Silicotungstic Acid Research Articles

Efficient Proton Conductor Based on Bismuth Oxide Clusters and Polyoxometalates.

Developing new solid-state electrolyte materials for improving the proton conductivity remains an important challenge. Herein, a novel two-dimensional layered solid-state proton conductor Bi2O2-SiW12 nanocomposite, based on silicotungstic acid (H4SiW12O40) and Bi(NO3)3·5H2O, was synthesized and characterized. The composite consists of a layered cation framework [Bi2O2]2+ and interlayer-embedded counteranionic [SiW12O40]4-, which forms continuous hydrogen bond (O-H···O) networks through the interaction of adjacent oxygen atoms on the surface of the [Bi2O2]2+ and oxygen atoms of the H4SiW12O40. Facile proton transfer along these pathways endows the Bi2O2-SiW12 (30:1) nanocomposite with an excellent proton conductivity of 3.61 mS cm-1 at 90 °C and 95% relative humidity, indicating that the nanocomposite has good prospects as a highly efficient proton conductor.

(Invited) Microelectrode-Based Diagnosis of Charge Propagation and Redox Transitions in Concentrated Polyoxometallate Electrolyte of Potential Utility for Redox Flow Battery

Concentrated solutions of Keggin-type silicotungstic acid, as well as the system’s single crystals (H4SiW12O40*31H2O) and their colloidal suspensions have been tested using the microelectrode methodology to determine mass-transport, electron self-exchange and apparent (effective) diffusion-type coefficients for charge propagation and homogeneous (electron self-exchange) rates of electron transfers. Silicotungstic acid facilitates proton conductivity, and undergoes fast, reversible, multi-electron electron transfers leading to the formation of highly conducting, mixed-valence (tungsten(VI,V) heteropoly blue) compounds. To develop useful electroanalytical diagnostic criteria, electroanalytical approaches utilizing microdisk electrodes have been adapted to characterize redox transitions of the system and to determine kinetic parameters. Combination of micoroelectrode-based experiments performed in two distinct diffusional regimes: radial (long-term experiment; e.g., slow scan rate voltammetry or long-pulse chronoamperometry) and linear (short-term experiment; e.g., fast scan rate voltammetry or short-pulse chronocoulometry) permits absolute determination of such parameters as effective concentration of redox centers (C0 ) and apparent transport (diffusion) coefficient (Dapp ). The knowledge of these parameters, in particular of [Dapp 1/2 C0 ] seems to be of importance to the evaluation of utility of redox electrolytes for charge storage.While current densities which reflect dynamics of electrochemical processes have an influence on the systems’ current densities, the viscosity of the electrolyte and the mass transport dynamics are also affected by the nature of the redox-active material and its concentration. Trying to develop useful electroanalytical diagnostic approaches, we have successfully utilized microelectrode-based probes, as well as the historical concepts of charge propagation in semi-solid or semi-liquid systems developed for mixed-valence polynuclear materials in order to characterize concentrated redox electrolytes. Among important parameters are concentration of redox centers (C0 ) and apparent transport (diffusion) coefficient (Dapp ). The knowledge of these parameters and, in particular of [Dapp 1/2 C0 ], are crucial when it comes to evaluation of the diffusional-type charge propagation dynamics in the concentrated electrolyte which may reflect both physical mass transport and electron self-exchange (electron-hopping) contributions. Both potential-step (chronocoulometry, chronoamperometry) and cyclic voltammetric experiments utilizing microdisk electrodes have been adapted to characterization (identification of redox transitions and determination of kinetic parameters) of model inorganic redox electrolytes, namely highly-concentrated solutions or colloidal suspensions of Keggin-type polyoxometallate, silicotungstic acid.

Proton Exchange Membrane Fuel Cell Chemical and Mechanical Durability Study of Heteropoly Acid Functionalized Perfluorinated Sulfonic Acid with Expanded Polyteterafluoroethylene Support

The application of proton exchange membrane fuel cells to heavy-duty vehicles has been a new trend for fuel cell society due to high efficiency, power density, faster refueling, and ability to remove auxiliary power units. However, the critical bottleneck for the commercialization and technology transfer from already-commercialized light-duty fuel cell vehicles is the chemical and mechanical durability of the proton exchange membranes. Chemical degradation is initiated by H2O2 which forms ▪OH radicals during the fuel cell operation. The radicals that are formed during the fuel cell operation can be suppressed by adding a radical decomposing catalyst such as cerium, cerium oxide, manganese, manganese oxide, and heteropoly acids. However, those metal oxides and heteropoly acids lack immobilization. We have previously reported the chemical immobilization of silicotungstic acid (HPA), a heteropoly acid with radical decomposing functionality, using dehydrofluorination. This has resulted in improvements in both the chemical durability and proton conductivity, wherein the HPA serves as a proton conductor.In this study, we applied the chemical anchoring synthesis method to multiple polymers with different binding monomer group ratios and supported with expanded-polyterafluorethylene (e-PTFE) support. We investigated the optimized HPA ratio to the perfluorinated sulfonic acid membrane and studied the chemical and mechanical durability of the composite membrane. The structure-property relationship of composite membranes was studied using scanning electron microscopy (SEM), small angle x-ray scattering, and dynamic mechanical analysis (DMA). The chemical degradation was tested with open-circuit voltage (OCV) and fluoride release rate (FRR) under the accelerated standard condition (AST).

Glycerol dehydration catalyzed by solid acid in nonthermal plasma and simulation analysis of plasma electric field

AbstractNonthermal plasma (NTP), for the first time, was integrated in glycerol dehydration reaction catalyzed by silicotungstic acid supported on mesoporous silica with argon as the carrier and discharge gas. A range of reaction temperatures (220–320°C) and NTP discharge field strengths (2.06–6.87 kV/cm) were studied for the individual and interactive effects regarding the glycerol conversion and product selectivity. Results showed that the presence of NTP always improved the glycerol conversion, and NTP increased acrolein selectivity if properly conditioned. An optimal condition of 275°C and 4.58 kV/cm NTP field strength achieved a glycerol conversion of 94.4 mol%, acrolein selectivity of 88.0 mol%, with an acrolein yield of 83.1 mol%, representing a 10% improvement in acrolein production over that conducted at the same temperature but without NTP. Results of this study will also have significant implication for other heterogeneously catalyzed dehydration reactions. Simulation of the high‐voltage electric field distribution as function of NTP electrical conductivity and relative permittivity of catalyst materials also offers insight for the future design of reactors and catalysts.

Photo-/electro-chromic underwater adhesive coacervate from self-assembly of zwitterions and polyoxometalate

Wet/underwater adhesion is a matter of common occurrence to some marine organisms, but it is a quite thorny problem in practical engineering field and even in our daily lives. Meanwhile, preparation of an instantly available underwater adhesive with good adhesion strength is another great challenge. Herein, inspired by the oppositely charged polyelectrolytes coacervate of sandcastle worm glue, a zwitterion-based self-assembled underwater adhesive coacervate is reported. This coacervate can be deployed in real-time by mixing together of zwitterionic poly (HEMA-co-SBMA) (PHS), silicotungstic acid (STA) and arginine (Arg). It is an entirely new construction strategy via synergistical self-assembly of low- and high-molecular-weight zwitterions and polyanions by electrostatic force. The coacervate plays well in underwater adhesion to substrates such as organic plastic and inorganic ceramic. It also achieves outstanding performance in dry substrates, due to multiple interactions formed at the interface of adhesive coacervate and substrate. Moreover, this coacervate shows underwater sealing property and resistance to violent water flush. Additionally, the coacervate possesses electro/photo-chromic properties that may achieve stimuli-responsive color switching, therefore broadening its potential applications for external signals responsive devices like energy-efficient windows, wearable electronics, and warning devices.

Degradation of sulfamethoxazole by super-hydrophilic MoS2 sponge co-catalytic Fenton: Enhancing Fe2+/Fe3+ cycle and mass transfer

To promote the cycle of Fe2+/Fe3+ in co-catalytic Fenton and enhance mass transfer in an external circulation sequencing batch packed bed reactor (ECSPBR), super-hydrophilicity MoS2 sponge (TMS) modified by tungstosilicic acid (TA) was prepared for efficiently degrading sulfamethoxazole (SMX) antibiotics in aqueous solution. The influence of hydrophilicity of co-catalyst on co-catalytic Fenton and the advantages of ECSPBR were systematically studied through comparative research methods. The results showed that the super hydrophilicity increased the contact between Fe2+ and Fe3+ with TMS, then accelerated Fe2+/Fe3+ cycle. The max Fe2+/Fe3+ ratio of TMS co-catalytic Fenton (TMS/Fe2+/H2O2) was 1.7 times that of hydrophobic MoS2 sponge (CMS) co-catalytic Fenton. SMX degradation efficiency could reach over 90% under suitable conditions. The structure of TMS remained unchanged during the process, and the max dissolved concentration of Mo was lower than 0.06 mg/L. Additionally, the catalytic activity of TMS could be restored by a simple re-impregnation. The external circulation of the reactor was conducive to improving the mass transfer and the utilization rate of Fe2+ and H2O2 during the process. This study offered new insights to prepare a recyclable and hydrophilic co-catalyst and develop an efficient co-catalytic Fenton reactor for organic wastewater treatment.

From CO2 to DME: Enhancement through Heteropoly Acids from a Catalyst Screening and Stability Study.

The direct synthesis of dimethyl ether (DME) via CO2 hydrogenation in a single step was studied using an improved class of bifunctional catalysts in a fixed bed reactor (T R: 210-270 °C; 40 bar; gas hourly space velocity (GHSV) 19,800 NL kgcat -1 h-1; ratio CO2/H2/N2 3:9:2). The competitive bifunctional catalysts tested in here consist of a surface-basic copper/zinc oxide/zirconia (CZZ) methanol-producing part and a variable surface-acidic methanol dehydration part and were tested in overall 45 combinations. As dehydration catalysts, zeolites (ferrierite and β-zeolite), alumina, or zirconia were tested alone as well as with a coating of Keggin-type heteropoly acids (HPAs), i.e., silicotungstic or phosphotungstic acid. Two different mixing methods to generate bifunctional catalysts were tested: (i) a single-grain method with intensive intra-particular contact between CZZ and the dehydration catalyst generated by mixing in an agate mortar and (ii) a dual-grain approach relying on physical mixing with low contact. The influence of the catalyst mixing method and HPA loading on catalyst activity and stability was investigated. From these results, a selection of best-performing bifunctional catalysts was investigated in extended measurements (time on stream: 160 h/7 days, T R: 250 and 270 °C; 40 bar; GHSV 19,800 NL kgcat -1 h-1; ratio CO2/H2/N2 3:9:2). Silicotungstic acid-coated bifunctional catalysts showed the highest resilience toward deactivation caused by single-grain preparation and during catalysis. Overall, HPA-coated catalysts showed higher activity and resilience toward deactivation than uncoated counterparts. Dual-grain preparation showed superior performance over single grain. Furthermore, silicotungstic acid coatings with 1 KU nm-2 (Keggin unit per surface area of carrier) on Al2O3 and ZrO2 as carrier materials showed competitive high activity and stability in extended 7-day measurements compared to pure CZZ. Therefore, HPA coating is found to be a well-suited addition to the CO2-to-DME catalyst toolbox.

Heteropolyacid-loaded MOF-derived mesoporous zirconia catalyst for chemical degradation of rhodamine B

Abstract In this article, silicotungstic acid (STA)-loaded metal–organic framework (MOF)-derived composites (C-STA@ZrO2) were successfully synthesized by simple strategies. X-ray diffraction, Fourier transform infrared, scanning electron microscopy, energy-dispersive X-ray, N2 physisorption, UV-vis diffuse reflection spectroscopy, and X-ray photoelectron spectroscopy techniques were used to characterize the as-obtained composites. Intriguingly, C-STA@ZrO2 exhibits excellent photocatalytic performance, and rhodamine B (RhB) (40 mg·L−1) in water can be degraded to 93.9% after 120 min of irradiation. Moreover, various catalysts, catalyst dosage, and dye concentrations on RhB degradation were evaluated. Besides, the reusability of C-STA@ZrO2 was also investigated. This work may provide a new and significant guideline for exploring excellent performance of MOF-derived hybrid material for wastewater purification.

Fabrication and immobilization of heteropoly acids (HPAs) and hexadecyl trimethyl ammonium bromide (CTAB) co-modified ternary zinc indium sulfide (ZnIn2S4): Capture photogenerated electrons and pollutant molecules by co-photocatalyst for enhancing the photocatalytic ability

In this article, a series of HPAs, including phosphotungstic acid (H3PW12O40), silicotungstic acid (H4SiW12O40), phosphomolybdic acid (H3PMo12O40), and hexadecyl trimethyl ammonium bromide (CTAB) co-modified ZnIn2S4 photocatalysts (HPAs/CTAB@ZnIn2S4) were successfully fabricated for the first time by a simple one-pot hydrothermal strategy. As a photogenerated electron capture tool, HPAs and CTAB can capture photogenerated electrons by W 5d (or Mo 4d) unsaturated electron orbitals and quaternary ammonium groups (–N+), thus improving the photogenerated carrier (e––h+) separation efficiency of the main photocatalyst ZnIn2S4. As a pollutant molecule capture tool, HPAs and CTAB can capture pollutant molecules to the surface of photocatalyst through acid-base interaction and hydrogen bonding, so that the target pollutants can be efficiently degraded in the environment of high concentration hydroxyl radicals (·OH). In order to improve the engineering application value of as-prepared photocatalyst, we also successfully fabricated immobilized photocatalyst (H3PMo12O40/CTAB@ZnIn2S4@CC) by using clay ceramsite (CC) as a carrier. The photocatalytic activity of immobilized H3PMo12O40/CTAB@ZnIn2S4@CC is higher than that of H3PMo12O40/CTAB@ZnIn2S4 due to the trapping effect of CC carrier on photons.

Polymerization-Induced Aggregation Approach toward Uniform Pd Nanoparticle-Decorated Mesoporous SiO2/WO3 Microspheres for Hydrogen Sensing

Hydrogen as an important clean energy source with a high energy density has attracted extensive attention in fuel cell vehicles and industrial production. However, considering its flammable and explosive property, gas sensors are desperately desired to efficiently monitor H2 concentration in practical applications. Herein, a facile polymerization-induced aggregation strategy was proposed to synthesize uniform Si-doped mesoporous WO3 (Si-mWO3) microspheres with tunable sizes. The polymerization of the melamine-formaldehyde resin prepolymer (MF prepolymer) in the presence of silicotungstic acid hydrate (abbreviated as H4SiW) leads to uniform MF/H4SiW hybrid microspheres, which can be converted into Si-mWO3 microspheres through a simple thermal decomposition treatment process. In addition, benefiting from the pore confinement effect, monodispersed Pd-decorated Si-mWO3 microspheres (Pd/Si-mWO3) were subsequently synthesized and applied as sensitive materials for the sensing and detection of hydrogen. Owing to the oxygen spillover effect of Pd nanoparticles, Pd/Si-mWO3 enables adsorption of more oxygen anions than pure mWO3. These Pd nanoparticles dispersed on the surface of Si-mWO3 accelerated the dissociation of hydrogen and promoted charge transfer between Pd nanoparticles and WO3 crystal particles, which enhanced the sensing sensitivity toward H2. As a result, the gas sensor based on Pd/Si-mWO3 microspheres exhibited excellent selectivity and sensitivity (Rair/Rgas = 33.5) to 50 ppm H2 at a relatively low operating temperature (210 °C), which was 30 times higher than that of the pure Si-mWO3 sensor. To develop intelligent sensors, a portable sensor module based on Pd/Si-mWO3 in combination with wireless Bluetooth connection was designed, which achieved real-time monitoring of H2 concentration, opening up the possibility for use as intelligent H2 sensors.

Prerequisites for Development of Electrochemical Planar Sensor Based on RGO–PPD–SiW Composite for Determining Isoniazid Content in Biological Liquids

A new redox-active composite material based on reduced graphene oxide (RGO), poly-o-phenylenediamine (PPD), and silicotungstic acid (SiW) is studied. The SEM data showed an abrupt decrease in the content of oxygen atoms in the composite as compared to pure graphene oxide (GO). This is associated with its reduction to RGO in the course of RGO–PPD–SiW synthesis. A combination of RGO conductivity and redox catalysis due to the electroactive components (PPD and SiW) enables one to develop various sensors by applying RGO–PPD–SiW onto planar electrodes (screen-printed carbon electrodes, SPCE). In this work, the possibility of developing a sensor for the content of antituberculous antibiotic isoniazid (isonicotinic acid hydrazide C6H7N3O, INAH) is studied. Using the CVA method, it is shown that the concentration dependence of isoniazid oxidation current is linear. The electrocatalytic behavior of the composite during the isoniazid oxidation is also supported by the impedance spectroscopy.

Microelectrode-based probing of charge propagation and redox transitions in concentrated polyoxometallate electrolyte of potential utility for redox flow battery

Concentrated solutions of Keggin-type silicotungstic acid, as well as the system’s single crystals (H4SiW12O40*31H2O) and their colloidal suspensions have been tested using the microelectrode methodology to determine mass-transport, electron self-exchange and apparent (effective) diffusion-type coefficients for charge propagation and homogeneous (electron self-exchange) rates of electron transfers. Silicotungstic acid facilitates proton conductivity, and undergoes fast, reversible, multi-electron transfers leading to the formation of highly conducting, mixed-valence (tungsten(VI,V) heteropoly blue) compounds. To develop useful electroanalytical diagnostic criteria, electroanalytical approaches utilizing microdisk electrodes have been adapted to characterize redox transitions of the system and to determine kinetic parameters. Combination of microelectrode-based experiments performed in two distinct diffusional regimes: radial (long-term experiment; e.g., slow scan rate voltammetry or long-pulse chronoamperometry) and linear (short-term experiment; e.g., fast scan rate voltammetry or short-pulse chronocoulometry) permits absolute determination of such parameters as effective concentration of redox centers (C0) and apparent transport (diffusion) coefficient (Dapp). The knowledge of these parameters, in particular of [Dapp1/2 C0] seems to be of importance to the evaluation of utility of redox electrolytes for charge storage. For the colloidal suspension of silicotungstic acid (H4SiW12O40) crystals in the saturated solution, the following values have been obtained: Dapp = 1.8*10-6 cm2 s−1 and C0 = 1.1 mol dm−3, as well as the [Dapp1/2 C0] diagnostic parameter has reached the value as high as 6*10-3 mol/dm−3 cm s−1/2, provided that four electrons are involved in the H4SiW12O40 redox transitions. In this respect, the fact that crystals (dispersed solids) are characterized by high electron self-exchange rate (kex = 1.1*108 dm3 mol−1 s−1) and low activation energy (EA = 18.7 kJ mol−1) facilitating electron transfers between immobilized WVI and WV redox sites is also advantageous.

Dynamic co-assembly behaviors of polyoxometalates and giant surfactants in dual solvents

Inorganic-organic hybridization is a widely used method to develop new functional materials involving polyoxometalates (POMs), affording them with unique synergistic physical and chemical properties. As one of the core topics in hybrid materials, the study of their assembly structures is critical for the optimization of their performances.In the present work, dynamic co-assembly behaviors of several giant surfactants XPOSS-PS (X, POSS and PS denote different polar groups, polyhedral oligomeric silsesquioxane and polystyrene, respectively) and Keggin-type silicotungstic acid H4SiW12O40 (H4SiW for short) were investigated. We designed and synthesized three series of giant surfactants that possess heads bearing cationic (NPOSS-PS, N for ammonium group), neutral (DPOSS-PS, D for dihydroxyl group) and anionic charges (APOSS-PS, A for carboxylic acid group), respectively. The different charge types of POSS heads lead to different electrostatic interactions with the anionic POM clusters, resulting in different co-assembly structures in dual mixed solvents. Moreover, we found the POM's loading content and PS chain length are another two important factors that can determine the morphology of co-assembly structures. This work expands the scope of co-assembled structures of POM-based hybrid materials, and provides a platform for the study of the basic physical principles of their co-assembly behaviors.

An elementary-step kinetic model for ethyl acetate synthesis by direct addition of acetic acid to ethylene on a silicotungstic acid catalyst

An elementary-step kinetic model for ethyl acetate synthesis by direct addition of acetic acid to ethylene over a silica supported silicotungstic acid catalyst is developed. A reaction network comprising 5 reactions, i.e. 3 direct additions, an esterification and a condensation, between 6 major components (ethylene, acetic acid, water, ethyl acetate, ethanol and diethyl ether) is accounted for. The reactions are described by means of Langmuir-Hinshelwood-Hougen-Watson and Eley-Rideal type rate expressions, including the adsorptions of all components, except diethyl ether, on the active sites of the catalyst. The model can quantitatively capture the effects of space time, temperature, pressure and feed composition, on conversions and also qualitatively reproduces the observed selectivities. However, it is necessary to include two physicochemical phenomena, i.e. i) silicotungstic acid solvation by water for the adequate description of the pressure effect on kinetics and ii) the proton-ethanol cluster formation to improve the fit between the experimental and model predicted values. Estimates for activation energies, adsorption enthalpies, solvation and cluster formation enthalpies and entropies are obtained through regression. At a temperature of 442 K, pressure equal to 1.2 MPa, an ethylene:acetic acid:water:dinitrogen feed molar ratio of 78.2:6.5:5.3:10.0 and relative space time amounting to 0.5, ethyl acetate is for 84 % produced by direct addition of acetic acid to ethylene, while the esterification between acetic acid and ethanol contributes for 16 %. Hence, besides reproducing conversions and selectivities, the kinetic model provides insights on fundamental level, which are essential for the optimization and innovation of production plants utilizing direct addition technology.

Improved Fuel Cell Chemical Durability of an Heteropoly Acid Functionalized Perfluorinated Terpolymer-Perfluorosulfonic Acid Composite Membrane

Commercial proton exchange membrane heavy-duty fuel cell vehicles will require a five-fold increase in durability compared to current state-of-the art light-duty fuel cell vehicles. We describe a new composite membrane that incorporates silicotungstic heteroply acid (HPA), α-K8SiW11O40▪13H2O, a radical decomposition catalyst and when acid-exchanged can potentially conduct protons. The HPA was covalently bound to a terpolymer of tetrafluoroethylene, vinylidene fluoride, and sulfonyl fluoride containing monomer (1,1,2,2,3,3,4,4-octafluoro-4-((1,2,2-trifluorovinyl)oxy)butane-1-sulfonyl fluoride) by dehydrofluorination followed by addition of diethyl (4-hydroxyphenyl) phosphonate, giving a perfluorosulfonic acid-vinylidene fluoride-heteropoly acid (PFSA-VDF-HPA). A composite membrane was fabricated using a blend of the PFSA-VDF-HPA and the 800EW 3M perfluoro sulfonic acid polymer. The bottom liner-side of the membrane tended to have a higher proportion of HPA moieties compared to the air-side as gravity caused the higher mass density PFSA-VDF-HPA to settle. The composite membrane was shown to have less swelling, more hydrophobic properties, and higher crystallinity than the pure PFSA membrane. The proton conductivity of the membrane was 0.130 ± 0.03 S cm−1 at 80 °C and 95% RH. Impressively, when the membrane with HPA-rich side was facing the anode, the membrane survived more than 800 h under accelerated stress test conditions of open-circuit voltage, 90 °C and 30% RH.

Oxidative desulfurization of model oil over the bowl-shaped N-doped carbon material loaded by the defective silicotungstic acid

The Keggin-type silicotungstic acid (SiW12) with oxygen vacancies (Ov) defects was facilely supported on the bowl-shaped N-doped carbon (NC) material through the one-step carbonization of the precursor consisting of acryloxyethyl trimethylammonium chloride gel microspheres (CPDAC) and intact SiW12 in air. The catalyst SiW12/NC prepared at a calcination temperature of 400 °C showed an outstanding oxidative desulfurization (ODS) performance with H2O2, due to the Ov defect SiW12 with high activity and its excellent dispersion in NC as well as more exposed active sites. Consequently, dibenzothiophene (DBT) in model oil could be almost completely removed within 20 min at 60 °C with a high kinetic constant (0.2034 min−1) and low apparent activation energy (38.06 kJ/mol). In addition, based on the radical experiments, a HO radical mechanism for ODS reaction of model oil over SiW12/NC-400 was mainly uncovered. Furthermore, SiW12/NC-400 could be reused for 7 cycles with no significant loss of activity.

Catalytic Performance and Kinetic Modeling of n-Butane Isomerization over Metal Bearing Silicotungstic Acid Supported on Mesoporous KIT-6

In this study, mesoporous KIT-6 support was synthesized hydrothermally. Its structure was improved by impregnation with phosphotungstic acid (HPW), silicotungstic acid (HSiW), and some metals such as Pt, Pd, and Ce. This work converts mesoporous KIT-6 into a bifunctional catalyst containing acid and metal sites. The structures of the synthesized catalysts were characterized by various analyses such as XRD, XRF, FTIR, SEM, EDS, BET, NH3-TPD, and TGA. Furthermore, the catalytic performances of heteropoly acids (HPW and HSiW) and KIT-6 modified samples were investigated in an n-butane isomerization process. Impregnation of HSiW on mesoporous support resulted in higher initial n-butane conversion and isobutane selectivity and improved catalyst stability compared to the unsupported sample. The introduction of 0.5 wt % platinum on the 60%HSiW/KIT-6 led to the highest n-butane conversion (72%) and isobutane yield (56.8%) at 250 °C and weight hourly space velocity (WHSV) of 0.15 h–1, at the beginning of the reaction. The 0.5%Pt/60%HSiW/KIT-6 sample was the most stable catalyst against deactivation compared to other modified samples. Its conversion and its selectivity to isobutane reached 51.8 and 73.8%, respectively, after 7 h of reaction. Also, the influence of different process variables such as reaction temperature, WHSV, and carrier gas on the catalyst activity (n-butane conversion, isobutane selectivity, and yield) was investigated. In addition, the classical bifunctional model was used to describe the kinetic behavior of 0.5%Pt/60%HSiW/KIT-6 in the isomerization reaction. This model inhibits the hydrogen and n-butane pressure effects on the reaction rate and agrees with the ideal bifunctional metal–acid mechanism. The activation energy for this model was found to be 29.64 kJ mol–1. The classical bifunctional model provided a reasonable fit for the experimental data and allowed to specify the kinetic parameters.

Silicotungstic acid as electron transfer mediator in Z-scheme g-C3N4/H4SiW12O40/Ag3PO4: Accelerated charge interface transportation for high-efficient photocatalysis

Photocatalytic degradation of organic pollutants has shown its promise in wastewater purification, however the photocatalytic activity on most catalysts are still unsatisfactory due to the poor reactive oxygen species production as a result of sluggish charge separation. Here, an innovative silicotungstic acid mediated charge transfer system over the Z-scheme g-C3N4/H4SiW12O40/Ag3PO4 photocatalyst is proposed, exhibiting remarkable photocatalytic activity toward oxygen activation for reactive oxygen species generation. We verify that the H4SiW12O40 with the unique Keggin units could serve as charge transfer mediator to speed up charge transportation between g-C3N4 and Ag3PO4, as a result showing dramatically enhanced charge separation efficiency. By virtue of the aforementioned advantages, the as-prepared Z-scheme photocatalyst of g-C3N4/H4SiW12O40/Ag3PO4 shows excellent photocatalytic performance toward carbamazepine degradation, where the pseudo-first-order rate constant is estimated to be 78, 18, and 9 times higher than that of g-C3N4, Ag3PO4, and g-C3N4/Ag3PO4. The innovative design of using H4SiW12O40 as solid charge transfer mediator offers new viewpoints in designing high-efficient photoctalysts for environmental related applications.

Glycerol Dehydration to Acrolein Catalyzed by Silicotungstic Acid: Effect of Mesoporous Support

To facilitate value-added chemical production from renewable glycerol, gas-phase glycerol dehydration to acrolein was conducted using supported silicotungstic acid as solid acid catalysts, focusing on the effects of mesoporous catalyst supports on the catalytic performance. One alumina (Al) support with average mesopore size of 30 nm and two silica supports (Si1254 and Si1252) with mesopore size of 6 nm and 11 nm, respectively, were comparatively evaluated in this study. It was found that the Si1254 silica support with the smallest pore size (6 nm) deactivated the fastest, decreasing both the glycerol conversion and acrolein selectivity along the time-on-stream. The other silica support Si1252 with 11 nm pore size provided an acrolein yield comparable to the Al support over the tested 7.5 h time-on-stream (73.9 mol% for Si1252 vs. 74.1 mol% for Al). However, the mechanisms for achieving the comparable yield are different. Si1252 showed higher acrolein selectivity than Al, but it also deactivated faster than Al due to its quicker coking. On the other hand, Al showed more stable performance in terms of glycerol conversion rate and less coking, but it had lower acrolein selectivity and a higher selectivity to byproducts, especially the undesired byproducts of acetaldehyde and propionaldehyde, which posed difficulties in downstream separation.

Organic-Exchanged Silicotungstic Acid Compounds as Efficient and Environmental-Friendly Catalysts for Synthesis of Glycerol Monolaurate

A series of organic-exchanged silicotungstic acid catalysts were synthesized by changing the variety and amount of organic compounds. The structure, thermal stability and acidic properties of the catalysts were characterized by FT-IR, XRD, TGA and 31P-MAS NMR. The catalytic performances of the catalysts were investigated on the selective esterification of lauric acid with glycerol to glycerol monolaurate. Among the various catalysts, [QuH]1H3SiW12O40 with molar ratio of quinoline to silicotungstic acid of 1:1 showed excellent activity and reusability due to strong Brand#248;nsted acidity and “pseudo-liquid” catalytic modes. The optimal conditions optimized by response surface methodology were as follows: the molar ratio of glycerol to lauric acid was 5.3:1, the amount of catalyst was 4.8 wt%, the reaction temperature was 424 K, and the reaction time was 1.5 h. Under these conditions, the average yield of glycerol monolaurate was 79.7%, which was basically consistent with the values predicted by the mathematical model. Moreover, the kinetic data of this reaction were fitted to a second-order kinetic model and the apparent activation energy Ea was 52.35 kJ / mol