Mixed Catalysts Research Articles

One-pot conversion of wheat straw into biobased chemicals in methanol/water medium using cheap mixed acid catalyst.

Environmental concerns and the diminishing availability of unrenewable resources have spurred research into the use of agricultural waste as a feedstock for industrial applications. Efficient conversion of wheat straw into biobased chemicals is an important way to realize the potential value of renewable agricultural biomass. This study investigated one-pot conversion of wheat straw into two notable platform chemicals, levulinic acid (LA) and methyl levulinate (ML). A mixed acid catalyst system, including 1% H2 SO4 and 0.015mol L-1 Al2 (SO4 )3 , was an efficient catalyst for the conversion of wheat straw due to the combination of Brønsted acid and Lewis acid. A ratio of wheat straw to methanol of 5g/50 mL was identified as the preferred solid/liquid ratio, and a methanol/H2 O medium with 25% water content aided the simultaneous production of LA and ML from wheat straw. Under optimum conditions, the maximum total yield of LA and ML reached 23.01% at 220 °C and 3h. The kinetics of biobased chemical formation and the reaction pathways in methanol/water were investigated. The presence of water in the methanol/H2 O medium affected the distribution of products and promoted hydrolysis reactions. The methanol/H2 O medium not only inhibited the side reactions but also promoted the degradation of wheat straw and increased the total yield of LA and ML. This study provides a feasible method for the conversion of wheat straw to prepare biobased chemicals. © 2021 Society of Chemical Industry.

Catalytic Synthesis of the Biofuel 5-Ethoxymethylfurfural (EMF) from Biomass Sugars

A new generation of bioplatform molecule 5-ethoxymethylfurfural (EMF) has excellent energy density and combustion performance, which makes it a potential fuel additive. This article reviews the factors that affect the production of EMF from different feedstocks, including platform compounds, monosaccharides, polysaccharides, and raw lignocellulosic biomass. Focus is placed on discussing the catalytic efficiency with pros and cons of different acid catalysts, including homogeneous catalysts (i.e., liquid acids and metal salts), heterogeneous catalysts (i.e., zeolites, heteropolyacid-based hybrids, and SO3H-based catalysts), ionic liquids, mixed acid catalysts, and deep eutectic solvents (DESs). Except for the commonly used ethanol solvent, this review also summarizes the influence of the cosolvent system (e.g., ethanol/dimethylsulfoxide (DMSO), ethanol/tetrahydrofuran (THF), and ethanol/γ-valerolactone (GVL)) on the EMF yield.

Progress on Noble Metal-Based Catalysts Dedicated to the Selective Catalytic Ammonia Oxidation into Nitrogen and Water Vapor (NH3-SCO).

A recent development for selective ammonia oxidation into nitrogen and water vapor (NH3-SCO) over noble metal-based catalysts is covered in the mini-review. As ammonia (NH3) can harm human health and the environment, it led to stringent regulations by environmental agencies around the world. With the enforcement of the Euro VI emission standards, in which a limitation for NH3 emissions is proposed, NH3 emissions are becoming more and more of a concern. Noble metal-based catalysts (i.e., in the metallic form, noble metals supported on metal oxides or ion-exchanged zeolites, etc.) were rapidly found to possess high catalytic activity for NH3 oxidation at low temperatures. Thus, a comprehensive discussion of property-activity correlations of the noble-based catalysts, including Pt-, Pd-, Ag- and Au-, Ru-based catalysts is given. Furthermore, due to the relatively narrow operating temperature window of full NH3 conversion, high selectivity to N2O and NOx as well as high costs of noble metal-based catalysts, recent developments are aimed at combining the advantages of noble metals and transition metals. Thus, also a brief overview is provided about the design of the bifunctional catalysts (i.e., as dual-layer catalysts, mixed form (mechanical mixture), hybrid catalysts having dual-layer and mixed catalysts, core-shell structure, etc.). Finally, the general conclusions together with a discussion of promising research directions are provided.

Structure and Phase Evolution of Nife Hydroxide during Electrochemical Water Oxidation

Achieving stable, low-cost electrocatalysts represents a daunting challenge towards practical water oxidation reactions. Here, we report that a degraded electrocatalyst can be revivified under catalytic operating conditions by manipulating reversible phase segregation. Under the oxygen evolution reaction conditions, Fe segregation develops in the Ni–Fe hydroxide host lattice, with the formation of FeOOH, resulting in an interface between the FeOOH and the host lattice. A dynamic metal dissolution–redeposition process accelerates the Fe segregation and formation of the FeOOH secondary phase, resulting in catalyst deactivation. Operando synchrotron spectroscopic and microscopic analyses suggest that the phase segregation is reversible between the water oxidation potential and the catalyst reduction potential. Therefore, we have developed an intermittent reduction methodology to revivify the catalytic activity under the operating conditions, enhancing catalyst durability. The present study highlights that tailoring phase segregation at the catalyst/electrolyte interface constitutes an important strategy for revivifying and stabilizing catalytic activity.Reference:1. Kuai, C.; Zhang, Y.; Wu, D.; Sokaras, D.; Mu, L.; Spence, S.; Nordlund, D.; Lin, F.; Du, X.-W. Fully Oxidized Ni-Fe Layered Double Hydroxide with 100% Exposed Active Sites for Catalyzing Oxygen Evolution Reaction. ACS Catalysis 9, 6027-6032 (2019)2. Kuai, C.; Xu, Z.; Xi, C.; Hu, A.; Yang, Z.; Zhang, Y.; Sun, C. J.; Li, L.; Sokaras, D.; Dong, C.; Qiao, S. Z.; Du, X. W; Lin, F. Phase segregation reversibility in mixed metal hydroxide water oxidation catalysts. Nat Catal 3, 743–753 (2020)

Synthesis of mesoporous BiOI flower and facile in-situ preparation of BiOI/BiOCl mixture for enhanced photocatalytic degradation of toxic dye, Rhodamine-B

Porous flower-like BiOI possessing excellent and wonderful activity in visible light induced photo-catalytic degradation of Rhodamine-B, have been synthesized by facile solvothermal method. X-ray diffractometer, microscopes and spectroscopes are employed to study the phase structure, nano-dimension, purity and morphology of synthesized and used catalysts. The degradation using BiOI is increased from 74 to 99.2 % within 1 h for in-situ formation of BiOI/BiOCl mixture in media of aqueous BiOI containing Cl− ion. The study of reaction parameters reveals high efficiency of mixed catalyst with maximum removal of the dye achieved up to 99.2 % in 1 h for a dye concentration of 5 mg/L at pH 3. Possible degradation products are detected, scavenger-effects determined and mechanisms proposed.

The Effect of Material Properties on Oxygen Evolution Activity and Assessing Half-Cell Screening as a Predictive Tool in Electrolysis

Iridium-based oxygen evolution catalysts are screened in this study for activity and stability with rotating disk electrode (RDE) half-cells. This study focuses on the electrochemical and materials approaches needed to characterize oxygen evolution catalysts, and include testing for activity, stability, composition, oxide content, and structure. Findings also discuss recommendations for data interpretation and detail the difficulties of comparing catalysts across materials sets with different elemental and oxide compositions, and linking RDE activity to device-level performance. The materials evaluated are a mixture of oxides and metals, and several methods are used to quantify metal content, qualitatively assess oxide content, and determine total surface area. Oxygen evolution activities and stabilities are compared, where a wide range of results are reported. In general, higher RDE performances are found for catalysts that contained larger amounts of ruthenium and metals. Higher durability, however, is found for catalysts that only contained iridium and a higher proportion of oxides. Additionally, catalysts are evaluated for performance in membrane electrode assemblies to assess RDE as a predictive tool in electrolysis. While activity trends within individual material sets generally held between ex- and in-situ testing, RDE tends to overestimate the activity of more metallic catalysts when compared to device-level performance. These results stress the need for multiple metal/oxide baselines for mixed catalysts, to better project in-situ kinetics.

Synergistic action of Pt and Nb2O5 ultrafine nanoparticles for bidirectional conversion of polysulfides in high-performance lithium-sulfur cells

The shuttling effect in Lithium-sulfur (Li-S) cells can be effectively minimized by increasing the polysulfide redox reaction rate via catalysis. However, previous research has focused on this reaction in a single direction (i.e., either oxidation or reduction of polysulfides), but the acceleration of sulfur species cycling relies on advances in both directions. Herein, a Pt-Nb2O5 mixed catalyst was synthesized by dispersing Pt nanoparticles on the surface of Nb2O5 ultrafine nanoparticles to synergistically enhance bidirectional catalysis. During reduction, Nb2O5 served as a trap while Pt catalytically converted the polysulfides. During oxidation, Nb2O5 and Pt both exhibited enhanced catalytic activity for Li2S dissolution to refresh the catalytic surfaces. Consequently, a sulfur cathode with Pt-Nb2O5 separator achieved an initial discharge capacity as high as 1283 mA h g−1, which was degraded minimally to 979 mA h g−1 after 100 cycles (0.2C). This outstanding cycling stability was further demonstrated, where a discharge capacity of 915 mAh g−1 and average capacity fading rate of 0.093% were achieved after 500 cycles (0.5C). In addition, minimal self-discharge was observed. This work demonstrates the use of two compounds to achieve synergistic action for the bidirectional catalytic transformation of polysulfides for high-efficiency Li-S cells.

Metal-based catalysts for persulfate and peroxymonosulfate activation in heterogeneous ways: A review

A growing number of emerging organic contaminants associated with the potential risks for ecosystem and human health are frequently detected in environment. Sulfate radical-based advanced oxidation processes have attracted increasing attention during the past decades, owing to their high reactivity and oxidation capability of a wide range of toxic and non-biodegradable organic compounds. Metal-based materials have been proven to be effective heterogeneous catalysts for activating persulfate to degrade many refractory organic pollutants. This article reviews the up-to-date research progresses on various heterogeneous metal-based catalysts for persulfate (PS) and peroxymonosulfate (PMS) activation, including single metal and mixed metal catalysts. The activation mechanisms of these catalysts and their fundamental behaviors in PS/PMS activation are emphatically elucidated, in which contaminants can be eliminated through radical and/or non-radical reaction pathways. In addition, an in-depth discussion about metal composite namely metal spinel, metallic glasses and other metal hybrids in PS or PMS systems for organic degradation and possible environmental applications are presented. Finally, the perspectives on the metal-based PS/PMS activation method and their remediation potential for recalcitrant compounds in practical application are also proposed.

Hydrogen production by sewage sludge gasification in supercritical water with high heating rate batch reactor

Sewage sludge gasification in supercritical water was studied with high heating rate batch reactor. Effect of temperature, pressure, residence time and catalyst were investigated. The hydrogen yield, gasification efficiency, carbon gasification efficiency and hydrogen yield potential were mainly affected by temperature. The maximum values of them reached 20.66 mol/kg, 73.49%, 61.16% and 41.34% without catalyst at 750 °C and 30 min respectively. The modified detailed kinetics indicated steam reforming, water-gas shift and pyrolysis promoted the formation of H2 and CO2 when temperature was ranged from 550 to 750 °C at the initial residence time. As residence time increased, the water-gas shift was dominant. Meanwhile, the formation of CO and CH4 were inhibited when temperature and residence time increased. The addition of mixed catalysts promoted the three reactions and formation of hydrogen better at lower reaction condition. The mixed use of both catalysts could enhance the gasification and the formation of hydrogen better. The increased loading of RNi-Mo2 could enhance the formation of hydrogen better because the heterogeneous catalyst could promote steam reforming and alkali catalyst could promote water-gas shift reaction better.

Bisphenol S degradation via persulfate activation under UV-LED using mixed catalysts: Synergistic effect of Cu–TiO2 and Zn–TiO2 for catalysis

A photocatalyst composed of Zn–TiO2 and Cu–TiO2 through simple physical mixing was used to activate persulfate(PS) for Bisphenol S (BPS) degradation. Zn–TiO2 and Cu–TiO2 were prepared with a sol gel method and were characterized by X-ray diffraction (XRD), Raman, Transmission electron microscope (TEM), Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The two catalysts have shown an obvious synergistic effect in the photocatalytic degradation process. When 5 mM persulfate and 0.3 g/L catalyst were used, the removal rate of mixed catalyst (0.2 g/L Zn–TiO2 and 0.1 g/L Cu–TiO2) is 100 % in 18 min, which is significantly better than that of 0.3 g/L Zn–TiO2(58 %) and 0.3 g/L Cu–TiO2(90 %). Typically, the effects of various operation parameters, including the ratio of Cu–TiO2/Zn–TiO2, catalyst dosage, persulfate dosage, initial concentration of BPS, and initial solution pH, were examined. Reactive oxygen species (ROS) in the UV/mixed catalyst/PS process was identified by scavenger and electron paramagnetic resonance (EPR) tests. The superoxide radicals generated by both Zn–TiO2 and the hydrolysis of persulfate in the system could accelerate the Cu (II)/Cu(I) redox cycles and results in the synergistic effect. This study proposed a new and effective way to improve the reaction by simply combining two catalysts, and unraveled the mechanism behind the synergistic effect, which could provide new ideas to use the catalyst more effectively for wastewater treatment or other areas.

Influence of Anatase-Rutile Ratio on Band Edge Position and Defect States of TiO2 Homojunction Catalyst

Removal of toxic air and water dissociation in the environment has become a major challenging issue throughout the world. Mixed phase rutile-anatase titanium dioxide catalysts are very effective in photocatalysis and have been studied extensively. However, the mechanism causing this effect and band alignment of the two phases are not fully understood. Pointing to the issue, we have designed one-dimensional mixed-phase TiO2 and introduced defects near the valence band. Experimental results showed that band alignment between two phases, up-shift of the band edge, and optimum anatase percentage play a key role in the enhancement of the photocatalytic activity. We predicted shifts in band edge originating from surface electric dipole layer induced by defects.

Methanol to Formaldehyde: An Overview of Surface Studies and Performance of an Iron Molybdate Catalyst

Formaldehyde is a primary chemical in the manufacturing of various consumer products. It is synthesized via partial oxidation of methanol using a mixed oxide iron molybdate catalyst (Fe2(MoO4)3–MoO3). This is one of the standard energy-efficient processes. The mixed oxide iron molybdate catalyst is an attractive commercial catalyst for converting methanol to formaldehyde. However, a detailed phase analysis of each oxide phase and a complete understanding of the catalyst formulation and deactivation studies is required. It is crucial to correctly formulate each oxide phase and influence the synthesis methods precisely. A better tradeoff between support and catalyst and oxygen revival on the catalyst surface is vital to enhance the catalyst’s selectivity, stability, and lifetime. This review presents recent advances on iron molybdate’s catalytic behaviour for formaldehyde production—a deep recognition of the catalyst and its critical role in the processes are highlighted. Finally, the conclusion and prospects are presented at the end.

Catalytic upgrading of ethanol to n-butanol over a novel Ca-Fe modified mixed oxide Mg-Al catalyst from hydrotalcite-base precursor

n-Butanol is used in a wide range of applications and recently, the use of n-butanol as a fuel, which can be employed pure or blended with gasoline or diesel, has been proposed. So, in an attempt to deepen in the one-step catalytic process to produce n-butanol from ethanol, bifunctional catalysts in different chemical/spatial environment as MgAl- and CaFeMg-multioxide catalysts were developed, prepared and characterized. Both mixed oxides were obtained by thermal decomposition of the synthesized hydrotalcites considering the partial substitution of Mg2+ and Al3+ by Ca2+ and Fe3+, namely MgAl-Ox and Ca20Fe20MgAl-Ox. The nature of acid and basic properties of the samples were analyzed employing NH3 and CO2 as probe molecules, and TPD analysis were performed to quantify the relative contribution of acidic/basic sites. Ca20Fe20MgAl-Ox sample presented an improved basicity with minimal acidity reduction. The performances of the activated catalysts were measured in a fixed-bed reactor under transient and continuous operation modes by DRIFT-MS studies and under transient pulse experiments. It was verified that both catalysts, but specially Ca20Fe20MgAl-Ox, promote the synthesis of C4-compounds from ethanol due to the modulated acid and basic sites capable of modify the ethanol adsorption in the form of ethoxy-species and a combined higher basicity with centers to catalyze the hydrogenation using the ethanol as the hydrogen donor. Ca20Fe20MgAl-Ox reached ethanol conversion values of 36% at 280°C and 71% at 400°C with a higher selectivity to n-butanol and other C4-compounds. Two parallel routes at differentiated temperatures: direct acetaldehyde self-condensation and the intermediary crotyl alcohol transfer hydrogenation, were evidenced and prevailing in n-butanol formation.

Operando Surface Studies on Metal-Oxide Interfaces of Bimetal and Mixed Catalysts

The formation of metal-oxide interfaces in catalytic systems exhibits a synergistic phenomenon between metal and reducible oxides, often referred to as the strong metal–support interaction (SMSI). This unusual characteristic has been connected to the origin of highly enhanced catalytic performance for decades, but the mechanistic explanation of SMSI remains a long-standing issue in heterogeneous catalysis. To understand this matter at the molecular level, geometric and electronic functions of metal-oxide interfaces during catalytic reactions should be clearly interpreted using advanced microscopic and spectroscopic analysis techniques. In this Review, we highlight recently performed investigations at metal-oxide interfaces by operando characterization tools to identify active sites in working conditions. We introduce two kinds of catalysts, platinum-based bimetallic alloys and mixed metal-oxide catalysts. Selected operando techniques reveal their atomic-scale morphology, surface electronic structure, and charge transfer/transport at surfaces under oxidation, reduction, and gas mixture environments. With bimetallic model catalysts, topographic morphology observations present critical evidence for the structural modulation between the topmost layer and the subsurface lattice in oxygen conditions. For the mixed metal-oxide catalysts, we note that metal nanoparticles on reducible oxides demonstrate the catalytic activity enhancement, which is obviously influenced by the change of oxidation states at the metal-oxide interface. Environmental transmission electron microscopy images unveil the atomic-scale redox behaviors at the nanoparticle interfaces with evolutions of the reducible oxide under the catalytic reaction. The important role of reactive interfaces between the transition metal atom and oxide-support explains the surface chemistry and heterogeneous catalysis over active sites on well-defined single crystal model surfaces, as well as nanoparticle catalysts. Overall, operando studies for metal-oxide interfaces can shed light on mechanistic insights into the tuning of catalytic activity at the molecular level and on improving catalytic performance by the SMSI effect.

The fabrication of Ce promoted Ni/Mg/Al mixed oxides hydrotalcite washcoated alloy, monolith catalyst for catalytic steam cracking of vacuum gas oil

Ce-promoted Ni/Mg/Al mixed oxides hydrotalcite-derived catalyst washcoated on metallic FeCrAlloy monolith was investigated in catalytic steam cracking of Vacuum Gas Oil (VGO) over a mild temperature range (300–400 °C). Hydrotalcite-derived powder solids were used as a slurry for the washcoating process were synthesized using co-precipitation and subsequent thermal decomposition. The as-fabricated catalyst exhibited over 40% VGO conversion with 46% light cut (Naphtha, Kerosene and Diesel) and 47.7% light VGO selectivity and Total Acidity Number of 0.9 mg KOH/g sample. This result seems promising for steam cracking of VGO over a novel structured catalyst. The washcoated catalyst was characterized using X-ray diffraction, surface area and X-ray Photoelectron Spectroscopy. Also, the liquid products composition/ quality and gas products composition were measured with various techniques such as simulation distillation, gas chromatography, viscosimeter and micro carbon residue.

Low temperature SCR of NOx over Mn/Fe mixed oxides catalyst: comparison of synthesis methods

AbstractBACKGROUNDWith the increasing environmental pollution issues arising from NOx, the low‐temperature selective catalytic reduction (LT‐SCR) of NOx by NH3 is becoming more important. Mn/Fe mixed oxides type catalysts have been proven to be particularly effective at low temperature reactions; however, the synthesis method can be a key factor determining the SCR activities.RESULTSA comprehensive study of LT‐SCR was carried out on a series of Mn/Fe mixed oxides catalysts prepared using diverse synthesis methods, namely, sonication assisted continuous coprecipitation (SACP), equilibrium adsorption (EA), precipitation method using either NaOH (P‐OH) or Na2CO3 (P‐CO) as precipitant, and one pot hydrothermal synthesis (CA). The morphology, composition, crystal property, oxidation status, and surface property were systematically characterised. LT‐SCR of the NOx performance of prepared Mn/Fe catalysts was conducted in temperatures from 75 to 225 °C. It was demonstrated that, at reaction temperatures under 125 °C, LT‐SCR performance showed the trend of P‐OH > SACP > EA ~ CA > P‐CO; meanwhile, the trend was CA > SACP > P‐OH ~ EA > P‐CO at temperatures over 125 °C. However, N2 selectivity showed the trend SACP > CA > P‐OH overall.CONCLUSIONThe characterisation results suggested that NOx conversion performance is controlled by several parameters, especially uniformity of materials, high surface area, Mn crystallinity, surface oxygen defects, Fe (III) on the surface; these are important parameters to achieve high denitrification performance as shown by P‐OH and SACP under low temperature. At higher temperatures, the stability of materials and high Brønsted acid sites on the surface are important, leading to better performance by CA and SACP.

Efficient Syntheses of Biobased Terephthalic Acid, p-Toluic Acid, and p-Methylacetophenone via One-Pot Catalytic Aerobic Oxidation of Monoterpene Derived Bio-p-cymene.

An efficient elevated-pressure catalytic oxidative process (2.5 mol % Co(NO3)2, 2.5 mol % MnBr2, air (30 bar), 125 °C, acetic acid, 6 h) has been developed to oxidize p-cymene into crystalline white terephthalic acid (TA) in ∼70% yield. Use of this mixed Co2+/Mn2+ catalytic system is key to obtaining high 70% yields of TA at relatively low reaction temperatures (125 °C) in short reaction times (6 h), which is likely to be due to the synergistic action of bromine and nitrate radicals in the oxidative process. Recycling studies have demonstrated that the mixed metal catalysts present in recovered mother liquors could be recycled three times in successive p-cymene oxidation reactions with no loss in catalytic activity or TA yield. Partial oxidation of p-cymene to give p-methylacetophenone (p-MA) in 55–60% yield can be achieved using a mixed CoBr2/Mn(OAc)2 catalytic system under 1 atm air for 24 h, while use of Co(NO3)2/MnBr2 under 1 atm O2 for 24 h gave p-toluic acid in 55–60% yield. Therefore, access to these simple catalytic aerobic conditions enables multiple biorenewable bulk terpene feedstocks (e.g., crude sulfate turpentine, turpentine, cineole, and limonene) to be converted into synthetically useful bio-p-MA, bio-p-toluic acid, and bio-TA (and hence bio-polyethylene terephthalate) as part of a terpene based biorefinery.

Magnetron Sputtered Iridium-Ruthenium Thin-Film Catalyst for Oxygen Evolution Reaction

In today´s developed world, there is a huge pressure on increasing the amount of electricity produced by renewable sources. With growing percentage of electricity from wind and solar power plants, new challenges arise. The biggest issue seems to be the instability of generated electricity during the days. Possible solution can be offered by Proton Exchange Membrane Water Electrolyzers (PEM-WE) and Proton Exchange Membrane Fuel Cell (PEM-FC) through electricity-hydrogen-electricity conversion cycle. Although PEM-WE technology is well suited for scale-up, one major drawback – its dependence on noble metal catalysts remains to be solved. Both, Ir on the anode and Pt on the cathode, which are traditionally used, are extremely rare and expensive, thus their partial replacement by other materials can lead to the noticeable decrease of PEM-WE price. More focus is usually laid on the anodic oxygen evolution reaction (OER) which is catalytically much more demanding. Ruthenium catalyst appears to be an interesting alternative due to its high activity towards OER. However, low electrochemical stability of Ru renders it inapplicable in its pure form. This problem can be solved by using mixed iridium-ruthenium catalyst which benefits from stability of iridium and from the lower price and high activity of ruthenium.In this work we present magnetron sputtered thin-film iridium-ruthenium mixed catalyst for the OER on the anode of PEM-WE. Magnetron sputtering is a mean of catalyst deposition which allows the preparation of a thin films of exact concentration and thickness. Moreover, it is also possible to use it on industrial scales. Usage of magnetron sputtering provides several important advantages. Firstly, we are able to cut down the amount of used catalyst significantly -- usually 10 times less than in the case of powder catalyst. Secondly, it is possible to prepare small systems for detailed electrochemical and surface analysis and also bigger systems for testing of our catalysts at real electrolyzer. This allows us to narrow the gap between the model and controlled studies and real industrial systems.In our work, we present four concentration of mixed iridium-ruthenium catalyst prepared by magnetron sputtering. Each catalyst was prepared either on Glassy Carbon electrode, or on Nafion® NR212. Measurement on Nafion® NR212 helps us to pick the industrially most suitable candidate. Measurements on the Glassy Carbon electrodes allows to investigate the activity and stability of given catalysts and correlate it with their structural and chemical properties. Numerous techniques were used, specifically Rotation Disk Electrode (RDE), Potential Electrochemically Impedance Spectroscopy (PEIS), Scanning Electron Microscopy, Energy Dispersive X-Ray spectroscopy (EDX), X-Ray Photoelectron Spectroscopy (XPS) and X-Ray Diffraction (XRD). Combination of these techniques revealed that 25:75 Ir:Ru sputtered thin-film catalyst outperforms the benchmark pure Ir counterpart while retaining comparable electrochemical stability. Figure 1

(Invited) Highly Stable Nanocarbon Catalysts for Reversible Energy Storage and Conversion Via Oxygen Electrocatalysis

Energy conversion and storage via direct electrochemical oxidation and reduction processes, such as the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER), can provide a clean, efficient, and economically viable means of meeting this sustainability challenge, by allowing stored renewable energy to be reliably delivered where and when it is needed. During the development of the highly demanded nonprecious metal catalysts to replace precious metals for these applications, carbon catalysts have many advantages over metal oxides, including excellent electrical conductivity, high surface area, and easy functionalization. However, most carbon-based catalysts suffer from poor activity and stability for the more challenging OER under a highly oxidative conditions. This represents one of grand challenges in energy conversion research societies.For the first time, this work demonstrated that a new class of large-diameter tubular nanocarbon (>500 nm in diameter) catalyst is capable of catalyzing both the ORR and the OER with activity comparable to Pt and exceeding Ir, respectively, for these two reactions. Most importantly, the tube catalyst exhibited good stability upon cycling across a wide potential window (0 to 1.9 V vs RHE) in 0.1 M NaOH electrolyte. The high OER activity was verified using well-designed electrochemical tests, demonstrating that the current generated during the OER arose solely from oxygen evolution, rather than carbon oxidation. This is the first example of such excellent OER activity and durability of a nanostructured carbon-based electrocatalyst across the complete ORR-OER potential window. The newly developed carbon tubes were synthesized via a one-step template-free graphitization process using inexpensive dicyandiamide (DCDA) precursor as carbon/nitrogen source and a ternary FeCoNi alloy as a catalyst. Generation of a mixed metal catalyst, i.e., FeCoNi during the graphitization process is the key factor to yield the largest tube size for maximum electrochemically accessible surface areas, dominant graphitic nitrogen doping, and thicker tube walls, which are associated with the significantly improved activity and durability. The cost effective, easily scalable, single step and environmentally benign synthesis procedure further favors this nanocarbon’s application as a practical bifunctional electrocatalyst for the ORR and OER, with potential to advance the development and commercialization of regenerative fuel cell systems and rechargeable metal-air batteries. The use of nanostructured carbon as bifunctional ORR/OER catalysts will open up new research direction in this field and further advance the role of carbon nanomaterials in oxygen electrocatalysis for energy conversion and storage.

Construction of the Fe3+-O-Mn3+/2+ hybrid bonds on the surface of porous silica as active centers for efficient heterogeneous catalytic ozonation

The Fe3+-O-Mn3+/2+ hybrid bonds were constructed on the surface of the amorphous and porous silica molecular sieve (MCM-41) by a three-step method that involved impregnation, hydrothermal incorporation, and annealing. The obtained FeMn-MCM-41 has an amorphous, less-ordered mesoporous structure with uniformly distributed Fe and Mn and a large specific surface area. It exhibits high activity, good recyclability, and wide pH applicable range for the heterogeneous catalytic ozonation (HCO). The TOC removal of methyl orange at high concentration of 327.5 ​mg ​L−1 is 78% on FeMn-MCM-41, which is not only much higher than the value of single ozonation (43%) but also much higher than the value on mixed catalysts of Fe-MCM-41 and Mn-MCM-41 (52%). We demonstrate that large amounts of the Fe3+-O-Mn3+/2+ hybrid bonds were created on the surface of porous silica, and the partial electron migration occurs in the hybrid Fe3+-O-Mn2+ (or Fe3+-O-Mn3+) bonds. As is well known, Fe3+ and Mn3+/2+ are very strong and weak Lewis acid sites in their oxides, respectively, and the partial electron migration lowers the acidity of Fe3+ sites and in the meantime increases the acidity of Mn3+/2+ sites, making both sites more suitable for catalytic production of free hydroxyl radicals (•OH). The synergetic effect of Fe3+ and Mn3+/2+ significantly improve the intrinsic activity of the FeMn-MCM-41 for HCO. This work may offer a new strategy for developing efficient mesoporous catalysts for catalytic ozonation.