摘要 :
A series of 12-Phosphotungstic (PW) acid and its cesium salt catalysts supported on various porous carriers,such as silica gel,mesoporous silica SBA-15,ultra-stable Y (USY) and dealuminated USY were prepared,and their catalytic pe...
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A series of 12-Phosphotungstic (PW) acid and its cesium salt catalysts supported on various porous carriers,such as silica gel,mesoporous silica SBA-15,ultra-stable Y (USY) and dealuminated USY were prepared,and their catalytic performances were evaluated in the liquid-phase acetali/ation of ethyl acetoacetate and ethylene glycol into fructone.It was found that the supported PW catalysts exhibited high activity,but their reusability was very poor due to the severe leaching of heteropoly anions into water.On the contrary,supported Cs salt of PW catalysts showed high conversion and selectivity with high water-tolerance.The dealuminated USY was revealed to be the suitable support for cesium salt of PW.Catalytic activity was discussed in relation with the surface area and acid strength of catalysts.
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In this study, we report the one-pot synthesis of 2-amino-3,5-dicarbonitrile-6-thiopyridines with benzaldehyde, malononitrile, and thiophenol by using phosphotungstic acid as an efficient catalyst in aqueous media. This method has...
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In this study, we report the one-pot synthesis of 2-amino-3,5-dicarbonitrile-6-thiopyridines with benzaldehyde, malononitrile, and thiophenol by using phosphotungstic acid as an efficient catalyst in aqueous media. This method has the advantages of easy separation, high storage stability, and environmental friendliness.
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The mechanism of phosphotungstic acid modification CeO2 catalysts (P-WiCeO(2)) with different CeO2 supports were investigated by in situ diffuse reflectance infrared transform spectroscopy for the selective catalytic reduction of ...
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The mechanism of phosphotungstic acid modification CeO2 catalysts (P-WiCeO(2)) with different CeO2 supports were investigated by in situ diffuse reflectance infrared transform spectroscopy for the selective catalytic reduction of NO by NH3. The results indicated that the NH3-SCR reaction over P-WiCeO(2) followed both the Langmuir-Hinshelwood mechanism and the Eley-Rideal mechanism. The reaction between NH4+ and bidentate nitrate (NO3-) took place, and then the H2O, N-2 and adsorbed NO2 were formed. The coordinated NH3 species reacted with adsorbed NO2 and gaseous NO to generate N-2 and H2O The interaction between CeO2 and phosphotungstic acid contributed to the favored surface acidity (Lewis and Bronsted acid sites) and excellent redox property. The Bronsted acid sites facilitated the generation of NO2-adsorbed and Lewis acid sites accelerated the Eley-Rideal mechanism, while the NO oxidation to bidentate nitrate or NO2-adsorbed species was an important step in the reaction mechanism of P-WiCeO(2). (C) 2016 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
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The UV-photon-induced degradation of heptafluorobutanoic acid was investigated in acidic aqueous solutions in the presence of titanium dioxide. Heptafluorobutanoic acid could be degraded with this photocatalyst in a light-induced ...
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The UV-photon-induced degradation of heptafluorobutanoic acid was investigated in acidic aqueous solutions in the presence of titanium dioxide. Heptafluorobutanoic acid could be degraded with this photocatalyst in a light-induced reaction generating carbon dioxide and fluoride anions. Carbon dioxide evolution in a significant amount occurred only in the presence of molecular oxygen and the photocatalyst. The light-induced degradation of trifluoroacetic acid, pentafluoropropanoic acid, nonafluorobutanoic acid, pentadecafiuorooctanoic acid, nonafluorobutanesulfonic acid, and heptadecafluorooctanesulfonic acid in the presence of titanium dioxide was also studied. The perfluorocarboxylic acids under investigation are degraded to generate CO_2 and fluoride anions while both perfluorinated sulfonic acids are persistent under the experimental conditions employed in this study. For all compounds photonic efficiencies of the mineralization reaction were estimated to be smaller than 1 x 10~(-5). To increase the photocatalytic activity mixed systems containing homogeneous phosphotungstic acid and heterogeneous titanium dioxide catalysts were also investigated. In the mixtures of these two photocatalysts, the formation rate of CO_2 increased with illumination time.
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? 2023 The Korean Society of Industrial and Engineering ChemistryThe dehydration of formic acid over supported phosphotungstic acid (H3PW12O40, HPW) catalysts was investigated for the production of hydrogen-free carbon monoxide (C...
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? 2023 The Korean Society of Industrial and Engineering ChemistryThe 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 Br?nsted 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).
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The vapor phase dehydration of glycerol was carried out on niobia-supported phosphotungstic acid (PTA) catalysts. The catalysts were prepared by varying the active component PTA loadings ranging from 10 to 40 wt% on the support. T...
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The vapor phase dehydration of glycerol was carried out on niobia-supported phosphotungstic acid (PTA) catalysts. The catalysts were prepared by varying the active component PTA loadings ranging from 10 to 40 wt% on the support. The catalysts were characterized by powder X-ray diffraction, laser Raman spectroscopy, temperature programmed desorption of ammonia, ex-situ FT-IR spectra of adsorbed pyridine, BET surface area and pore size distribution. The XRD results suggest that the active phase of phosphotungstic acid was found to be highly dispersed at lower PTA loadings on the support. The findings of Raman spectra reveals that the catalyst with 30 PTA/Nb-400 clearly exhibit the primary structure of Keg-gin ion of hetropolyacid on the niobia support. NH3-TPD experiments confirm that the acidity of the catalyst increases with increase of PTA loading and decreases at higher loadings. The nature of acidic sites on the catalyst surface was investigated by the ex-situ pyridine adsorbed FT-IR spectroscopy and the results suggest that the catalyst with 30 PTA/Nb has shown stronger Br0nsted acidic sites. Pore size distribution reveals that 30 PTA/Nb-400 exhibited lager average pore diameter than the other loadings. The Nb2O5-supported PTA catalysts have shown remark-able catalytic performance during the dehydration of glycerol to acrolein. The catalytic properties during glycerol dehydration are related to the surface acidic functionality of the catalyst.
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The liquid-phase benzoylation of veratrole with benzoic anhydride (BA) to 3,4-dimethoxy benzophenone was investigated using zirconia-supported silicotungstic acid (STA) as a catalyst.Catalysts with different STA loadings (5-25 wt%...
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The liquid-phase benzoylation of veratrole with benzoic anhydride (BA) to 3,4-dimethoxy benzophenone was investigated using zirconia-supported silicotungstic acid (STA) as a catalyst.Catalysts with different STA loadings (5-25 wt%) and calcination temperatures (600-850 deg C) were prepared by suspending zirconium oxyhydroxide in methanol solution of STA followed by drying and calcination.These catalysts were characterized by XRD,Raman spectroscopy,DTA,XPS,NH_3-TPD,FTIR pyridine adsorption,and DRUV-vis spectroscopy.XRD results indicated that the presence of STA retarded the crystallization of zirconia and stabilized ZrO_2 in tetragonal phase.Characterization of the catalyst with optimum STA loading (15%) by Raman spectroscopy showed the presence of zirconia-anchored mono-oxotungstate as the major tungsten species up to 750 deg C.The catalysts showed both Bronsted and Lewis acidity,and 15% STA on zirconia calcined at 750 deg C (15 SZ-750) had the highest Bronsted acidity and total acidity.The catalytic activity was found to depend on STA coverage,and the highest activity corresponded to the monolayer of silicotungstate on zirconia.Further,a comparison of the catalytic activity of 15 SZ-750 with zirconia-supported phospho-tungstic acid (15%,calcined at 750 deg C,15 PZ-750) and silica-supported silicotungstic acid (15%,calcined at 300 deg C,15 SS-300) showed that silicotungstic acid and phosphotungstic acid supported on zirconia acted as efficient and stable solid acid catalysts,whereas silicotungstic acid supported on silica was leached into the reaction medium and catalyzed the reaction homogeneously.Under the reaction conditions of 120 deg C and a veratrole-to-BA molar ratio of 5,the most active catalyst,15 SZ-750,showed 99% BA conversion,and the deactivated catalyst could be regenerated by calcination without appreciable loss in activity.
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In this study, a sensor for the simultaneous determination of uric acid (UA) and theophylline (TP) has been reported for the first time. The sensor was simply constructed by modifying glassy carbon electrode (GCE) with cadmium sul...
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In this study, a sensor for the simultaneous determination of uric acid (UA) and theophylline (TP) has been reported for the first time. The sensor was simply constructed by modifying glassy carbon electrode (GCE) with cadmium sulfide nanoparticles (CdS NPs), phosphotungstic acid (PTA) and Nafion. Electrochemical behavior of the modified electrode was evaluated by cyclic voltammetry (CV) technique. The modified electrode (CdS/PTA/Nafion/GCE) shows excellent electrocatalytic capability by substantially reducing the oxidation potential of TP. CdS/PTA/Nafion/GCE also exhibits extraordinary stability by effectively preventing the aggregation of the oxidation product of TP on the electrode surface. The differential pulse voltammetric (DPV) results indicated that there was good linear relationship between anodic peak currents and the concentrations of TP and UA in the range from 1 × 10~(-6) to 2 × 10~(-4) M and 5 × 10~(-6) to 1 × 10~(-3) M with the detection limit of 6 × 10~(-7) M and 2 × 10~(-6) M (S/N = 3), respectively. Furthermore, the applicability of the sensor for TP and UA analysis in urine has been successfully demonstrated.
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A series of catalysts of 12-Phosphotungstic acid (PW) and its cesium salts immobilized on dealuminated ultra-stable Y zeolite (DUSY) were prepared. Their specific surface area and acid strength were characterized, and their cataly...
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A series of catalysts of 12-Phosphotungstic acid (PW) and its cesium salts immobilized on dealuminated ultra-stable Y zeolite (DUSY) were prepared. Their specific surface area and acid strength were characterized, and their catalytic activity, selectivity and stability were evaluated in the liquid-phase esterification of acetic acid with n-butanol. It was found that the catalytic activity could be improved remarkably by introducing PW onto dealuminated USY (from 49.5% to 86.4%). However, this obvious promotion effect of PW could not be observed on USY supported PW catalyst, which showed rather low conversion of less than 25.0%. The supported cesium salt of PW on DUSY catalyst gave a very high conversion of n-butanol of 94.6% and the 100% selectivity for n-butyl acetate. The catalytic stability test revealed that after 5 reaction cycles, the catalytic activity over PW/DUSY drastically dropped to 47.6%, by contrast, the PW cesium salt/DUSY still showed a high conversion of 81.6%. The leaching test for catalysts in water showed that the decrease of activity was closely associated with the solubility of the active heteropoly components on supports into the polar solvent, which indicates that the catalytic deactivation was mainly due to the lose of the heteropoly species in the reaction medium. The high catalytic stability of the supported cesium salts of PW is suggested to be derived from the water-tolerance of cesium salts of PW in the polar reaction system.
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Metal organic frameworks (MOFs) have exhibited potential for application as heterogeneous catalytic materials because they consist of empty space, which can be used for encapsulation. Encapsulation of H3PW12O40 (HPW) in MOFs, such...
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Metal organic frameworks (MOFs) have exhibited potential for application as heterogeneous catalytic materials because they consist of empty space, which can be used for encapsulation. Encapsulation of H3PW12O40 (HPW) in MOFs, such as the fabrication of MIL-101, by direct synthesis method or impregnation has drawn significant interest. However, few researches have used MOFs as catalysts for acetalization. This study evaluates the use of HPW encapsulated in MIL-101(Cr) to make it a catalyst in the acetalization of vanillin propylene glycol. Samples fabricated using various techniques (encapsulation and impregnation) were characterized by SEM, TEM, N-2 adsorption-desorption, XRD, and FT-IR. The synthesis conditions of HPW@MIL-101 and their effects on vanillin conversion were examined. The reaction kinetics was also investigated under optimal conditions. Vanillin conversion showed that introducing HPW directly into MIL-101(Cr) during synthesis induced a 14% increase, compared with impregnation. The results indicated that HPW@MIL-101(Cr) is an effective method for vanillin propylene glycol acetal production and is reusable.
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