Solid Heteropolyacids Research Articles

Polydopamine-coated polyimide nanofiber to anchor HPW and construct the pocket-like composite membrane with excellent proton conductivity and stability

Solid heteropolyacids with high intrinsic proton conductivity, like phosphotungstic acid (HPW), were added to further enhance the proton conductivity of sulfonated poly ether ketone (SPEEK). The great solubility of solid acid within water, however, would produce a dramatic decline in stability and durability. In this study, we utilized polydopamine (PDA) coated polyimide (PI) nanofiber to form the acid-base pair between PDA@PI nanofiber and HPW/SPEEK to anchor the HPW. Additionally, a pocket was constructed in the sandwich-structure PDA@PI/SPEEK + HPW membrane to help better anchor the HPW. After 6 weeks of durability treatment during 60 °C and 100% RH, proton conductivity of PDA@PI/SPEEK + HPW-20 was 163.5 mS cm−1, which was only 23.0% lower than that of the initial state. By sharp contrast, it was 55.2% lower than the initial state for pristine SPEEK. And its swelling ratio is only 54% compared with 128% of pristine SPEEK under the same condition. We first revealed and investigated the acid-base pair created by PDA@PI and HPW/SPEEK, which was beneficial for proton conductivity and durability. This pocket-like PDA@PI/SPEEK + HPW membrane would inspire a wide application in PEM among excellent proton conductivity, better stability, with endurance.

Sequential Fractionation of Lignocellulosic Biomass Using CO2‐Assisted Hydrolysis Combined with γ‐Valerolactone Treatment

A biomass biorefinery strategy for the selective fractionation of poplar into its three main compositions (hemicellulose sugars, lignin, and high‐purity cellulose) with a two‐step process is developed. The first step consists of the selective hydrolysis of hemicellulose at mild conditions in a CO2/H2O system. This leads to various hemicellulose sugars and other intermediates in the water‐soluble fraction, with more than 87.90% of the hemicellulose being extracted from the original poplar (180 °C, 2.0 MPa CO2, 10 min). The pretreated sample is subsequently used for extracting lignin in a γ‐valerolactone (GVL)/H2O with acid catalysts for the next step. Meanwhile, four acid catalysts, including sulfuric acid and solid heteropoly acids (phosphomolybdic acid, silicotungstic acid, and phosphotungstic acid), are studied for the selective delignification in the GVL/H2O system, resulting in more than 91.35% of the original lignin being removed in the cellulose‐rich substrates (140 °C, 30 mM silicotungstic acid, 3 h). Overall, the biorefinery approach fractions the poplar wood into three primary components: 1) various oligosaccharides, monosaccharides, and other intermediates derived from hemicellulose; 2) cellulose‐rich substrate with a purity of cellulose as high as 90.76%, which has great potential as biochemicals or biomaterials; and 3) high‐purity and proportion lignin recovered from biomass.

A kinetic model for a single step biodiesel production from a high free fatty acid (FFA) biodiesel feedstock over a solid heteropolyacid catalyst

Production of biodiesel from yellow grease (waste cooking oil and waste animal fats) is fast emerging as a promising alternative to address the twin challenges before the biodiesel industry today-fluctuation in prices of vegetable oil and the food versus fuel debate. Yellow grease has a high percentage of free fatty acids (FFA) and proves to be an unsuitable feedstock for biodiesel production from commercially viable alkali-catalyzed production systems due to saponification problems.“Green” methodologies based on heterogeneous solid acid catalyzed reactions have the potential to simultaneously promote esterification and transesterification reactions of yellow grease to produce biodiesel without soap formation and offer easy catalyst separation without generation of toxic streams. This paper presents kinetic studies for the conversion of model yellow grease feeds to biodiesel using a heteropolyacid supported on alumina (HSiW/Al2O3) using a batch autoclave. Three model yellow grease feeds were prepared using canola oil with added FFA such as palmitic, oleic and linoleic acid. A pseudo homogeneous kinetic model for the parallel esterification and transesterification was developed. The rate constants and activation parameters for esterification and transesterification reactions for the model yellow grease feeds were determined. The rate constants for esterification are higher than the transesterification rate constants. The kinetic model was validated using the experimental biodiesel data obtained from processing a commercial yellow grease feed. The kinetic model could be used to design novel processes to convert various low-value waste oils, fats and non-food grade oils to sustainable biodiesel.

Alcohols dehydration in heterogeneous system – FTIR method development for quantitative determination of catalytic parameters

Quantification of the FTIR spectra makes it possible to monitor in situ the catalytic reactions in heterogeneous systems using a batch-mode microreactor. The tested catalysts included a series of solid heteropolyacids (HPAs): H3PW12O40, H3PMo12O40, H6P2W18O62 and H6P2Mo18O62 with Keggin and Wells-Dawson anion structures. The FTIR has been used to monitor the reaction progress in the alcohol dehydrations, by in situ detection of changes in composition of the gas phase over the catalyst surface. This procedure made it possible to evaluate both the degree of conversion and the yields of products as a function of time and temperature. The studied reactions included dehydrations of methanol and of 2-propanol, both processes relying on the catalyst’s acidity. In both the reactions, the HPAs performance turned out to compare well with their acidity determinations carried out by measuring their heats of the NH3 sorption with the gas flow-through microcalorimetry. In case of the 2-propanol dehydration, the catalytic performance of the HPAs in this reaction has also been tested using a more typical setup of the flow-through mode microreactor, combined the gas chromatograph for down-stream detection, and the results have been compared to the batch-mode results for the process. A qualitative agreement between the two microreactor techniques has been found.

Ethylene Conversion over Catalysts Based on Solid Superacids and Heteropoly Acids

Catalytic properties of solid superacids (WO3/ZrO2 and SO4/ZrO2), and monolith and H-Beta zeolite-supported phosphotungstic heteropoly acid in gas-phase alkylation of benzene with ethylene to ethylbenzene and in the side reaction of ethylene oligomerization are studied. It was found that H-Beta zeolite had the highest activity and selectivity to ethylbenzene. The use of solid superacid (WO3/ZrO2) was shown to be more efficient in low-temperature oligomerization of ethylene.

Flower-like WO3/CoWO4/Co nanostructures as high performance anode for lithium ion batteries

The uniformly flower-like WO3/CoWO4/Co nanostructures were synthesized via a facile one-step hydrothermal reaction with solid heteropolyacid of W and Co as precursors and followed by heating process and calcination under the air condition. The as-prepared WO3/CoWO4/Co composite showed a high discharge capacity of 1104 mAhg−1 after 40 cycles at 100 mAg−1, and delivered excellent rate performance of 1074, 685, 509, 335 mAhg−1 at 200,400,800,1600 mAg−1, respectively. The excellent electrochemical performance of WO3/CoWO4/Co nanostructures is attributed to the uniform dispersion of discrete nanoparticles, and it also can be highly optimized by the freestanding combination of Co-doped tungsten trioxide and cobalt tungstate, which helps to provide high specific capacity, high rate cycling and stable life performance.

Biodiesel production from Mucor circinelloides using ethanol and heteropolyacid in one and two-step transesterification

Biodiesel production from Mucor circinelloides biomass was investigated by conventional method involving the lipid extraction using ethanol followed by transesterification (two-step process) in comparison with directly producing from the whole biomass without extraction (one-step process). Both processes used solid heteropolyacid catalyst (12-molybdophosphoric acid (H3PMo12O40) support on alumina (Al2O3) under conditions previously set up (200°C for 4h). Either one or two-step process was able to convert the microbial lipids into ethyl esters (FAEE) with high yields (97%), though the former simplifies the production process due to the elimination of an oil extraction step that incurs oil loss. Moreover, to minimize the energy used for dewatering, this method can be also used for transesterification of wet M. circinelloides biomass. Direct transesterification of wet biomass greatly simplifies the process of FAEE production by eliminating the drying and oil extraction steps, making this a renewable and environmental friendly process.

Kinetic Study on Catalytic Conversion of Glycerol to Renewable Acrolein

Biodiesel is a suitable alternative to gasoline and diesel since it emits less carbon emission. There has been a surplus of glycerol in the market due to biodiesel production. Glycerol may be a good source of bio-based feed since it is from a renewable source. The kinetic study of gas-phase glycerol dehydration reaction using a supported ?-Al2O3 nanoparticle based solid heteropoly acid catalyst (SiW20-Al/Zr10) has been investigated. A kinetic model was established, based on the reaction mechanism, taking into account two parallel reactions of glycerol degradation into acrolein or acetol. All the reaction rate constants and activation energies were determined at various reaction temperatures (280 – 340 °C). The first-order kinetic model and the experimental data fitted-well. Results revealed that all the rate constants increased with temperature, and the activation energies of glycerol dehydration to acrolein and acetol were 46.0 and 53.3 kJ/mol. The results from this study are useful for simulation and process modelling of a bio-refinery for sustainable production of bio- based chemicals.

A new synthetic route for compounds prepared from Keggin heteropolyacids and pyridine derivatives

The synthesis of inorganic/organic hybrid compounds by solid–solid reactions of the hydrated heteropolyacids H3[PM12O40]·nH2O (M=Mo, W) with selected substituted pyridines having different sizes and functionalities is described. Several new compounds were prepared at room temperature and characterised by infrared and UV–Vis absorption spectroscopies, powder X-ray diffraction and analytical techniques. Related materials prepared by precipitation from solution were also studied and the comparison was made between results obtained with the different preparative procedures. This is the first systematic account on the acid–base reaction of solid heteropolyacids and solid pyridine derivatives, without the addition of any solvent. The obtained results indicate that the obtained crystalline powders may present physical properties different from related materials prepared by precipitation from solution.

Selective hydrolysis of cellulose for the preparation of microcrystalline cellulose by phosphotungstic acid

Microcrystalline cellulose (MCC), prepared from natural cellulose through acid hydrolysis, has been widely used in the food, chemical and pharmaceutical industries because of its high degree of crystallinity, small particle size and other characteristics. Being different from conventional mineral acids, phosphotungstic acid (H3PW12O40, HPW) was explored for hydrolyzing cellulose selectively for the preparation of MCC in this study. Various reaction parameters, such as the acid concentration, reaction time, temperature and solid-liquid ratio, were optimized. Rod-like MCC was obtained with a high yield of 93.62 % and also exhibited higher crystallinity and narrower particle diameter distribution (76.37 %, 13.77–26.17 μm) compared with the raw material (56.47 %, 32.41–49.74 μm) at 90 °C for 2 h with 58 % (w/w) HPW catalyst and a solid-liquid radio of 1:40. Furthermore, HPW can easily be extracted and recycled with diethyl ether for four runs without affecting the quality of the MCC products. The technology of protecting the crystalline region while selectively hydrolyzing the amorphous region of cellulose as much as possible by using HPW is of great significance. Due to the strong Bronsted acid sites and highest activity in solid heteropoly acid, the use of effective homogeneous HPW may offer an eco-friendly and sustainable way to selectively convert fiber resources into chemicals in the future.

Characterization and Dynamics of the Different Protonic Species in Hydrated 12-Tungstophosphoric Acid Studied by2H NMR

Solid heteropolyacids (HPAs) are promising nonpolluting superacids used as catalysts and solid proton conductors. The catalytic and conducting properties of HPAs are very sensitive to the amount of hydration water present in the system, as water molecules tend to interact with the HPA acid protons to form [H3O]+ and [H5O2]+ ions. These ions constitute active species that govern the catalytic reaction pathways and the proton migration mechanism. Establishing the structure and mobility of protonic species could yield important information concerning the functions of material based on HPA hydrates. In this work, we have performed the analysis of both 2H NMR line shape and the evolution of T1, T2 relaxation with temperature for the deuterated analogue of the solid 12-tungstophosphoric acid (TPA × nH2O) at different hydration levels (0 < n < 6) in the wide temperature range of 103–503 K. This allowed us to characterize in detail the mobility of different protonic species, including acidic OH groups, water molecules, and hydroxonium ions. Kinetic parameters of internal and diffusional motions for different protonic species at different hydration levels n of TPA × nH2O were derived.

Esterification of 2-keto-l-gulonic acid catalyzed by a solid heteropoly acid

The efficacy of a potassium 12-phosphotungstate (KPW) catalyst in the synthesis of methyl 2-keto-L-gulonat from 2-keto-L-gulonic acid (2-KLGA) and methanol is investigated. The KPW catalyst gives high yields in short reaction times. The present procedure represents a clean, efficient, practical, simple, mild, time-saving and eco-friendly method for the synthesis of methyl 2-keto-L-gulonat. The KPW catalyst is found to be a truly heterogeneous catalyst, highly efficient and reusable in the synthesis of methyl 2-keto-L-gulonat.

Selective Synthesis of Glycerol Monoester with Heteropoly Acid as a New Catalyst

In this work, we were study the selective synthesis of GME from oleic acid and glycerol using two types of solid heteropoly acid catalysts, namely silicotungstic acid bulk (STAB) and STA-silica sol gel (STA-SG). The performance and selectivity of STAB and STA-SG in the esterification reaction have been investigated and compared to the sulphuric acid (H2SO4) as conventional homogeneous catalyst. The catalysts were then characterized their physical and chemical properties using BET, XRD, TEM and XPS. XPS analyses were shown a significant formation of W-O-Si, W-O-W and Si-O-Si bonding in STA-SG compared to that in STAB. The main spectra of O1s (90.74 %, 531.5 eV) followed by other O1s peak (9.26 %, 532.8 eV) were due to the presence of W-O-W and W-O-Si bonds, respectively. The STA-SG catalyst was found to be the more environmentally benign solid acid catalyst for the esterification reaction between oleic acid and glycerol due to its lower toxicity in terms of the relatively lower pH value (pH 3.7) than the STAB (pH 2.8). In addition, the ease of separation for STA-SG catalyst was attributed to its insoluble state in the product phase. The esterification products were then analysed by FTIR and HPLC. Both the H2SO4 and the STAB gave high conversion of 100 % and 98 %, but at a lower selectivity of GME with 81.6% and 89.9%, respectively. On the contrary, the STA-SG enabled a conversion of 94 %, but with a significantly higher GME selectivity of 95 % rendering it the more efficient solid acid catalyst.

Continuous production of biodiesel from waste cooking oil in a reactive distillation column catalyzed by solid heteropolyacid: Optimization using response surface methodology (RSM)

This study aims to develop an optimal continuous process to produce fatty acid methyl esters (biodiesel) from waste cooking oil in a reactive distillation column catalyzed by a heteropolyacid, H3PW12O40·6H2O. The conventional production of biodiesel in the batch reactor has some disadvantage such as excessive alcohol demand, short catalyst life and high production cost. Reactive distillation combines reaction and separation to simplify the process operation. The reaction catalyzed by H3PW12O40·6H2O overcomes the neutralization problem that occurs in conventional transesterification of waste cooking oil with high free fatty acid (FFAs) and water content. Response surface methodology (RSM) based on central composite design (CCD) was used to design the experiment and analyzed four operating parameters: total feed flow, feed temperature, reboiler duty and methanol/oil ratio. The optimum conditions were determined to be 116.23 (mol/h) total feed flow, 29.9°C feed temperature, 1.3kW reboiler duty, and 67.9 methanol/oil ratio. The optimum and actual free fatty acid methyl ester (FAME) yield was 93.98% and 93.94%, respectively, which demonstrates that RSM is an accurate method for the current procedure.

Synthesis and Characterization of Silicotungstic Acid Nanoparticles via Sol Gel Technique as a Catalyst in Esterification Reaction

Glycerol monooleate (GMO) as an esterification product of oleic acid and glycerol is highly potential as an anti-friction substance in the engine lubricant. The purpose of this work is to study the synthesis, characterization and catalytic performance of solid heteropoly acid catalysts, namely silicotungstic acid bulk (STAB) and STA-silica sol gel (STA-SG). The activity and selectivity of STAB and STA-SG in the esterification reaction have been investigated and compared to the homogeneous catalyst i.e. sulphuric acid (H2SO4). The synthesized catalysts were characterized by BET, XRD, TEM, XPS and TPD-NH3. BET analyses shown that the STA-SG catalyst is very high in surface area compared to STAB of 460.11 m2/g and 0.98 m2/g, respectively. From the XPS analyses, there was a significant formation of W-O-Si, W-O-W and Si-O-Si bonding in STA-SG compared to that in STAB. The main species of O1s (90.74 %, 531.5 eV) followed by other O1s peak (9.26 %, 532.8 eV) were due to the presence of W-O-W and W-O-Si bonds, respectively. In addition, the ease of separation for STA-SG catalyst was attributed to its insoluble state in the product phase. The esterification products were then analysed by FTIR and HPLC. Both the H2SO4 and the STAB gave high conversion of 100% and 98%, while lower selectivity of GME with 81.6% and 89.9%, respectively. On the contrary, the STA-SG enabled a conversion of 94%, while significantly higher GME selectivity of 95% rendering it the more efficient solid acid catalyst.

Conversion of fructose and glucose into 5-hydroxymethylfurfural catalyzed by a solid heteropolyacid salt

Abstract A solid heteropolyacid salt Ag3PW12O40 has been used as a heterogeneous catalyst for the production of 5-hydroxymethylfurfural (HMF) from fructose and glucose. The fructose was selectively dehydrated into HMF with the HMF yield as high as 77.7% and selectivity of 93.8% within 60 min at 120 °C. In addition, Ag3PW12O40 also exhibited catalytic activity for conversion of glucose into HMF. Moreover, the catalyst is tolerant to high concentration feedstock and can be recycled. The results illustrate that the Ag3PW12O40 is an excellent acid and environmentally benign solid catalyst for the production of HMF from fructose and glucose.

High selective production of 5-hydroymethylfurfural from fructose by a solid heteropolyacid catalyst

A clean, facile, economical, and environmental friendly method for converting fructose into 5-hydroymethylfurfural (HMF) has been developed, in the presence of a solid heteropolyacid Cs2.5H0.5PW12O40 catalyst in a biphasic system. A 5-HMF yield of 74.0% and a higher selectivity of 94.7% were obtained in 60min at 388K. More importance is that this catalyst is tolerant to high concentration feedstocks (50wt.% fructose) and it can be recycled.

Synthesis, Characterization and Catalytic Performance ofH3SiW12O40/SiO2Prepared by Sol-Gel Technique

The purpose of this work is to study the synthesis, characterization, and catalytic performance of two types of solid heteropoly acid catalysts, namely, silicotungstic acid bulk (STAB) and STA-silica sol-gel (STA-SG) compared with sulfuric acid. From the XPS analyses, there was a significant formation of W-O-Si, W-O-W, and Si-O-Si bonding in STA-SG compared to that in STAB. The main spectra of O1s (90.74%, 531.5 eV) followed by other O1s peak (9.26%, 532.8 eV) were due to the presence of W-O-W and W-O-Si bonds, respectively. The STA-SG catalyst was found to be the more environmentally benign solid acid catalyst for the esterification reaction between oleic acid and glycerol due to its lower toxicity supported by silica via sol-gel technique. In addition, the ease of separation for STA-SG catalyst was attributed to its insoluble state in the product phase. The esterification products were then analysed by FTIR and HPLC. Both the H2SO4and the STAB gave high conversion of 100% and 98% but at a lower selectivity of GME with 81.6% and 89.9%, respectively. On the contrary, the STA-SG enabled a conversion of 94% but with a significantly higher GME selectivity of 95%, rendering it the more efficient solid acid catalyst.

α-Pinene isomerisation over heteropoly acid catalysts in the gas-phase

The isomerisation of α-pinene was studied in the gas phase over solid heteropoly acid (HPA) catalysts in a fixed-bed continuous flow reactor at 200 °C and ambient pressure. The catalysts included bulk and SiO 2-supported H 3PW 12O 40 and bulk Cs 2.5H 0.5PW 12O 40 possessing strong Brønsted acid sites, as well as composites prepared by supporting 15 wt% H 3PW 12O 40 on Nb 2O 5, ZrO 2 and TiO 2 possessing both Brønsted and Lewis acid sites of moderate strength. The reaction yielded camphene as the main product in a mixture with monoterpene by-products such as limonene, terpinolenes, terpinenes, β-pinene, p-cymene and others. The HPA catalysts with strong Brønsted acid sites exhibited high initial activities, but suffered from catalyst deactivation, resulting in low camphene yields. Conversely, the HPA catalysts supported on Nb 2O 5, ZrO 2 and TiO 2, although weaker acids, showed more stable performance in α-pinene isomerisation. The HPA catalyst supported on TiO 2 gave a camphene yield of 51% and a total camphene and limonene yield of 58%.

ChemInform Abstract: Characterization of Surface Active Sites of Catalysts with High- Resolution Solid-State NMR

Abstract Results obtained in studies of the surface active sites of heterogeneous catalysts by use of high-resolution solid-state NMR are presented. The 1 H NMR MAS (magic angle spinning) data on chemical shifts of surface OH groups and their interaction with the supported catalytically active complexes are discussed. The relation between the 1 H chemical shift values of OH groups, on the one hand, and characteristics of their acid strength, such as the proton affinity PA OH of the acid residue formed on heterolytic dissociation of the OH groups, on the other hand, is presented. Changes in the intensity of 1 H NMR lines for OH groups of commonly used supports (Al 2 O 3 , TiO 2 , SiO 2 etc.) on interaction with supported oxides suggest the selective interaction of surface OH groups with supported complexes. For the solid heteropolyacid H 3 PW 12 O 40 (HPA) supported on SiO 2 , the binding of the HPA molecule with the SiO 2 surface is most probably multicentred and results in the formation of supported species with different proton structures. Studies of 1 H NMR MAS spectra of zirconium hydrides supported on SiO 2 have revealed the formation of four types of zirconium hydride complex. Solid-state high-resolution 1 H NMR spectra of H 2 S adsorbed on Al 2 O 3 modified with KOH, K 2 CO 3 and HF and on zeolites NaX, NaY and H-ZSM indicate dissociative adsorption of H 2 S which occurs on the coordinatively unsaturated aluminium sites and Na + cations in zeolite cavities. The 1 H and 13 C NMR spectra indicate that adsorbed CH 3 OH reacts more readily with SH − species than with H 2 S adsorbed in the molecular form. Also presented are results of studies on Lewis acid sites in Al 2 O 3 , and zeolites Y and ZSM-5 using the NMR ( 1 H, 13 C and 15 N) of weak adsorbed bases. The formation of Lewis acid sites in HY zeolites during their hydrothermal treatment has been studied by 15 N NMR of adsorbed N 2 O. The strongest Lewis sites are the isolated or weakly associated extralattice Al atoms. The 1 H, 13 C and 15 N NMR chemical shifts of CH 4 , N 2 and N 2 O molecules, as well as 1 H and 15 N relaxation rates of CH 4 and N 2 O adsorbed on a series of HY and H-ZSM zeolites, SiO 2 and Al 2 O 3 , containing controlled amounts of iron impurities, show that unlike SiO 2 , γ-Al 2 O 3 and HY zeolites, the H-ZSM-5 zeolites have strong electron-accepting sites formed by Fe 3+ and probably Al 3+ cations. The possible structure of these sites and the geometry of complexes formed during N 2 O and CH 4 adsorption are discussed. In the final section the results obtained with 109 Ag NMR of supported silver catalysts are presented. The potential of 109 Ag NMR for studying catalysts of this type is discussed.