interfacial structure between noble metals and oxides, particularly on the surface of non-reducible oxides, is a challenging yet promising approach to enhancing the performance of heterogeneous catalysts. The interface site can alter the electronic and d-band structure of the metal sites, facilitating the transition of energy levels between the reacting molecules and promoting the reaction to proceed in a favorable direction. Herein, we created an active Pd-Si interface with tunable electronic metal-support interaction (EMSI) by growing a thin permeable silica layer on a non-reducible oxide ZSM-5 surface (termed Pd@SiO₂/ZSM-5). Our experimental results, combined with density functional theory calculations, revealed that the Pd-Si active interface enhanced the charge transfer from deposited Si to Pd, generating an electron-enriched Pd surface, which significantly lowered the activation barriers for O₂ and H₂O. The resulting reactive oxygen species, including O₂ ^-, O₂ ^2-, and -OH, synergistically facilitated formaldehyde oxidation. Additionally, moderate electronic metal-support interaction can promote the catalytic cycle of Pd⁰ ⇆ Pd²⁺, which is favorable for the adsorption and activation of reactants. This study provides a promising strategy for the design of high-performance noble metal catalysts for practical applications.

Nano-sized alumina supported palladium catalysts for methane combustion with excellent thermal stability

Pd/Al₂O₃ catalysts supported on Al₂O₃ of different particle sizes were synthesized and applied in methane combustion. These catalysts were systematically characterized by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), high resolution-transmission electron microscopy (HR-TEM), high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM), H₂-temperature-programmed reduction (H₂-TPR), O₂-temperature-programmed oxidation (O₂-TPO), X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine structure (XAFS). The characterization results indicated that nano-sized Al₂O₃ enabled the uniform dispersion of palladium nanoparticles, thus contributing to the excellent catalytic performance of these nano-sized Pd/Al₂O₃ catalysts. Among them, Pd/Al₂O₃-nano-10 (Pd/Al₂O₃ supported by alumina with an average particle size of 10 nm) showed superior catalytic activity and stability for methane oxidation under harsh practical conditions. It maintained excellent catalytic performance for methane oxidation for 50 hr and remained stable even after harsh hydrothermal aging in 10 vol.% steam at 800°C for 16 hr. Characterization results revealed that the strong metal-support interactions and physical barriers provided by Al₂O₃-nano-10 suppressed the coalescence ripening of palladium species, and thus contributed to the superior sintering resistance of the Pd/Al₂O₃-nano-10 catalyst.

Effects of Palladium Precursors on the Activity of Palladium Nanocatalysts for the Oxidation of Volatile Organic Components

To screen a suitable precursor, the effects of palladium salts on performance of Pd nanocatalysts for the oxidation of volatile organic components (VOCs) were investigated. A series of catalysts was prepared by impregnating Pd(NO₃)₂, PdCl₂ and Pd(NH₃)₄Cl₂ on alumina-coated cordierites. These catalysts were characterized by XRF, ICP-OES, XRD, N₂ adsorption-desorption, TEM, EDS, Raman spectroscopy, pulse-CO chemisorption, H₂-TPR, NH₃-TPD, and XPS. Pulse-CO chemisorption and TEM showed that Pd species formed by Pd(NO₃)₂ have the highest metal dispersion (17.7%), while the other two were aggregating. For the same Pd loading, the higher the metal dispersion, the more the number of PdO species, so the number of PdO particles in the catalyst prepared from Pd (NO₃) ₂ is the largest. The catalytic oxidation activities of these catalysts were evaluated by ethane and propane. Based on a 99% conversion in the oxidation of ethane and propane at 598 K and 583 K, respectively, the catalyst prepared from Pd(NO₃)₂ was considered to be the best performing catalyst. The chloride species in precursors can promote the aggregation of Pd species and poison the catalysts. The results show that Pd(NO₃)₂ is more suitable as the precursor of VOC oxidation catalyst than PdCl₂ and Pd(NH₃)₄Cl₂.

Spectroscopic Study of Five-Coordinated Thermal Treated Alumina Formation: FTIR and NMR Applying

This work represents research into materials designed to improve the environment. The study was carried out on aluminum hydroxide xerogels and alumina catalysts obtained by the Controlled Double Jet Precipitation (CDJP) process at different pH values. It has been shown that the pH of the CDJP process determines the content of aluminum-bound nitrate ions in the aluminum hydroxide. These ions are removed at a higher temperature than the decomposition of ammonium nitrate. The high content of aluminum-bound nitrate ions determines the structural disorder of the alumina and the high content of the penta-coordinated alumina catalyst.

Current Progress on Methods and Technologies for Catalytic Methane Activation at Low Temperatures

Methane (CH4 ) is an attractive energy source and important greenhouse gas. Therefore, from the economic and environmental point of view, scientists are working hard to activate and convert CH4 into various products or less harmful gas at low-temperature. Although the inert nature of CH bonds requires high dissociation energy at high temperatures, the efforts of researchers have demonstrated the feasibility of catalysts to activate CH4 at low temperatures. In this review, the efficient catalysts designed to reduce the CH4 oxidation temperature and improve conversion efficiencies are described. First, noble metals and transition metal-based catalysts are summarized for activating CH4 in temperatures ranging from 50 to 500 °C. After that, the partial oxidation of CH4 at relatively low temperatures, including thermocatalysis in the liquid phase, photocatalysis, electrocatalysis, and nonthermal plasma technologies, is briefly discussed. Finally, the challenges and perspectives are presented to provide a systematic guideline for designing and synthesizing the highly efficient catalysts in the complete/partial oxidation of CH4 at low temperatures.

Highly Efficient Oxidation of Propane at Low Temperature over a Pt-Based Catalyst by Optimization Support

Pt-based catalysts have attracted widespread attention in environmental protection applications, especially in the catalytic destruction of light alkane pollutants. However, developing a satisfying platinum catalyst with high activity, excellent water-resistance, and practical suitability for hydrocarbon combustion at low temperature is challenging. In this study, the Pt catalyst supported on the selected Nb₂O₅ oxide exhibited an efficient catalytic activity in propane oxidation and exceeded that of most catalysts reported in the literature. More importantly, the Pt/Nb₂O₅ catalyst maintained excellent activity and durability even after high-temperature aging at 700 °C and under harsh working conditions, such as a certain degree of moisture, high space velocity, and composite pollutants. The excellent performance of the Pt/Nb₂O₅ catalyst was attributed to the abundant metallic Pt species stabilized on the surface of Nb₂O₅, which prompted the C-H bond dissociation ability as the rate-determining step. Furthermore, propane was initially activated via oxidehydrogenation and followed the acrylate species path as a more efficient propane oxidation path on the Pt/Nb₂O₅ surface. Overall, Pt/Nb₂O₅ can be considered a promising catalyst for the catalytic oxidation of alkanes from industrial sources and could provide inspiration for designing superb catalysts for the oxidation of light alkanes.

Responsive Ag@NiCo2O4 Nanowires Anchored on N-Doped Carbon Cloth as Array Electrodes for Nonenzymatic Glucose Sensing

The development of responsive materials in a predictable manner is high on the list of the material industry's trends. In this work, responsive Ag@NiCo₂O₄ nanowires were, firstly, anchored on N-doped carbon cloth (NC) and, then, employed as array electrodes for a nonenzymatic glucose-sensing application. The results showed that the highly conductive NiCo₂O₄ nanowires supported Ag nanoparticles and exhibited high conductivity and electrocatalytic properties. The fully exposed crystalline planes of Ag nanoparticles provided more active surface sites. As a result, the assembled Ag@NiCo₂O₄-NC electrodes for the glucose-sensing evaluation delivered a selectivity of 2803 μA mM^-1 cm^-2 and a detection limit of 1.065 μM, which outperformed the literature-reported Ag- and NiCo₂O₄-based glucose-sensing catalysts.

Elucidating the role of confinement and shielding effect over zeolite enveloped Ru catalysts for propane low temperature degradation

Volatile organic compounds (VOCs) are the main precursor for ozone formation and hazardous to human health. Light alkane as one of the typical VOCs is difficult to degrade to CO₂ and H₂O by catalytic degradation method due to its strong C-H bond. Herein, a series of ultrafine Ru nanoclusters (<0.95 nm) enveloped in silicalite-1 (S-1) zeolite catalysts were designed and prepared by a simple one-pot method and applied for catalytic degradation of propane. The results demonstrate that the enveloped Ru₁@S-1 catalyst has excellent propane degradation performance. Its T₉₅ is as low as 294 °C with moisture, and the turnover frequency (TOF) value is up to 5.07 × 10^-3 s^-1, evidently higher than that of the comparison supported catalyst (Ru₁/S-1). Importantly, Ru₁@S-1 exhibits superior thermal stability, water resistance and recyclability, which should be attributed to the confinement and shielding effect of the S-1 shell. The in-situ DRIFTS result reveals that the propane degradation over Ru₁@S-1 follows the Mars-van-Krevelen (MvK) mechanism, where the hydroxy from the framework of zeolite can provide the active oxygen species. Our work provides a new candidate and guideline for an efficient and stable catalyst for the low-temperature degradation of the light alkane VOCs.

Total Oxidation of Light Alkane over Phosphate-Modified Pt/CeO2 Catalysts

Developing efficient catalysts for the total oxidation of light alkane at low temperatures is challenging. In this study, superior catalytic performance in the total oxidation of light alkane was achieved by modulating the acidity and redox property of a Pt/CeO₂ catalyst through phosphorus modification. Surface modification with phosphorus resulted in electron withdrawal from Pt, leading to platinum species with high valency and the generation of Brönsted acid sites, leading to increased acidity of the Pt/CeO₂ catalyst. Consequently, the ability of the Pt/CeO₂ catalyst to activate the C-H bond increased with increasing P content in the catalyst owing to the synergistic effect of Pt^δ+-(CeO₂-PO_x)^δ- dipolar catalytic sites. In contrast, the redox property of the Pt/CeO₂ catalyst weakened at first; subsequently, it was partially restored owing to the recovery of a part of the bare ceria surface with increasing P content. The turnover frequency in propane oxidation over the phosphate-modified Pt/CeO₂ catalyst with a P/Ce atomic ratio of 0.06 was 10-fold higher than that over the unmodified Pt/CeO₂ catalyst at 220 °C. This comprehensive study not only sheds light on the mechanism underlying the surface modification process but also offers a strategy for realizing higher catalytic activity in the total oxidation of light alkanes.

Developing a thermally stable Co/Ce-Sn catalyst via adding Sn for soot and CO oxidation

The thermal stability of the catalysts is of particular importance but still a big challenge for working under harsh conditions at high temperature. In this study, we report a strategy to improve the thermal stability of the ceria-based catalyst via introducing Sn. XRD, Rietveld refinement, and other characterizations results indicated that the formation of Sn-Co solid solution plays a key role in the thermal stability of the catalyst. The developed ternary 3%Co/Ce_0.5Sn_0.5O₂ catalyst not only exhibits outstanding thermal stability and resistance to SO₂ and H₂O for soot oxidation from diesel vehicle exhaust but also remains extraordinary thermal stability for CO oxidation. Remarkably, even after thermal aging at 1000°C, it still possessed high catalytic activity similar to that of the fresh catalyst.

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The developed 3%Co/Ce-Sn catalyst processes extraordinary thermal stability

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The Sn species could restrain the aggregation of Co active component

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The Sn-Co solid solution plays a key role in improving the thermal stability

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The 3%Co/Ce-Sn catalyst exhibited perfect and stable resistance to H₂O and SO₂

Synthesis of a Spatially Confined, Highly Durable, and Fully Exposed Pd Cluster Catalyst via Sequential Site-Selective Atomic Layer Deposition

Bottom-up synthesis based on site-selective atomic layer deposition is a powerful atomic-scale processing approach to fabricate materials with desired functionalities. Typical selective atomic layer deposition (ALD) can be achieved using selective activation of a growth area or selective deactivation of a protected area. In this work, we explored the site selectivity based on the difference of the inherent surface reactivity between different materials and within the same materials. By sequentially applying two site-selective atomic layer deposition, the ALD Pd catalyst is spatially confined on ALD SnO₂ modified h-BN substrate Pd/SnO₂/h-BN shows improved catalytic activity and stability due to strong metal-support interactions and spatial confinement. The results reveal that sequential site-selective ALD is a feasible and effective synthesis strategy that provides an attractive path toward designing and developing highly stable catalysts.

Nickel Hydroxide Nanosheets Prepared by a Direct Manual Grinding Strategy for High-Efficiency Catalytic Combustion of Methane

Nickel hydroxide nanosheets were prepared by a very simple direct manual grinding strategy and then calcined at 200, 300, 400, and 500°. The synthesized samples were tested in lean methane (1.0% CH₄, air balanced) catalytic combustion and subjected to a series of physical and chemical characterizations. The sample calcined at 200 °C (Ni(OH)₂-200) presented a typical nanosheet structure and the best methane catalytic activity in all the samples, which can completely catalyze methane at 400 °C. The crystal structure changed from β-Ni(OH)₂ to NiO at a calcination temperature of 300 °C. The β-Ni(OH)₂ nanosheets began to partially agglomerate into nanoparticles at 400 °C and almost transformed into nanoparticles at 500 °C. Interestingly, the original nanosheet samples Ni(OH)₂-200 and NiO-300 still maintained their morphology and structure although they all went through an activity test at 500 °C in a 1.0% CH₄ atmosphere, which proves that the calcination of nanosheets in a CH₄ atmosphere tended to maintain their nanosheet morphology compared with calcination in the air. Furthermore, through the activity test, X-ray photoelectron spectroscopy results, TPx, and in situ DRIFTS characterization, it was proved that the hydroxyl groups on the Ni(OH)₂-200 and NiO nanosheets were beneficial to the dissociation of methane on the catalyst surface, and the nanosheet structure was also prone to generating more active adsorbed oxygen, so the activation energy of methane was lowered. A methane catalytic mechanism on the Ni(OH)₂ nanosheets and NiO nanoparticles was proposed, which further proved the key role of hydroxyl groups in methane combustion.

A Review of High-Energy Density Lithium-Air Battery Technology: Investigating the Effect of Oxides and Nanocatalysts

In vehicles that require a lot of electricity, such as electric vehicles, it is necessary to use high-energy batteries. Among the developed batteries, the lithium-ion battery has shown better performance. This battery has an energy density of 10 equal to that of a lithium-ion battery and uses air oxygen as the active material of the cathode and anode like a lithium-ion battery made of lithium metal. The cathode used in these batteries must have special properties such as strong catalytic activity and high conductivity, and nanotechnology has greatly helped to improve the materials used in the cathode of lithium-air batteries. The importance of proper catalyst distribution and the relationship between the oxide product and the catalyst and the indirect effect of the ORR catalyst on the OER reaction is not present in the fuel cell. The maximum capacity of lithium-air battery theory using graphene under optimal electron conduction conditions and the experimental maximum obtained for graphene by optimizing the structure geometry, examples of structural engineering using carbon fiber and carbon nanotubes in cathode fabrication with the ability to perform the reaction properly while providing space for lithium oxide placement, are examined. This article describes the mechanism of this battery, and its components are examined. The challenges of using this battery and the application of nanotechnology to solve these challenges are also discussed.

Intra-crystalline mesoporous zeolite encapsulation-derived thermally robust metal nanocatalyst in deep oxidation of light alkanes

Zeolite-confined metal nanoparticles (NPs) have attracted much attention owing to their superior sintering resistance and broad applications for thermal and environmental catalytic reactions. However, the pore size of the conventional zeolites is usually below 2 nm, and reactants are easily blocked to access the active sites. Herein, a facile in situ mesoporogen-free strategy is developed to design and synthesize palladium (Pd) NPs enveloped in a single-crystalline zeolite (silicalite-1, S-1) with intra-mesopores (termed Pd@IM-S-1). Pd@IM-S-1 exhibited remarkable light alkanes deep oxidation performances, and it should be attributed to the confinement and guarding effect of the zeolite shell and the improvement in mass-transfer efficiency and active metal sites accessibility. The Pd−PdO interfaces as a new active site can provide active oxygen species to the first C−H cleavage of light alkanes. This work exemplifies a promising strategy to design other high-performance intra-crystalline mesoporous zeolite-confined metal/metal oxide catalysts for high-temperature industrial thermal catalysis.

Zeolite-confined metal nanoparticles (NPs) have attracted much attention owing to their superior sintering resistance and broad applications. Here the authors develop a facile in situ mesoporogen-free strategy to design and synthesize palladium NPs enveloped within a single-crystalline zeolite with intra-mesopores.

Spherical Ni Nanoparticles Supported by Nanosheet-Assembled Al2O3 for Dry Reforming of CH4: Elucidating the Induction Period and Its Excellent Resistance to Coking

The design and preparation of efficient coking-resistant catalysts for dry reforming of methane (DRM) is significant for industrial applications but a challenge for supported Ni catalysts. Nanosheet-assembled Al₂O₃ (NA-Al₂O₃) with hierarchical hollow microspheres was used to support Ni nanoparticles, which exhibits superior long-time stability and coking resistance for the DRM reaction from 700 to 800 °C without coke deposition. Active Ni species, exsolved from NiAl₂O₄ spinel, are aggregated into Ni nanoparticles and finally stabilize as spherical Ni nanoparticles of 18.0 nm due to the spatial confinement of hierarchical hollow microspheres of the NA-Al₂O₃ support after the DRM reaction for 60 h. The catalytic activity in the induction period of the Ni/(NA-Al₂O₃) catalyst increases because of the enhancement of the surface Ni⁰/(Ni⁰+Ni²⁺) ratio, that is, the increment of the amount of active Ni sites. The spherical Ni nanoparticles embedded in the NA-Al₂O₃ support, superior CO₂ adsorption ability, and more surface hydroxyl groups on the Ni/(NA-Al₂O₃) catalyst are the determining factors for its long-time stability and excellent anti-coking for the DRM reaction.

Sabatier principle of metal-support interaction for design of ultrastable metal nanocatalysts

[Figure: see text].

Controlling Heterogeneous Catalysis with Organic Monolayers on Metal Oxides

ConspectusA key theme of heterogeneous catalysis research is achieving control of the environment surrounding the active site to precisely steer the reactivity toward desired reaction products. One method toward this goal has been the use of organic ligands or self-assembled monolayers (SAMs) on metal nanoparticles. Metal-bound SAMs are typically employed to improve catalyst selectivity but often decrease the reaction rate as a result of site blocking from the ligands. Recently, the use of metal oxide-bound organic modifiers such as organophosphonic acid (PA) SAMs has shown promise as an additional method for tuning reactions on metal oxide surfaces as well as modifying oxide-supported metal catalysts. In this Account, we summarize recent approaches to enhance catalyst performance with oxide-bound monolayers. These approaches include (1) modification of metal oxide catalysts to tune surface reactions, (2) formation of SAMs on the oxide component of supported metal catalysts to modify sites at the metal-support interface, and (3) enhancement of catalyst performance (e.g., stability) through modification of sites remote from the active sites.Both the headgroups and organic tail groups of PA SAMs or other ligands can influence reactions on metal oxide surfaces. Binding of the headgroup can selectively poison certain active sites, altering the selectivity in a manner analogous to metal-bound ligands (at the expense of active site quantity). Moreover, tail groups can be functionalized to interact favorably with reactants and intermediates, for instance through dipole-dipole interactions. On supported metal catalysts like Pt/Al₂O₃, PA SAMs can selectively form on the oxide support. This selective deposition allows for modification of the metal-support interface with minimal blockage of metal sites. PA headgroups were shown to provide tunable acid sites at the interface, dramatically improving hydrodeoxygenation rates of various alcohols. Additionally, organic tail functionality was used to activate or stabilize specific reactants at the interface, such as with the use of amine-functionalized PAs to stabilize chemisorption of CO₂ during the reverse water gas shift reaction. PAs have also been found to affect the electronic properties of bulk metal sites through long-range electron withdrawal via the oxide, providing an additional avenue to tune catalytic behavior. Finally, organic modifiers were shown to enhance catalytic performance without directly modifying the active site. For instance, in biphasic liquid environments the modification of catalyst particles with hydrophobic or hydrophilic SAMs shifts the selectivity of multipath reactions on the basis of the hydrophobicities of different intermediates and products. As another "long-range" effect, the deposition of ligands on oxide supports improved catalyst stability through both improved resistance to sintering and suppression of active site poisoning. The recent contributions discussed in this Account demonstrate the versatility and significant potential for the approach of modifying catalysts with oxide-bound organic monolayers.

Exploring chemistry features of favipiravir in octanol/water solutions

Favipiravir (Fav) has become a well-known drug for medication of patients by appearance of COVID-19. Heterocyclic structure and connected peptide group could make changes for Fav yielding different features from those required features. Therefore, it is indeed a challenging task to prepare a Fav compound with specific features of desired function. In this work, existence of eight Fav structures by tautomeric formations and peptide group rotations were obtained using density functional theory (DFT) optimization calculations. Gas phase, octanol solution, and water solution were employed to show impact of solution on features of Fav besides obtaining partition coefficients (LogP) for Fav compounds. Significant impacts of solutions were seen on features of Fav with the obtained LogP order: Fav-7 >  Fav-8 >  Fav-4 >  Fav-3 >  Fav-2 >  Fav-5 >  Fav-1 >  Fav-6. As a consequence, internal changes yielded significant impacts on features of Fav affirming its carful medication of COVID-19 patients.

Si-doped Al2O3 nanosheet supported Pd for catalytic combustion of propane: effects of Si doping on morphology, thermal stability, and water resistance

Catalytic combustion of propane as typical light alkanes was important for the purification of industrial VOCs and automobile hydrocarbon emissions. Si-doped Al₂O₃ nanosheet was synthesized by a hydrothermal method, and effects of Si content on the morphology and thermal stability of Al₂O₃ were investigated. The doping of SiO₂ could tune the thickness of Al₂O₃ nanosheets and significantly improve its thermal stability, the θ phase was still maintained, and the specific surface area was as high as 56.3 m² g^-1 after calcination at 1200 °C. And then the Si-doped Al₂O₃ nanosheets were used as support of Pd catalysts (Pd/Si-Al₂O₃ nanosheets) for catalytic combustion of propane, especially Pd/3.6Si-Al₂O₃ nanosheets, which presented high activity, stability, and resistance to sintering and H₂O due to the promotion of Si on the thermal stability of Al₂O₃ and the stabilization (dispersion, isolation, and strong interaction) of PdO_x species.

Promoting Effect of Palladium on ZnAl2O4-Supported Catalysts Based on Cobalt or Copper Oxide on the Activity for the Total Propene Oxidation

Palladium-modified Co-ZnAland Cu-ZnAl materials were used and found active for the catalytic oxidation of propene and propane. According to the results obtained by XRD, TPR and XPS, the zinc aluminate-supported phases are oxide phases, Co₃O₄, CuO and PdO_x for Co-ZnAl, Cu-ZnAl and Pd-ZnAl catalysts, respectively. These reducible oxide species present good catalytic activity for the oxidation reactions. The addition of palladium to Co-ZnAl or Cu-ZnAl samples promoted the reducibility of the system and, consequently, produced a synergic effect which enhanced the activity for the propene oxidation. The PdCo-ZnAl sample was the most active and exhibited highly dispersed PdO_x particles and surface structural defects. In addition, it exhibited good catalytic stability. The H₂ pre-treated PdCu-ZnAl, PdCo-ZnAl and Pd-ZnAl samples showed higher activity than the original oxide catalysts, evidencing the important role of the oxidation state of the species, mainly of the palladium species, on the catalytic activity for the propene combustion. The synergic effect between metal transition oxides and PdO_x could not be observed for the propane oxidation.

Quantification of critical particle distance for mitigating catalyst sintering

Supported metal nanoparticles are of universal importance in many industrial catalytic processes. Unfortunately, deactivation of supported metal catalysts via thermally induced sintering is a major concern especially for high-temperature reactions. Here, we demonstrate that the particle distance as an inherent parameter plays a pivotal role in catalyst sintering. We employ carbon black supported platinum for the model study, in which the particle distance is well controlled by changing platinum loading and carbon black supports with varied surface areas. Accordingly, we quantify a critical particle distance of platinum nanoparticles on carbon supports, over which the sintering can be mitigated greatly up to 900 °C. Based on in-situ aberration-corrected high-angle annular dark-field scanning transmission electron and theoretical studies, we find that enlarging particle distance to over the critical distance suppress the particle coalescence, and the critical particle distance itself depends sensitively on the strength of metal-support interactions.

Deactivation of supported metal catalysts via thermally induced sintering is a major concern in the catalysis community. Here, the authors demonstrate that enlarging particle distance to over the critical distance could suppress the particle coalescence greatly up to 900 °C.

Significant Improvement of Catalytic Performance for Chlorinated Volatile Organic Compound Oxidation over RuOx Supported on Acid-Etched Co3O4

Ru catalysts have attracted increasing attention in catalytic oxidation of chlorinated volatile organic compounds (CVOCs). However, the development of Ru catalysts with high activity and thermal stability for CVOC oxidation still poses significant challenges due to their restrictive relationship. Herein, a strategy for constructing surface defects on Co₃O₄ support by acid etching was utilized to strengthen the interaction between active RuO_x species and the Co₃O₄ support. Consequently, both the dispersity and thermal stability of RuO_x species were significantly improved, achieving both high activity and stability of Ru catalysts for CVOC oxidation. The optimized Ru catalyst on the HF-etched Co₃O₄ support (Ru/Co₃O₄-F) achieved complete oxidation of vinyl chloride at 260 °C under 30 000 mL·g^-1·h^-1, which was lower than 300 °C for the Ru catalyst on the original Co₃O₄ (Ru/Co₃O₄). More importantly, the Ru species on the Ru/Co₃O₄-F catalyst were hardly lost after calcination at 500-700 °C and even reacting at 650 °C for 120 h. On this basis, the polychlorinated byproducts over the Ru/Co₃O₄-F catalyst were almost completely effaced by phosphate modification on the catalyst surface. These findings show that the method combining acid etching of the support and phosphate modification provides a strategy for the advancement of catalyst design for CVOC oxidation.