HPW Content Research Articles

Hydrogen-free carbon monoxide production through decomposition of formic acid over a HPW/TiO2 catalyst

The dehydration of formic acid over supported phosphotungstic acid (H3PW12O40, HPW) catalysts was investigated for the production of hydrogen-free carbon monoxide (CO). The variations in the support type (SiO2, Al2O3, ZrO2, and TiO2) and HPW content (0.0–20.0 wt.%) affect the acidity of catalysts, which was demonstrated by the temperature-programed desorption of iso-propanol (IPA-TPD) and pyridine-adsorbed infrared spectroscopy (Py-IR). The catalytic activity in formic acid dehydration exhibited a volcano-type distribution in accordance with the HPW content and was maximized at 15 wt.% loading. Furthermore, the catalytic activity was more closely related to the density of Brønsted acids than that of Lewis acids and inversely proportional to the peak temperature of propylene desorption during IPA-TPD. The strongly adsorbed H2O on the catalysts, which is generated during formic acid dehydration, induces deactivation of the catalyst, particularly at lower reaction temperatures (<230 °C).

Esterification of 1-hexene and acetic acid using resin-supported phosphotungstic acid catalysts

As an atom economy technology, the direct esterification reaction of olefins plays a significant role in the production of organic esters. In this work, a series of resin-supported HPW catalysts were prepared using D101, D152, RM027, and A15 as the carriers, and they were used to prepare 1-methylpentyl acetate by the esterification of 1-hexene and acetic acid. The composition, structure, morphology, acid content, and other parameters of catalysts were characterized. In the esterification reaction, the activity order of catalysts is as follows: 20.0%HPW/A15 > 20.0%HPW/D101 > 20.0%HPW/D152 > 20.0%HPW/RM027. It depends on the acid strength of the carrier, the interaction between the carrier and HPW, and the HPW content. Moreover, it can be concluded that the weak acid resin carrier is completely inactive for the esterification reaction of 1-hexene, and the ratio of acetic acid to 1-hexene has a significant influence on the product selectivity. When n (acetic acid)/n (1-hexene) = 2, the optimum 1-methylpentyl acetate selectivity is 38.2%. Results of repeated experiments confirm that the stability of the active constituent is related to the type of functional groups on the carrier. Graphical Abstracts. 1-Methylpentyl acetate was successfully prepared by the direct esterification of 1-hexene and acetic acid using resin-supported HPW catalysts. The catalytic activity depends on the HPW content, the acid strength of the resin, and the interaction between HPW with the carrier, while the stability of the active constituent is related to the type of functional groups on the carriers.

Composite membranes anchoring phosphotungstic acid by β-cyclodextrins modified halloysite nanotubes

Anchoring phosphotungstic acid (HPW) on insoluble inorganic fillers is a facile and effective approach to suppress its leakage in the proton exchange membrane. In this work, we introduced β-cyclodextrin (β-CD) on halloysite nanotubes (HNTs) with the aid of polydopamine coating to prepare water-insoluble β-CD-DHNTs, which was dispersed in the SPEEK matrix to anchor HPW. Both HPW and β-CD-DHNTs are well dispersed in the SPEEK matrix because of the hydrogen bonding complexation between [PW12O40]3- and β-CD. For the SPEEK/β-CD-DHNTs/HPW composite membranes, the proton conductivity increased with the increase of HPW content, reaching the maximum of ~120% increase relative to that of the SPEEK membrane. The HPW immobilized by the β-CD and polydopamine on the nanotubes could provide more active sites, resulting in the construction of more continuous proton transfer pathways. Therefore, as compared to the SPEEK membrane, lower activation energy for the proton transport was observed for the composite membrane, which also exhibited stable proton conductivity during the water immersion test for 30 days.

Mesoporous Silica Encapsulated Phosphotungstic Acid Catalysts for Alkylation Desulfurization of Gasoline

An effective, green method was proposed to prepare mesoporous SiO2 encapsulated phosphotungstic acid (HPW) catalysts for alkylation desulfurization of 3-methylthiophene (3-MT). 3-aminopropyl triethoxysilane (APTES) was added to promote the formation of SiO2 gel and immobilize HPW during preparation. Then, SiO2 encapsulated HPW catalysts were characterized by XRD, N2 physical adsorption, SEM, TEM, EDS, Ultraviolet–Visible spectrum, FTIR, NH3-TPD to study the physical and chemical properties. Characterization results show that the initial Keggin structure of HPW was remained during the preparation and there exist strong interaction between HPW and SiO2. Activity of catalysts is superior to that of reported SBA-15 encapsulated HPW catalysts, due to more effective encapsulation of HPW. The conversion of 3-MT could reach 99% with HPW content of 30.8% under reaction conditions (reaction temperature of 363 K, reaction time of 60 min and 1% catalyst dosage). Reducing the olefin content will not reduce the conversion of 3-MT but could effectively reduce the self-polymerization of olefin, which is also beneficial to reusability of catalysts.

Influence of the support on the catalytic properties of Keggin type heteropolyacids supported on niobia according to two different methodologies: evaluation of isopropanol dehydration and Friedel–Crafts alkylation reaction

In this study, Keggin type heteropolyacids (HPW) supported on niobia were prepared following two different methodologies, including the incipient wetness impregnation technique, and using water as a polar solvent. In methodology I, the support was impregnated after calcination at 300 °C, with HPW concentrations equivalent to 30 and 50% of coverage, while in methodology II the support, without pretreatment, was impregnated with HPW concentrations equivalent to 30 and 50% of coverage and further calcined at 300 °C. The catalysts were characterized by X-ray diffraction, nitrogen adsorption, chemical analysis by optical emission spectrometry from plasma, FT-IR, FT-Raman, 31P MAS NMR, and acidity determination by catalytic decomposition of isopropanol. It was found that the best catalysts, after lixiviation tests, were the ones with 50% of HPW content produced through methodology II (50MIIL300). After identification of the best catalyst in the reaction of dehydration of isopropanol, we studied the reaction of anisole with benzyl alcohol and benzyl chloride and the results obtained were comparable to other catalysts reported in literature.

Synthesis and characterization of 12-phosphotungstic acid supported on BEA zeolite

An optimized synthetic route for obtaining heteropoly acid (HPA) species supported on BEA zeolite was applied, and different samples, comprising 20 to 50 wt% of 12-phosphotungstic acid (HPW) were prepared. The as-synthesized supported HPW were subjected to different post-synthesis routes, which involved calcination and ultrasound treatment. Characterization of these materials was performed by means of Scanning Electron Microscopy, zeta potential measurements, Infrared Spectroscopy and X-ray Powder Diffraction analysis. Results suggest strong interaction of HPW with the support and revealed that ultrasound treatment resulted in better dispersion of active phase and thus homogeneous morphology of the samples. The zeta potential was found to be dependent on the preparation procedure and HPW content in these materials, while higher HPW loadings induced its agglomeration. Catalytic activity of the synthesized materials was investigated in an ethanol dehydration reaction, where lower HPW loadings induced higher ethanol conversion. Acid sites distribution and accessibility for ethanol molecules were found to be more essential for catalytic activity than HPW loadings, i.e., amount of active sites present in these hybrid materials.

Fabrication of sulfonated poly(aryl ether ketone sulfone) membranes blended with phosphotungstic acid and microporous poly(vinylidene fluoride) as a depository for direct-methanol fuel cells

A series of sulfonated poly(aryl ether ketone sulfone)/poly(vinylidene fluoride) phosphotungstic acid (SPAEKS/PVDF-HPW) composite membranes were prepared and characterized by Fourier transform infrared spectroscopy. No phase separation was observed by scanning electron microscopy. The HPW particles are evenly dispersed in the membranes, probably because the microporous structure of PVDF stabilized the dispersion of HPW particles in the membranes. Thermogravimetric analysis showed that the thermal stability of the membranes increased with increase in HPW content. Moreover, the composite membranes exhibited outstanding oxidative stability. The methanol permeability coefficient of the SPAEKS/PVDF-HPW10% membrane at 20 °C was 1.68 × 10−7 cm2 s−1, and the highest proton conductivity of the membrane at 80 °C was 0.098 S cm−1, slightly lower than that of Nafion® 117. However, the relative selectivity of the membrane was higher than that of Nafion® 117. The swelling ratio of the membrane at 80 °C was 16%, and the methanol uptake of the membrane at room temperature was only 10.2%, much lower than those of Nafion® 117. The results indicate that the SPAEKS/PVDF-HPW membranes can be used as an alternative proton exchange membrane for direct-methanol fuel cells.

Synthesis and performance of mesoporous phosphotungstic acid/alumina composite as a novel oxidative desulfurization catalyst

A series of mesoporous phosphotungstic acid/alumina composites (HPW/Al2O3) with various HPW contents were synthesized by evaporation-induced self-assembly method. These composites were characterized by nitrogen adsorption-desorption, TEM, FTIR, and UV-vis, and were tested as catalysts in oxidation desulfurization of model fuel composed of dibenzothiophene (DBT) and hydrocarbon, using H2O2 as the oxidant. These composites exhibited high activity in catalytic oxidation of DBT in model fuel and good reusing ability. The best performance was achieved by using the mesoporous HPW/Al2O3 with 15wt% HPW content, which resulted in a DBT conversion of 98% after 2 h reaction at 343 K, and it did not show significant activity degradation after 3 recycles. Characterization results showed that the mesoporous structure of alumina and the Keggin structure of HPW were preserved in the formed composite. These results suggested that HPW/Al2O3 could be a promising catalyst in oxidative desulfurization process.

One-pot generation of mesoporous carbon supported nanocrystalline H3PW12O40 heteropoly acid with high performance in microwave esterification of acetic acid and isoamyl alcohol

Ordered mesoporous carbon-supported H3PW12O40 heteropoly acid materials (HPW/OMCs) have been rationally synthesized for the first time. The method is based on the evaporation-induced triconstituent co-assembly effect using the sol–gel process, wherein soluble resol polymer is used as an organic precursor, and triblock copolymer F127 is used as a template. The ordered mesoporous carbon-supported H3PW12O40 heteropoly acid materials were analyzed and characterized by X-ray diffraction, N2 adsorption and desorption (BET), and transmission electron microscope. The mesoporous carbon-supported H3PW12O40 materials possess an ordered mesostructure, narrow pore size distributions (around 2.8–3.6 nm), high pore volumes (up to 0.49 cm3 g−1), high specific BET surface areas (up to 590 m2 g−1), tailorable HPW content (up to 30 wt%), and well dispersion of HPW particles. Moreover, the resultant mesoporous ordered mesoporous carbon-supported H3PW12O40 materials exhibit high catalytic activity in microwave esterification of acetic acid and isoamyl alcohol. The obtained 20 % HPW/OMC catalyst exhibits high catalytic performance with 96.7 % of isoamyl acetate yield at temperature of 120 °C, alcohol/acid molar ratio of 2, catalyst amount of 0.2 g, microwave irradiation power of 800 W, and reaction time of 18 min. It was believed that the concentration of H3PW12O40 have a crucial effect on the HPW/OMCs’ porosity, mesostructure and catalytic performance.

Periodically Ordered Mesoporous Co3O4/Heteropoly Acid Composite Frameworks for Catalytic Applications

ABSTRACTMesoporous cobalt oxide-tungstophosphoric acid composite frameworks have been synthesized by structure replication from cubic mesoporous KIT-6 silica. The products possess a regular structure with uniform wall thickness (~7 nm) and large internal BET surface area (~87-141 m2/g). The pore walls of these materials consist of nanocrystalline Co3O4 and 12-tungstophosphoric acid (HPW) components with different HPW content, i.e. 6, 15 and 36 wt. %. Total X-ray scattering analysis and UV/vis spectroscopy confirmed the Keggin structure of HPW into the mesoporous frameworks. Preliminary catalytic experiments found that Co3O4-HPW composites exhibited a remarkable activity in the direct decomposition of nitrous oxide into N2 and O2.

A novel inorganic proton exchange membrane based on self-assembled HPW-meso-silica for direct methanol fuel cells

Direct methanol fuel cells (DMFCs) based on high-temperature (100–300 °C) proton exchange membranes (HT-PEMs) offer significant advantages over the current low-temperature DMFCs based on perfluorosulfonic acid (e.g., Nafion™), such as reduction in CO poisoning via faster reaction kinetics, thus increasing the energy efficiency and reducing precious metal loading. This paper reports a novel inorganic proton exchange membrane based on 12-tungstophosphoric acid mesoporous silica (HPW-meso-silica) nanocomposites. The HPW-meso-silica was synthesized via a one-step self-assembly route assisted by a triblock copolymer, Pluronic P123, as the structure-directing surfactant. The threshold of the HPW content in the nanocomposites for the conductivity of mesoporous silica is 5 wt%. The best results were obtained at 25 wt% HPW-meso-silica, delivering a high proton conductivity of 0.091 S cm−1 at 100 °C under 100% relative humidity (RH) and 0.034 S cm−1 at 200 °C under 3% RH and a low activation energy of 14.0 kJ mol−1. The maximum power density of a cell with a 25 wt% HPW-meso-silica membrane is 19 mW cm−2 at 25 °C and increased to 235 mW cm−2 at 150 °C in methanol fuel.

Oxidative Removal of Dibenzothiophene by H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; over Activated Carbon-Supported Phosphotungstic Acid Catalysts

Phosphotungstic acid (HPW) supported on activated carbon (AC) combined with hydrogen peroxide formed an oxidative desulfurizaiton (ODS) system to oxidize sulfur-containing compounds in diesel fuel. Dibenzothiophene (DBT) dissolved in n-octane was selected as a model feedstock for studying this new ODS system. The HPW/AC catalysts were characterized with XRD, FTIR and N2 adsorption-desorption measurements. HPW was highly dispersed on the surface of carbon support. It was found that the DBT adsorption capacity decreased from 42 mg S/g to 33.13 mg S/g as HPW loading amount increased from 0 to 15 wt.%. Oxidative removal of DBT in the model oil significantly increased with increasing HPW loadings on the support from 0 to 10 wt.%. 100 % DBT was removed by using the catalysts with HPW content higher than 10 wt. %. At 80 °C, oxidative removal of DBT reached 100 % after 40 min of reaction when O/S molar ratio ranged from 4 to 10.

Synthesis and characterization of mesoporous phosphotungstic acid/TiO 2 nanocomposite as a novel oxidative desulfurization catalyst

A series of mesoporous phosphotungstic acid/TiO 2 (HPW/TiO 2) nanocomposites with various HPW contents have been synthesized by evaporation-induced self-assembly method. These nanocomposites were used as catalysts for oxidative desulfurization of model fuel, which was composed of dibenzothiophene (DBT) and hydrocarbon, and used H 2O 2 as oxidant. These catalysts were characterized by X-ray diffraction (XRD), nitrogen adsorption–desorption isotherm, transmission electron microscopy (TEM), FTIR and UV–vis. Characterization results suggest that these mesoporous HPW/TiO 2 possessed relatively uniform channel-like pores with Barrett–Joyner–Halenda (BJH) pore size of about 4 nm. The Brunauer–Emmett–Teller (BET) surface of the mesoporous HPW/TiO 2 slightly increases with the increase of HPW content and reach to a peak value of 176 m 2/g and 0.25 cm 3/g when the HPW content is 30 wt%. Keggin-type heteropolyacids (HPAs) has been encapsulated into anatase TiO 2 framework and the average size of TiO 2 nanoparticles is 8 nm. Catalytic oxidation results show that the catalysts are very active in refractory bulky molecule organosulfur compounds in fuel oil. The oxidative removal of DBT increases as the HPW content increases. The mesoporous HPW/TiO 2 also shows high selectivity for DBT oxidation in the DBT–petroleum ether–benzene system. The selective desulfurization ratio reach to 95.2% with mesoporous HPW/TiO 2 (20 wt%) catalyst under the reaction condition of 333 K, 2 h. In addition, the mesoporous HPW/TiO 2 catalyst shows excellent reusing ability, which makes it a promising catalyst in oxidative desulfurization process.

Supported heteropolyacid (HPW) catalysts for the continuous alkylation of isobutane with 2-butene: The benefit of using MCM-41 with larger pore diameters

12-Tungstophosphoric acid (HPW) has been supported on three different carriers: a commercial silica, a high surface area amorphous aluminosilicate (MSA), and an all-silica mesoporous MCM-41; and their catalytic properties have been determined for the alkylation of 2-butene with isobutane at 33°C and 2.5 MPa. A maximum in activity, selectivity to TMP and stability with time on stream was found for the HPW/SiO 2 catalyst with 40 wt% acid loading, despite the higher acid dispersions achieved with the high surface area MCM-41 and MSA supports. The lower activity of the HPW/MSA samples is due to a stronger interaction of HPW with the surface sites of the aluminosilicate, which in turn decreased both the number and the average acid strength of the Bronsted acid sites of the heteropolyacid. When the HPW was supported on MCM-41 a continuous decrease of the catalytic activity with the HPW content was observed. This fact, together with the characterization results, suggests a partial blockage of the monodimensional pores of MCM-41, which decreased the accessibility of the reactants to the Bronsted acid sites of the heteropolyacid located inside the pores. We show that this pore blockage can be decreased, and the catalytic activity of HPW/MCM-41 catalysts increased, by using a MCM-41 sample with larger pore diameter.