Oxide Support Research Articles

Observation of Support-Dependent Water Oxidation Kinetics on Molecularly-Derived Heterogeneous Ir-Oxide Catalysts

Heterogeneous water oxidation catalysis is central to the development of renewable energy technologies. Understanding the material properties that determine water oxidation activity is critically important for the design of efficient and durable water oxidation catalysts. The electronic structure and surface chemistry of the catalyst influence the accumulation of oxidative charge (holes) on catalytically active sites. Hole distribution dynamics and molecular structure of the active sites are generally accepted to jointly determine activity. However, these properties are typically inherent to materials; it has been difficult to independently tune them on most heterogeneous catalysts, hindering the development of an understanding of their relative influence. Herein, heterogenized dinuclear Ir catalysts (Ir-DHC) supported on different oxides were employed to overcome this challenge. It was found that at low temperatures (288-298 K), the photocatalytic activities of Ir-DHC on indium tin oxide (ITO) and CeO2 supports are comparable within the studied range of fluences (62-151 mW/cm2). By contrast, at higher temperatures (310-323 K), Ir-DHC on ITO exhibits a ∼100% higher water oxidation activity than on CeO2. The divergent activities under these conditions were attributed to the distinct abilities of the supporting substrates to redistribute surface holes. Specifically, ITO is relatively efficient in distributing photogenerated holes between Ir-DHC active sites, whereas CeO2 exhibits sluggish hole redistribution because of its reducibility, thereby limiting hole accumulation at Ir-DHC active sites. The temperature dependence was explained by a temperature induced switch in the rate-determining step of the reaction. These findings highlight the critical role of the supporting substrate in determining the turnover at active sites of heterogeneous catalysts.

Multiphysics Modeling of Solid Oxide Iron Air Battery with New Catalyst and Proton Conductor Oxide Support

Long-duration energy storage (LDES) (10+ hours) is widely regarded as an enabling technology to deepen the penetration of renewable energy into the commercial utility market. However, the current storage technologies cannot achieve LDES’s duration requirement at a competitive cost. Therefore, new LDES technologies are highly sought after in recent years. Solid oxide iron air battery is a newly emerging battery based on oxide-ion chemistry and stores energy in energy-dense solid iron. Our recent results have shown that the battery in a laboratory size (f1”) delivers 12.5-hour storage per cycle for 20 cycles with high energy capacity and round-trip efficiency. This presentation focuses on the description of a high-fidelity 2D axis symmetrical multi-physics model to simulate the performance of a solid oxide iron air battery. The model battery system consists of an anode-supported solid oxide cell and energy storage unit (ESU) of iron bed with a proton conducting oxide BaZr0.4Ce0.4Y0.1Yb0.1O3 (BZC4YYb) based support and iridium as a catalyst. The Multiphysics model encompasses charge transfer, mass transport, and chemical redox kinetic cycle occurring across all components of the battery and is validated with experimental results. The kinetic JMA (Johnson-Mehl-Avrami) model is used for describing the oxidation and reduction kinetics of Fe-BZC4YYb-IrO2 ESU. The motivation for combing the Ir catalyst with proton conductor oxide support in ESU is to boost the sluggish FeOx reduction kinetics. Compared to the baseline ESU, i.e. Fe2O3/ZrO2, the newly developed BZC4YYb-IrO2 shows great catalytic activity toward FeOx reduction, thus allowing SOIAB to operate at 500-550oC with excellent capacity, stability, and high round trip efficiency. The presentation will also show the experimental data of improved reduction kinetic rate of Fe-BZC4YYb-IrO2 over the baseline Fe2O3/ZrO2.

Iridium Nanosheet Catalysts Supported on Titanium Oxide for Oxygen Evolution Reaction in Polymer Electrolyte Membrane Water Electrolysis

In order to overcome the disadvantage of intermittent production of renewable energy, Polymer electrolyte membrane water electrolysis(PEMWE), which is one of the technologies of producing hydrogen by electrolyzing water, is attracting attention. For the commercialization of PEMWE, it is important to reduce usage of iridium(Ir) for oxygen evolution reaction(OER) in the anode electrode. Many studies have been reported to reduce the amount of iridium used by developing a catalyst with higher performance than the iridium nanoparticle catalyst used as a commercial catalyst. As one of the strategies, the introduction of support materials that can increase the active area of the catalyst is drawing attention. While carbon-based supports are mainly used in other applications, in OER environments, carbon is easily corroded due to high voltage and strong acid conditions. Therefore, it is necessary to use a metal oxide support with high corrosion resistance. In particular, titanium oxide(TiO2) is one of the suitable support candidates because it is a stable material in an acidic OER environment. However, catalysts loaded on TiO2 with nanoparticles cause an electrical contact problem due to the low electrical conductivity of TiO2, which causes a degradation in activity. Many studies have reported doping methods to increase the conductivity of TiO2, but there are also reports that these methods reduce the durability of support. Thus, a new approach to synthesizing a better structure of catalysts is needed to utilize metal oxide support.Herein, we present an approach to iridium nanosheet (NS) catalysts supported on TiO2(Ir NS/TiO2). Ir NSs were synthesized by an facile method by directly annealing a mixture of Ir precursor and alkali salt. Ir NSs were supported on TiO2 to be utilized as a reaction site and also acts as an electron path to compensate for the low electrical conductivity of TiO2. Ir NS/TiO2 showed superior OER activity and stability under acidic conditions. These results showed that Ir NS/TiO2 could be utilized to reduce the amount of precious metal catalyst in PEMWE and increase the stability of OER supported catalysts.

Partial oxidation of methane to methyl oxygenates with enhanced selectivity using a single-atom copper catalyst on amorphous carbon support

In this study, we report a single-atom Cu catalyst on the amorphous carbon support for direct methane partial oxidation. The catalyst was prepared by the carbonization of Cu-doped ZIF-8 to implant single-atom Cu active centers that coordinate with four nitrogen (CuN4) on the amorphous N-doped carbon. Carbonization enhanced the oxidation resistance of the catalyst by preventing the oxidation of Cu-coordinating ligands, leading to a 40% reduction in CO2 production. Our prepared catalyst showed higher methanol selectivity than other single-atom copper catalysts. Mechanistic studies revealed that Cu and the surface carbon atom facilitated the dissociation of H2O2 into OOH and H, which further transformed into Cu–O and led to proton abstraction from methane. We highlight a simple approach to prepare a single-atom catalyst that is supported on amorphous N-doped carbon, derived from a metal-doped ZIF. This catalyst exhibits enhanced selectivity and stability for the partial oxidation of methane.

Effect of Mo content on oxidative dehydrogenation of propane with CO2 over ZnOx catalysts supported on Mo–Zr mixed–oxides

The production of propylene from readily available propane sources is of great importance as it serves as a crucial building block for producing numerous value-added chemicals. Oxidative dehydrogenation of propane with carbon dioxide (ODPC) has been proposed as a viable and eco-friendly approach for simultaneous propylene production and carbon dioxide reduction. In this study, ZnOx catalysts were prepared by supporting them on a range of molybdenum–zirconium (Mo–Zr) mixed–oxides with varying Mo contents, aiming to utilize them for ODPC applications. The incorporation of suitable quantities of Mo in zirconium dioxide (ZrO2) supports increases the surface concentration and enhances the dispersion of ZnOx, thereby demonstrating promotional effects on the surface properties of the supported ZnOx catalysts. Notably, the ZnOx catalyst supported on a Mo–Zr mixed–oxide, with an optimized Mo content, exhibits a propane conversion rate more than two-fold higher than that of the catalyst without Mo in ODPC. Furthermore, the introduction of Mo into the ZrO2 supports effectively inhibits the formation of coke by suppressing the cleavage of C–C bonds in propane. In comparison, the supported ZnOx catalysts with higher Zn loadings, show that a Mo–Zr mixed–oxide support effectively suppresses the formation of bulk ZnOx more than an unmodified ZrO2 support, leading to improved ODPC performance. The promoting effects of Mo emphasize the potential of utilizing mixed–oxide supports for ZnOx catalysts in ODPC, demonstrating a promising opportunity for enhancing catalytic performance.

Ni–Pd Nanocomposites on Reduced Graphene Oxide Support as Electrocatalysts for Hydrogen Evolution Reactions

Ni–Pd Nanocomposites on Reduced Graphene Oxide Support as Electrocatalysts for Hydrogen Evolution Reactions

Boosting the catalysis of gold supported on perovskites by strong metal-support interaction

Gold catalysts show excellent selectivity in chemoselective hydrogenation reactions. However, their reactivity and stability are relatively inferior to Pt-group metal catalysts due to the moderate hydrogen activation and carbonaceous deposits. Herein, we reported that the strong metal-support interaction (SMSI) between gold nanoparticles and perovskites can increase the catalytic performance of gold-based catalysts in 3-nitrostyrene chemoselective hydrogenation reaction. HAADF-STEM elemental mapping images and line scan profiles confirmed that the oxide support can partially cover the surface of gold NPs, increasing the interfacial area between gold NPs and perovskites support. H2-D2 exchange reaction, reaction kinetic analysis and density functional theory calculations revealed that the apparent activation energy of 3-NS chemoselective hydrogenation reaction over gold supported on perovskites with SMSI effect was significantly decreased by the more facile H2 dissociation, 3-NS and its’ intermediate activation at the increased interface. This discovery of SMSI effect in Au and perovskites offers new insights into tuning performance of gold-based catalysts via changing the types of metal ions in perovskites.

Effect of Surface Temperature on the Distribution and Reactivity of Rh Active Sites for CO Oxidation

AbstractSingle‐atom catalysts are a fast‐emerging area in which late‐transition metal atoms are supported on oxides, metals, and carbonaceous supports. They show great promise for selective chemical reactions due to their well‐defined active sites, and significantly reduce precious metal loading. However, oxide‐supported single‐atom catalysts have drawbacks such as deactivation due to sintering, and there are on‐going debates about the exact nature of the active sites. Herein we report a model system where the surface temperature during Rh deposition on a copper oxide support dictates the Rh size distribution. Our temperature‐programmed desorption experiments reveal that Rh clusters perform CO oxidation at lower temperature than single atoms, and isotopic labelling demonstrates differences in the mechanism in that the C−O bond is broken and reformed on clusters, as opposed to a pure Mars van Krevelen mechanism for CO oxidation at the single‐atom Rh sites. We further examine the cluster size distributions with scanning tunneling microscopy and X‐ray photoelectron spectroscopy which confirm the presence of both clusters and single atoms for the lower temperature deposition and only single atoms for the higher temperature deposition. Together, these results provide a fundamental understanding of the differences in the CO oxidation mechanism on Rh atoms and clusters.

A Surfactant-Free and General Strategy for the Synthesis of Bimetallic Core-Shell Nanocrystals on Reduced Graphene Oxide through Targeted Photodeposition.

Tunable physicochemical properties of bimetallic core-shell heterostructured nanocrystals (HNCs) have shown enormous potential in electrocatalytic reactions. In many cases, HNCs are required to load on supports to inhibit catalyst aggregation. However, the introduction of supports during the process of growing core-shell HNCs makes the synthesis much more complicated and difficult to control precisely. Herein, we reported a universal photochemical synthetic strategy for the controlled synthesis of well-defined surfactant-free core-shell metal HNCs on a reduced graphene oxide (rGO) support, which was assisted by the fine control of photogenerated electrons directly transferring to the targeted metal seeds via rGO and the precisely tuned adsorption capacity of the added second metal precursors. The surface photovoltage microscopy (SPVM) platform proved that photogenerated electrons flowed through rGO to Pd particles under illumination. We have successfully synthesized 24 different core-shell metal HNCs, i.,e., MA@MB (MA = Pd, Au, and Pt; MB = Au, Ag, Pt, Pd, Ir, Ru, Rh, Ni and Cu), on the rGO supports. The as-prepared Pd@Cu core-shell HNCs showed outstanding performance in the electrocatalytic reduction of CO2 to CH4. This work could shed light on the controlled synthesis of more functional bimetallic nanostructured materials on diverse supports for various applications.

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

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

Technological solutions for NOx, SOx, and VOC abatement: recent breakthroughs and future directions.

NOx, SOx, and carbonaceous volatile organic compounds (VOCs) are extremely harmful to the environment, and their concentrations must be within the limits prescribed by the region-specific pollution control boards. Thus, NOx, SOx, and VOC abatement is essential to safeguard the environment. Considering the importance of NOx, SOx, and VOC abatement, the discussion on selective catalytic reduction, oxidation, redox methods, and adsorption using noble metal and non-noble metal-based catalytic approaches were elaborated. This article covers different thermal treatment techniques, category of materials as catalysts, and its structure-property insights along with the advanced oxidation processes and adsorption. The defect engineered catalysts with lattice oxygen vacancies, bi- and tri-metallic noble metal catalysts and non-noble metal catalysts, modified metal organic frameworks, mixed-metal oxide supports, and their mechanisms have been thoroughly reviewed. The main hurdles and potential achievements in developing novel simultaneous NOx, SOx, and VOC removal technologies are critically discussed to envisage the future directions. This review highlights the removal of NOx, SOx, and VOC through material selection, properties, and mechanisms to further improve the existing abatement methods in an efficient way.

Tunable CO2-to-syngas conversion via strong electronic coupling in S-scheme ZnGa2O4/g-C3N4 photocatalysts

The conversion of CO2 into syngas, a mixture of CO and H2, via photocatalytic reduction, is a promising approach towards achieving a sustainable carbon economy. However, the evolution of highly adjustable syngas, particularly without the use of sacrifice reagents or additional cocatalysts, remains a significant challenge. In this study, a step-scheme (S-scheme) 0D ZnGa2O4 nanodots (∼7 nm) rooted g-C3N4 nanosheets (denoted as ZnGa2O4/C3N4) heterojunction photocatalyst was synthesized vis a facial in-situ growth strategy for efficient CO2-to-syngas conversion. Both experimental and theoretical studies have demonstrated that the polymeric nature of g-C3N4 and highly distributed ZnGa2O4 nanodots synergistically contribute to a strong interaction between metal oxide and C3N4 support. Furthermore, the desirable S-scheme heterojunction in ZnGa2O4/C3N4 efficiently promotes charge separation, enabling strong photoredox ability. As a result, the S-scheme ZnGa2O4/C3N4 exhibited remarkable activity and selectivity in photochemical conversion of CO2 into syngas, with a syngas production rate of up to 103.3 μ mol g−1 h−1, even in the absence of sacrificial agents and cocatalyst. Impressively, the CO/H2 ratio of syngas can be tunable within a wide range from 1:4 to 2:1. This work exemplifies the effectiveness of a meticulously designed S-scheme heterojunction photocatalyst for CO2-to-syngas conversion with adjustable composition, thus paving the way for new possibilities in sustainable energy conversion and utilization.

Ultrasound-Driven Defect Engineering in TiO2-x Nanotubes─Toward Highly Efficient Platinum Single Atom-Enhanced Photocatalytic Water Splitting.

Single-atom catalysts (SACs) have demonstrated superior catalytic activity and selectivity compared to nanoparticle catalysts due to their high reactivity and atom efficiency. However, stabilizing SACs within hosting substrates and their controllable loading preventing single atom clustering remain the key challenges in this field. Moreover, the direct comparison of (co-) catalytic effect of single atoms vs nanoparticles is still highly challenging. Here, we present a novel ultrasound-driven strategy for stabilizing Pt single-atomic sites over highly ordered TiO2 nanotubes. This controllable low-temperature defect engineering enables entrapment of platinum single atoms and controlling their content through the reaction time of consequent chemical impregnation. The novel methodology enables achieving nearly 50 times higher normalized hydrogen evolution compared to pristine titania nanotubes. Moreover, the developed procedure allows the decoration of titania also with ultrasmall nanoparticles through a longer impregnation time of the substrate in a very dilute hexachloroplatinic acid solution. The comparison shows a 10 times higher normalized hydrogen production of platinum single atoms compared to nanoparticles. The mechanistic study shows that the novel approach creates homogeneously distributed defects, such as oxygen vacancies and Ti3+ species, which effectively trap and stabilize Pt2+ and Pt4+ single atoms. The optimized platinum single-atom photocatalyst shows excellent performance of photocatalytic water splitting and hydrogen evolution under one sun solar-simulated light, with TOF values being one order of magnitude higher compared to those of traditional thermal reduction-based methods. The single-atom engineering based on the creation of ultrasound-triggered chemical traps provides a pathway for controllable assembling stable and highly active single-atomic site catalysts on metal oxide support layers.

Electro-oxidation Reaction of Methanol over Reducible Ce1-x-yNixSryO2-δ: A Mechanistic Probe of Participation of Lattice Oxygen.

Methanol oxidation reaction crucially depends on the formation of -OOH species over the catalyst's surface. Ni-based catalysts are by far the choice of materials, where the redox couple of Ni2+/Ni3+ facilitates the formation of -OOH species by surface reconstructions. However, it is challenging to oxidize Ni2+ as it generates charge-transfer orbitals near the Fermi energy level. One possible solution is to substitute Ni2+ with a reducible oxide support, which will not only facilitate the Ni2+ → Ni3+ oxidation but also adsorb oxygenated species like -OOH at a lower potential owing to its oxophilicity. This work shows with the help of structural and surface studies that the reducible CeO2 support in Ni and Sr co-doped Ce1-x-yNixSryO2-δ solid solution can easily facilitate Ni2+ → Ni3+ oxidation as well as evolution of lattice oxygen during the methanol oxidation reaction. While the Ni3+ species helped in formation of -OOH surface intermediates, the evolved lattice oxygen eased the CO oxidation process in order to bring out the better CO-tolerant methanol oxidation activity over Ce1-x-yNixSryO2-δ. The study shows the unique importance of the electronic interactions between the active site and support and involvement of lattice oxygen in the methanol oxidation reaction.

Realizing Influence of Supports in Aqueous‐Phase Hydrogenation of Furfural over Nickel Catalysts

AbstractThe catalytic activity of nickel nanoparticles (5% Ni w/w loading) dispersed on different metal oxide supports has been explored for the hydrogenation of furfural. Nickel, supported on reducible oxides (CeO2 and TiO2), displays higher (almost 100%) conversion compared to that on non‐reducible oxide supports (SiO2, Al2O3, Mg3AlOx). H2‐TPR and XPS analyses bring out the influence of metal‐support interaction during the reduction of nickel precursor and their electronic properties. The adsorption and activation of furfural on the catalyst has been studied using infrared spectra and DFT calculations. The reaction proceeds via both ring‐rearrangement and ring hydrogenation pathways, with furfuryl alcohol as the primary intermediate. At higher reaction temperature, reducible oxide supported catalysts, particularly titania, favours deep‐hydrogenated products and higher conversion than non‐reducible oxide supported catalysts. Among all the catalysts, nickel on titania displayed maximum conversion of furfural. TiO2 possessing higher acidity than ceria, favoured ring‐rearrangement of furfuryl alcohol to cyclopentanone at high temperatures, while the latter retarded reduction of cyclopentanone due to blockage of active‐sites by unreacted furfural and strongly adsorbing intermediates. The combined effects of the electronic‐state of supported metal and surface acidity of catalyst provide a new strategy to tune catalytic properties for selective transformation during hydrogenation of furfural.

Alloyed Ru0.48Re0.52 nanocatalysts with electronic structure regulation for intensified alkaline hydrogen evolution reaction

Converting electricity into hydrogen is vital for harnessing concentrated renewable energy. To achieve this, cost-effective electrocatalysts capable of withstanding mildly corrosive alkaline hydrogen evolution reaction (HER) conditions are necessary. Ru shows potential as a substitute for Pt-based electrocatalysts due to its comparable hydrogen bond strength. However, improvements are needed to overcome obstacles in water dissociation and hydrogen desorption during alkaline HER. In this work, Ru was alloyed with Re which is water dissociation-efficient to induce a redistribution of electron density in Ru0.48Re0.52 nanoparticles (NPs). These Ru0.48Re0.52NPs exhibited superior hydrogen desorption, outperforming Pt, highlighting their effectiveness in HER. The Re component received electrons from adjacent Ru while maintaining low energy barriers for water decomposition. Additionally, self-aggregation of Ru0.48Re0.52NPs was prevented by incorporating reduced graphene oxide (rGO) support, resulting in improved conductivity and electrochemical durability in Ru0.48Re0.52NPs@rGO. Through various analyses, the optimal synthesis and electronic structure adjustments in Ru0.48Re0.52NPs@rGO were confirmed, which exhibited remarkable HER overpotentials with values of 14 and 74 mV at current densities of 10 and 100 mA cm−2, respectively, in a 1 M KOH solution. These findings establish Ru0.48Re0.52NPs@rGO as a universal approach for designing efficient electrocatalysts for HER, surpassing both the activity and cost of commercialized Pt/C.

Investigation of palladium catalysts in mesoporous silica support for CO oxidation and CO2 adsorption

The oxidation of Carbon monoxide (CO) to Carbon dioxide (CO2) is one of the most extensively investigated reactions in the field of heterogeneous catalysis, and it occurs via molecular rearrangements induced by catalytic metal atoms with oxygen intermediates. CO oxidation and CO2 capture are instrumental processes in the reduction of green-house gas emissions, both of which are used in low-temperature CO oxidation in the catalytic converters of vehicles. CO oxidation and CO2 adsorption at different temperatures are evaluated for palladium-supported silica aerogel (Pd/SiO2). The synthesized catalyst was active and stable for low-temperature CO oxidation. The catalytic activity was enhanced after the first cycle due to the reconditioning of the catalyst’s pores. It was found that the presence of oxide forms of palladium in the SiO2 microstructure, influences the performance of the catalysts due to oxygen vacancies that increases the frequency of active sites. CO2 gas adsorption onto Pd/SiO2 was investigated at a wide-ranging temperature from 16 to 120 °C and pressures ∼1 MPa as determined from the isotherms that were evaluated, where CO2 showed the highest equilibrium adsorption capacity at 16 °C. The Langmuir model was employed to study the equilibrium adsorption behavior. Finally, the effect of moisture on CO oxidation and CO2 adsorption was considered to account for usage in real-world applications. Overall, mesoporous Pd/SiO2 aerogel shows potential as a material capable of removing CO from the environment and capturing CO2 at low temperatures.

Synthesis and Properties of a Carbon Monoxide Oxidation Catalyst Based on Titanium Dioxide and Platinum Nanoparticles

Carbon monoxide oxidation catalysts comprising Pt clusters on titanium dioxide with an oxide particle size of 6 and 20 nm have been synthesized. The catalysts have been studied using TEM, XRD, and XPS techniques, and it has been found that platinum clusters coated with a mixture of platinum oxides are formed on the support surface. The coherent scattering region of the Pt cluster is close to 5–6 nm for the studied oxide supports. The catalytic properties in the CO oxidation reaction at 295 K and low CO concentrations(less than 100 mg/m3) have been examined. The catalyst based on titania with a particle size of 20 nm and a platinum loading of 10 wt % has been found to have the CO oxidation rate 100 times higher than that on platinum black with a specific surface area of 30 m2/g. The catalysts are promising for use in catalytic air purification systems.

Ti doped CeO2 nanosheets supported Pd catalyst for alcohol oxidation: Catalysis of interfacial sites

AbstractThe oxidation of alcohols is a significant chemical reaction, and the efficient oxidation of alcohols over heterogeneous catalysts using oxygen as oxidant has attracted much attention in recent years. Among them, Pd/CeO2 exhibits excellent alcohol oxidation performance. However, the structure-activity relationship between the catalyst's structure and its catalytic performance for alcohol oxidation is still not clearly understood. This study involved the preparation of CeO2 nanosheets with different concentrations of surface oxygen vacancies (Ov) and their subsequent loading with Pd to explore their catalytic performance for alcohol oxidation. The findings obtained through XPS, Raman, and XAS indicated a positive correlation between the surface Ov concentration of CeO2 as well as the ratio of Pd2+ fraction. The alcohol oxidation results and structure-performance relationship studies showed that there was a good linear relationship between the Pd2+ ratio as well as the surface Ce3+ concentration and the TOF of benzyl alcohol oxidation reaction, respectively. And the interfacial site (Pd–O–Ce) formed by Pd and CeO2 was the main catalytic site for this type of alcohol oxidation catalysts. This study contributes to the understanding of the catalytic role of interfacial sites in metal and oxide support for the development of better alcohol oxidation catalysts.

Strong metal oxide-support interaction in MoO2/N-doped MCNTs heterostructure for boosting lithium storage performance

The low-rate capability and fast capacity decaying of the molybdenum dioxide anode material have been a bottleneck for lithium-ion batteries (LIBs) due to low carrier transport, drastic volume expansion and inferior reversibility. Furthermore, the lithium-storage mechanism is still controversial at present. Herein, we fabricate a new kind of MoO2 nanoparticles with nitrogen-doped multiwalled carbon nanotubes (MoO2/N-MCNTs) as anode for LIBs. The strong chemical bonding (MoOC) endows MoO2/N-MCNTs a strong metal oxide–support interaction (SMSI), rendering electron/ion transfer and facilitate significant Li+ intercalation pseudocapacitance, which is evidenced by both theoretical computation and detailed experiments. Thus, the MoO2/N-MCNTs exhibits high-rate performance (523.7 mAh/g at 3000 mA g−1) and long durability (507.8 mAh/g at 1000 mA g−1 after 500 cycles). Furthermore, pouch-type full cell composed of MoO2/N-MCNTs anodes and commercial LiNi0.6Co0.2Mn0.2O2 (NCM622) cathodes demonstrate impressive rate performance and cyclic life, which displays an unparalleled energy density of 553.0 Wh kg−1. Ex-situ X-ray absorption spectroscopy (XAS) indicates the enhanced lithium-storage mechanism is originated from a partially irreversible phase transition from Li0.98MoO2 to Li2MoO4 via delithiation. This work not only provides fresh insights into the enhanced lithium-storage mechanism but also proposes new design principles toward efficient LIBs.