Phosphotungstic Acid Loading Research Articles

Sorption enhanced DME synthesis by one-step CO2 hydrogenation

DME synthesis by direct CO2 hydrogenation was studied on physical mixture of commercial CuZnO/Al2O3 (CZA) and in-house synthesized PTA (phosphotungstic acid)/γ-Al2O3 catalysts. Effects of PTA loading (0–50 % by mass) and relative amounts of the catalysts on CO2 conversion and DME yield were investigated. The process was intensified through integration of in-situ steam separation by Zeolite 3A (Z3A) adsorbent mixed with the catalysts. Experiments were run at 498 K, 30 bar, H2:CO2=3:1 and GHSV=1750 h−1 (based on CZA catalyst). Optimum PTA loading and CZA:PTA/γ-Al2O3 mass ratio were 30 % and 1:2, respectively, that gave ∼21 % CO2 conversion and 6.3 % DME yield. These values remained below the respective thermodynamic limits (28.5 % and 21 %), which were exceeded upon adsorbent integration. Catalytic performance depended strongly on adsorbent quantity studied at the catalyst (CZA+PTA/γ-Al2O3):adsorbent mass ratio range of 1:0.33–4. Catalysts and the adsorbent remained stable during the pressure swing driven adsorption-regeneration cycles. Sorption assistance at catalyst:adsorbent ratio=1:4 increased catalyst productivity from 5.5×10−3 to 2×10−2 kgDME h−1 kgcat−1. The latter value was comparable to those of the sorption enhanced CO2+CO hydrogenation systems due to the PTA-based dehydration catalyst with strong acidic features and was promising when the strong thermodynamic limitations of CO2-DME conversion was considered.

Preparing prehydrolyzed kraft dissolving pulp via phosphotungstic acid prehydrolysis from grape branches

Dissolving pulp was successfully prepared via phosphotungstic acid (PTA) prehydrolysis kraft (PHK) cooking followed by an elemental chlorine-free (ECF) bleaching process from grape branches. The effects of prehydrolysis temperature, reaction time, and PTA concentration that potentially affect the quality of dissolving pulp product on chemical components of pulp were studied via an orthogonal experiment. The structure of lignin was activated during the PTA prehydrolysis phase, and lignin was easily removed during the following cooking process. Thus, relatively mild conditions (140°C, 100 min) can be used in the cooking process. During the prehydrolysis phase, temperature exhibited the most significant influence on the cellulose purity of the obtained pulp fiber, followed by reaction time and PTA concentration. The optimized prehydrolysis conditions were as follows: prehydrolysis temperature, 145°C; reaction time, 75 min; and PTA concentration, 1 wt%. Whether the excessively high prehydrolysis temperature or prolonging the reaction time did not favor the retention of long chain cellulose, the delignification selectivity for the cooking process could not be further improved by excessive PTA loading. Under these prehydrolysis conditions, 94.1% and 29.0% for α-cellulose content and total yield could be achieved after the given cooking and bleaching conditions, respectively. Moreover, the chemical structure and crystal form of cellulose were scarcely changed after PTA prehydrolysis, which could be confirmed by results from Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD). PTA prehydrolysis could be considered as an alternative method for preparing PHK dissolving pulp under relatively mild cooking conditions.

Rearrangement of α-terpineol by using PTA/TiO2 catalyst synthesized by ultrasonic-assisted impregnation method

1,8-cineole was synthesized via α-terpineol rearrangement over SiO2- and TiO2-supported phosphotungstic acid (PTA) catalysts prepared by ultrasonic impregnation. The structures of the catalysts were analyze using X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared (FT-IR) spectroscopy. The effects of reaction conditions on α-terpineol conversation and 1,8-cineole selectivity were investigated and the optimal reaction conditions are PTA loading of 20 wt%, mass fraction of 0.02, reaction temperature of 50 °C, and reaction time of 6 h. Under these conditions, the α-terpineol conversion and 1,8-cineole selectivity over PTA/TiO2 were 98.96% and 48.77%, respectively, which were better than that over PTA/SiO2.

Catalytic Degradation of Chitosan by Supported Heteropoly Acids in Heterogeneous Systems

Several kinds of composite materials with phosphotungstic acid (PTA) as the catalyst were prepared with activated carbon as support, and their structures were characterized. According to the Box–Behnken central combination principle, the mathematical model of the heterogeneous system is established. Based on the single-factor experiments, the reaction temperature, the reaction time, the amount of hydrogen peroxide and the loading capacity of PTA were selected as the influencing factors to study the catalyzed oxidation of hydrogen peroxide and degradation of high molecular weight chitosan. The results of IR showed that the catalyst had a Keggin structure. The results of the mercury intrusion test showed that the pore structure of the supported PTA catalyst did not change significantly, and with the increase of PTA loading, the porosity and pore volume decreased regularly, which indicated that PTA molecules had been absorbed and filled into the pore of activated carbon. The results of Response Surface Design (RSD) showed that the optimum reaction conditions of supported PTA catalysts for oxidative degradation of high molecular weight chitosan by hydrogen peroxide were as follows: reaction temperature was 70 ℃, reaction time was 3.0 h, the ratio of hydrogen peroxide to chitosan was 2.4 and the catalyst loading was 30%. Under these conditions, the yield and molecular weight of water-soluble chitosan were 62.8% and 1290 Da, respectively. The supported PTA catalyst maintained high catalytic activity after three reuses, which indicated that the supported PTA catalyst had excellent catalytic activity and stable performance compared with the PTA catalyst.

Quaternary ammonium functionalized polyacrylonitrile fiber supported phosphotungstic acid as efficient heterogeneous catalyst: Hydrophobic tuning of the catalytic microenvironment

Thirteen novel amine or quaternary ammonium functionalized polyacrylonitrile fiber (PANF) supported phosphotungstic acid (PTA) catalysts were designed and prepared, and their catalytic activities were screened by choosing condensation/annulation tandem synthesis of 2,3-dihydroquinazolin-4(1H)-one compound via C–N bond formation between 2-aminobenzamide and p-chlorobenzaldehyde as a model reaction. By adjusting the functionality and hydrophobic/hydrophilic property of the amine/ammonium structure as well as the density of PTA sites, the fiber catalyst CAT-12 prepared from quaternary ammonium functionalized PANF containing benzyl group with high PTA loading achieved the best catalytic activity for most reactions in water. The CAT-12 can be easily separated from the reaction system and recycled for 7 times without significant loss of catalytic activity. Moreover, the reaction proceeded smoothly in gram scale and gave nearly quantitative yield using this efficient, eco-friendly and easily recyclable catalyst with great industrial potential which was also demonstrated in Friedel-Crafts alkylation of indoles with β-nitrostyrene. Vivid PTA immobilization processes and the corresponding “catch-catalyze” catalytic modes were further schematically described to address the effect of microenvironment-tuning on immobilization and catalysis, and accordingly the possible catalytic mechanisms of the two reactions were proposed.

Synthesis of Biodiesel Catalyzed by Phosphotungstic Acid Supported on Silica

Using tetraethyl orthosilicate as silicon source, silica supported phosphotungstic acid catalyst was prepared by sol-gel method, and then biodiesel was synthesized from Vegetable oil and methanol with self-made solid acid as catalyst. Through the temperature, time, dosage, use times and other factors. The optimal conditions for conversion were found to be 40% phosphotungstic acid loading. 6: 1 ratio of alcohol to oil, the catalyst dosage is 10% of the rapeseed oil mass, and the reaction temperature was set at 68°C and the reaction time was 2.5h. Under these conditions, the conversion rate of biodiesel can reach 96.0%.

Spherical hollow mesoporous silica supported phosphotungstic acid as a promising catalyst for α-arylstyrenes synthesis via Friedel-Crafts alkenylation

In this work, a spherical hollow mesoporous silica (SHMS) with high surface area (902 m2/g) and large mesopore volume (1.31 cm3/g) was prepared via a facile and scalable two-step soft-hard dual template-assisted sol-gel approach (OSDSG) by using glucose-derived carbon nano/micro particles (NMCP) as a hard template and cetyltrimethylammonium bromide (CTAB) as a soft template, respectively, in which the size-preselected carbon submicro-particle was used to replace ploymer sphere, and no extra precious additives like n-octadecyltrimethoxysilane (C18TMS). Supported phosphotungstic acid (PTA) catalysts on SHMS (PTA/SHMS) and on previously reported spherical mesoporous silica (PTA/SMS) with 25 wt% of PTA loading were prepared and employed as solid acid catalysts for diverse reactions. Transmission electron microscopy (TEM), N2 adsorption-desorption, X-ray diffraction (XRD), and NH3 temperature-programmed desorption (NH3-TPD) techniques were employed to characterize the nature of carriers and supported PTA catalysts for revealing the structure-performance relationship. The developed PTA/SHMS catalyst demonstrates much higher catalytic activity than PTA/SMS for diverse reactions including alkenylation, esterification, alkylation, and benzylation, ascribed to the strengthened mass transfer and enlarged exposure degree of acidic sites to reactants those resulting from unique hollow and mesoporous morphology. Moreover, PTA/SHMS catalyst also exhibits outstanding catalytic performance for the diverse α-arylstyrenes via solid acid-mediated alkenylation. PTA/SHMS could be considered as a practical solid acid catalyst for diverse transformations.

Pushing the Limits on Metal-Organic Frameworks as a Catalyst Support: NU-1000 Supported Tungsten Catalysts for o-Xylene Isomerization and Disproportionation.

Acid-catalyzed skeletal C-C bond isomerizations are important benchmark reactions for the petrochemical industries. Among those, o-xylene isomerization/disproportionation is a probe reaction for strong Brønsted acid catalysis, and it is also sensitive to the local acid site density and pore topology. Here, we report on the use of phosphotungstic acid (PTA) encapsulated within NU-1000, a Zr-based metal-organic framework (MOF), as a catalyst for o-xylene isomerization at 523 K. Extended X-ray absorption fine structure (EXAFS), 31P NMR, N2 physisorption, and X-ray diffraction (XRD) show that the catalyst is structurally stable with time-on-stream and that WO x clusters are necessary for detectable rates, consistent with conventional catalysts for the reaction. PTA and framework stability under these aggressive conditions requires maximal loading of PTA within the NU-1000 framework; materials with lower PTA loading lost structural integrity under the reaction conditions. Initial reaction rates over the NU-1000-supported catalyst were comparable to a control WO x-ZrO2, but the NU-1000 composite material was unusually active toward the transmethylation pathway that requires two adjacent active sites in a confined pore, as created when PTA is confined in NU-1000. This work shows the promise of metal-organic framework topologies in giving access to unique reactivity, even for aggressive reactions such as hydrocarbon isomerization.

Synthesis, Characterization and Catalytic Dehydration of Glycerol to Acrolein Over Phosphotungstic Acid Supported Y-Zeolite Catalysts

Vapour phase catalytic dehydration of glycerol to acrolein was studied over phosphotungstic acid (PTA) supported (with different loadings of PTA) on Y-zeolite catalysts. The active component PTA was varied between 10 and 40% w/w on the support Y-zeolite and was synthesized by the wet impregnation method. The physico-chemical characterization of the catalyst samples was investigated by X-ray diffraction (XRD), FT-IR, Raman and by the gas adsorption measurements. The XRD results showed that active component PTA is highly dispersed in an amorphous form at lower loadings of PTA and attained a crystalline state beyond 20 wt% of PTA. Both Raman and FT-IR spectra indicated that the Keggin ion structure of PTA was present in a highly dispersed state in the supported PTA/zeolite catalysts as compared to the bulk form of PTA. Temperature programmed desorption (TPD) of ammonia and FT-IR spectra of pyridine adsorption were used to determine the acidic properties of the PTA catalysts. The TPD of ammonia showed the presence of moderate acidity on the catalyst surface. The total acidity increased with raise in PTA loading up to 20 wt% and beyond this, it had decreased. The FT-IR results suggested the presence of Bronsted acidity. The Pore size increased with PTA loading until 20 wt%. Finally, the PTA/zeolite catalysts were tested for the gas phase dehydration of glycerol in a fixed-bed, micro-reactor in the temperature range between 250 and 300 °C. Among all the catalysts tested, PTA (20 wt%)/zeolite showed a total conversion of 100% glycerol and a selectivity of 79% for acrolein. These results are correlated with surface acidity, textural and structural properties of the PTA/zeolite catalysts. Glycerol dehydration products over Lewis and Bronsted acidic sites.

Hydroisomerization of n-Hexane Using Acidified Metal-Organic Framework and Platinum Nanoparticles.

Exceptionally high surface area and ordered nanopores of a metal-organic framework (MOF) are exploited to encapsulate and homogeneously disperse a considerable amount of phosphotungstic acid (PTA). When combined with platinum nanoparticles positioned on the external surface of the MOF, the construct shows a high catalytic activity for hydroisomerization of n-hexane, a reaction requiring hydrogenation/dehydrogenation and moderate to strong Brønsted acid sites. Characterization of the catalytic activity and acidic sites as a function of PTA loading demonstrates that both the concentration and strength of acidic sites are highest for the catalyst with the largest amount of PTA. The MOF construct containing 60% PTA by weight produces isoalkanes with 100% selectivity and 9-fold increased mass activity as compared to a more traditional aluminosilicate catalyst, further demonstrating the capacity of the MOF to contain a high concentration of active sites necessary for the isomerization reaction.

Supported phosphotungstic acid catalyst on mesoporous carbon with bimodal pores: A superior catalyst for Friedel-Crafts alkenylation of aromatics with phenylacetylene

Supported phosphotungstic acid (PTA) catalysts on diverse carriers containing the modified commercially available activated carbon (AC), classical mesoporous carbon via SBA-15 hard template method (CMK-3), and the mesoporous carbon with high surface area and bimodal pores through evaporation-induced tri-constituent co-assembly approach (MC) by using a facile wet impregnation method were employed as solid acid catalysts for Friedel-Crafts alkenylation of p-xylene with phenylacetylene. N2 adsorption–desorption, X-ray diffraction (XRD), and NH3 temperature-programmed desorption (NH3-TPD) characterization techniques were employed to reveal the structure-performance relationship. PTA/MC exhibits much superior catalytic performance to the previously reported PTA/AC, and even to PTA/CMK-3. The PTA/MC catalysts were optimized by varying the PTA loading, and the optimum PTA loading is 35%. The close to 100% of conversion towards phenylacetylene can be achieved in the presence of 2.67% of the 35% PTA/MC solid acid catalyst. It is also found that catalytic properties of the solid acids are strongly depended on acidic properties that affected by the textural properties of supports and PTA loading, as well as the accessibility of active sites affected by specific surface area and pore structure of catalyst. Moreover, the 35wt.% PTA/MC catalyst has demonstrated outstanding catalytic performance for the Friedel-Crafts alkenylation of diverse aromatics to their corresponding α-arylstyrenes.

Vapor Phase Dehydration of Glycerol to Acrolein Over Phosphotungstic Acid Catalyst Supported on Niobia

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 Keggin 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 Bronsted 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 remarkable 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.

Direct alkenylation of aromatics with phenylacetylene over supported H3PW12O40 catalysts as a clean and highly efficient approach to producing α-arylstyrenes

Phosphotungstic acid (PTA) catalysts supported on MCM-41 prepared via a wet impregnation method assisted by vacuum with heating (IMPVH) were first employed for direct alkenylation of different aromatics with phenylacetylene to synthesize α-arylstyrenes. N2 adsorption–desorption, FT-IR, X-ray diffraction (XRD), and NH3 temperature-programmed desorption (NH3 TPD) characterization techniques were used to reveal the relationship between the catalyst’s nature and properties. The results demonstrate that the fabricated 25wt.% PTA/MCM-41 catalyst exhibits outstanding catalytic performance, remarkably better than that on HY zeolite. It is also found that the catalytic properties of the catalysts are strongly dependent on PTA dispersity, the nature of the acid sites, the preservability of PTA Keggin structure, and the mesopore architecture, notably affected by PTA loading and calcination temperature. The results for catalytic stability illustrate that more than 99% of maximum conversion can be obtained, and more than 92% conversion can be maintained for up to 540min time on stream. We find that the decrease in catalytic activity, along with the long reaction time, is mainly ascribable to deactivation by coke deposition. The spent catalyst can be refreshed, and 97.1% conversion can be obtained over the regenerated catalyst. This approach is also highly efficient for extra-substituted benzene, polycyclic aromatics, and even heteroaromatics, suggesting that the method presented in this paper can be a green and highly efficient synthesis protocol for α-arylstyrenes.

Zirconia-supported phosphotungstic acid as catalyst for alkylation of phenol with benzyl alcohol

The liquid-phase alkylation of phenol with benzyl alcohol was carried out using zirconia-supported phosphotungstic acid (PTA) as catalyst. The catalysts with different PTA loadings (5–20 wt.% calcined at 750 °C) and calcination temperature (15 wt.% calcined from 650 to 850 °C) were prepared and characterized by 31P MAS NMR and FT-IR pyridine adsorption spectroscopy. The catalyst with optimum PTA loading (15%) and calcination temperature (750 °C) was prepared in different solvents. 31P MAS NMR spectra of the catalysts showed two types of phosphorous species, one is the Keggin unit and the other is the decomposition product of PTA and the relative amount of each depends on PTA loading, calcination temperature and the solvent used for the catalyst preparation. The catalysts with 15% PTA on zirconia calcined at 750 °C showed the highest Brönsted acidity. At 130 °C and phenol/benzyl alcohol molar ratio of 2 (time, 1 h), the most active catalyst, 15% PTA calcined at 750 °C gave 98% benzyl alcohol conversion with 83% benzyl phenol selectivity.