Transition Metal Oxide Catalysts Research Articles

Electrocatalytic Oxygen Reduction Reaction Improved By Facilitated Proton Transfer

Electrocatalytic oxygen reduction reaction (ORR) in aqueous media proceeds along a pathway having multiple steps in which multiple surface intermediates are involved (* -> *OO -> *OOH -> *O -> *OH where * = active site of catalyst). Proton supplied from media plays a crucial role on the ORR mechanism. Therefore, pH of media affects the kinetics of ORR significantly. In the same vein, it is expected that the ORR activity is improved in the presence of proton donor (HD) around active sites of catalysts. In this presentation, we demonstrate a possibility that a series of proton donors are involved in protonation of the surface intermediates. The ORR overpotential was improved by 100 mV at pH 13 on transition metal oxide catalysts. The overpotential improvement was intensified as the pH of media decreased. It is suspected that the pH affects deprotonation of the proton donors (HD -> H+ + D-). High pH deprotonate the proton donors so that the effects of proton donors decrease. However, the proton of HD survives in acidic media so that the proton transfer from HD to active site is facilitated. The ORR overpotential gain was as large as 400 mV at pH 4 even if the oxide catalyst was not stable at the acidic pH. At pH 7, the overpotential improvement was estimated at 200 mV.

Atomic Layer Deposition of a Manganese-Iron Mixed Oxide As a Bifunctional Oxygen Catalyst for Zinc-Air Batteries

Carbon-free energy sources will become a necessary step in order to mitigate the effects of climate change. In order to integrate these renewable energy sources, which are usually intermittent and not on-demand, into the power grid, a significant amount of energy storage will be required. The popularity of lithium-ion batteries as an energy storage option has exploded in recent years; however, a safer and less expensive alternative may be zinc-air batteries.Zinc-air batteries combine zinc, an abundant and safe metal, with oxygen from the air. Using oxygen as a battery component, however, presents issues because of the slow kinetics of both oxygen reduction and oxygen evolution, the necessary steps in battery discharge and charge, respectively [1]. To compensate, catalysts are utilized that improve reaction kinetics for both the charge and discharge reactions. The benchmark in oxygen reaction catalysis is rare and expensive noble metals, such as platinum and ruthenium, which hinders practicality. On the other hand, inexpensive and abundant transition metal oxides have also shown promising catalytic activity towards these oxygen reactions [2]. Unfortunately, transition metal oxide catalysts that improve the reaction kinetics of the oxygen reduction reaction are typically not active towards the oxygen evolution reaction, and vice versa. However, a ternary oxide of two transition metals may result in a bifunctional catalyst, which is active towards both charge and discharge reactions.The aim of this work is to produce a bifunctional, mixed oxide catalyst through atomic layer deposition (ALD). ALD employs self-terminating surface reactions of a metal-containing gaseous precursor and an oxygen co-reactant to produce very conformal and thin oxide films. Highly porous carbon paper, which typically serves as the air electrode in metal-air batteries, acts as the substrate for ALD of these transition metal oxide films. ALD can conformally coat the high surface area substrate with minimal loss in porosity. Furthermore, ALD can penetrate deeper into the pores of the electrode as compared with other deposition techniques. Together this allows ALD to yield high surface area nanostructured catalysts that maximizes the three-phase region between gaseous oxygen, liquid electrolyte, and the solid catalyst, thereby improving battery performance [3].Previously studies have shown manganese oxides to be active towards the oxygen reduction reaction, while iron oxide is a component of many oxygen evolution catalysts [3]–[5]. Therefore, a recipe to deposit iron oxide films using ethylferrocene and an oxygen plasma is combined with an already established manganese oxide deposition procedure, with the ultimate goal of creating a mixed transition metal oxide catalyst. Electrochemical characterization techniques are employed to evaluate the bifunctional activity of synthesized transition metal oxides films. The atomic-level control of ALD means that the mixed oxide can be grown in various different proportions. An optimization process to establish the best ALD sequence is showcased, resulting in a bifunctional efficiency of 55% at 20 mA/cm2 for a 10 nm catalytic film.[1] F. Cheng and J. Chen, “Metal-air batteries: From oxygen reduction electrochemistry to cathode catalysts,” Chem. Soc. Rev., vol. 41, no. 6, pp. 2172–2192, 2012.[2] H. Osgood, S. V. Devaguptapu, H. Xu, J. Cho, and G. Wu, “Transition metal (Fe, Co, Ni, and Mn) oxides for oxygen reduction and evolution bifunctional catalysts in alkaline media,” Nano Today, vol. 11, no. 5, pp. 601–625, 2016.[3] M. P. Clark, M. Xiong, K. Cadien, and D. G. Ivey, “High Performance Oxygen Reduction/Evolution Electrodes for Zinc − Air Batteries Prepared by Atomic Layer Deposition of MnOx,” ACS Appl. Energy Mater., vol. 3, no. 1, pp. 603–313, 2020.[4] M. Xiong, M. P. Clark, M. Labbe, and D. G. Ivey, “A horizontal zinc-air battery with physically decoupled oxygen evolution/reduction reaction electrodes,” J. Power Sources, vol. 393, pp. 108–118, 2018.[5] D. Aasen, M. P. Clark, and D. G. Ivey, “(Co,Fe)3O4 Decorated Nitrogen-Doped Carbon Nanotubes in Nano-Composite Gas Diffusion Layers as Highly Stable Bifunctional Catalysts for Rechargeable Zinc-Air Batteries,” Batter. Supercaps, vol. 3, no. 2, pp. 174–184, 2020.

Epitaxial strain dependent electrocatalytic activity in CaRuO3 thin films

The systematic tunability of electrocatalytic activity is indispensable not only for realizing highly efficient catalysts but also for understanding the underlying mechanism of chemical reactions at the surface. Epitaxial strain is a powerful tool for tailoring various physical and chemical properties of perovskite transition metal oxides, including electrocatalytic activity. We present single-crystalline CaRuO3 epitaxial thin films as a model system, in which the oxygen evolution reaction was systematically controlled by the epitaxial strain. With an increase in the degree of tensile strain, the interband transition energy and hybridization strength within the Ru–O bond decreased, which enhanced the oxygen evolution reaction. Our study facilitates the understanding of the correlation between the lattice/electronic structure and the electrocatalytic activity, which might be applied to other transition metal oxide catalysts.

Low-temperature and stable CO oxidation of in-situ grown monolithic Mn3O4/TiO2 catalysts

Transition metal oxide catalysts have attracted considerable attention for their promising potential as an alternative to replace noble metal catalysts in the application of various catalytic reactions. Herein, we report the design of monolithic Mn3O4/TiO2 catalysts in-situ grown on Ti mesh substrate for efficient and stable CO oxidation. Porous TiO2 film which is fabricated from the oxidation of Ti mesh using conventional plasma electrolytic oxide process plays an important role in the in-situ nucleation of TiO2 nanosheets with strong adhesion to maintain the long-term stable CO oxidation, as well as providing Ti precursors for the formation of TiO2 nanosheets. The decoration of Mn3O4 co-catalysts on TiO2 nanosheet support could significantly enhance the catalytic property of monolithic Mn3O4/TiO2 catalysts due to the synergetic effect. Thus, a complete CO oxidation can be achieved as low as 160 °C without the involvement of any noble metal catalyst. The novel synthesis strategy of Mn3O4/TiO2 heterogeneous catalysts shows overwhelming advantages of outstanding catalytic performance and superior stability in comparison with other traditional methods of powder-based catalysts. More importantly, it can be extended to the rational design of a variety of TiO2-based transition metal oxide catalysts which can be used for diverse applications including CO oxidation, de-NOx, CHx decomposition etc.

Graphene-based nanocomposite cathodes architecture with palladium and α-MnO2 for high cycle life lithium-oxygen batteries

High-efficiency electrocatalysts of palladium and α-MnO2 nanowires supported on reduced graphene oxide (rGO) sheets are developed through an effective process to enhance the electrochemical performance of current lithium-oxygen batteries. Palladium is known as an oxygen evolution reaction (OER) electrocatalyst in Li–O2 cathode to reduce the charge overpotential and exhibit stable cycling performance. On the other hand, MnO2 is an attractive, functional transition metal oxide catalyst in Li–O2 batteries due to its low cost, high catalytic activity, and good oxygen reduction behavior. This study integrates the synergic effects of α-MnO2 nanowires and palladium nanoparticles by decorating on graphene sheets to improve cyclability and capacity to obtain highly efficient performance of Li–O2 cells. As-prepared rGO/Pd/α-MnO2 hybrid nanocomposite cathode indicates an initial discharge capacity of 7500 mA h g−1 and stable cycle life for 50 cycles at a limited capacity of 800 mA h g−1. As a result, although the polarization of the cell dramatically decreases and stable capacity behavior is observed with the contribution of α-MnO2 and Pd catalysts, the limited stable cycle life of 50 is obtained due to the consumption of lithium metal which causes total capacity failure after 60 cycles.

Performance evaluation of poly(aniline-co-pyrrole) wrapped titanium dioxide nanocomposite as an air-cathode catalyst material for microbial fuel cell.

A simple, inexpensive in situ oxidative polymerization of aniline and pyrrole using ammonium persulfate (APS) as oxidant and hydrochloric acid (HCl) as dopant has been used to synthesize a hybrid (PAni-Co-PPy)@TiO2 nanocomposite with titanium oxide (TiO2) nanoparticles (NPs) wrapped into (PAni-Co-PPy) copolymer. The synthesized nanocomposite has been shown with higher oxygen reduction reactions (ORR) as an excellent cathode material for higher performance in the complex of (PAni-Co-PPy)+/TiO2(O-). The charge transport phenomenon between TiO2 and (PAni-Co-PPy)+ were found adequate with subsequent delocalization of electron/s at PAni and PPy. The self-doping nature of TiO2 (O-) played a vital role in oxygen adsorption and desorption process. With higher electrical conductivity and surface area, these were tested in microbial fuel cells (MFCs) for ORRs at cathode. This yielded a relatively higher current and power density output as compared to PAni@TiO2, PPy@TiO2, and commercially available Pt/C cathode catalysts in MFC system. In overall, the prepared (PAni-Co-PPy)@TiO2 nano-hybrid cathode delivered ~2.03 fold higher power density as compared to Pt/C catalyst, i.e. ~987.36±49mW/m2 against ~481.02±24mW/m2. The properties of electro-catalysts established an improved synergetic effect between TiO2 NPs and (PAni-Co-PPy). In effect, the enhanced surface area and electrochemical properties of the prepared (PAni-Co-PPy)@TiO2 nano-hybrid system is depicted here as an effective cathode catalyst in MFCs for improved performance.

Insights into the electronic origin of enhancing the catalytic activity of Co3O4 for oxygen evolution by single atom ruthenium

Abstract The surface electronic structure of transition-metal oxide catalysts plays a decisive role in binding the intermediates of the oxygen evolution reaction (OER) to the oxide surface, in turn influencing the catalytic activity of these materials. However, the approaches to modulating the electronic structure of surface metal ions are rare and far behind the demands. Here, we report a surface single atom decoration for adjusting the surface electronic structure of Co3O4, leading to enhanced electrocatalytic activity for OER, in which the isolated Ru single atoms were uniformly deposited on the surface of Co3O4 by an atomic layer deposition technology. As the OER catalyst, the as-made catalysts have exhibited a significantly enhanced catalytic activity (with increasing to 95.5 times) and a dramatically decreased overpotential. The density functional theory calculations reveal that the single-atom Ru acts as a promotor to adjust the 3d electronic structure of adjacent Co atoms and to tune the binding energy between intermediates and activity sites, finally leading to enhanced catalytic activity.

High catalytic activity for formaldehyde oxidation of an interconnected network structure composed of \u03b4-MnO2 nanosheets and \u03b3-MnOOH nanowires

Among the transition metal oxide catalysts, manganese oxides have great potential for formaldehyde (HCHO) oxidation at ambient temperature because of their high activity, nontoxicity, low cost, and polybasic morphologies. In this work, a MnO2-based catalyst (M-MnO2) with an interconnected network structure was successfully synthesized by a one-step hydrothermal method. The M-MnO2 catalyst was composed of the main catalytic agent, δ-MnO2 nanosheets, dispersed in a nonactive framework material of γ-MnOOH nanowires. The catalytic activity of M-MnO2 for HCHO oxidation at room temperature was much higher than that of the pure δ-MnO2 nanosheets. This is attributed to the special interconnected network structure. The special interconnected network structure has high dispersion and specific surface area, which can provide more surface active oxygen species and higher surface hydroxyl groups to realize rapid decomposition of HCHO.

An Advanced Dual‐Function MnO2‐Fabric Air Filter Combining Catalytic Oxidation of Formaldehyde and High‐Efficiency Fine Particulate Matter Removal

AbstractComprehensive treatment of indoor contaminants such as volatile organic compounds (VOCs) and fine particulate matter (PM2.5) using transition metal oxide catalysts or functional fibrous filters has gained substantial attention recently. However, coupling VOC oxidation catalysts into high‐performance filter systems remains a challenge. Herein, an overall solution to strongly bind manganese dioxide (MnO2) nanocrystals onto polypropylene (PP) nonwoven fabrics is provided. For the first time, uniform heterogeneous nucleation and growth of MnO2 onto PP nonwoven fabrics using intermediate inorganic nucleation films, including Al2O3, TiO2, and ZnO, formed conformally on the fabrics via atomic layer deposition (ALD) are demonstrated. How different ALD thin films influence the crystallinity, morphology, surface area, and surface oxygen species of the MnO2 grown ALD‐coated PP fibers is further investigated. In addition to uniformity and integrity, ZnO thin films give rise to MnO2 crystals with the largest fraction of available surface oxygen, enabling 99.5% catalytic oxidation of formaldehyde within 60 min. Moreover, the metal oxide filters provide excellent PM removal efficiencies (ePM), achieving ePM2.5 90% and ePM10 98%, respectively, making the approach an outstanding method to produce fully dual‐functional filtration media.

Thermocatalytic upgrading and viscosity reduction of heavy oil using copper oxide nanoparticles

A transition metal oxide catalyst of copper oxide nanoparticles was synthesized by a conventional non-hydrothermal method. It was studied as a catalyst in thermocatalytic upgrading and viscosity reduction of heavy oil in the laboratory. The experimental results showed that the viscosity of heavy oil may be reduced by 85.75% with 0.2 wt% catalyst at 350 °C for 40 min. With determinations of analyzation, it was found that under the thermocatalytic action of copper oxide nanoparticles, the presence of hydrogen-donor in the reaction could further improve the chemical constitution of resin and asphaltene in heavy oil.

Copper Selenide–Derived Copper Oxide Nanoplates as a Durable and Efficient Electrocatalyst for Oxygen Evolution Reaction

Earth‐abundant transition metal–based nanomaterials play a significant role in oxygen evolution reaction (OER). Among them, copper has attracted significant attention due to its excellent electrocatalytic activity, low price, and abundance. Herein, a nanostructured copper oxide (CuO‐A) is generated in situ from a cuprous selenide (Cu2Se) precursor under oxygen evolution reaction conditions. The as‐prepared CuO‐A/copper foam (CF) electrode delivers a current density of 10 mA cm−2 at an overpotential of 297 mV with good stability for over 50 h in 1 m KOH solution, which is superior to most recently reported copper‐based water oxidation catalysts. The high catalytic performance of CuO‐A is mainly attributed to the improved surface area offered by the morphology reconstruction during the in situ transformation process. As a result, it paves a way to synthesize effective and stable transition metal oxide catalysts via the in situ conversion of transition metal chalcogenides for energy conversion and storage applications.

An ultrastable heterostructured oxide catalyst based on high-entropy materials: A new strategy toward catalyst stabilization via synergistic interfacial interaction

Designing high-performance catalysts that can stabilize catalytic active sites against sintering to deactivation at temperature higher than 900 °C is significant but challenging. Here we report a new strategy to obtain a transition metal oxide catalyst with high temperature stability for CO oxidation. This is achieved through a synergistic interfacial interaction at the interface of a heterostructure between high–entropy oxides (HEO, high temperature stability) and CuCeOx (catalytic site). The catalytic site (CuCeOx) for CO oxidation is realized by dissolving an amount of Cu species in HEO into CeO2 via an entropy–driven mechanochemical process. In situ XRD and HAADF–STEM have confirmed the high temperature stability of the heterostructure CuCeOx–HEO, which can remain its CO oxidation catalytic activity at elevated temperatures. It should be expected that this innovative will offer the potential to the synthesis of catalysts with high temperature stability in industry.

Iron Oxide As an Oxygen Evolution Catalyst for Zinc-Air Batteries Synthesized Via Atomic Layer Deposition

Implementation of renewable energy into the power grid is a necessary step for a more sustainable future. However, this process is strongly dependent on the capacity of practical energy storage technologies available. Zinc-air batteries show great promise for energy storage, boasting high theoretical energy density, inexpensive electrode materials, and excellent safety. Current development of zinc-air batteries is, however, stifled by the sluggish oxygen kinetics occurring both during discharge and charge. While precious metals such as platinum and ruthenium are considered to be good catalysts, more abundant, inexpensive transition metal catalysts have been found to perform just as well and with better cycling stability [1], [2].This work focuses on the development of transition metal oxide catalysts using atomic layer deposition (ALD). ALD is a gas phase deposition technique that generates conformal thin films through the use of self-terminating surface reactions. In particular, iron oxide catalysts, which promote the oxygen evolution reaction, are synthesized via ALD using an ethylferrocene precursor. Iron oxide growth from this precursor is enabled by an oxygen plasma reactant. Recipe development is showcased, demonstrating saturating behaviour for the growth of iron oxide films.The synthesized catalytic films are deposited directly onto a porous carbon substrate (gas diffusion layer or GDL), which is used as the air electrode in metal-air batteries. The high surface area GDL takes full advantage of ALD’s conformal nature to maximize the surface area of the deposited catalytic film, optimizing catalytic performance. As well, compared with other deposition techniques, ALD increases the depth of catalytic loading into the pores of the electrode. This increases the three-phase boundary volume consisting of gaseous oxygen, aqueous hydroxide ions, and solid catalytic active sites, thereby improving battery performance [3]. Deposited iron oxide films are tested through various electrochemical techniques to quantify catalytic activity. Iron oxide is combined with other transition metal oxides with the goal of creating a bifunctional catalyst, which is active for both the charge and discharge reactions in a zinc-air battery.[1] M. Xiong, M. P. Clark, M. Labbe, and D. G. Ivey, “A horizontal zinc-air battery with physically decoupled oxygen evolution/reduction reaction electrodes,” J. Power Sources, vol. 393, pp. 108–118, 2018.[2] D. Aasen, M. Clark, and D. G. Ivey, “A Gas Diffusion Layer Impregnated with Mn3O4 -Decorated N-Doped Carbon Nanotubes for the Oxygen Reduction Reaction in Zinc-Air Batteries,” Batter. Supercaps, vol. 2, pp. 1–13, 2019.[3] Y. Li and H. Dai, “Recent advances in Zinc-air batteries,” Chem. Soc. Rev., vol. 43, no. 15, pp. 5257–5275, 2014.

Single-Facet Dominant Anatase TiO2 (101) and (001) Model Catalysts to Elucidate the Active Sites for Alkanol Dehydration

Alkanol dehydration on Lewis acid–base pairs of transition metal oxide catalysts is a reaction of importance in oxygen removal from biomass-derived feedstocks and their conversion to chemicals in general. However, catalysts with a high degree of structural heterogeneity, such as commercial TiO2 powders, are not well-suited to establish rigorous structure–function relationships at an atomic level. Here, we provide compelling evidence for the effects of surface orientation of TiO2 catalyst on elimination reactions of alcohols. Two anatase titania model catalysts, with preferential exposure of (101) and (001) facets, were synthesized and studied for 2-propanol dehydration using kinetic, isotopic, microscopic, and spectroscopic measurements, coupled with DFT calculations. Surface Lewis acid sites were found to be active for 2-propanol dehydration, and (101) facets are more reactive than (001) facets under the reaction conditions studied. On both anatase surfaces, 2-propanol was found to dehydrate via concerted E2 elimination pathways, but with different initial states and thus also different intrinsic activation barriers. Molecular 2-propanol dehydration dominates on TiO2 (101) while on TiO2 (001), 2-propanol simultaneously converts to more stable 2-propoxide before dehydration, which then requires higher activation energies for E2 elimination.

The kinetic study of the methane oxidation reaction catalyzed by transition metal oxides RuO/RhO/PdO

ABSTRACTThe relative stability and kinetics of CH4 … O2 … MO and the reaction potential energy surface under the transition metal oxide catalysts (RuO/RhO/PdO) during methane oxidation reaction were studied with density functional calculations. The results show that the reaction can be easily carried out under the catalysis of transition metal oxides. The transition barriers and the reaction rate constant all show oscillation modes that are consistent with the increase of atomic number at 298 K. while the calculated reaction energies (Er/kcal mol−1) are gradually increased. The oxidised dioxide can be treated to form metal and oxygen that can still be used as a catalyst for methane oxidation; the resulting oxygen can continue to be used as an oxidant. We also calculated the rate constant of methane oxidation reaction to give the resulting methanol pathway. The calculated dynamic characterisation shows that the rate constant has a positive temperature dependence. Our calculation show that this reaction is exothermic reaction via the RuO/RhO/PdO catalyst, and the reaction is thermodynamically feasible. This study also provides theoretical reference data for us to identify new catalysts for the catalytic oxidation of methane.

Cu−Mn Hydroxyapatite Materials for Toluene Total Oxidation

AbstractThe oxidation of 800 ppmv toluene in air has been investigated over CuMnOx ((Cu+Mn) loading: 10 wt%) dispersed on hydroxyapatite (Hap: Ca5(PO4)3(OH)) with different molar Cu/Mn compositions (2; 1; 0.5) to be compared with the corresponding supported single transition metal oxide catalysts. The solids have been prepared by wet aqueous co‐impregnation method followed by a calcination at 400 °C for 4 h and physicochemically characterized by different techniques. The catalytic performances of the supported Cu−Mn oxide catalysts revealed the existence of a synergetic effect in terms of activity and selectivity towards CO2 through the formation of Cu−Mn mixed oxides. The strongest synergetic effect is observed for a Cu/Mn molar ratio of 2 as confirmed by the standardized conversion rate values determined at 190 °C (r190) which followed the decreasing sequence (/10−2 h−1): Cu2MnHap (2.57)>CuMnHap (2.04)>CuMn2Hap (1.59)>MnHap (1.13)>CuHap (0.13). The highest activity of Cu2MnHap can be explained by a better reducibility of the active phase in line with a high density of Cu‐O−Mn interactions at the outermost layers as shown by ToF‐SIMS results.

Advances in transition metal oxide catalysts for carbon monoxide oxidation: a review

The transition metal catalysts have much concerned over the last two to three decades due to their different properties from their bulk-counterparts, which cover the way for their application in various fields. It has shown superior efficiency in selectivity, performances, and stability to the heterogeneous catalysis. Carbon monoxide (CO) is a very harmful gas that exists in the atmosphere and ambient-temperature complete oxidation of it is an important process for human health protection. The performances of transition metal catalysts are highly dependent on the crystallite size, surface area, and pore volume of the catalysts. The chemisorptions of CO over transitional metal and supported catalysts were studied in this review. The transition metal catalysts have been represented an excellent catalyst from lower cost, thermally, activity, and selectivity point of view. This investigation will show scientific basis for potential design of transition metal oxide catalysts for CO oxidation.

N-Doped Porous Carbon Self-Generated on Nickel Oxide Nanosheets for Electrocatalytic N2 Fixation with a Faradaic Efficiency beyond 30%

The electrocatalysis conversion of N2 to NH3 at ambient conditions is promising for achieving clean and sustainable NH3 production with low energy consumption. However, this process suffers from the low yield rate of NH3 and low Faradaic efficiency (FE) by the previously reported electrocatalysts. In this work, a nanocomposite of nickel oxide coated with nitrogen-doped porous carbon distributed on graphite paper (N-C@NiO/GP) with remarkable electrocatalytic activity for nitrogen reduction reaction (NRR) is reported. N-C@NiO/GP attains an impressive Faradaic efficiency of 30.43% for NH3 production, and the NH3 yield rate reaches 14.022 μg h–1 mgcat.–1 (1.15 × 10–10 mol s–1 cm–2) at −0.2 V vs the reversible hydrogen electrode. The composite also shows excellent electrocatalytic activity and structure stability with an electrocatalytic period of up to 20 h. When the 15N2 is used as the feeding gas, the produced species are 14NH4+ and 15NH4+, which suggests that the reaction follows a Mars–van Krevelen mechanism. The synthesized NH3 is determined from the introduced N2 as indicated by no obvious change in N/Ni ratio. The microstructure before and after the durability test is similar and the catalytic performance during the 2 h NRR process, which is repeated six times, is stable. This work not only exploits an excellent electrocatalyst for N2 fixation to NH3 but also provides a direction for the inexpensive preparation of highly active and stable transition metal oxide catalysts.

Low-Temperature Benzene Abatement over Active Manganese Oxides with Abundant Catalytic Sites

Benzene is a typical volatile organic pollutant, and catalytic oxidation is promising for its abatement at low temperatures. Here, we prepared tunnel-structured hollandite-type manganese oxide (HMO) nanoparticles with abundant catalytically active sites (CASs). The HMO nanoparticles are more active than a traditional noble-metal catalyst, namely, Pt/Al2O3. The former catalyst can achieve 100% benzene conversion at 200 °C at a very high space velocity of 120 000 mL gcat–1 h–1. The results from relevant physicochemical characterizations and reaction kinetics studies demonstrate that the CASs are located at the tunnel openings of the HMO{001} surfaces. These CASs not only provide surface-active lattice oxygen species for benzene oxidation, but also efficiently activate O2 during the catalytic process. Moreover, HMO nanoparticles also have more CASs than HMO nanorods, thus leading to higher activity in benzene oxidation. This work may assist in the rational design of active transition-metal oxide catalysts fo...

Constructing Conductive Interfaces between Nickel Oxide Nanocrystals and Polymer Carbon Nitride for Efficient Electrocatalytic Oxygen Evolution Reaction

AbstractCombining transition metal oxide catalysts with conductive carbonaceous material is a feasible way to improve the conductivity. However, the electrocatalytic performance is usually not distinctly improved because the interfacial resistance between metal oxides and carbon is still large and thereby hinders the charge transport in catalysis. Herein, the conductive interface between poorly conductive NiO nanoparticles and semi‐conductive carbon nitride (CN) is constructed. The NiO/CN exhibits much‐enhanced oxygen evolution reaction (OER) performance than corresponding NiO and CN in electrolytes of KOH solution and phosphate buffer saline, which is also remarkably superior over NiO/C, commercial RuO2, and mostly reported NiO‐based catalysts. X‐ray photoelectron spectroscopy and extended X‐ray absorption fine structure spectrum reveal that a metallic Ni–N bond is formed between NiO and CN. Density functional theory calculations suggest that NiO and CN linked by a Ni–N bond possess a low Gibbs energy for OER intermediate adsorptions, which not only improves the transfer of charge but also promotes the transmission of mass in OER. The metal–nitrogen bonded conductive and highly active interface pervasively exists between CN and other transition metal oxides including Co3O4, CuO, and Fe2O3, making it promising as an inexpensive catalyst for efficient water splitting.