Tungsten Oxide Catalysts Research Articles

Electrocatalytic Upgrading of Plastic and Biomass-Derived Polyols to Formamide under Ambient Conditions.

Electrocatalytic upgrading of wasted plastic and renewable biomass represents a sustainable method to produce chemicals but is limited to carbohydrates, leaving other value-added chemicals, such as organonitrogen compounds, being scarcely explored. Herein, we reported an electrocatalytic oxidation strategy to transform polyethylene terephthalate (PET) plastic-derived ethylene glycol (EG) and biomass-derived polyols into formamide, in the presence of ammonia (NH3) over a tungsten oxide (WO3) catalyst. Taking EG-to-formamide as an example, we achieved a high formamide productivity of 537.7 μmol cm-2 h-1 with FE of 43.2 % at a constant current of 100 mA cm-2 in a flow electrolyzer with 12-h test, representing a more advantageous performance compared with previous reports for formamide electrosynthesis. Mechanistic understanding revealed that the cleavage of the C-C bond in the EG was facilitated by nucleophilic attack of in situ formed nitrogen radicals from NH3, with resultant C-N bond construction and eventually formamide production. Furthermore, this strategy can be extended to transformation of PET bottle and a series of biomass-derived polyols with carbon number from three (glycerol) to six (glucose), producing formamide with high efficiencies. This work demonstrates a sustainable upgrading strategy of plastic and biomass that may have implications to more value-added chemicals production beyond carbohydrates.

Electrocatalytic Upgrading of Plastic and Biomass‐Derived Polyols to Formamide under Ambient Conditions

AbstractElectrocatalytic upgrading of wasted plastic and renewable biomass represents a sustainable method to produce chemicals but is limited to carbohydrates, leaving other value‐added chemicals, such as organonitrogen compounds, being scarcely explored. Herein, we reported an electrocatalytic oxidation strategy to transform polyethylene terephthalate (PET) plastic‐derived ethylene glycol (EG) and biomass‐derived polyols into formamide, in the presence of ammonia (NH3) over a tungsten oxide (WO3) catalyst. Taking EG‐to‐formamide as an example, we achieved a high formamide productivity of 537.7 μmol cm−2 h−1 with FE of 43.2 % at a constant current of 100 mA cm−2 in a flow electrolyzer with 12‐h test, representing a more advantageous performance compared with previous reports for formamide electrosynthesis. Mechanistic understanding revealed that the cleavage of the C−C bond in the EG was facilitated by nucleophilic attack of in situ formed nitrogen radicals from NH3, with resultant C−N bond construction and eventually formamide production. Furthermore, this strategy can be extended to transformation of PET bottle and a series of biomass‐derived polyols with carbon number from three (glycerol) to six (glucose), producing formamide with high efficiencies. This work demonstrates a sustainable upgrading strategy of plastic and biomass that may have implications to more value‐added chemicals production beyond carbohydrates.

Direct photo-curing 3D printed bionic multistage Mo-doped tungsten oxide catalysts for static and dynamic oxidative desulfurization of fuels

3D printed monolithic catalysts have attracted increasing attention in the petrochemical industry due to their advantages of the freedom of configuration, the rapidity of fabrication and the control of the fluid properties of the reaction medium. However, this remains challenging in constructing of micromorphology, reliable manufacturing, and adaptive functionality. Herein, inspired by the function of acicular plant fractal structure, we have developed bionic multistage monolithic catalysts based on direct photo-curing 3D printing technology. We also design two configuration strategies for static and dynamic oxidative desulfurization of fuels. Below the catalyst surface, the porous structure prepared by the hard template method can increase the specific surface area of the catalyst to disperse the active center and adsorb organic sulfur to strengthen the oxidation effect. The 3D-MoWO/PC-CE monolithic catalyst shows excellent activity in the static reaction with 100% sulfur removal. Above the catalyst surface, microcrystalline cellulose is introduced in-situ in 3D printed ink to build needle-like structures to enhance mass transfer efficiency and reduce surface pressure in dynamic fixed bed reaction. This work provides valuable ideas for the fabrication of efficient monolithic catalysts in various reactions.

Comparative study of catalytic conversion of glucose over γ-alumina supported tungsten oxide catalysts with controlling acidity

For the advancement of sustainable energy systems, biomass holds the potential to become a primary energy source worldwide. Glucose is one of the most economical and abundant carbohydrates, which can be converted to more value-added chemical feedstock. Here, a series of tungsten oxide catalysts supported on γ-alumina with varying tungsten content were synthesized using the wet impregnation method, and applied on the glucose conversion. The physicochemical properties of the prepared catalysts were investigated through powder X-ray diffraction, N2 sorption, scanning electron microscopy, UV-diffuse reflectance spectroscopy, and Raman spectroscopy. Pyridine-adsorption IR analysis was conducted to elucidate the acidic properties of the catalysts. As the loaded tungsten content increased, the concentration of Brønsted acid sites increased while the Lewis acid sites exhibited a decreasing trend. By controlling the acid concentration by the tungsten content, it was possible to adjust the optimal glucose conversion and the product selectivity in this cascade chemical reaction. When the tungsten content is too high, the Brønsted acid site is excessively present, and the resulting side reaction can be occurred. Here, we propose a catalyst design with appropriate acidity, which can obtain the target product with high yield.

Synthesis of palladium-decorated defective tungsten oxide heterostructures with enhanced photothermal catalytic activity for hydrodeoxygenation of vanillin

The selective hydrodeoxygenation (HDO) of sustainable lignocellulosic biomass plays a pivotal role in the conversion of biomass into high-value fuels and chemicals. Nevertheless, HDO for biomass upgrading always demands high temperatures and high hydrogen (H2) pressure. Photothermal catalysis has been recognized as an effective approach for boosting chemical reactions under mild conditions while maintaining superior selectivity. Herein, we report the design of palladium-decorated defective tungsten oxide (Pd/WO3-x) catalysts with enhanced photothermal catalytic performances for the efficient HDO of vanillin. Pd/WO3-x nanoflowers have been synthesized through a solvothermal/in-situ reduction two-step strategy, and they exhibit notable photoabsorption in a wide range (200–1100 nm), high photothermal conversion and efficient charge separation efficiency. Under simulated sunlight irradiation (0.3 W cm−2), Pd/WO3-x exhibits a maximum vanillin conversion up to 86.8 % with a 2-methoxy-4-methylphenol (MMP) selectivity of 100 %, which is obviously higher than that (vanillin conversion = 33.1 %, MMP selectivity = 100 %) in the oil bath at the same temperature. Such higher conversion efficiency and selectivity under sunlight should result from the synergistic integration of hot electrons and photothermal heating, both of which are derived from localized surface plasmon resonance (LSPR) in WO3-x. Importantly, Pd/WO3-x catalyst demonstrates good stability and high selectivity to MMP even after 5 cycles. This work may offer a novel viewpoint on the advancement of photothermal catalysts and the realization of photothermal catalytic biomass conversion under mild conditions.

Electrochemical synthesis and characterization of tungsten oxide catalysts for photoelectrochemical water splitting

In the present paper, synthesis of porous tungsten oxide via anodization in sulfate-fluoride electrolytes at different voltages and process durations, followed by thermal treatment at 500 °C, is reported. The porosity of the obtained oxides is estimated by re-anodization in a non-dissolving electrolyte. Electronic conductivity is assessed using voltammetric measurements. Electronic properties of the oxide are determined using high-frequency capacitance–potential measurements. The results are interpreted by contemporary models for the semiconductor/electrolyte junction. Spectral characteristics of modulated photocurrent are also registered to estimate the optical band gap of oxides. The photo-induced carrier dynamics in the oxides is assessed by intensity modulated photocurrent spectroscopy (IMPS). Based on the multi-method characterization, conclusions are drawn on the photo-absorbing and photo-catalytic properties of the oxides depending on anodization conditions.

Selective Oxidation of Glucose using Hydrogen Peroxide as an Oxidant: On the Structure Sensitivity of the Apparent Activation Energy

AbstractThe selective oxidation of glucose to gluconic acid with hydrogen peroxide was studied using different heterogeneous catalysts with alumina (Al2O3) and titanium silicate (TS‐1, TiMWW) as supports and different noble (Au, Pd) and non‐noble metals (Fe, W) as the catalytically active phases. Supported tungsten oxide catalysts showed a moderate selectivity and activity compared to palladium and iron catalysts. The best performance in the selective oxidation of glucose among the studied catalysts was displayed by gold on alumina. For this kind of catalyst, the structure sensitivity in glucose oxidation was explored, revealing a maximum rate shifted to larger gold particle sizes at higher temperatures in comparison with other studies involving activation of molecular oxygen on gold particles. A significant change in the apparent activation energy was established while changing the particle size of gold. These changes of the activation energy were adequately explained by a theoretical model for the cluster size dependence of the apparent activation energy.

First principles calculations on the structures, electronic and magnetic properties of the TMn@W12O36 (TM=Mn, Fe, Co and Ni, n = 1–4) clusters

Transition metal (Mn, Fe, Co and Ni)-doped tungsten oxides nanoparticles with magnetic properties may be applied in various catalysts such as water treatment as they are easy to be recycled. Structural, electronic and magnetic properties of TMn@W[Formula: see text]O[Formula: see text] (TM=Mn, Fe, Co and Ni, n=1–4) clusters have been calculated at PBE level. The results reveal that the centers of the TM[Formula: see text] clusters are in accordance with that of the W[Formula: see text]O[Formula: see text] clusters while the TM4 clusters deviate obviously from the center of the W[Formula: see text]O[Formula: see text] cages. All TMn@W[Formula: see text]O[Formula: see text] clusters exhibit slightly less structural stability and obviously more chemical reactivity than the W[Formula: see text]O[Formula: see text] clusters. Mülliken spin densities of a TM atom embedded are almost kept except for the Ni@W[Formula: see text]O[Formula: see text] clusters. The spin densities of TMn clusters in the TM3@W[Formula: see text]O[Formula: see text] and TM4@W[Formula: see text]O[Formula: see text] clusters are offset. The magnetic TM modification strategy is helpful to design recyclable tungsten oxide catalysts.

Hydrogen spillover effect – harnessing hydrogen evolution reaction from diverse carbon-based supports with a tungsten oxide catalyst

The phenomena of the hydrogen spillover mechanism on different carbon supports.

Kinetic Conversion of Carbon Dioxide in Supported Tungsten Carbide Catalysts and Oxide Catalysts for the Reverse Water Gas Shift Reaction

The reverse water-gas shift reaction (RWGS) had a critical stage in the conversion of abundant carbon dioxide into chemicals or hydrocarbon fuels and has attracted widespread interest as a renewable fuel assembly system in unconventional ways. Interest has been in industrial applications such as the catalytic activity, carbon dioxide conversion, kinetics, and efficacy levels of tungsten carbide-supported catalysts and carbide oxide catalysts for the production of RWGS reaction. Additionally, carbide oxides have the ability to enhance RWGS and develop high-performance catalysts in RWGS. The RWGS reaction was (CO2 + H2 ↔ CO + H2O; ΔG°=27.94kJ/mol) an exothermic reaction that exhibits equilibrium conversion with temperature.

Tuning the Electronic Structure of Tungsten Oxide for Enhanced Hydrogen Evolution Reaction in Alkaline Electrolyte

AbstractEngineering the electronic structure of HER catalysts has been suggested to improve the performance of noble metal‐free catalysts in alkaline electrolytes. Herein, we demonstrated that a suitable cation doping in the tungsten oxide catalyst modified the interfacial structure, surface chemical state and band gap value, which enhanced the HER performance. For the experiments, the cation (Ni, Co and Fe) doped tungsten oxide catalysts were synthesized on nickel foam, on which Ni‐based alloy was decorated. The Co doped catalyst (Co−WO) exhibited an extraordinary HER activity, with a low overpotential of 30 mV at a current density of 10 mA cm−2, Tafel slope of 32 mV dec−1. In this system, the Ni‐based alloy–tungsten oxide interface facilitated water dissociation. Moreover, the decreased band gap and improved conductivity induced by Co doping, further enhanced the charge transfer ability in the HER process. The regulated metal‐oxide heterostructure coupled with cation doping endowed the catalyst with efficient interface active sites, superior electrical conductivity, and enhanced electron transfer kinetics, facilitating the HER performance.

INVESTIGATION OF THE ISOMERIZATION REACTION OF BUTENE-1 TO BUTENES-2 ON BINARY TUNGSTEN-CONTAINING CATALYSTS

The activity of tungsten-containing catalysts in the reaction of isomerization of butene-1 to butenes-2 was studied in the work. The results obtained showed that the ^ introduction of the second element into the composition of the tungsten oxide catalyst had a different effect on its activity in the butene-1 isomerization reaction. It was established that an increase in the amount of molybdenum in the composition of a binary tungsten-containing catalyst at low temperatures leads to a decrease in the degree of butene-1 isomerization while at high temperatures it leads to an increase in the rate of butene-1 isomerization. It found that the addition of titanium to the composition of the tungsten oxide catalyst leads to an increase in the butene-1 isomerization rate. When copper is added to the composition of the tungsten oxide catalyst, the total yield of butene-2 passes through a maximum, and on samples rich in copper, the isomerization of butene-1 practically does not occur. It revealed that the activity of binary tungsten oxide catalysts in the isomerization reaction of butene-1 to butenes-2 changes in the following order: Ti-W-O > Mo-W-O > Cu-WO.

Structure–Activity Relationships of Hydrothermally Aged Titania-Supported Vanadium–Tungsten Oxide Catalysts for SCR of NOx Emissions with NH3

Structure–Activity Relationships of Hydrothermally Aged Titania-Supported Vanadium–Tungsten Oxide Catalysts for SCR of NO_<i>x</i> Emissions with NH₃

Elucidating the Effects of Mn Promotion on SiO2-Supported Na-Promoted Tungsten Oxide Catalysts for Oxidative Coupling of Methane (OCM)

Elucidating the Effects of Mn Promotion on SiO₂-Supported Na-Promoted Tungsten Oxide Catalysts for Oxidative Coupling of Methane (OCM)

Tungsten-Based Catalysts for Environmental Applications

This review aims to give a general overview of the recent use of tungsten-based catalysts for wide environmental applications, with first some useful background information about tungsten oxides. Tungsten oxide materials exhibit suitable behaviors for surface reactions and catalysis such as acidic properties (mainly Brønsted sites), redox and adsorption properties (due to the presence of oxygen vacancies) and a photostimulation response under visible light (2.6–2.8 eV bandgap). Depending on the operating condition of the catalytic process, each of these behaviors is tunable by controlling structure and morphology (e.g., nanoplates, nanosheets, nanorods, nanowires, nanomesh, microflowers, hollow nanospheres) and/or interactions with other compounds such as conductors (carbon), semiconductors or other oxides (e.g., TiO2) and precious metals. WOx particles can be also dispersed on high specific surface area supports. Based on these behaviors, WO3-based catalysts were developed for numerous environmental applications. This review is divided into five main parts: structure of tungsten-based catalysts, acidity of supported tungsten oxide catalysts, WO3 catalysts for DeNOx applications, total oxidation of volatile organic compounds in gas phase and gas sensors and pollutant remediation in liquid phase (photocatalysis).

Steering Electron-Hole Migration Pathways Using Oxygen Vacancies in Tungsten Oxides to Enhance Their Photocatalytic Oxygen Evolution Performance.

The overall water splitting efficiency is mainly restricted by the slow kinetics of oxygen evolution. Therefore, it is essential to develop active oxygen evolution catalysts. In this context, we designed and synthesized a tungsten oxide catalyst with oxygen vacancies for photocatalytic oxygen evolution, which exhibited a higher oxygen evolution rate of 683 μmol h-1 g-1 than that of pure WO3 (159 μmol h-1 g-1 ). Subsequent studies through transient absorption spectroscopy found that the oxygen vacancies can produce electron trapping states to inhibit the direct recombination of photogenerated carriers. Additionally, a Pt cocatalyst can promote electron trap states to participate in the reaction to improve the photocatalytic performance further. This work uses femtosecond transient absorption spectroscopy to explain the photocatalytic oxygen evolution mechanism of inorganic materials and provides new insights into the design of high-efficiency water-splitting catalysts.

Steering Electron–Hole Migration Pathways Using Oxygen Vacancies in Tungsten Oxides to Enhance Their Photocatalytic Oxygen Evolution Performance

AbstractThe overall water splitting efficiency is mainly restricted by the slow kinetics of oxygen evolution. Therefore, it is essential to develop active oxygen evolution catalysts. In this context, we designed and synthesized a tungsten oxide catalyst with oxygen vacancies for photocatalytic oxygen evolution, which exhibited a higher oxygen evolution rate of 683 μmol h−1 g−1 than that of pure WO3 (159 μmol h−1 g−1). Subsequent studies through transient absorption spectroscopy found that the oxygen vacancies can produce electron trapping states to inhibit the direct recombination of photogenerated carriers. Additionally, a Pt cocatalyst can promote electron trap states to participate in the reaction to improve the photocatalytic performance further. This work uses femtosecond transient absorption spectroscopy to explain the photocatalytic oxygen evolution mechanism of inorganic materials and provides new insights into the design of high‐efficiency water‐splitting catalysts.

Reactive Species and Reaction Pathways for the Oxidative Cleavage of 4-Octene and Oleic Acid with H2O2 over Tungsten Oxide Catalysts

Oxidative cleavage of carbon–carbon double bonds (C═C) in alkenes and fatty acids produces aldehydes and acids valued as chemical intermediates. Solid tungsten oxide catalysts are low cost, nontoxi...

Pyrolysis of digestate from anaerobic digestion on tungsten oxide catalyst

This study presents the catalytic pyrolysis of conditioned digestate from anaerobic digestion co-digestion plants, in the presence of WO3/γ-Al2O3 catalyst under nitrogen atmosphere. The experimental program was performed at atmospheric pressure, temperature in the isothermal reaction zone 425 °C and feeding flow rate of 0.33 mL/min. The analysis of bio-oil composition suggested the presence of a large number of linear and branched aliphatic hydrocarbon components, alcohols, phenols and alkyl aromatic hydrocarbons with two or three methyl-type substituents. The major components present in the cracking gas are methane and carbon oxide. The simulation data obtained for compression at equilibrium of cracking gas indicates an olefin content of LPG higher than the values imposed in the technical specifications of similar products on the market.

Facile synthesis of WOx/ZrO2 catalysts using WO3·H2O precipitate as synthetic precursor of active tungsten species

Zirconia-supported tungsten oxide (WOx/ZrO2) catalysts were successfully synthesized using a suspension containing amorphous hydrous zirconia precipitates [ZrOx(OH)4-2x·yH2O]n and tungstate monohydrate (WO3·H2O) precipitates. The procedure involved the dissolution of the WO3·H2O precipitate during the aging process with the release of oxyanion [WO4]2- species, interaction of this species with the surface of the [ZrOx(OH)4-2x·yH2O]n precipitate and, formation of active WOx species after thermal treatment. Non-bridging hydroxyl (OH−) groups present in the [ZrOx(OH)4-2x·yH2O]n precipitate act as an active agent for the WO3·H2O dissolution. N2 physisorption, X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), temperature-programmed reduction using hydrogen (H2-TPR), temperature-programmed desorption of ammonia (NH3-TPD), Fourier-transform infrared (FTIR) spectroscopy of adsorbed pyridine, and Raman spectroscopy were used to elucidate the catalyst structure–performance relationship. The catalytic activity was evaluated for the oxidative desulfurization (ODS) of a model fuel containing dibenzothiophene (DBT). For a fixed WO3·H2O content, longer aging times improved the catalyst activity, reaching a maximum when WO3·H2O was completely dissolved. The increase in surface area and formation of more active Zr-WOx clusters and polytungstates are observed for the highest active catalysts. A synergetic effect between local Lewis and Brønsted acid sites seems to have contributed to the observed superior activity. The proposed strategy provides an efficient approach to produce active WOx/ZrO2 catalysts and may be applicable for designing other heterogeneous catalytic systems.