Active Oxygen Sites Research Articles

The promotional effects of plasma treating on Ni/Y2Ti2O7 for steam reforming of methane (SRM): Elucidating the NiO-support interaction and the states of the surface oxygen anions

To explore the interaction between NiO and Y2Ti2O7 support, and fabricate improved catalysts for SRM, several Ni/Y2Ti2O7 catalysts have been prepared by an impregnation method with the assistance of dielectric barrier discharge (DBD) plasma treating in different atmospheres. It is found that both the reaction performance and anti-coking ability are improved for the catalysts in comparison with the untreated sample, following the sequence of Ni/Y2Ti2O7–H2P > Ni/Y2Ti2O7-ArP > Ni/Y2Ti2O7-AirP > Ni/Y2Ti2O7. H2-TPR and XPS results have demonstrated that plasma treatment effectively strengthens the interaction between NiO and Y2Ti2O7 support, and Ni2+ cations preferentially interact solely with the Y3+ cations in the A site of Y2Ti2O7. As a consequence, the agglomeration of the metallic Ni species during the reduction process can be impeded, thus obtaining catalysts possessing higher Ni dispersion. As evidenced by Raman, EPR and XPS results, superoxide O2− anions induced by the intrinsic 8a oxygen vacancies of Y2Ti2O7 pyrochlore phase is the only kind of active surface oxygen sites, which might play a critical role for coking removing, and whose formation can be significantly facilitated by plasma treating. In conclusion, the improved active Ni surface area and the surface active superoxide O2− amount by DBD plasma treating are the major factors responsible for the enhanced reaction performance and coking resistance of the catalysts.

Ni nanocatalysts supported on mesoporous Al2O3-CeO2 for CO2 methanation at low temperature.

The selectivity and activity of a nickel catalyst for the hydrogenation of carbon dioxide to form methane at low temperatures could be enhanced by mesoporous Al2O3–CeO2 synthesized through a one-pot sol–gel method. The performances of the as-prepared Ni/Al2O3–CeO2 catalysts exceeded those of their single Al2O3 counterpart giving a conversion of 78% carbon dioxide with 100% selectivity for methane during 100 h testing, without any deactivation, at the low temperature of 320 °C. The influence of CeO2 doping on the structure of the catalysts, the interactions between the mesoporous support and nickel species, and the reduction behaviors of Ni2+ ions were investigated in detail. In this work, the addition of CeO2 to the composites increased the oxygen vacancies and active metallic nickel sites, and also decreased the size of the nickel particles, thus improving the low temperature catalytic activity and selectivity significantly.

Exsolved Nickel Nanoparticles Acting as Oxygen Storage Reservoirs and Active Sites for Redox CH4 Conversion

The growing demand for H2 and syngas requires the development of new, more efficient processes and materials for their production, especially from CH4 that is a widely available resource. One proce...

Identifying Surface Active Sites of SnO2: Roles of Surface O2–, O22– Anions and Acidic Species Played for Toluene Deep Oxidation

To elucidate the nature and states of the surface oxygen sites on SnO2 and the relationship between the surface vacancies and the active oxygen sites, a series of SnO2 samples have been fabricated ...

Syngas production via chemical looping reforming biomass pyrolysis oil using NiO/dolomite as oxygen carrier, catalyst or sorbent

Chemical looping reforming (CLR) with biomass pyrolysis oil (BPO) for syngas production was investigated using NiO/dolomite as the bed material which was prepared by the wet impregnation method. The NiO/dolomite was used as catalyst and oxygen carrier in the whole temperature range, while it was also acted as in-situ CO2 sorbent at 600 °C and 700 °C. The syngas production was dominated by the sorption enhanced and catalytic reforming of BPO, due to the formation of NiO–MgO solid solution, which had a lower reducibility at low temperatures. Although, the low level CGE at low temperature could be improved by elevating the oxygen coefficient at the certain extent, poor cyclic performance of NiO/dolomite at 700 °C was observed, owning to the sintering and agglomeration during the repeated carbonation/calcination reactions. High temperatures inhibited the carbonation reaction and facilitated the reduction of NiO–MgO solid solution to provide more lattice oxygen and catalytic active sites. The syngas production was governed by the synergistic effect of lattice oxygen and catalysis at high temperatures. The optimum operating condition for syngas production in CLR was obtained by the analysis showed as follows: the temperature at 900 °C with ϕ = 0.4 in fuel reactor. The corresponding values of cold gas efficiency (CGE), syngas yield (Ysyn) and syngas purity (Psyn) were 80.76%, 1.318 Nm3/kg and 92.06%, respectively. Besides that, the NiO/dolomite exhibited a good cycle performance under this condition. The CGE and Ysyn decreased slightly to 76.26% and 1.265 Nm3/kg after 10 cycles, respectively. Overall, NiO/dolomite is a promising multifunctional material in the CLR process with BPO for syngas production. More attention should be paid to improve the mechanical strength of NiO/dolomite in the future.

Constructing copper-ceria nanosheets with high concentration of interfacial active sites for enhanced performance in CO oxidation

The interaction of the metal and support in copper-ceria oxide catalysts has been proven to have extremely favorable effects on catalytic performance in CO oxidation. Therefore, how to construct more copper-ceria interfaces becomes the key to improve the catalytic activity. Herein, we developed a facile approach to prepare copper-ceria nanosheets with high concentration of interfacial active sites (active copper species sites and oxygen vacancies) using GO as a sacrificial template. Notably, GO was used as an excellent platform to grow precursors of both the Cu and Ce on its surface. Then, transfer them to metal oxides nanosheets by calcination. The CuCe-GO-X catalysts were characterized by SEM, TEM, In situ DRIFT, AFM, XRD, XPS, H2-TPR and Raman spectra and applied in CO oxidation. The results demonstrate that CuCe-GO-600 nanosheets catalyst with about 10 nm thickness shows a higher concentration of oxygen vacancies (7.79%) and active copper species sites (2756 μmol g−1) in the interface of copper-ceria than those of other CuCe-GO-X catalysts. Moreover, CuCe-GO-600 displays a highest catalytic activity (complete conversion at 90 °C with a space velocity of 54,000 mL (h gcat)−1).

Engineering highly active oxygen sites in perovskite oxides for stable and efficient oxygen evolution

Perovskite oxides, represented by Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF), with O anion partially substituted by F anion are designed. Introduction of F in perovskite lattice initiated the transition of Co(III) and Fe(III) species to lower oxidation states and triggered the surface O anion to be activated to highly oxidative O2−/O‒, which is deemed to be efficient active sites for oxygen evolution reaction (OER) catalysis. As a consequence, the F substituted BSCF (F-BSCF) catalyst exhibits outstanding electrocatalytic activity with overpotential of only 280 mV to deliver 10 mA cm‒2 OER, which is among the results for state-of-the-art metal oxide based catalysts. Strikingly, an stable chronoamperometric response prolonged for 100 h and an impressive cycling stability demonstrate its prominent durability, much superior to the commercial IrO2 catalyst. These findings highlight the promising potential of F substitution as an efficient strategy for active site engineering in traditional precious metal-free OER electrocatalysts.

A Cobalt‐Based Amorphous Bifunctional Electrocatalysts for Water‐Splitting Evolved from a Single‐Source Lazulite Cobalt Phosphate

AbstractOver the years, cobalt phosphates (amorphous or crystalline) have been projected as one of the most significant and promising classes of nonprecious catalysts and studied exclusively for the electrocatalytic and photocatalytic oxygen evolution reaction (OER). However, their successful utilization of hydrogen evolution reaction (HER) and the reaction of overall water‐splitting is rather unexplored. Herein, presented is a crystalline cobalt phosphate, Co3(OH)2(HPO4)2, structurally related to the mineral lazulite, as an efficient precatalyst for OER, HER, and water electrolysis in alkaline media. During both electrochemical OER and HER, the Co3(OH)2(HPO4)2 nanostructure was completely transformed in situ into porous amorphous CoOx (OH) films that mediate efficient OER and HER with extremely low overpotentials of only 182 and 87 mV, respectively, at a current density of 10 mA cm−2. When assemble as anode and cathode in a two‐electrode alkaline electrolyzer, unceasing durability over 10 days is achieved with a final cell voltage of 1.54 V, which is superior to the recently reported effective bifunctional electrocatalysts. The strategy to achieve more active sites for oxygen and hydrogen generation via in situ oxidation or reduction from a well‐defined inorganic material provides an opportunity to develop cost‐effective and efficient electrocatalysts for renewable energy technologies.

Ni/La2O3 Catalysts for Dry Reforming of Methane: Insights into the Factors Improving the Catalytic Performance

AbstractTo understand the structure‐reactivity relationship of Ni/La2O3, and eventually get more applicable catalysts for DRM, glycine nitrate combustion (GNC), precipitation (PP) and thermal decomposition (TD) methods have been used to prepare La2O3 supports. Although all the supports possess a hexagonal La2O3 phase, their bulk and surface properties are significantly changed. By using them as supports, the interactions between NiO/Ni and La2O3 are varied, thus achieving Ni/La2O3 catalysts with different activity, stability and anti‐coking ability, which follow the order of 5Ni/La2O3‐GNC>5Ni/La2O3‐PP>5Ni/La2O3‐TD. On La2O3 having a higher surface area, a catalyst with a higher active metallic Ni surface area can be achieved. Therefore, the interfaces between Ni and La2O2CO3 can be enlarged, which effectively facilitates the reaction between carbon deposits and the La2O2CO3 formed during the DRM, thus preventing the accumulation of both and keeping the catalyst surface clean, active and stable. In addition, the amount of surface alkaline and active oxygen sites of the reduced catalysts obey the order of 5Ni/La2O3‐GNC>5Ni/La2O3‐PP>5Ni/La2O3‐TD, which is well consistent with the reaction performance. Therefore, these two factors are also believed to be critical to decide the reaction performance. It is concluded that Ni/La2O3 catalysts with high activity, stability and potent anti‐coking ability for DRM can be achieved by preparing catalysts with high Ni dispersion.

Perylene-3,4,9,10-tetracarboxylic acid accelerated light-driven water oxidation on ultrathin indium oxide porous sheets

Engineering the organic/inorganic nanocomposites by taking advantage of the high electrical conductivity of the inorganic semiconductors and the structure flexibility of the organic semiconductors (OSCs) provides chances to understand the structural and electronic contributions that give rise to increased activities, which is the imperious demand for methodical design of next-generation of oxygen evolution photocatalysts. Herein, perylene-3,4,9,10-tetracarboxylic acid (PTCAD) bonded porous In2O3 nanosheets, PTCAD/In2O3 NSs, were fabricated to elucidate the performance of OSCs in light harvesting and charge separation toward photo-driven oxygen evolution reaction (OER). PTCAD coupled strongly to the conduction band (CB) of In2O3 NS and type-II energy alignment was constructed between these two organic-inorganic components. Consequently, upon excitation, electrons injected smoothly from PTCAD to In2O3 NS, leaving holes behind to perform water oxidation, which results in accelerated charge separation and transportation. Associated with the large specific area, high-speed electron transmission channels, abundant oxygen vacancies and active sites provided by the In2O3 NS, the PTCAD/In2O3 composites demonstrated highly reduced band gap (BG), boosted and stable photocurrent, as well as largely reduced overpotential, suggesting promises for broadband-light-triggered OER. In addition to the synergistic effects in promoting charge separation and inhibiting electron-hole recombination, the π-conjugated molecule, PTCAD, played a role of manipulating the lattice plane of the In2O3 nanostructure without disturbing its porous 2D structure, providing another potential approach for enhancement of catalytic activity by regulating the crystal faces. Importantly, water oxidation over PTCAD/In2O3 NSs is indeed a proton-coupled electron transfer (PCET) processes, a key process for charge separation and water oxidation, which is significantly promoted by PTCAD. Ultimately, the photo-catalytic oxygen evolution yield enhanced greatly at the presence of PTCAD, indicating that our findings may provide clues for development of organic/inorganic hybrid semiconducting photocatalysts for solar fuels generation.

Facile synthesis of magnesium ferrite nanoparticles supported on nitrogen and sulfur co-doped carbon black as an efficient electrocatalyst for oxygen reduction reaction

Novel nanohybrid MgFe2O4 (MFO) supported on carbon black co-doped by nitrogen and sulfur (CNS) was facilely synthesized as an efficient electrocatalyst (namely, MFO/CNS) for oxygen reduction reaction (ORR) in alkaline medium. Structural analysis by X-ray diffraction revealed the formation of MFO and confirmed its spinel structure in MFO/CNS nanocomposite. Transmission electron microscope images showed that the products synthesized by different annealing temperature displayed a diverse particle size and dispersion of active component. Electrochemical results indicated that the MFO/CNS hybrid with the controllable N, S-co-doping shows an enhanced ORR catalytic activity and desired direct four-electron reaction pathway, which is better than MFO and CNS synthesized under the same conditions. The excellent electrochemical performance of MFO/CNS should be attributed to the synergistic effect of MFO and CNS to form a conductive network structure, which offers the increased electrochemical active surface area, the facilitated electron transfer, and effective mass transport between oxygen molecules and active sites. The results demonstrated that the MFO/CNS nanohybrid in this study appears to be a promising cathodic electrocatalyst in alkaline fuel cells.

In situ detection of trace pollutants: a cost-effective SERS substrate of blackberry-like silver/graphene oxide nanoparticle cluster based on quick self-assembly technology.

To realize fast detection of trace hazardous chemicals, a SERS substrate with the structure of a blackberry-like silver/graphene oxide nanoparticle cluster (Ag/GO NPC) has been designed and prepared through a quick capillarity-assistant self-assembly technology in this paper. Benefitting from the abundant "hot spots" and active oxygen sites brought by this Ag/GO NPC, the substrate shows good Raman performance for malachite green (MG), a common abusive germicide in aquaculture, with lowest limit of detection below 0.1 µg/L (3.48 × 10-10 mol/L). Detailed analyses are taken on both the formation process and enhancement mechanism of this SERS substrate, and the finite-difference time-domain simulations are utilized as well to prove our hypotheses. Further constructing this structure on polyethylene terephthalate (PET) film, a translucent flexible SERS substrate can be obtained, realizing a fast in situ detection of trace MG in the fishpond subsequently. In consideration of the facile preparation process, good SERS enhancement and affordable materials (PET, Cu, Ag and GO, etc.), this substrate presents high cost performance and a promising application prospect.

Role of the Acid Site for Selective Catalytic Oxidation of NH3 over Au/Nb2O5

Selective catalytic oxidation (SCO) of NH3 to harmless N2 and H2O is an ideal technology for its removal. To develop air purification systems for a living environment, catalysts that can work at room temperature with high selectivities to N2 are required. However, it has been a technical challenge because the reported catalysts either needed high operating temperatures or showed low selectivities to N2. In this study, we first demonstrated that acidic metal-oxide-supported gold catalysts showed good N2 selectivities compared with that of other metal-oxide-supported gold catalysts. A gold catalyst with niobium oxide synthesized by the hydrothermal method as a support showed high catalytic activity and high selectivity to N2 at low temperatures (18% NH3 conversion with 100% N2 selectivity at 25 °C) and at high temperatures (100% NH3 conversion with 95% N2 selectivity at 245 °C). Important roles of Brønsted acid sites and formation of active oxygen sites in improving N2 selectivity were revealed in this study. To the best of our knowledge, this is the first report of efficient catalysts that presented high NH3 conversion with high N2 selectivity at 25 °C which will offer great scopes for commercial applications related to control of odors. In addition, this breakthrough finding that acid sites would greatly affect N2 selectivity and catalytic activity will provide a new trend in designing efficient catalysts not only for SCO of NH3 but also for the other selective catalytic oxidation.

Optimizing the Reaction Performance of La2Ce2O7‐Based Catalysts for Oxidative Coupling of Methane (OCM) at Lower Temperature by Lattice Doping with Ca Cations

To optimize the reaction performance of La2Ce2O7 for OCM, catalysts with varied La/Ce molar ratios and doped by Ca additive have been synthesized and characterized by different techniques. It is discovered that a La2Ce2O7 compound having a disordered cubic defective fluorite phase is predominantly formed in all the samples. Varying the La/Ce ratio influences the fine crystalline structure of the catalysts. As a result, the abundance of the surface facile oxygen and alkaline sites increase by increasing the La/Ce ratio. Moreover, the Ca additive exists on the surface of Ca0.5La2Ce2O7 and Ca0.5La1.5Ce2O7 as dispersed CaCO3, which covers the active sites and is harmful to the OCM reaction. However, for La2Ce1.5Ca0.5O7, the major part of the Ca additive has entered into the lattice of La2Ce2O7 phase as Ca2+ cations, thus creating more oxygen vacancies and improving the surface alkalinity of the catalyst, which is favorable to the OCM reaction. Both the active surface oxygen and alkaline sites are vital for OCM, and their synergism determines the reactivity. By increasing La/Ce ratio and doping Ca2+ into La2Ce2O7 lattice, the quantities of both kinds of active sites can be significantly improved, thus obtaining catalysts with much improved reaction performance. La2Ce1.5Ca0.5O7 owns the largest amount of both types of active sites, hence depicting the best reaction performance, over which the highest C2 yield of 22.5 % can be achieved even at 750 °C.

An electronic structure descriptor for oxygen reactivity at metal and metal-oxide surfaces

Identifying and understanding relationships between the electronic and atomic structure of surfaces and their catalytic activity is an essential step towards the rational design of heterogeneous catalysts for both thermal and electrochemical applications. Herein, we identify a relationship between the atom-projected density of states of surface oxygen and its ability to make and break bonds with the surrounding metal atoms and hydrogen. This structure-property relationship is shown to hold across different classes of materials (metals, rutile metal-oxides, and perovskite metal-oxides) and for different oxygen binding sites (i.e. different oxygen coordination numbers). We utilize understanding from the d-band model and the simple two-level quantum coupling problem to shed light on the physical origin of this relationship for transition metal surfaces and we hypothesize similar principles extend to the other materials considered. Finally, we demonstrate the utility of the identified descriptor to serve as a tool for high throughput screening of oxygen active sites for large systems where many unique oxygen sites exist and can be computationally expensive to probe individually. As an example, we predict the reactivity of 36 unique oxygen atoms at a kinked RuO2 extended surface from a single self-consistent DFT calculation.

Ball-flower-like carbon microspheres via a three-dimensional replication strategy as a high-capacity cathode in lithium–oxygen batteries

The robust porous architectures of active materials are highly desired for oxygen electrodes in lithium–oxygen batteries to enable high capacities and excellent reversibility. Herein, we report a novel three-dimensional replication strategy to fabricate three-dimensional architecture of porous carbon for oxygen electrodes in lithium–oxygen batteries. As a demonstration, ball-flower-like carbon microspheres assembled with tortuous hollow carbon nanosheets are successfully prepared by completely replicating the morphology of the nanostructured zinc oxide template and utilizing the polydopamine coating layer as the carbon source. When used as the active material for oxygen electrodes, the three-dimensional porous architecture of the prepared ball-flower-like carbon microspheres can accommodate the discharge product lithium peroxide and simultaneously maintain the ions and gas diffusion paths. Moreover, their high degrees of defectiveness by nitrogen doping provide sufficient active sites for oxygen reduction/evolution reaction. Thus the prepared ball-flower-like carbon microspheres demonstrate a high capacity of 9,163.7 mA h g−1 and excellent reversibility. This work presents an effective way to prepare three-dimensional architectures of porous carbon by replicating the controllable nanostructures of transition metal oxide templates for energy storage and conversion applications.

Tuning SnO2 Surface Area for Catalytic Toluene Deep Oxidation: On the Inherent Factors Determining the Reactivity

To understand the fundamental aspects of SnO2 catalytic materials and develop applicable catalysts for VOCs combustion, SnO2 samples possessing stable and varied surface areas are controllably constructed and applied to toluene deep oxidation. By improving SnO2 surface area, the Sn4+ cation exposure is improved, thus increasing its surface acidity, which benefits toluene molecule adsorption and activation. Furthermore, more surface defects can be generated, hence inducing the generation of more abundant surface active oxygen sites, which is favorable for further oxidizing the adsorbed and activated toluene intermediates. Therefore, the intrinsic activity of SnO2 is eventually promoted. The coexistence of both kinds of active sites is crucial for the reaction, and the concerted interaction between them controls the reaction performance. Catalysts with good activity, superior stability, and potent water vapor tolerance can be achieved by controllably constructing SnO2 possessing large and stable surface are...

First-principles and Molecular Dynamics simulation studies of functionalization of Au32 golden fullerene with amino acids

With the growing potential applications of nanoparticles in biomedicine especially the increasing concerns of nanotoxicity of gold nanoparticles, the interaction between protein and nanoparticles is proving to be of fundamental interest for bio-functionalization of materials. The interaction of glycine (Gly) amino acid with Au32 fullerene was first investigated with B3LYP-D3/TZVP model. Several forms of glycine were selected to better understand the trends in binding nature of glycine interacting with the nanocage. We have evaluated various stable configurations of the Gly/Au32 complexes and the calculated adsorption energies and AIM analysis indicate that non-Gly, z-Gly and also tripeptide glycine can form stable bindings with Au32 at aqueous solution via their amino nitrogen (N) and/or carbonyl/carboxyl oxygen (O) active sites. Furthermore, cysteine, tyrosine, histidine and phenylalanine amino acids bound also strongly to the Au32 nanocage. Electronic structures and quantum molecular descriptors calculations also demonstrate the significant changes in the electronic properties of the nanocage due to the attachment of selected amino acids. DFT based MD simulation for the most stable complex demonstrate that Gly/Au32 complex is quite stable at ambient condition. Our first-principles findings offer fundamental insights into the functionalization of Au32 nanocage and envisage its applicability as novel carrier of the drugs.

Multifunctional C-Doped CoFe2O4 Material as Cocatalyst to Promote Reactive Oxygen Species Generation over Magnetic Recyclable C–CoFe/Ag–AgX Photocatalysts

Photocatalytic water disinfection has been demonstrated as a promising technology for rapid water treatment in terms of utilizing sustainable solar energy. In this paper, C-doped CoFe2O4 magnetic nanoparticles (named C–CoFe) modified C–CoFe/Ag–AgX (X = Cl, Br, I) composites were synthesized via solvothermal process. The photocatalytic performance of the C–CoFe/Ag–AgX composites were evaluated by bacterial inactivation in aqueous solution under visible light irradiation; the results showed that the C–CoFe/Ag–AgX composites were able to inactivate E. coli with a low photocatalysts concentration. In comparison to pure Ag–AgX, the C–CoFe/Ag–AgX composites exhibited enhanced photocatalytic performance, in which the 5% C–CoFe/Ag–AgBr showed the most inactivate activities that can achieve rapid water disinfection with 7 log inactivation of Escherichia coli within 40 min under visible light. With the analysis and discussion of photoelectrochemistry test, ESR trapping experiments, H2O2 yield measurement, and O2 control photocurrent response text, it was demonstrated that C–CoFe can work as a cocatalyst component in the C–CoFe/Ag–AgX composite to extract the photogenerated electrons and offer more oxygen activation sites to yield more reactive oxygen species (ROSs) for the photocatalytic inactivation. More importantly, the as-prepared C–CoFe/Ag–AgX composite possess magnetic properties which can be recovered easily by a magnetic field.

The promoting effect of CeO2@Ce-O-P multi-core@shell structure on SO2 tolerance for selective catalytic reduction of NO with NH3 at low temperature

A series of CeO2@Ce-O-P “multi-core@shell” catalysts were synthesized in this paper for selective catalytic reduction (SCR) of NO with NH3. The experimental results had showed that CeO2@Ce-O-P-30:3 yielded best SO2 tolerance of an over 70% deNOx efficiency at 250 °C in the presence of 100 ppm SO2 for 20 h, which was much higher compared to pure Ce-O-P and CeO2 samples. Further characterization results indicated that Ce-O-P coating layer could somewhat inhibit sulfur depositing on the catalysts during SCR reaction in the presence of SO2, thereby protecting the active sites from SO2 poisoning. Especially, O2-TPD results illustrated that a great amount of active oxygen species were retained on used CeO2@Ce-O-P catalyst after a long term reaction. The synergetic effect of “multi-core@shell” structure could be attributed to such enhanced performances. The “core” CeO2 devoted abundant active oxygen sites to fulfill the SCR reaction. And the “shell” Ce-O-P could not only provide acid sites, but also protect the active oxygen species by avoiding the over-adsorption of SO2 on the catalyst. This work could provide a new way to increase the sulfur resistance for low temperature SCR catalysts.