Solid Superacid Research Articles

One-step synthesis of SO42−/ZrO2‑SEP solid-acid catalyst for energy-efficient CO2 capture

The application of solid-acid catalysts in the regeneration process of CO2-rich amine solutions is currently considered as a promising method for reducing the relative heat duty of CO2 capture processes. In this study, sepiolite (SEP) was selected as a cost-efficient catalyst carrier to support the solid superacid SO42-/ZrO2 (SZ) for preparing a series of composite SO42−/ZrO2‑SEP (SZ@SEP) catalysts with different SZ/SEP ratios. The physical–chemical properties of the prepared catalysts were carefully studied using various characterization techniques. The catalytic CO2 desorption performance was tested in the conventional 5 M MEA solution at 88 °C. The amount of desorbed CO2, desorption rate and relative heat duty were accurately measured for each catalyst and a potential catalytic reaction mechanism was proposed. The results indicated that all catalysts significantly enhanced CO2 desorption performance. Specifically, SZ@SEP-1/2 achieved a 37.3 % increase in average desorption rate and a 48.6 % decrease in heat duty compared to the blank solvent. Furthermore, SZ@SEP-1/2 demonstrated excellent stability over 20 cycles, suggesting its potential as an energy-efficient catalyst for CO2 capture.

The catalysts for synthesis of citrate esters plasticizers and the application of citrate esters plasticizers

The latest research progress in citrate esters plasticizers at home and abroad was introduced. The advance in the catalysts for the syn thesis of citrate esters plasticizers and the application of citrate esters plasticizers were reviewed in detail. The catalysts for the synthesis of citrate esters included sulfonic acid, solid super acid, heteropolyacids, ionic liquids and inorganic salts. The citric acid ester plasticizers were applied in the fields of food packaging, children's toys and medical instrument. The development prospects of citric acid ester plasticizers were outlined.

Efficient alcoholysis of total saponins in D. zingiberensis to diosgenin using ionic liquid-grafted MOF superacids

Diosgenin is an indispensable intermediate in the production of various steroid drugs. Conventional hydrolysis of sulfuric acid produces large amounts of acidic wastewater and has always faced stringent restrictions from environmental requirements. Here, UiO-66-NH2 and its derivative of UiO-66-NH2-AT (AT = 3-amino-1,2,4-triazole) were synthesized, and these two compounds were further grafted with high-concentration CF3SO3H molecules to obtain the MOF-based solid superacids, namely UiO-66-NH2-[SO3CF3] and UiO-66-NH2-AT-[SO3CF3], respectively. They have been applied to the alcoholysis of total saponins to extract diosgenin, and the alcoholysis conditions, including the solid acid dosage, extraction temperature and extraction time, have been optimized by single-factor experiments. Subsequently, the alcoholysis conditions of UiO-66-NH2-AT-[SO3CF3] with more prominent catalytic performance and cycle stability were further optimized by the response surface method, and under the optimum conditions, the diosgenin yield reached 20.8 %, which was close to the predicted value of 21.3 % and was superior to the conventional hydrolysis of sulfuric acid and our previously reported solid acids. Additionally, the alcoholysis pathways and alcoholysis mechanism of the total saponins catalyzed by UiO-66-NH2-AT-[SO3CF3] have been proposed by the analysis of high-resolution electrospray mass spectrometry.

The Overlooked Potential of Sulfated Zirconia: Reexamining Solid Superacidity Toward the Controlled Depolymerization of Polyolefins.

Closed-loop recycling via an efficient chemical process can help alleviate the global plastic waste crisis. However, conventional depolymerization methods for polyolefins, which compose more than 50% of plastics, demand high temperatures and pressures, employ precious noble metals, and/or yield complex mixtures of products limited to single-use fuels or oils. Superacidic forms of sulfated zirconia (SZrO) with Hammet Acidity Functions (H0) ≤ - 12 (i.e., stronger than 100% H2SO4) are industrially deployed heterogeneous catalysts capable of activating hydrocarbons under mild conditions and are shown to decompose polyolefins at temperatures near 200 °C and ambient pressure. Additionally, confinement of active sites in porous supports is known to radically increase selectivity, coking and sintering resistance, and acid site activity, presenting a possible approach to low-energy polyolefin depolymerization. However, a critical examination of the literature on SZrO led us to a surprising conclusion: despite 40 years of catalytic study, engineering, and industrial use, the surface chemistry of SZrO is poorly understood. Ostensibly spurred by SZrO's impressive catalytic activity, the application-driven study of SZrO has resulted in deleterious ambiguity in requisite synthetic conditions for superacidity and insufficient characterization of acidity, porosity, and active site structure. This ambiguity has produced significant knowledge gaps surrounding the synthesis, structure, and mechanisms of hydrocarbon activation for optimized SZrO, stunting the potential of this catalyst in olefin cracking and other industrially relevant reactions, such as isomerization, esterification, and alkylation. Toward mitigating these long extant issues, we herein identify and highlight these current shortcomings and knowledge gaps, propose explicit guidelines for characterization of and reporting on characterization of solid acidity, and discuss the potential of pore-confined superacids in the efficient and selective depolymerization of polyolefins.

Copper-induced formation of Lewis acid sites enhancing sulfated zirconia catalyzed i-butane normalization

Sulfated zirconia (SO42-/ZrO2) has been reported as an efficient and stable solid superacid catalyst for normalizing i-butane to n-butane, and may potentially substitute Pt-based catalysts. In this work, sulfated zirconia with Cu addition (Cu-SO42-/ZrO2) is prepared through a one-step method and exhibits comparable performance to commercial Pt-Cl/Al2O3, with an i-butane average conversion of 43.8% and n-butane average selectivity as high as 86.1%, while maintaining a stable n-butane yield for up to 120 hours. The relationship between Cu-promoter-induced physicochemical properties and catalytic performance for sulfated zirconia catalysts is investigated in detail, with the help of XPS, NH3-TPD, pyridine-IR, and density functional theory calculation. A volcano-type relationship is found between Cu content and n-butane yield, where n-butane yield first increases from 32.23% to 37.71%, and then decreases to 29.56%, with the gradual increase of Cu content. The moderate Cu species additive is beneficial to release Zr Lewis acid site from sulfate and increase its Lewis acid density, which accounts for its excellent catalytic selectivity for i-butane normalization. The excess Cu promoter covers the exposed Zr Lewis active sites, leading to the decayed i-butane conversion. Therefore, Lewis active sites density is regarded as descriptor to corelate n-butane yield, accounting for the volcano relationship between Cu content and n-butane yield for Cu-SO42-/ZrO2. This work demonstrates the feasibility of Cu modification and provides insight into the promotion mechanism, which may be extended to other solid superacid catalysts beyond sulfated zirconia.

Application of SO42–/Fe2O3-CuO solid superacid materials in cyclic compounds from wastewater: Performance and mechanism

In wastewater treatment, the degradation of refractory cyclic compounds by catalytic ozonation using sulfated solid superacid has not been thoroughly investigated. The doped S element alters the electronic activity and drives the ozone oxidation of recalcitrant organic pollutants, potentially leading to an increase in catalytic efficiency. This study aimed to develop a novel iron-copper sulfate (SO42–/Fe2O3-CuO) solid superacid composite to strengthen catalytic reactions. According to the characterization results, the embedding of SO42– enhanced the electron transfer inside the material, leading to more Lewis acid sites, which facilitated the catalytic decomposition of O3. The catalytic degradation and reaction kinetics experiments on quinoline verified the superior catalytic performance of the SO42–/Fe2O3-CuO system compared to other systems. Fluorescence, UV–Vis spectrophotometry, and EPR experiments demonstrated that the hydroxyl radicals (OH), superoxide radicals (O2−), and singlet oxygen (1O2) were generated in the SO42–/Fe2O3-CuO system, and their presence accelerated the redox cycling of Fe(III)/Fe(II) and Cu(II)/Cu(I). In addition, the possible degradation pathways of quinoline were verified by density functional theory (DFT) calculations, and the toxicity of intermediates was assessed by quantitative structure–activity relationship (QSAR) analysis. Finally, the applicability of the SO42–/Fe2O3-CuO catalytic system in bio-treated coking wastewater (BTCW) was validated. GC–MS experiments further confirmed that it was mainly the cyclic compounds that contributed to the removal rate during the catalytic process. In summary, this study demonstrated the significant potential of the SO42–/Fe2O3-CuO catalytic system in degrading refractory cyclic compounds, providing valuable technical support for the field of wastewater treatment.

A potential catalyst for α-pinene isomerization: a solid superacid

The calcination temperature affects the crystallinity of the catalyst.

Solid superacid catalysts promote high-performance carbon dots with narrow-band fluorescence emission for luminescence solar concentrators

Facile and efficient method for constructing carbon dots (CDs) with narrow full width at half maximum (FWHM) is a major challenge in the field, and researches on regulating the FWHM of CDs are also rare and scarce. In this work, we delved into the synthesis of CDs with narrow fluorescence emission FWHM (NFEF-CDs) in the m-phenylenediamine (m-PD)/ethanol system, utilizing solid superacid resin as catalyst with solvothermal method. The resulting NFEF-CDs exhibit a photoluminescent (PL) emission peak at 521 nm with a narrow FWHM of 41 nm, an absolute PL quantum yield (QY) of 80%, and display excitation-independent PL behavior. Through comprehensive characterization, we identified the protonation of edge amino on NFEF-CDs as the key factor in achieving the narrow FWHM. Subsequently, we validated the broad applicability of solid superacid resins as catalysts for synthesizing CDs with narrow FWHM in the m-PD/ethanol system. Finally, we utilized a self-leveling method to prepare NFEF-CDs film on the surface of poly(methyl methacrylate) (PMMA) substrate and investigated the solid-state fluorescence properties of NFEF-CDs as well as their performance as luminescence solar concentrator (LSC) for photovoltaic conversion. The results revealed that the as-prepared LSC exhibit an internal quantum efficiency (ηint) of 42.39% and an optical efficiency (ηopt) of 0.68%. These findings demonstrate the promising prospects of NFEF-CDs in the field of LSCs and provide a theoretical basis for their application in photovoltaic conversion.

A soft processible polyoxometalate-zwitterion eutectic electrolyte for superprotonic conduction

Proton conductors are important for propelling the development of energy and electronic technologies. Polyoxometalates (POMs), as a class of crystalline solid superacids with nanocluster form and high proton conductivity, are intriguing candidates for this. However, the use of POMs as practical proton conductors is hindered by their low processability coming from inherent brittleness, and their humidity-dependent conductivity. Here, we report a deep eutectic strategy to convert brittle POM powders to soft processible electrolytes through supramolecular complexation with hydroxyl‑containing zwitterions. The resulting POM-zwitterion eutectics exhibit good malleability and high modulus over 1 MPa, promoting them easily processed into self-supporting eutectics. Due to the soft state and percolated hydrogen bonding networks, these eutectics can transport protons by both diffusing and hopping processes, that is, a Vehicle-Grotthuss synergistic mechanism, which enables them to show superprotonic conductivities up to 1.0 × 10−3 S cm−1 at 30 °C (25 % RH) and 2.4 × 10−2 S cm−1 at 150 °C (anhydrous condition). This work paves a new route to designing advanced electrolyte materials based on the supramolecular eutectic concept.

S2O82−/CeO2 Solid Superacid Catalyst Prepared by Radio-Frequency Plasma-Assisted Hydrothermal Method

CeO2 was prepared using a hydrothermal method, modified by radio-frequency plasma in the form of glow discharge, and then the solid superacid S2O82−/CeO2 was prepared by the impregnation method. A series of properties such as pore structure was characterized by N2 adsorption–desorption experiments, surface morphology was characterized by TEM, crystal phase was characterized by XRD, and surface acidity of the catalyst was characterized by Py-IR and Hammett titration. The methyl esterification reaction of tryptophan was used to evaluate the activity of the solid superacid. The results showed that the catalyst modified by radio-frequency plasma had a larger specific surface area, more surface oxygen vacancies, smaller particle size, and higher total acid content. The yield of tryptophan methyl ester reached a higher level of 94.5% (150 °C, 1 MPa, 2 h), catalyzed by the modified S2O82−/CeO2. This work verified the feasibility of plasma technology in the field of catalytic activity enhancement of solid superacid.

Benzylation of 1,3‐Dicarbonyl Compounds with Benzyl Alcohols Promoted by Perfluorosulfonic Acid Resin

AbstractThe catalytic performance of Perfluorosulfonic acid resin (PFSA), a solid superacid, was studied in the catalytic benzylation of 1,3‐dicarbonyl compounds with benzylic alcohols. The PFSA‐catalyzed reactions could proceed smoothly to provide the products under solvent‐free conditions or in toluene and dichloromethane, which gave moderate to excellent yields. Due to its high chemical stability, PFSA was quite stable under the reaction conditions and could be recovered at least eight times without significant reduction of its catalytic effect. Moreover, this reaction was investigated at a 20 mmol scale, which indicated the potential applicability of the large‐scale industrial synthesis. Finally, the mechanism of the PFSA‐catalyzed benzylation of 1,3‐dicarbonyl compounds with benzylic alcohols was also investigated.

Preparation, characterization, and catalytic properties of SO42-/SnO2-Hangjin2#Clay solid superacid catalyst

A new sulfate oxide solid acid catalyst SO42-/SnO2-Hangjin2# clay was compounded with Hangjin2#clay, activated by sulfuric acid, as a carrier. In the catalysis of Xanthoceras sorbifolium Bunge, using the yield of oil and methanol synthesis of biodiesel as an index, the effect of SO42-/SnO2–Hangjin2#clay and the preparation conditions on the activity of solid acid were investigated. The variables included in the optimization process were concentration of Sn, impregnation sulfuric acid concentration, and calcination temperature. The optimal conditions were found as 0.4 M SnCl4, 3.0 M H2SO4 impregnation, and 350 °C calcination temperature. The catalyst was examined by scanning electron microscope, X-ray diffraction meter, Fourier transform infrared spectroscopy, surface area, and thermal weight analysis. The results showed that the introduction of Hangjin2#clay in the SO42--SnO2 solid acid catalyst improves its catalytic activity.

TiO2/SO42- Solid Superacid: A Rapid, Solventless, Recoverable Nanocatalyst for Eco-Friendly Synthesis of Piperidin-4-one Oximes

: A potent, eco-friendly approach for converting 2,6-arylpiperidin-4-ones into their corresponding oximes in the presence of hydroxylamine hydrochloride and catalysed by nanosize sulfated titania (TiO2/SO4 2-) solid superacid was developed. Sol-gel method was employed to synthesize the catalyst and confirmed standard characterization techniques viz., by FT-IR, XRD, TEM, SEM, and EDS analysis. After adding 0.05 g of catalyst, the reaction was carried out under stirring in an oil bath at 130oC for 3-7 min under solvent-free conditions. This approach has advantages like catalyst recyclability, high yields, shorter reaction time, and simple work-up. Additionally, the catalyst TiO2/SO4 2- exhibited good stability, recoverability, and reusability for five consecutive runs without tremendous loss in its catalytic activity. The compounds 3a-o were characterised by IR, 1H and 13C NMR spectral analysis. The coupling constant values in NMR results suggested that the compounds 3a-o exhibit chair conformation with equatorial orientations with all the substituents. This is in agreement with the X-ray crystallography of 3c, confirming that the chair conformation of =N-OH group is syn to C-5 and anti to benzyl group at C-3 and hence if forms more stable (E)-configuration of the oxime 3c.

Novel S2O82−/Fe-ZrO2 solid superacid catalyst combined with O2-Ac2O for highly efficient catalytic nitration of 1-nitronaphthalene with NO2 to 1,5-dinitronaphthalene

Novel S2O82−/Fe-ZrO2 solid superacid catalyst combined with O2-Ac2O for highly efficient catalytic nitration of 1-nitronaphthalene with NO2 to 1,5-dinitronaphthalene

Enhanced Brønsted acid strength of HCl-promoted SO42−/TiO2 solid composite superacid: Synergetic effect of hydrogen chloride with induced titanium site

Development of the strategy to regulate the acidic properties of solid superacids had been attracting widespread attention in the acidic catalysis-related fields. In the present work, an HCl-promoted SO42−/TiO2 solid composite superacid was synthesized by incorporation of hydrogen chloride into sulfated titania (SO42−/TiO2). The Brønsted acid strength of HCl-promoted SO42−/TiO2 was significantly increased compared with that of SO42−/TiO2. Friedel-Crafts alkylation reaction results of HCl-promoted SO42−/TiO2 showed an increase by 27% in reaction rate and decreased byproduct selectivity (1% versus 10% for HCl-promoted SO42−/TiO2 and SO42−/TiO2, respectively). Structural characterizations demonstrated that HCl had the synergetic effect with induced titanium ion of HCl-promoted SO42−/TiO2 to form a new type of Brønsted acidic site. The configuration of enhanced Brønsted acidic site verified by DFT calculations was more liable to release the proton than that of conventional Brønsted acidic site, consequently increasing the Brønsted acid strength of HCl-promoted SO42−/TiO2.

TiO2/SO42− Solid Superacid Catalyst Prepared by Recovered TiO2 from Waste SCR and Its Application in Transesterification of Ethyl Acetate with n-butanol

TiO2/SO42− Solid Superacid Catalyst Prepared by Recovered TiO2 from Waste SCR and Its Application in Transesterification of Ethyl Acetate with n-butanol

Recent advances in Pb resistance over SCR catalysts: Reaction mechanisms and anti-inactivation measures

The study of SCR catalysts for nitrogen oxides reduction with NH3 had recently attracted much attention. As a typical heavy metal element, Pb was prone to seriously damage the denitrification performance of SCR catalysts in flue-gas environment. This work systematically reviewed the mechanisms of Pb poisoning and anti-deactivation measures reported these years for SCR catalysts. The mechanisms of Pb poisoning were summarized from both physical and chemical aspects, including the specific surface area, redox ability and surface acidity of the catalysts, and the corresponding reaction paths of the catalysts were also considered during the SCR process. In the meantime, this paper reviewed the anti-deactivation mechanisms and measures currently used to solve the problem of lead poisoning for SCR catalysts. The main methods included adding active substances to improve the redox ability and surface acidity of the catalysts, using ions or anti-poisoning sites to preferentially bind to Pb species, or using the structural characteristics of the carriers to prevent Pb from contacting with active substances. The concrete measures included the modification of catalysts with metal oxides and solid super acids, the change of carriers’ structure, and the dual effect of carriers and active materials. Finally, a prospect of lead poisoning for further research on SCR catalysts was proposed.

Researches on heterogeneous acid-base catalysis in Institute for sorption and problems of endoecology of the National Academy of Sciences of Ukraine

In chronological order, the reaseach results of Department of heterogeneous acid-base catalysis at Institute for sorption and endoecology problems in 2003-2023 are described. It relates to the synthesis, study and application of solid superacids WO3/ZrO2, WO3/ZrO2-SiO2, ZrO2-SiO2-Al2O3, ZrO2-SiO2-SnO2, as catalysts, in vacuum gas oil cracking, alkylation of isobutane with isobutanol, acylation toluene, oligomerization of tetrohydrofuran, acylation of methyl tert-butyl ether and other. Some study deals with a search of the correlations between of acid site strength of a catalyst and its activity, in particular, in dehydration reaction of C2-C4 alcohols, and the correlations between ability of primary and secondary alcohols to dehydrogenation and oxidation and their chemical shifts δ (R17OH) and δ (R13СОH ). For the first time, the values of Hammett's acidity function have been measured at elevated (up to 200 °C) temperatures for solid acids. In particular, for H-Y faujasite, H0 reaches superacidic value H0 at 160 °С. Since 2010, the main focus has been on the catalytic conversion of renewable raw materials, mainly bioalcohols (ethanol, glycerol) and C6 carbohydrates, into important products of organic synthesis (ethyl acetate, 1,1 diethoxyethane, n-butanol, propylene glycol, alkyl lactates, lactide, glycolide). In cooperation with “Techinservice Manufacturing Group”, new processes for obtaining ethyl acetate, 1,1 diethoxyethane, n-butanol from bioethanol and racemic lactide from glycerol were developed. Also, new technologies for obtaining propylene oxide from propylene and hydrogen peroxide (НРPОа-process), vapor phase hydrogenation of the pyrolysis C4-5 fraction, and direct high-temperature chlorination of ethylene to vinyl chloride have been developed for Kalush “Karpatnaftochim” plant. The HHPOa installation (2000 t/y) has been started at “Karpatnaftochim” in 2020.

Solid superacid SO42−-S2O82−/SnO2-Nd2O3-catalyzed esterification of α-aromatic amino acids

α-Aromatic amino acid esters are important platform compound for drugs, sweeteners and fluorescent sensors. Due to the amphoteric dissociation and steric effect, the esterification of α-aromatic amino acids is difficult. Here, a green and efficient solid superacid, SO42−-S2O82−/SnO2-Nd2O3 (SSSN), was synthesized and firstly used for the methyl esterification of α-aromatic L-tyrosine and L-tryptophan. The methyl esters yield was optimized with the highest L-TyrOMe yield of 93.1% and L-TrpOMe yield of 92% over SSSN-650 (SO42−-S2O82−/SnO2-Nd2O3 calcined under 650 °C). Furthermore, it was clarified that the doping of Nd enhanced the electron-withdrawing inductive effect of SO42−/S2O82− with increased Brønsted and Lewis acidity, which were beneficial to the esterification of L-tyrosine and L-tryptophan. Besides, Nd-doping reduced the activation energy during L-Tyr esterification by kinetics study. Finally, SSSN-650 could be recycled six times with > 70% of their initial ester yield. The decrease of catalyst activity was caused by carbon deposition and species leaching. This work launched a novelty, rapid and environmental-benign technology for the esterification of α-aromatic amino acid using solid superacid.

Sulfonated polyether ether ketone composite proton exchange membranes incorporated with a novel hierarchical‐structure hybrid nanofiller consisting solid superacid zirconium phosphate and CNTs

AbstractHow to simultaneously improved the proton conductivity and mechanical strength is a key problem facing currently used proton exchange membranes (PEMs). Herein, a solid inorganic superacid‐zirconium phosphate (ZrP) with a two‐dimensional layer structure was combined with one‐dimensional carbon nanotubes (CNTs) to prepare hybrid nanofiller ZrP‐CNTs by an in situ chemical deposition method. The new hybrid nanofiller was then applied to modify sulfonated polyether ether ketone (SPEEK), a widely used PEM matrix, to obtain a series of composite membranes. The structure and properties of the membranes were fully characterized by SEM, XRD, FTIR, TG, tensile properties, and proton conductivity. The results showed that the proton conductivities of the membranes were significantly improved due to the addition of super solid acid‐ZrP that has abundant proton sources or proton sites. Moreover, the composite membranes exhibited better mechanical properties and thermal stability than those of pure SPEEK membrane, owing to the great interface interaction and good compatibility between ZrP‐CNTs and SPEEK. The composite membrane (2 wt% ZrP‐CNTs) demonstrated the optimal comprehensive performance. Its proton conductivity was 36.63 mS cm−1 and its tensile strength was 37.56 MPa, which was 70% and 10%, respectively, higher than those of the pure SPEEK membrane under the same condition.