Heteropoly Acid Content Research Articles

Catalytic conversion of isopropyl alcohol on the heteropolic acid –titanium oxide system

A complex of modern physicochemical methods (X-ray phase analysis, low-temperature adsorption of nitrogen, scanning electron microscopy, element analysis)was used to studythe phase and texture properties of the phosphomolybdenum heteropoly acid–titanium oxide catalytic system. It was found that the optimal content of phosphomolybdenum heteropoly acid, which leads to an increase in the catalytic activity of titanium dioxide, is 7% wt.: the diisopropyl ether yield is higher,it reaches maximum values in a shorter period of time, and the samples are characterized by greater stability. It is shown that the textural characteristics of the specific surface area and dispersion are not the key factors responsible for the catalytic activity.It has been suggested that the activity of phosphomolybdenum heteropoly acid-containing samples is associated with the emergence of a new type of active centers that exhibit increased electron-donorproperties(terminal oxygen atoms of the outer frag-ments of octahedra М = О heteropolyacids). A drop in the catalytic activity of samples with a phosphomolyb-denum heteropoly acid content of more than 7% wt. associated with the formation of surface metaphosphoric acid and entails a decrease in active centers.

Preparation and testing of ceasium Brønsted ion-exchanged Al-SBA-15 supported heteropoly acid as heterogeneous catalyst in the fructone fragrancy synthesis

Here we report a new ceasium Bronsted ion-exchanged Al-SBA-15 (Cs/AS15) supported heteropoly acid (HPA) H3PW12O40 (HPA-Cs/AS15) material which can be prepared and used as heterogeneous catalyst for the fructone fragrancy synthesis. It was demonstrated that Cs+ was more effective than NH4+ as counter cation of ion-exchanged AS15 support for preparing HPA/AS15 catalyst with higher acidity and HPA leaching stability. HPA-Cs/AS15 material showed high acidity with the maximum NH3 desorption peak appeared at 759.6 °C in the NH3-TPD spectrum, stronger than pure HPA (635.7 °C) and the ammonium Bronsted ion-exchanged Al-SBA-15 supported HPA (HPA-NH4/AS15) (559.1 °C) materials. The HPA leaching stability test showed that the HPA content of HPA-Cs/AS15 catalyst reduced only by 2.55% after five washing times, much less than that of HPA-NH4/AS15 catalyst (49.22%). The higher acidity helped improve the HPA-Cs/AS15 catalyst performance in the fructone fragrancy synthesis. The ethyl acetoacetate conversion over this catalyst was 94.82%, better than those over HPA-NH4/AS15 (93.49%) and pure HPA (89.52%) catalysts, although HPA-Cs/AS15 catalyst had lower HPA content (23.16 wt%) than HPA-NH4/AS15 (24.28 wt%). In addition, it was shown that the reaction conditions such as ethyl acetoacetate:ethanediol reactant molar ratio of 1:1.5, ethanediol used as the diol reactant, and toluene used as the solvent, the fructone fragrancy synthesis reaction over HPA-Cs/AS15 catalyst reached the highest ethyl acetoacetate conversion (95.58%). The toluene’s boiling temperature of 110.6 °C can promote the dispersion and contact abilities of the reactants with HPA molecules presented inside the pores of HPA-Cs/AS15 catalyst.

Bifunctional Silicotungstic Acid and Tungstophosphoric Acid Impregnated Cu–Zn–Al & Cu–Zn–Zr Catalysts for Dimethyl Ether Synthesis from Syngas

In the present study, a set of methanol synthesis catalysts with different Cu/Zn/Al or Cu/Zn/Zr molar ratios were synthesized by a co-precipitation method. Silicotungstic acid and tungstophosphoric acid were impregnated into these materials to synthesize new bifunctional catalytic materials to be used in direct synthesis of dimethyl ether (DME) from syngas. In the case of methanol production, synthesized Cu/Zn/Al catalysts exhibited quite high methanol selectivity, reaching to approximately 87%. These results indicated that the dispersion of copper particles profoundly affected the selectivity of methanol. Direct synthesis of DME was investigated in the presence of heteropoly acid impregnated copper-based novel hybrid type bifunctional catalysts. Results revealed that product distributions were strongly influenced by the reaction temperature, pressure, heteropoly acid content, and type. Results proved that silicotungstic acid (STA) impregnated bifunctional catalysts showed much better catalytic performance than the tungstophosphoric acid (TPA) impregnated ones in DME synthesis from syngas. Very high dimethyl ether selectivity values were achieved in direct synthesis of dimethyl ether over the 25%, and 30% STA impregnated methanol synthesis catalysts, at 275 °C and 50 bar. DME selectivity presented an increasing trend due to the increase in heteropoly acid content over methanol synthesis catalysts. The silicotungstic acid incorporated (30%) Cu/Zn/Al catalyst, having a composition of 6/3/1 (30STA@CZA:631), showed the highest CO conversion and DME selectivity. However, coke formation over this catalyst was much more than the catalyst containing 25% STA. This is mainly due to the higher Bronsted acidity of 30STA@CZA:631 than 25STA@CZA:631. Low coke formation, together with quite high DME selectivity values achieved with 25STA@CZA:631, is a worthy distinction of this catalyst for the direct synthesis of DME from synthesis gas. Novel hybrid type catalysts are successfully synthesized for direct synthesis of dimethyl ether process. Heteropoly acid incorporated methanol synthesis catalysts are very active and stable in the direct synthesis of dimethyl ether process. Silicotungstic acid (STA) impregnated copper-based catalyst exhibits a superior performance than the tungstophosphoric acid impregnated catalyst.

Heteropolyacid (H3PW12O40)-impregnated mesoporous KIT-6 catalyst for green synthesis of bio-diesel using transesterification of non-edible neem oil

Mesoporous Ia3d cubic structured KIT-6 support was prepared by hydrothermal strategy and heteropoly acid content (10, 20 and 30%) was stacked on KIT-6 by wet-impregnation technique. The synthesized catalysts were characterized by XRD, N2-sorption, NH3-TPD, ATFT-IR, TEM and SEM–EDAX analyses. Acid properties of the supported catalysts were investigated by pyridine-adsorbed ATFT-IR and NH3-TPD, respectively. Poly-anion coordination present in the catalyst was confirmed by the DRS-UV spectrum. The dispersion of heteropoly acid on the catalyst surface was observed by TEM analysis. Also, the presence of the elements such as W and P on the catalyst and its morphology were represented by the HRSEM–EDAX technique. The catalytic activity of HPWA/KIT-6 was investigated by the transesterification of neem oil with methanol. Among the different wt% catalyst, 20% catalyst showed highest neem oil conversion and selectivity at an optimized reaction temperature of 60 °C. Further, the spent catalyst was recovered and recycled three times, and it showed activity losses of less than 4%.

Direct synthesis of hydrogen peroxide from hydrogen and oxygen over palladium catalyst supported on heteropolyacid-containing ordered mesoporous carbon

A series of palladium catalysts supported on ordered mesoporous carbon (Pd/OMC-T) were prepared with a variation of preparation temperature (T=8, 15, 25, 35, and 45°C) of ordered mesoporous carbon (OMC). Conversion of hydrogen and yield for hydrogen peroxide over Pd/OMC-T catalysts showed volcano-shaped trends with respect of preparation temperature in the presence of halide and acid additives. The catalytic performance was found to be closely related to the palladium surface area. With an attempt not to use acid additive, another series of palladium catalysts supported on heteropolyacid (HPA)-containing ordered mesoporous carbon (Pd/OMC-XHPA) were prepared with a variation of HPA content (X=5, 10, 20, 30, and 40wt%) using OMC-25 as a support. Selectivity and yield for hydrogen peroxide showed volcano-shaped trends with respect to HPA content. The superior catalytic performance of the catalyst at a certain HPA content (Pd/OMC-20HPA) was attributed to its high acidity caused by introduction of HPA into the pores of the catalyst.

Catalytic hydrothermal depolymerization of nylon 6

Depolymerization of nylon 6 to produce e-caprolactam using an environmentally friendly heteropoly acid catalyst was studied at temperatures between 553 and 603 K in water. The products of depolymerization were analyzed qualitatively and quantitatively by means of mass spectrometry and high-performance liquid chromatography. The results showed that the depolymerized product was mainly e-caprolactam with a little 6-aminocaproic acid and oligomers. The phosphotungstic heteropoly acid used as a catalyst can improve the hydrolysis rate and yield of e-caprolactam. The optimum hydrolysis conditions for e-caprolactam yield were as follows: phosphotungstic heteropoly acid content, 3%; reaction temperature, 573 K; and reaction time, 85 min. Under these conditions, the yield of e-caprolactam was 77.96%. In the temperature range 553–603 K, the activation energy of 3% phosphotungstic heteropoly acid-catalyzed depolymerization was evaluated as 77.38 kJ/mol, which is lower than the 86.64 kJ/mol value for no catalyst.

Investigation of sulfonated poly(ether ether ketone sulfone)/heteropolyacid composite membranes for high temperature fuel cell applications

AbstractThe sulfonated poly(ether ether ketone sulfone) (SPEEKS)/heteropolyacid (HPA) composite membranes with different HPA content in SPEEKS copolymers matrix with different degree of sulfonation (DS) were investigated for high temperature proton exchange membrane fuel cells. Composite membranes were characterized by Fourier transfer infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). FTIR band shifts suggested that the sulfonic acid groups on the copolymer backbone strongly interact with HPA particles. SEM pictures showed that the HPA particles were uniformly distributed throughout the SPEEKS membranes matrix and particle sizes decreased with the increment of copolymers' DS. The holes were not found in SPEEKS‐4/HPA30 (consisting of 70% SPEEKS copolymers with DS = 0.8 and 30% HPA) composite membrane after composite membranes were treated with boiling water for 24 h. Thermal stabilities of the composite membranes were better than those of pure sulfonated copolymers membranes. Although the composite membranes possessed lower water uptake, it exhibited higher proton conductivity for SPEEKS‐4/HPA30 especially at high temperature (above 100 °C). Its proton conductivity linearly increased from 0.068 S/cm at 25 °C to 0.095 S/cm at 120 °C, which was higher than 0.06 S/cm of Nafion 117. In contrast, proton conductivity of pure SPEEKS‐4 membrane only increased from 0.062 S/cm at 25 °C to 0.078 S/cm at 80 °C. At 120 °C, proton conductivity decreased to poor 0.073 S/cm. The result indicated that composite membranes exhibited high proton conductivity at high temperature. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1967–1978, 2006

Preparation and conductivity of PVA films composited with decatungstomolybdovanadogermanic heteropoly acid

In this work, the polyvinyl alcohol (PVA) films composited with decatungstomolybdovanadogermanic heteropoly acid (HPA) were prepared. Infrared (IR) spectra revealed that the Keggin structure characteristic of the GeW 10MoVO 40 5− anion was present in PVA films. At room temperature (20 °C), the conductivity of the samples of different HPA content increased from 3.16 × 10 −3 to 1.22 × 10 −2 S cm −1. The results indicated that they are new kind of excellent high-proton conductor.

Anhydrous gel electrolytes doped with silicotungstic acid

Polyoxometalate additives were entrapped in the poly(methyl methacrylate) (PMMA) and poly (glycidyl methacrylate) (PGMA) swollen with polar aprotic solvents. Conductivities of 3×10 −3 S cm −1 at 25 °C and 5.6×10 −3 S cm −1 at 90 °C were measured, making the resulting electrolytes useful materials for application in electrochemical devices. Properties of these gel electrolytes, such as transparency, conductivity and thermal stability depend both on the type of plasticizing solvent and the heteropolyacid content. Interactions between gel components were studied using FT-IR and Raman spectroscopies.

Photochromic and thermal properties of poly(vinyl alcohol)/H 6P 2W 18O 62 hybrid membranes

Poly(vinyl alcohol) (PVA) films, which contained different content of heteropolyacid (HPA) with Dawson–Wells structure, were prepared. The photochromic behavior was investigated by using ultraviolet–visible (UV-Vis) absorption spectroscopy. The result indicated that the film was reduced photochemically to yield a blue species under UV irradiation, and the color of the film changed to deep blue with increasing irradiation time and HPA content. The photochromic sensibility of different UV wavelength was investigated. In the UV-Vis spectra of the irradiated films, an isobestic point was observed at about 352 nm. The reduction mechanism of the heteropolyanion (W 6+→W 5+) was suggested. The thermal property and the conductivity of the film were also studied. The thermal degradation step and the melting point of the film were influenced by different content of the HPA. Notably, the conductivity of 8.33×10 −6 S cm −1 was observed when the HPA content was 80 wt.%.

Preparation and performance of PVA films composited with 12-tungstogermanic heteropoly acid

PVA films containing 12-tungstogermanic heteropoly acid have been successfully prepared for the first time. Infrared (IR) spectra revealed that the Keggin structure characteristic of the GeW 12O 40 4− anion was present in the PVA films. The characteristic IR peaks have been identified and their change in wave number interpreted as a function of heteropoly acid (HPA) content. The film exhibited considerably high proton conductivity, which increased with the increase of the 12-tungstogermanic heteropoly acid content. At room temperature (20°C), the conductivity of the PVA film containing 80 wt.% 12-tungstogermanic heteropoly acid is 2.11×10 −2 S cm −1. The photochromism of the PVA film was observed. Its color changed into blue.

Changes in the Surface Area of Silica-supported 12-Molybdophosphoric Acid in Relation to the Degree of Loading and the Calcination Temperature

A technical silica gel (Grace-113) was impregnated with 12-molybdophosphoric solution to attain loadings of 0.72–13.4 wt.%. The air-dried solids were then calcined for 3 h at 400, 600 and 800°C, respectively, followed by determination of their N2 adsorption isotherms. The silica gel was thermally stable and suffered about 15% loss in area at 800°C. The impregnated silicas showed considerable decrease in surface area as a function of their heteropoly acid content. Two processes are suggested as taking part in the modification of pore structure: (1) diffusion of the aqueous heteropoly acid solution and its subsequent deposition; and (2) dissolution of silica gel in the acidic aqueous solution followed by interaction with HPMo to form either molybdosilicate or P–Si exchange products. Correlation with the previously studied catalytic conversion of isopropanol indicated that the activity was independent of the surface area. Catalytic dehydration on the 600°C and 800°C products seems to be associated with silicate, molybdate or MoO3 surface species rather than being due to surface acidity or the extent of the surface area.