Solid Superacid Research Articles

ChemInform Abstract: Toward Green and Sustainable Chemical Glycosylation: Enhanced Lewis Acidity of Recyclable Solid Super Acid Catalyst, SO4/ZrO2 by CaCl2 Doping.

AbstractThe enhanced glycosylation efficacy concerning the calcium chloride‐doped sulfated zirconia significantly depends on the ion radius of the calcium cation and how calcium chloride coordinates to the oxygen atom of sulfated zirconia to convert a Broensted acid site into a much more functional Lewis acid site.

Insight into esterification of eugenol to eugenol benzoate using a solid super acidic modified zirconia catalyst UDCaT-5

Eugenol benzoate is a potent lipoxygenase inhibitor prepared by esterification of eugenol with benzoic acid. The current paper depicts synthesis of eugenol benzoate using several solid acids among which super acid catalyst UDCaT-5 was found to be the best. UDCaT-5, a zirconia-based catalyst, with high sulfur content (9%w/w) but preservation of the tetragonal phase of zirconia was synthesized and is much better than the conventional sulfated zirconia (S-ZrO2). As compared to other solid acid catalysts it gives excellent conversion under moderate conditions of 110°C. The effects of various parameters were studied in a batch reactor to establish kinetics and mechanism of reaction under optimized conditions. The reaction is intrinsic kinetically controlled. The detailed kinetics of eugenol esterification by solid super acid catalyst is studied using various parameters. The reaction follows Langmuir–Hinshelwood–Hougen–Watson mechanism involving weak adsorption of the reactants and products. The apparent energy of activation was found to be 9.36kcal/mol. The catalyst is highly active and reusable.

Synthesis of PLA-PEG Block Polymer Catalyzed by Solid Super Acid

The PLA-PEG block polymer was prepared by opening ring polymerization catalyzed by solid super acid SO42-/ZrO2-CeO2. The acidic property was measured by IR spectra, Hammett Indicator and NH3-TPD techniques. The copolymer was measured by FTIR spectra. The results show the solid super acid SO42-/ZrO2-CeO2 had the strongest acid strength and maximal acid content roasted at 650. Under reaction conditions which were the amount of catalyst 1.0% vs lactide, and polymerization at 170 for 9 h, the intrinsic viscosity reached 1.562 dl. g-1.

Solid superacid-catalyzed hydroconversion of an extraction residue from Lingwu bituminous coal

A solid superacid was prepared as a catalyst. The catalyst was characterized by ammonia temperature-programmed desorption, surface property measurement, and analyses with scanning electron microscopy and Fourier transform infrared spectrometry. A extraction residue from Lingwu subbituminous coal was subject to non-catalytic and catalytic hydroconversion using cyclohexane as the solvent under pressurized hydrogen at 300°C for 3h. The results show that the total yield of petroleum ether-extractable arenes from catalytic hydroconversion is much higher than that from non-catalytic hydroconversion. The cleavage of Car–Calk bonds in the residue could significantly proceed during catalytic hydroconversion.

Synthesis, characterization and kinetics of AlCl3 supported on silica superacid catalysts for the formation of linear alkylbenzenes

The solid superacid catalysts were synthesized by loading AlCl3 on silica gel for benzene alkylation. The prepared catalysts were characterized by various techniques such as BET, FT-IR, MAS-NMR and scanning electron microscopy. The Hammett acidity function (Ho) was used to determine the acid strength of the solid catalysts by employing various Hammett indicators. These catalysts were found to be highly active for benzene alkylation with 1-dodecene. The catalyst prepared by the wet impregnation technique showed *33% selectivity of 2-LAB and AlCl3 vapor treated silica gel catalyst (SG-AlCl3v) showed *45% selectivity of 2-LAB. The FT-IR spectra of the SG-AlCl3v catalyst showed equal number of Bronsted and Lewis acidic sites. The life of SG-AlCl3v catalyst was evaluated in a packed bed reactor and was found to be *300 h for benzene alkylation with 1-dodecene. The 27 Al MAS-NMR of SG-AlCl3v catalyst showed a band at 96.578 ppm, which is attributed to 4-coordinated Al species (2O, 2Cl). The Ho of SG-AlCl3v catalyst was found in the range of -12.70 ( Ho ( 13.16, indicates the superacidic nature. A nonlinear optimization algorithm was developed in MATLAB 7.4.0 and used to determine the kinetic parameters of the benzene alkylation with 1 dodecene in presence of SG-AlCl3v catalyst. The concentrations of the products predicted by the model was found in good agreement with experiments.

适于木本植物油脂的催化剂研究：纳米固体超强酸催化剂对游离脂肪酸的酯化

木本植物油脂与草本相比多为高酸价，用碱性催化剂进行酯交换时易发生皂化。两步法是先将游离脂肪酸酯化，再进行碱催化生产，可以提高资源的利用率，拓展原料的来源，降低成本。锡是少数几个可制备固体超强酸的金属。本文以掺锑二氧化锡纳米材料为基体，进行表面硫酸化。在330℃煅烧得到催化剂 /Sb-SnO2，酸性强(H0 ≥ –14.5)，超过100%硫酸(–11.9)近1000倍，为固体超强酸。TEM照片显示为纳米催化剂。将其应用在高酸值米糠油的酯化反应中，在常压、常温(70℃)下进行游离脂肪酸的酯化催化反应，对游离酸的酯化率为95%以上，残余米糠油的酸值由58.94 mg/g降到3~4 mg/g，可用液体碱催化剂继续进行酯交换反应。从而证实该催化剂可用于高酸价木本油脂两步法生成生物柴油，提高资源的利用率。 Generally woody plant oil bears a higher acid value than the oil from herbaceous plant. Basic catalyst will lead to soap reaction in transesterification of oil. Tow step method divides the production of biodiesel into the esterification of free fatty acid and the transesterification of oil, which improves resource utilization greatly and broadens sources of oil, contributing to a low cost. Sin is a few metals by which solid superacid can be prepared. The present paper used nanocrystal of SnO2 doped with Sb as carrier to superficially sulfate on it. Nano-catalyst @Sb-SnO2 calcined at 330˚C for 3 h is a solid superacid with a strong acidy, Hammett function H0 ≥ –14.5, stronger than 100% sulfuric acid (–11.9) near to 1000 times. The image of TEM showed the solid superacid is nano size. In esterification of rice bran oil with high acid value, the ratio of esterification of free fatty acid was up to 95% under normal pressure at 70˚C, and the acid value of remains of rice bran oil decreased from 58.94 to 3 - 4 mg KOH/g. So the remains of rice bran oil can be directly used for transesterification by homogeneous basic catalyst, thereby the tow step method can be practiced and enhance the utilization of rate oil resources.

Urea as an efficient and reusable catalyst for the glycolysis of poly(ethylene terephthalate) wastes and the role of hydrogen bond in this process

Metal salts and solid super acids are the common catalysts used in the glycolysis of poly(ethylene terephthalate)(PET) wastes to obtain monomer bis(hydroxyethyl) terephthalate (BHET) with high conversion of PET and selectivity of BHET, but there are some drawbacks, such as severe reaction conditions, slow reaction rates and difficult recycling of the catalyst. In this study, urea, as a green, highly active, low-priced, extensive and easily produced catalyst, has been used for the degradation of PET to give BHET. The experimental results show that the catalyst has a high catalytic activity, fast reaction rate and is easily separated from the product. Then the effects of experimental parameters on the conversion of PET and the selectivity of BHET were investigated. The conversion of PET wastes is able to reach up to 100% under the conditions of m(PET wastes) : m(ethylene glycol (EG)) : m(urea) = 1 : 4 : 0.1, atmosphere pressure at 160 °C for 2.5 h. The recycling experiments showed that urea worked efficiently, even though it has been used ten times. In addition, the mechanism was proposed through in situ IR, density functional theory (DFT) calculations and experimental results. It shows that the hydrogen bonds (H-bonds) formed between EG and urea play a key role. Following on from this, five tetraalkylammonium-based amino acid-functionalized ionic liquids were synthesized and were used in the catalytic glycolysis of PET. The experimental results and DFT calculations further verify the important role of H-bonds in the glycolysis process of PET catalyzed by this type of carbonyl-containing catalysts.

SO<sub>4</sub><sup>2-</sup>/SnO<sub>2</sub>-Catalyzed C3-alkylation of 4-hydroxycoumarin with secondary benzyl alcohols and <i>O</i>-alkylation with <i>O</i>-acetyl compounds

Sulfated tin oxide (STO) has been found to be an efficient reusable solid superacid catalyst for C3-alkylation and O-alkylation of 4-hydroxycoumarins with benzylic, allylic alcohols/and corresponding acetates respectively, in acetic acid under reflux conditions with good yield of products.

Solid superacid catalyzed glycerol esterification of free fatty acids in waste cooking oil for biodiesel production

AbstractThe free fatty acids (FFAs) of waste cooking oil (WCO) are readily esterified with crude glycerol in the presence of the solid superacid SO/ZrO2–Al2O3. This reaction lowers the acidity of WCO before biodiesel production. The solid superacid SO/ZrO2–Al2O3 catalyzes both FFA esterification and TAG glycerolysis during the reaction. The conversion of FFA in the WCO with an acid value of 88.4 ± 0.5 mg KOH/g to acylglycerols was 98.4% under optimal conditions (mole ratio of glycerol to FFA = 1.4:1; reaction time = 4 h; reaction temperature = 200°C; catalyst loading = 0.3 wt%) obtained through an orthogonal experiment. The final FAME product with a FAME content of 96.9 ± 0.3 wt% yield was 94.8 wt%, after transesterification of the esterified WCO with methanol, catalyzed by potassium hydroxide. The FAME composition of the products produced by transesterification were identified and quantified by GC–MS. The results suggest that this new glycerol esterification process, using a solid superacid catalyst, affords a promising method to convert oils with high FFA levels, like WCO, to biodiesel. The process has the inherent advantage of easy separation steps for removing excess alcohol and significant savings in energy, when compared to acid catalyzed reactions with methanol to lower acidity.Practical applications: In this work, WCO with a high acid value was esterified with crude glycerol catalyzed by solid super acid, whose formula was expressed as SO/ZrO2–Al2O3. There are distinct advantages to this new esterification process, which include easy separation of the excess crude glycerol by sedimentation or centrifugation, the use of the low cost reactant crude glycerol direct from the byproducts of transesterification, the potential to achieve a very low content of FFAs by post‐refining to improve the yield of the final product, and time and energy saving are found as compared to the traditional methanol esterification process. This new technology provides a promising alternative method for processing feedstocks of high acid value, such as WCO, for the production of biodiesel.

Rare Earth Solid Superacid Catalyzed Friedel–Crafts Acylation of Ferrocene

The Friedel–Crafts acylation of ferrocene catalyzed by a new type of catalyst of rare-earth solid superacid sulfated zirconia SZR3+ was developed. Comparison of catalytic activities between different solid acid catalysts is presented. The catalyst, sulfated zirconia ytterbium SZNYb3+, showed interesting catalytic properties for preparation of acylferrocenes. Furthermore, the catalyst could be regenerated and reused in succession after simple filtration.

ChemInform Abstract: Sulfated Zirconia: An Efficient Catalyst for Solvent‐Free Synthesis of Silyl Ethers under Mild Conditions.

AbstractSulfated zirconia is successfully used as solid superacid catalyst for the O‐silylation of primary and secondary alcohols, phenols, and oximes.

SO42−/ZrO2–titania nanotubes as efficient solid superacid catalysts for selective mononitration of toluene

SO42 −/ZrO2–titania nanotubes–X (SO42 −/ZrO2–TNTs–X; X of Ti/Zr) solid superacid catalysts with different atom ratios (Ti/Zr) were successfully prepared. The SO42 −/ZrO2–TNTs–2 (Ti/Zr of 2) have a specific surface area of 394 m2/g and an acid intensity of 1.839 mmol/g. The SO42 −/ZrO2–TNTs–2 show excellent selectivity (p/o of 3.34) and activity (yield of 98%) in the selective mononitration of toluene. Importantly, the SO42 −/ZrO2–TNTs–2 can be efficiently recycled and regenerated by simple sulfuric acid soaking.

Probing the Catalytic Center of TiO2/SO4 2− Solid Superacid Catalyst by X-Band In Situ High-Temperature EPR Spectroscopy

Paramagnetic centers of the solid superacid catalyst in the sulfated TiO2 are prone to the electron paramagnetic resonance (EPR) spectroscopy. The induction of the catalytic-active sites in TiO2 powder presubmerged in H2SO4 solution as a function of the calcinated temperature of 293–873 K is investigated by X-band in situ continuous-wave EPR measurements. Sulfated-acid sites composed of the Ti3+ ion are formed upon calcination. The overall experimental results show that the population of these sites goes uphill with the elevating temperature, reaches a maximum at ~623 K and decreases afterward to close zero. During the process, the decomposition of the TiO2/SO4 2− leads to the formation of Ti3+ species and then to the increasing EPR signal amplitude, and the consecutive decomposition of the sulfur at higher temperature (>650 K) to the diminishing signal. The X-ray diffraction indicates that the introduction of SO4 2− stabilizes the geometric structure in the anatase phase.

Synthesis of acetyl salicylic acid over WO 3/ZrO 2 solid superacid catalyst

Solid superacid WO 3/ZrO 2 was prepared by co-precipitation of an aqueous zirconyl chloride and ammonium metatungstate solution. The as-prepared catalysts were characterized by using XRD, Laser Raman spectroscopy and BET. Acetyl salicylic acid was synthesized from salicylic acid and acetic anhydride using as-synthesized WO 3/ZrO 2. The effects of WO 3 concentration, reaction time, reaction temperature, molar ratio of reactants, as well as dosage of catalysts on synthesis of acetyl salicylic acid were investigated, and the reaction conditions were therefore optimized. The excellent yield (91.0%) of acetylsalicylic acid was obtained under optimized reaction conditions. The catalyst has been easily recovered and reused repeatedly with a consistent high yield.

Toward Green and Sustainable Chemical Glycosylation: Enhanced Lewis Acidity of Recyclable Solid Super Acid Catalyst, SO4/ZrO2 by CaCl2 Doping

The simple doping of calcium chloride allowed highly improved yields in the glycosylation promoted by sulfated zirconia (SZ) without calcination. It was revealed by means of per-O-benzylated galactose trichloroacetimidate as a model glycosyl donor that this effect depends greatly on the cationic ion radius of used metal chlorides. Temperature-programmed desorption of ammonia (NH3 TPD) and the pyridine IR method showed clearly that coordination of calcium ion provides the SZ surface with newly formed Lewis acidic sites while the Brønsted acid site disappeared, indicating that the enhanced catalytic potency of SZ is due to the increased Lewis acid sites by doping the optimal calcium ions. The present findings might give insight into the relationship between a catalytic mechanism and superacidity of SZ, which is crucial for the design of novel superacid–based catalysts and environmentally benign glycosylation processes.

The Preparation and Characterization of Solid Superacid S<sub>2</sub>O<sub>8</sub><sup>2-</sup>/SnO<sub>2</sub>-SiO<sub>2</sub>

The new type of solid superacid S2O82-/SnO2-SiO2 was prepared by precipitation and hydrothermal aging method with ammonium persufate as soaker instead of sulphuric acid. The samples with different tin oxide content were characterized by FT-IR, XRD, BET, TG/DTA and Hammett indicators techniques. Catalytic activities for esterification of butanol and acetic acid were also investigated. As a result, most sulfate-ion in surface of S2O82-/SnO2-SiO2 coordinate with Sn bidentatly, and the acidic strength of S2O82-/SnO2-SiO2 is related to the content of tin oxide. Besides, introducing appropriate Si can improve the combination of the tin with SO42- thus increases the amount of acid. Catalyst S2O82-/SnO2-SiO2 reveals high catalytic activity and stability in the esterification at very large range of composition.

Preparation and Characterization of Rare Earth Solid Superacids SO<sub>4</sub><sup>2-</sup>/TiO<sub>2</sub>-SnO<sub>2</sub>-Dy<sub>2</sub>O<sub>3</sub>

A new rare earth solid superacids catalyst SO42-/TiO2-SnO2-Dy2O3 was prepared by coprecipitation-impregnating method, and the optimum preparation conditions were obtained. The physic- chemical properties of the catalyst was characterized by FTIR, TG-DTA, XRD and BET. The results showed the prepared catalyst is superacid with good thermal stability and high specific surface area. The sulfuric groups were proved to be chelated and bridgingly connected on the surface of the catalyst.

α–Pinene Isomerization Catalyzed by a Nanometer Solid Superacid

Nanometer composite S2O82-/SnO2-TiO2, a novel solid superacid, was prepared by the sol-gel method and its structure was characterized by XRD, TEM, FT-IR and nitrogen adsorption. Results indicated that the composite S2O82-/SnO2-TiO2 had a narrow particle size distribution with an average particle diameter about 15~20nm. S2O82- combined with SnO2-TiO2 resulted in formation of strong acid sites on the surfaces. The surface area of catalysts obviously increased after incorporating SnO2. Nanometer S2O82-/ SnO2-TiO2 composite was used as a catalyst for a-pinene isomerization and the influence of catalyst preparation conditions on its performances were investigated. The optimum condition for superacid catalyst preparation was found to be with 2:1 Sn/Ti mole ratio, S2O82- 1 mol · L-1 of impregnation consideration and toasting temperature of 773K. With 3% of S2O82-/SnO2- TiO2 catalyst dosage at a reaction temperature at 403K for 2 h, the conversion of a-pinene was 98 % and the selectivity to camphene was 62 %.

Oligomeric Carbocation-like Species from Protonation of Chloroalkanes

The protonation of chloroethane by the strongest known solid superacid, the carborane acid H(CHB(11)Cl(11)), has been studied by quantitative IR spectroscopic methods to track mass balance and uncover previously unobserved chemistry. In the first step, an intermediate EtCl·H(CHB(11)Cl(11)) species without full proton transfer to EtCl can be observed when d(5)-deuterated chloroethane is used. It rapidly eliminates HCl (but not DCl) to form ethyl carborane, Et(CHB(11)Cl(11)), which binds a second molecule of chloroethane to form the Et(2)Cl(+) chloronium ion. This undergoes a slower, previously unrecognized HCl elimination reaction to form a butyl carborane, Bu(CHB(11)Cl(11)), beginning an oligomerization process whereby unsymmetrical dialkylchloronium ions decompose to alkyl carboranes of formula Bu(C(2)H(4))(n)(CHB(11)Cl(11)) up to n = 4. Over time, a parallel competing process of de-oligomerization take place in the presence of free carborane acid that finishes with the formation of hexyl or butyl carboranes. Upon heating to 150 C, the final products are all converted to the remarkably stable tert-butyl cation carborane salt.

Solid Super Acid of S<sub>2</sub>O<sub>8</sub><sup>2-</sup> /FexOy-CuOx Catalytic Degradation of Orange IV

Solid super acid (S2O82-/FexOy-CuOx) was prepared and used as a heterogeneous Fenton-like catalyst to decompose H2O2 for the degradation of refractory dye Orange IV in water. The factors that affected the degradation of Orange IV were discussed in this heterogeneous Fenton-like system. The catalytic activity of S2O82-/FexOy-CuOx was evaluated by the degradation of Orange IV and the decomposition of H2O2. The results show that the catalyst S2O82-/FexOy-CuOx has a good catalytic activity. The reaction follows pseudo-first-order kinetics; the reaction rate constant has a good relationship with the concentration of H2O2. The degradation rate of Orange IV and the decomposition rate of H2O2 increase with the increase of temperature and the dosage of catalyst whereas it decreases with the increase of the initial concentration of Orange IV and the initial pH.