Heteropolyacid Catalysts Research Articles

Electrospun Pt-TiO2 nanofibers Doped with HPA for Catalytic Hydrodeoxygenation

Electrospinning is utilized to fabricate catalytic nanofiber scaffold for biocrude upgrading in hydrodeoxygenation (HDO) following computational studies suggesting the need for nano-catalysts for efficient HDO conversion and selectivity. Here, Pt-TiO2 nanofibers are fabricated through electrospinning, followed by wet impregnation with a heteropoly acid (HPA), tungstosilicic acid. Intensive heat treatments were incorporated during and after processes to obtain a HPA doped Pt-TiO2 nano-catalyst. Catalytic HDO was performed in a batch reactor with phenol as the raw biocrude dissolved in hexadecane. The HPA doped Pt-TiO2 catalyst demonstrated promising HDO performance of 37.2% conversion and a 78.9% selectivity to oxygen free benzene and the remainder 21.1% as diphenyl ester as a result of esterification by acidic components of the catalyst. Additionally, BET surface area characterization show a low surface area 16.9 m2 g−1 significantly lower than existing commercial catalysts and a mesoporous nature suitable for selectivity. The presence of HPA on the anatase nanofiber compensated for low platinum nanoparticles crystallinity on the nanofibers. This work might create needed alternatives for preparing HDO catalysts for efficient aromatics production.

Sustainable production of organic acids from chitin biomass catalyzed by Keggin-type heteropolyacid under hydrothermal condition

The “shell biorefinery,” which valorizes the shell waste chitin into fine chemicals, has developed rapidly in recent years. Herein, we present a novel base-free heteropolyacid-catalyzed oxidation method for the transformation of chitin biomass into organic acid. After a series of optimization experiments, a 5.93 % yield of formic acid and 25.09 % yield of acetic acid were achieved in the presence of 0.5 equivalent of Mo-V-P heteropolyacids (H4PMo11VO40·2H2O) and air at 180 °C under hydrothermal conditions for 4 h. Meanwhile, we have demonstrated that the Keggin-type heteropolyacid catalysts are capable of efficiently converting microcrystalline chitin into organic acids. The synthesized heteropolyacids are well characterized with FT-IR, XRD, ICP-AES, and TGA. The possible reaction pathway was speculated accordingly. This method offers several advantages, including readily available raw materials, simple operation, and relatively higher yield.

Direct application of tungstosilicic acid hydrate for the treatment of high free fatty acid in acidic crude palm oil and for biodiesel production

AbstractThis study explored the use of industrial acidic crude palm oil (ACPO) for biodiesel production, facing a significant obstacle due to its high free fatty acid (FFA) content, which complicates the biodiesel production process. Typically, esterification is employed to convert FFAs into fatty acid methyl ester (FAME). Herein, the effectiveness of tungstosilicic acid hydrate (TSAH) as an unsupported heteropoly acid (HPA) catalyst for FFA esterification in ACPO was investigated. The FFA content was reduced from 8.43% to 0.95% under optimum conditions (4 wt% catalyst dosage, a methanol to oil molar ratio of 10:1, 150 min and a temperature of 60°C). Noteworthy, the TSAH catalyst showed stability over 7 cycles. The kinetic analysis revealed that the FFA esterification process closely followed pseudo first‐order kinetics, with an R2 value of 0.94. Furthermore, the biodiesel produced from TSAH‐treated ACPO meets the standard specifications outlined by ASTM D6751 and EN 14214. This research highlights the effectiveness of TSAH in catalyzing FFA esterification without the need for additional support materials or modifications.

Biodiesel Production from Edible Oil Using Heteropoly Acid Catalysts at Room Temperature

Edible oils are one of the renewable sources that enable the possibility of producing biodiesel sustainably. The transesterification of canola oil with methanol using cesium-modified phosphotungstic acid (Cs2.5H0.5PW12O40) as a heterogeneous catalyst was studied. Reaction conditions, specifically reaction time, catalyst loading, and the ratio of methanol to canola oil, were systematically explored. The canola oil conversion reached 55% at room temperature after 24 h. The reusability tests showed that the conversion of canola oil to biodiesel was maintained.

Phosphomolybdic Acid‐Catalyzed One‐Pot Multicomponent Synthesis of 1,2,5,6‐Tetrahydropyridine Derivatives

AbstractWe report the synthesis of alkyl 1,2,6‐triaryl‐4‐arylaminopiperidine‐3‐ene‐3‐carboxylates in acceptable yields (42%–71%) and high trans‐diastereoselectivity (69:31 to 100:0) through a one‐pot multicomponent reaction of aromatic aldehydes, aromatic amines, and β‐ketoesters catalyzed by phosphomolybdic acid in methanol at room temperature. The structure and stereochemistry of tetrahydropyridines were confirmed by X‐ray crystallography. This protocol stands out for its operational simplicity, the use of an inexpensive and commercially available heteropolyacid catalyst, low catalyst loading, and purification via simple filtration, resulting in acceptable yields and high diastereoselectivity.

One Pot Synthesis of Phosphomolybdenate Based Hybrids for Efficient Oxidative Desulfurization

With increasing stringent standard of sulfur content in fuels, there is a growing need for high-efficiency deep desulfurization to meet ecological and environmental demands. Herein, a series of heteropolyacid catalysts with phosphomolybdic acid base melamine (MHPMo-n) were synthesized by one-pot method and applied to oxidative desulfurization. Further, the optimum conditions for desulfurizations could be explored, which the desulfurization rate of the catalyst could reach 100% within 60 min under the conditions of m(catalyst)= 0.01 g, T = 40 °C, O/S = 3. Furthermore, the catalyst demonstrated excellent catalytic efficiency during the five cycles. One-pot method of phosphomolybdic acid base melamine provides a new idea for the synthesis of catalysts with outstanding catalytic properties for oxidative desulfurization (ODS).

Processing and Recovery of Heavy Crude Oil Using an HPA-Ni Catalyst and Natural Gas.

To maintain economic profitability and stabilize fuel prices, refineries actively explore alternatives for efficiently processing (extra) heavy crude oils. These oils are challenging to process due to their complex composition, which includes significant quantities of asphaltenes, resins, and sulfur and nitrogen heteroatoms. A critical initial step in upgrading these oils is the hydrogenation of polyaromatic compounds, requiring substantial hydrogen sources. Methane from natural gas streams is known to act as an effective hydrogen donor. This study investigates the use of a heteropolyacid (HPA) catalyst modified with nickel and methane to enhance the quality of heavy crude oil with an initial 8.0°API (at 15.5 °C) and 2200 cSt viscosity (at 37.5 °C). After treatment in a batch reactor at 380 °C and 4.4 MPa for 2 h, the oil properties markedly improved: API gravity increased from 8.0 to 16.0 (at 15.5 °C), and kinematic viscosity reduced from 2200 to 125 cSt (at 37.5 °C). Additionally, there was a significant decrease in asphaltenes (from 38.7 to 16.4% by weight), sulfur (from 5.9 to 4.0% by weight), and nitrogen (from 971 to 695 ppm). This was accompanied by an increase in the volume of light distillates from 1.3 to 4.9%, and middle distillates from 8.8 to 21.0%. These results suggest that nickel-modified HPA catalysts, combined with methane as a hydrogen donor, are a promising option for upgrading heavy crude oils.

Humin‐free synthesis of levulinic acid from fructose using heteropolyacid catalysts

AbstractLevulinic acid (LA) is one of the top bio‐based platform molecules that can be converted into many valuable chemicals. Herein, we report the sustainable synthesis of LA acid from various sugars using heteropolyacid catalysts. By using a Box–Behnken design of experiment, both LA yield (up to 69 mol%) and complete suppression of parasitic humin formation could be achieved within a 5 h reaction time at 140°C using fructose as a substrate. The effects of various reaction parameters like temperature, sugar concentration, addition of organic co‐solvent and reaction time on LA yield and humin formation were examined in a three‐dimensional space. Moreover, the results could be successfully transferred to other sugars like glucose or cellobiose, paving the way for an atom‐efficient and sustainable LA synthesis process.

Furfural and Levulinic Acid: Synthesis of Platform Molecules from Keggin Heteropolyacid-Catalyzed Biomass Conversion Reactions

Among the different polyoxometalate compounds, Keggin heteropolyacids have been extensively used as catalysts in several acid-catalyzed reactions, due to their strong strength of Bronsted acidity. These metal–oxygen clusters have a highly versatile structure that allows their conversion to derivatives, which are catalysts that are much more efficient than their precursors, with a greater catalytic activity in a plethora of reactions of industrial interest. Particularly, due to the inevitable exhaustion of fossil sources, reactions to valorize biomass have attracted significant attention, since it is a precious renewable raw material that can provide fine chemicals or fuels, minimizing our dependence on petroproducts. Biorefinery processes can produce platform molecules to achieve this goal. In this review, the recent advances achieved in the development of routes to converting biomass feedstocks to levulinic acid and furfural, which are valuable ingredients in biorefinery processes, using Keggin heteropolyacid catalysts were assessed.

Direct Amide Formation via Carbamoylation of Aromatic Bromides using Heteropoly Acid and UV‐Light

AbstractWe performed direct carbamoylation using heteropoly acid (HPA) photocatalysts with a Keggin structure under UV‐light. Carbamoyl radicals were generated via the decarboxylation of N,N‐disubstituted dimethyloxamic acid under these conditions. The HPA catalyst functioned as a photocatalyst when the dicarbonyl bond was broken, generating carbon dioxide. We found that disubstituted carbamoyl radicals readily coupled with aromatic bromides to generate diverse benzoic amides. In particular, using a homogeneous HPA photocatalyst improved the reaction's transmittance, which had been a problem of the existing heterogeneous photocatalyst. This reaction condition can be easily handled, mild, and safer than the traditional benzoic amide synthesis. This method can be scaled up efficiently, is eco‐friendly, and can be applied to producing active pharmaceutical ingredients.

Tungstoborate heteropolyacid-catalyzed lignin liquefaction: Product yield and component distribution

Tungstoborate heteropolyacid catalysts have good catalytic degradation performance, especially for selective cleavage of C–C bonds in biomass. In this paper, the product yield and component distribution of tungstoborate heteropolyacid (BW12)-catalyzed lignin liquefaction were investigated at different parameters, including temperatures (120, 140, 160, 180, and 200 °C), catalyst amount (0, 2.5, 5, 10, and 20 wt. %), and reaction time (0, 30, 60, 90, and 120 min). It was found that a higher conversion (72.16 wt. %) and bio-oil yield (68.41 wt. %) could be obtained under suitable reaction conditions (180 °C, 60 min, 5 wt. %). Bio-oil analysis showed that the BW12 catalyst had a significant effect on the distribution of bio-oil fractions, in which mono-aromatic components increased from 32.96% to 47.56% compared to those without the catalyst. In particular, carbonyl substances in the mono-aromatic components increased from 18.66% to 26.97%. Spectroscopic analysis (FT-IR) found that the absorption peaks of C–O and C–C bonds in the liquefied residue catalyzed by BW12 decreased compared to the raw lignin. Moreover, the mechanism of BW12-catalyzed lignin depolymerization was investigated by DFT simulations. The simulation results demonstrated that the shortening of Cα–O bond, the breaking of Cβ–Cγ and Cα–Cβ bonds in lignin promoted the formation of vanillin and benzaldehyde, 3-hydroxy-4-methoxy. Finally, based on the experimental data and simulation results, a possible reaction pathway for the BW12-catalyzed liquefaction of lignin into mono-aromatic substances was proposed.

One-pot synthesis of acrylic acid from glycerol over SBA-15 supported heteropoly acid catalysts: Influence of mesoporosity and acidity

Heteropoly acids (HPAs) of the Keggin type exhibit substantial Brønsted acidity and are commonly utilized as acid catalysts, particularly in acrylic acid synthesis via glycerol oxydehydration. The primary goal of this research is to comprehensively assess the morphological and physicochemical properties of SBA-15 supported HPAs (H4SiW12O40.xH2O, H3PW12O40.xH2O, and H3PMo12O40.xH2O). The synthesized catalysts were characterized via physisorption analysis, XRD, SEM, FT-IR, NH3-TPD, and H2-TPR. Furthermore, the catalyst's catalytic activity in acrylic acid synthesis via single-step liquid phase glycerol oxydehydration was evaluated by correlating its characteristics with glycerol conversion and acrylic acid yields. The PW/SBA-15 catalyst exhibited the best performance, with the highest acrylic acid yield reaching 17.5% at 87.8% glycerol conversion. Given that the partial oxidation of acrolein to acrylic acid necessitates an optimal level of redox properties, the superior performance of PW/SBA-15 was characterized by high acid sites and moderate oxidative capabilities.

N-Sulfonyl-1,2,3,4-tetrahydroisoquinoline Derivatives: Synthesis, Antimicrobial Evaluations, and Theoretical Insights.

Microbial contamination remains a significant economic challenge in the food industry, emphasizing the need for innovative antimicrobial solutions. In this study, we synthesized N-sulfonyl-1,2,3,4-tetrahydroisoquinolines (NSTHIQ) derivatives using an environmentally friendly Preyssler heteropolyacid catalyst, obtaining moderate to high yields (35-91 %) under mild conditions. Two derivatives (5 and 6) exhibited significant antifungal properties against various fungal species, including Aspergillus spp, Penicillium spp, and Botrytis cinerea. ADMET (Absorption, Distribution, Metabolism, Excretion, and Toxicity) analysis revealed the absence of hepatic toxicity in all compounds, making derivatives 2, 3, 4, and 5 potential candidates for further development. However, derivatives 6 and 7 exhibited immunotoxicity. In support of our experimental findings, reactivity indices were computed using Density Functional Theory principles, deriving valuable insights into the chemical properties of these derivatives. This study underscores the potential of NSTHIQ compounds as potent antifungal agents, coupled with the importance of employing environmentally friendly catalysts in drug discovery.

Polydopamine modified heteropolyacids catalyst for methacrolein oxidation: Organic ammonia functionalized and regulation of morphology

The oxidation of methacrolein (MAL) to methacrylic acid (MAA) catalyzed by Keggin-type phosphomolybdovanadic acid catalyst belongs to the acid-catalyzed and oxygen-catalyzed co-promoted reactions. It is a challenge to design catalysts with suitable acidity and redox properties. In this paper, a strategy using organic ammonia to modify CsH3PMo11VO40 (CsPAV) was proposed. Core-shell polymerization precursors were synthesized by using polydopamine (PDA) microspheres as modifiers and templates, and regularly arranged PDA-CsPAV bowl-shaped catalysts were obtained via one-step calcination. The morphology, structure, thermal stability, acidity and redox properties of PDA-CsPAV catalysts were characterized by XRD, FT-IR, TG-DTA, XPS, SEM, H2-TPR and NH3-TPD, and the catalytic performance was evaluated by oxidation of MAL to MAA. The rich functional groups on the surface of PDA microspheres combine with H4PMo11VO40 (HPAV) through strong coordination bonds to form a catalyst film. The uniform spherical structure of PDA can adjust the dispersion and morphology of CsPAV. NH4+ was formed and rearranged with heteropoly anions during calcination, which positively regulated the acidity and redox property of the catalyst. The addition of PDA accelerated electron transfer and strengthened the self-reduction process of HPAV. Compared with CsPAV, PDA-CsPAV has more acid sites and oxidation catalytic active centers (VO2+), thus exhibiting better MAL oxidation performance and good thermal stability.

Theoretical aspects investigation of the structure of phosphormolybdenum heteropoly acid catalysts for the oxidation of methacrolein to methacrylic acid

Theoretical aspects investigation of the structure of phosphormolybdenum heteropoly acid catalysts for the oxidation of methacrolein to methacrylic acid

Indium exchanged heteropoly tungstates: Efficient catalysts for the synthesis of glycerol carbonate from glycerol and urea

In this study, heteropoly tungstate protons were exchanged with various amounts of indium to impart Lewis acidity in Keggin heteropoly acid catalysts. The synthesis of glycerol carbonate from urea and glycerol was investigated using the synthesized InxTPA catalysts. The prepared catalysts were characterized by Fourier transforms infrared (FTIR), X-ray diffraction (XRD), Laser Raman, and temperature programmed desorption of ammonia studies. The obtained characterization results confirmed that the existence of Keggin ion structure of heteropoly acid after modification with indium ions. The modification of heteropoly tungstate with transition metal ions was found to improve its acidity and the stability of heteropoly acids (HPAs). The presence of Lewis acidic sites associated with the indium ions present in the catalyst was indicated by pyridine adsorbed FT-IR spectra. The amount of indium ions in heteropoly tungstate had an impact on the catalysts acidity, which in turn affected the activity of catalyst. The partially exchanged In0.66TPA catalyst demonstrated 69.4% glycerol conversion with 98.8% selectivity to glycerol carbonate. The study also investigated the impact of various reaction parameters such as reaction time, mole ratio of glycerol to urea, reaction temperature, and catalyst concentration and established the optimum reaction conditions.

Heteropoly acid-catalyzed β-caryophyllene chemical transformations: Synthesis route of value-added commercial products from components found in biorenewable resources

More sustainable catalytic processes applied to different reactions for of biorenewable derivatives production is an important trend in chemical industry, which constantly needs to update its processes for obtaining inputs not produced in sufficient quantity by nature, or with superior physicochemical properties to those of compounds acquaintances. This work reports the chemical transformation of β-caryophyllene, a sesquiterpene present in biorenewable materials, using the commercial heteropoly acid catalyst H3PW12O40. The process performed under conditions technologically and environmentally attractive, using less harmful ketone solvents (2-butanone and acetone). The products obtained were (-)-clovene, β-caryolanol and β-clovanol, at total yield 70–80%, by isomerization reaction associated with hydration reactions. All these products have known applications in different sectors of the fine chemicals industry, whether in isolated forms or as mixtures. (-)-Clovene and β-caryolanol have significantly higher commercial value, compared to β-caryophyllene. There are known applications for β-clovanol, although the compound has not yet been commercialized, making the process described here attractive for its production on an industrial scale. H3PW12O40 showed catalytic performance superior to H2SO4, a conventional mineral acid catalyst.

Solid acid catalysts comprising heteropoly acids supported on SiO2, TiO2 and ZrO2: A microcalorimetric investigation of catalyst acidity and new insight into the mechanism of alcohol dehydration over HPA

Keggin-type heteropoly acids (HPAs) have strong Brønsted acidity and are widely used as acid catalysts. The aim of this work is the systematic characterisation of the acid strength of HPA catalysts comprising H3PW12O40 and H4SiW12O40 supported on SiO2, TiO2 and ZrO2 with 10–100% HPA loading and testing their activity in dehydration of alcohols to gain new mechanistic insight regarding the role of bulk-type and surface-type HPA catalysis in this reaction. The HPA catalysts were prepared by impregnation from an aqueous solution and characterised using BET, XRD, TGA, DRIFTS and ICP–OES. The acid strength of HPA catalysts was determined by NH3 adsorption microcalorimetry and found to decrease in the order HPA/SiO2 > HPA/TiO2 > HPA/ZrO2. For each type of HPA catalyst, the acid strength increased with increasing HPA loading. This can be attributed to HPA-support interaction reducing the strength of HPA proton sites at low HPA loadings. The activity of HPA catalysts was tested in the gas-phase dehydration of MeOH and i-PrOH in a fixed-bed reactor. Evidence was obtained that alcohol dehydration over HPA catalysts in a steady-state flow system occurs via the surface-type rather than bulk-type catalysis as suggested hitherto. This follows from a strong correlation between the reaction rate and the number of surface proton sites in HPA catalysts.

2‐Hydroxyadipic Acid Production by Oxidation of 2‐Hydroxycyclohexanone with Molecular Oxygen

AbstractOxidation of 2‐hydroxycyclohexanone (2‐HCO) which can be synthesized from both petroleum and biomass was investigated with heteropolyacids and oxygen as catalysts and oxidant, respectively. 2‐Hydroxyadipic acid (2‐HAA) was obtained in moderate yields, and H4PVW11O40 gave the highest yield (39 %). 2‐HAA is a dicarboxylic acid expected to be a monomer, and this work is the first report for production of 2‐HAA by catalytic oxidation reactions. The oxidation of 1,2‐cyclohexanedione (CHDO), which is a potential intermediate of 2‐HCO oxidation, produced similar yield of 2‐HAA even without catalyst. The effects of catalyst amount (first order), oxygen pressure (almost zero order) and the addition of radical scavenger (no effect) on the 2‐HCO oxidation with H4PVW11O40 catalyst were similar to those in a related case of 2‐methoxycyclohexanone oxidation to adipic acid with heteropolyacid catalyst. 2‐HCO is proposed to be oxidized to CHDO as a precursor of 2‐HAA in a similar mechanism to 2‐methoxycyclohexanone oxidation.

Extractive Catalytic Oxidative Deoxygenation of Model Fuels Catalyzed by a Vanadium-Substituted Heteropolyacid and Molecular Oxygen

Extractive catalytic oxidative deoxygenation (ECODO) completes extractive catalytic oxidative desulfurization (ECODS) and extractive catalytic oxidative denitrogenation by removing organic oxygen from fuels. This is particularly necessary for renewable fuels to make them more stable and efficient. In ECODO, compounds such as cresol, furan, and their derivatives could be completely oxidized under oxygen at 20 bar and 120 °C using an aqueous heteropolyacid catalyst solution. The oxidation products were separated in situ in the three-phase process, either as CO2 or CO in the gas phase or as water-soluble organic acids like formic and acetic acid as well as acetone. In the case of stable dibenzofuran (DBF), the conversion could be drastically increased from only 27% to above 50% by tuning the reaction conditions and optimizing the catalyst loading by a design of experiment. Moreover, the amount of oxygen in the gas phase could be drastically reduced from 20 to 4 bar operating in 20 bar of synthetic air without limiting the performance of the catalyst. Furthermore, it could be shown that the parallel ECODS in the presence of an oxygenate like DBF leads to better desulfurization of model gasoline than without. The ECODO therefore offers a potential alternative to the classical hydrodeoxygenation, which is not only more energy-efficient but also replaces the expensive hydrogen with cheap air and avoids additional unit operations for fuel cleaning.