Polymer-supported N-heterocyclic carbene-iron(III) catalyst and its application to dehydration of fructose into 5-hydroxymethyl-2-furfural

Polymer-supported NHC–metal catalysts were prepared from chloromethyl polystyrene resin via two-step reaction. Metals were loaded into 1.6 – 16 mol% of total imidazolium and the remaining imidazolium chloride salt provided ionic liquid moiety. The formation of metal complex with the polymer-supported NHC ligand was analyzed by ATR FT-IR, XRD, and XPS. The synthesized polymer-supported NHC–metal catalysts were applied to the dehydration of fructose into HMF. The environmentally benign and inexpensive polymer-supported NHC–Fe^III catalyst showed good catalytic activity and yielded HMF at 73% (with a conversion of 97%). It could also be reused without significant loss of catalytic activity.     

Catalytic hydrolysis of chlorofluorocarbon (CFC-12) over WO3/ZrO2

The catalytic decomposition of CFC-12 (CCl₂F₂) in the presence of water vapor was investigated over a series of solid acids WO₃/ZrO₂. Compared with tungstic acid, ammonium metatungstate is a better source of tungsten oxide for the preparation of WO₃/ZrO₂ catalysts. CFC-12 decomposition activities of WO₃/ZrO₂ catalysts are in good agreement with their acidities. Enhancing the acidities of catalysts is favorable to increase their CFC-12 decomposition activities. WO₃/ZrO₂ catalysts calcined at higher temperature exhibit good catalytic activity and stability for the hydrolysis of CFC-12, and show better structural stability during the reaction.     

Effect of active site distribution on liquid-phase olefin hydrogenation over polymer-supported palladium complex

Chloromethylated polystyrene beads with different distributions have been prepared and phosphinated. PdCl₂ was supported on the phosphinated supports to give polymer-supported Pd complex catalysts with different active site distributions. The effect of active site distribution on catalytic activity was investigated in the hydrogenation of olefins.     

Sodium nitrate modified SBA-15 and fumed silica for efficient production of acrylic acid and 2,3-pentanedione from lactic acid

The catalytic conversion of lactic acid to acrylic acid and 2,3-pentanedione over sodium nitrate-supported mesoporous SBA-15 and fumed silica was studied. The yields of acrylic acid, 2,3-pentanedione, and acetaldehyde are 44.8%, 25.1%, and 13.3%, respectively, over the 23%NaNO₃/SBA-15 catalyst. The performance of the catalysts is strongly affected by NaNO₃ loading, catalyst texture and porosity, and product diffusion efficiency. A proper control of NaNO₃ loading can result in modification catalyst structure for improvement of 2,3-pentanedione selectivity. Under certain reaction conditions, the surface NaNO₃ species can readily transform to sodium lactate that functions as active component to catalyze the target reactions.     

Tungstophosphoric and Molybdophosphoric Acids Supported on Zirconia as Esterification Catalysts

The preparation and characterization of supported acid catalysts, based on tungstophosphoric (TPA) or molybdophosphoric (MPA) acids using ZrO₂ as support, are presented. ZrO₂ was prepared from zirconium oxychloride aqueous solutions by adding ammonium hydroxide solution. Two different techniques were used to obtain the catalysts, equilibrium adsorption and incipient wetness impregnation. The catalyst characterization allowed us to determine the species present on the carrier surface and their acidic properties. The catalytic activity for esterification of acetic acid with isoamyl alcohol of the zirconia-supported TPA catalysts was greater than that corresponding to those based on MPA. Moreover, in the preparative conditions used, the incipient wetness impregnation led to heteropolyacids supported on ZrO₂ with better catalytic performance.     

Isomerization of 1-hexene catalyzed over polymer-supported RuCl2(PPh3)3

Polymer-supported ruthenium catalyst was prepared by anchoring dichlorotris(triphenylphosphine)ruthenium, RuCl₂(PPh₃)3, onto the phosphinated polystyrene bead. The polymer-supported RuCl₂(PPh₃)3 could be reused several times with only small loss of catalytic activity in the isomerization of 1-hexene. The activity rather increased during the few initial runs. In both homogeneous and heterogenized catalysts, an induction period was required to initiate the isomerization. The catalyst efficiency was promoted in the mixture of good swelling solvent and potent hydrogen donor. Upon heterogenizing, the activity was reduced by a factor of 2.0-8.2.     

Reaction between methanol and acetic acid catalyzed by SiO2‐supported V‐P‐O catalyst in oxygen atmosphere

SiO₂‐supported V‐P‐O catalysts prepared by the incipient‐wetness impregnation method beginning with ammonium metavanadate and phosphoric acid were used in the catalytic reaction between methanol and acetic acid in an oxygen atmosphere. The SiO₂‐supported V‐P‐O catalysts were composed of VOPO₄ and (VO)₂P₂O₇ phases. Both the acidic and alkaline sites were co‐present in the catalysts. The vanadium species catalyzed the oxidation of methanol to formaldehyde. The V‐P‐O(20–30 wt%)/SiO₂ catalysts with a P/V mole ratio of 2:1 exhibited higher catalytic activity for the formation of acrylic acid and methyl acrylate with a total selectivity of ～28 % at 380 °C. The acid sites of the catalysts also catalyzed the formation of methyl acetate with a selectivity of ～65 %. Methanol can be an alternative to formaldehyde for the synthesis of both acrylic acid and methyl acrylate through the aldol condensation reaction.     

Selective catalytic reduction of NOx by NH3 at low temperature over manganese oxide catalysts supported on titanate nanotubes

Abstract

We report the NO conversion with NH₃ at low temperature over MnO_x-supported on titanate nanotubes. The effect of SO₂ and water on catalytic activity was also analyzed. For the catalytic activity tests, three catalysts with 1, 3, and 5?wt.% of MnO_x were synthesized. A high NO conversion (92%) at 180?°C is reported for the 1Mn/NTiO₂ catalyst. The further addition of MnO_x to the support improves the catalytic activity but NO conversion (95%) was shifted to a higher temperature (from 180 to 220?°C). However, the presence of SO₂ (50?ppm) and water (5 vol.%) diminishes the NO conversion up to 60%, which remains after 300?min. We found that addition of MnO_x increases the Lewis acid sites concentration of the nanotubes. As the Lewis acid sites increase (from 1.86 to 3.56 µmol m^?2), the Mn⁴⁺/Mn³⁺ ratio on the surface of the nanotubes decreases (from 4 to 1.6), which indicates that the surface of the catalysts is deficient in electrons. We concluded that a high Lewis acid sites concentration and a low Mn⁴⁺/Mn³⁺ ratio, hence a surface deficient in electrons, improves the catalytic activity to remove NO on the Mn/NTiO₂ catalysts.     

Polymer‐Bound Pyridine‐Bis(oxazoline). Preparation through Click Chemistry and Evaluation in Asymmetric Catalysis

A pyridine‐bis(oxazoline) ligand was efficiently immobilized by copper(I)‐catalyzed azide‐alkyne cycloaddition onto a polystyrene resin. The so obtained click‐pybox resin 1a was associated with various metal salts (YbCl₃, LuCl₃, CuOTf) and the resulting resin‐bound catalysts were explored in ring‐opening of cyclohexene oxide, silylcyanation of benzaldehyde and alkynylation of imines. These new polymer‐supported catalysts exhibit good to excellent performances in terms of catalytic activity, enantioselectivity and recyclability.     

Immobilization of the heteropoly acid (HPA) H4SiW12O40 (SiW12) on mesoporous molecular sieves (HMS and MCM-41) and their catalytic behavior

Supported catalysts, consisting of SiW₁₂ immobilized on hexagonal mesoporous silica (HMS) and its aluminum-substituted derivative (MCM-41) with different loadings and calcination temperatures, have been prepared and characterized by X-ray diffraction, FT-IR and NH₃-temperature programmed desorption. It is shown that SiW₁₂ retains the Keggin structure on the mesoporous molecular sieves and no HPA crystal phase is developed, even at SiW₁₂ loadings as high as 50 wt%. In the esterification of acetic acid byn-butanol, supported catalysts exhibit a higher catalytic activity and stability and held some promise of practical application. In addition, experimental results indicate that the loaded amount of SiW₁₂ and the calcination temperatures have a significant influence on the catalytic activity, and the existence of aluminum has also an effect on the properties of supported catalysts.     

Cationic Polymerization Using Heteropolyacid Salt Catalysts

Acid catalysts are used in the production of several commercially important lubricant additives, including dispersants and antioxidants. While the use of conventional mineral and Lewis acids still dominate existing production, heterogeneous solid acid catalysts provide a future option for cost reduction and pollution prevention. The heteropolyacids discussed in this presentation are based on the parent phosphotungstic acid, H₃PW₁₂O₄₀, which has been studied for many years as solid acid catalysts especially by Japanese researchers. A particular class of heterpolyacid salts of the formula (M⁺)_2.5H_0.5PW₁₂O₄₀ exhibit enhanced catalytic activity, which is believed to be due to the formation of a phase with nano-sized crystallites, as has been reported by Misono and coworkers. This class of heteropolyacid salts has been successfully applied by Lubrizol researchers to the production of high-reactivity polyisobutylene, a polymer used in the production of dispersants for commercial lubricants. Most notably, the catalyst of the formula (NH₄ ⁺)_2.5H_0.5PW₁₂O₄₀ provides high conversion to the desired reactive vinylidene isomer and a unique polymer molecular weight distribution, which results in improved performance characteristics when compared to existing commercial AlCl₃ and BF₃ catalysts. Catalyst performance is effectively optimized by catalyst concentration in a slurry reactor, catalyst calcination temperature and loading on a silica support. This class of catalysts has also been successfully applied to a number of other acid-catalyzed processes for the production of additives, including for the antioxidant nonyl diphenylamine.     

Hydrogenation of CO2 to formic acid on supported ruthenium catalysts

We report on the preparation and application of novel heterogeneous supported ruthenium catalysts. The catalysts are active in the synthesis of formic acid from the hydrogenation of carbon dioxide and are characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray powder diffraction analysis and transmission electron microscopy. Abundant hydroxyl groups, which interact with the ruthenium components, play an important role in the catalytic reactions. Highly dispersed ruthenium hydroxide species enhance the hydrogenation of CO₂, while crystalline RuO₂ species, which are formed from the relatively high ruthenium content or the pH of the solution during preparation of the catalyst, restrict the production of formic acid. Optimal activity of ruthenium hydroxide as a catalyst for the hydrogenation of CO₂ to formic acid is achieved over a γ-Al₂O₃ supported 2.0 wt% ruthenium catalyst, which is prepared in a solution of pH 12.8 with NH₃·H₂O as a titration solvent. A possible hydrogenation mechanism for the hydroxide ruthenium catalyst is proposed.     

Preparation of High-Density Fuel Through Dimerization of β-Pinene

High-density fuel was prepared by catalytic dimerization and subsequent hydrogenation. Different amounts of phosphotungstic acid (H₃PW₁₂O₄₀, HPW) were loaded on mesoporous silica (SBA-15) by a simple impregnation method to prepare HPW/SBA-15 catalysts. The prepared catalysts were mesoporous. Characterizations indicated that the dispersion and the specific surface area depend on the HPW amount. The obtained dimers from catalytic dimerization of β-pinene underwent isomerization and then dimerized to form the heterogeneous products. At the optimum load of HPW, the HPW/SBA-15 catalyst displayed the highest catalytic activity and the increased yield of dimer for a 3-h reaction. After the subsequent hydrogenation reaction, the obtained hydrogenated dimer products displayed a density and a volume calorific value comparable to those of commercial JP-10.     

The role of nickel in hydrodesulphurisation catalysts

The acidity and activity of promoted (with NiO) and unpromoted MoO₃/A1₂O3 catalysts were studied by ammonia adsorption, titration using acid/base colour indicators, and thiophene hydrodesulphurisation. The incorporation of nickel into supported MoO₃ produced significant changes in activity, which was attributed to changes in the number and strength of the acid sites. Specifically, the nickel decreased the concentration of highly acid sites and increased the number of sites with intermediate acidity in the oxide catalyst. At the same time, the nickel markedly increased the steady state catalytic activity but decreased the initial activity. Carbon and sulphur analyses, as well as acid site concentration of used catalysts, suggest that this behaviour may be associated with modifications brought about by nickel on MoS₂ crystallite growth and on deactivation by carbon deposition. These suggestions are found to be consistent with other effects attributed to the promoter, such as hydrogen spill-over and p-semiconductivity.     

Synthesis of 5-ethoxymethylfurfural from glucose catalyzed by porous tetra-component metal oxides solid acid

The production of 5-ethoxymethylfurfural (EMF) from cheap and abundant glucose feedstock has attracted a great deal of attention because of its potential applications. Herein, three porous tetra-component metal oxide solid acid catalysts (SO₄²⁻/ZFSA-A, SO₄²⁻/ZFSA-F-10, SO₄²⁻/ZFSA-F-20) containing both Brønsted and Lewis acid sites have been successfully synthesized and can efficiently catalyze the synthesis of EMF from glucose. Particularly, the SO₄²⁻/ZFSA-A, SO₄²⁻/ZFSA-F-10, and SO₄²⁻/ZFSA-F-20 catalysts were prepared under the template of sodium alginate, 10% F127, and 20% F127, respectively. The prepared catalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), N₂-adsorption–desorption isotherm, X-ray photoelectron spectroscopy (XPS), thermogravimetry (TG), temperature-programmed desorption of ammonia (NH₃-TPD), and pyridine infrared spectra (Py-FTIR). The characterization results indicated that all three catalysts have a porous structure. The pore distribution of the SO₄²⁻/ZFSA-A catalyst is mainly macroporous and mesoporous, while the SO₄²⁻/ZFSA-F-10 and SO₄²⁻/ZFSA-F-20 catalysts are mainly mesoporous. The SO₄²⁻/ZFSA-F-20 catalyst exhibited the highest catalytic performance due to its large specific surface area, desirable mesoporous structure, high total acidity (especially strong and super strong acidity), and appropriate Lewis/Brønsted acid ratio. By applying SO₄²⁻/ZFSA-F-20, the formation of EMF from glucose was successfully catalyzed and EMF was obtained at a yield of 34.56% after 12 h at 160°C. This yield is much higher compared with most other results achieved by solid acids catalysis. In addition, the reaction parameters such as reaction temperature, reaction time, glucose amount, and catalyst dosage were shown to have a significant effect on the catalytic performance. Notably, the SO₄²⁻/ZFSA-F-20 catalyst exhibited good reusability, as its activity did not significantly diminish after four rounds of repeated experiments and was successfully reactivated after calcination.     

磺酸功能化离子液体催化制生物柴油的性能

通过1-烯丙基咪唑与1,4-丁基磺酸内酯反应制备的两性离子分别与硫酸、三氟甲基磺酸、磷钨酸、磷钼酸和硅钨酸直接反应制备了5种磺酸功能化离子液体。采用¹H NMR、FTIR、TG/DTA等技术手段对其结构及热稳定性进行了表征。最后通过催化油酸与甲醇酯化反应制生物柴油过程对催化剂的催化活性和重复使用性进行了评价。结果表明,5种离子液体均具有高催化活性（高于浓硫酸）,并且重复使用4次后,催化活性基本保持不变。3种杂多酸离子液体不溶于产物,以固态形式与产物混合,为其回收和重复利用提供了有利条件。     

Microwave-Assisted Esterification of Oleic Acid Using an Ionic Liquid Catalyst

The combination of 1-butyl-3-methylimidazolium hydrogen sulfate ([Bmim]HSO₄) ionic liquid (IL) and microwave heating was used to esterify oleic acid as a green approach in biodiesel synthesis. To compare the heating systems, conventional heating and the ultrasonic method were employed but the microwave method was found to be more effective. H₂SO₄ and 1-methyl imidazole hydrogen sulfate ([Hmim]HSO₄) were also used in the esterification of oleic acid and their catalytic activities were compared to that of [Bmim]HSO₄. ILs provided some advantages such as reusability, easy recyclability, and very stable activity. There was only a small decrease in the catalytic activity of [Bmim]HSO₄ after four successive applications, which means that ILs can be reused, contrary to homogeneous catalysts. The combination of IL catalysts and microwave irradiation proved to be a potential alternative method for biodiesel production.     

Kinetic study of cellulose hydrolysis with tungsten-based acid catalysts

Tungsten plays an important role in transforming cellulose to C2 C3 polyols. In previous reports, the research focus was mainly on the C C cleavage reactions of cellulose catalyzed by various tungsten-containing catalysts, but less on its catalytic role in cellulose hydrolysis although it is usually considered as the rate-determining step in cellulose conversion. In this article, the method of determining kinetics parameters for hydrolyzing cellulose into glucose was developed. The effects of reaction temperature, different tungsten-based acid catalysts, and H⁺ concentration on reaction rate of hydrolyzing cellulose into glucose were quantitatively addressed. The relevant reaction rate equations with using H₃O₄₀PW₁₂, H₄O₄₀SiW₁₂, and H₂WO₄ as tungsten acid catalysts were obtained in developed batch continuous stirred tank reactors and validated by experimental data. The simulating analysis indicates that the reaction mechanism of cellulose hydrolysis can change with the temperature. H₃O₄₀PW₁₂ is the best candidate catalyst for obtaining the maximum glucose concentration.     

固体酸催化剂在缩醛反应中的研究进展

介绍了固体超强酸、分子筛、杂多酸、离子交换树脂、离子液体等在缩醛催化反应中的应用。评述了不同酸性催化剂对缩醛的催化活性、选择性等方面的影响。特别是纳米和介孔固体酸催化剂,这类催化剂较微孔催化剂催化活性更高,且具有更好的稳定性能。     

Lewis and Brønsted acid catalysis with AlMCM-41 and AlMMS: dependence on exchange cation

Mesoporous solid acid catalysts based on AlMCM-41 and AlMMS have been prepared. The two catalysts exhibit similar unidimensional pore structures with hexagonal symmetries. AlMMS shows less long-range order than AlMCM-41 but is considerably easier to synthesise. The catalytic activities have been measured and compared in the Lewis-acid-catalysed alkylation of toluene with benzyl chloride, and the Brønsted-acid-catalysed alkylation of toluene with benzyl alcohol. Activities have been measured for catalysts ion-exchanged with H⁺, Fe³⁺, Al³⁺ and Na⁺, and following thermal activation at temperatures of 150–350°C. They have also been compared with K10, a mesoporous acid-treated clay catalyst. Results show that the acid-treated clay is the most active of the three catalysts in both reactions. For all catalysts, the Fe³⁺ forms exhibit the highest Lewis acid catalytic activities, and the Al³⁺ and H⁺ forms show higher Brønsted acid activities. Infrared spectra of adsorbed pyridine show relative concentrations of Lewis and Brønsted acid sites consistent with this. Differences in the dependence of catalytic activities on thermal activation temperature are interpreted in terms of the hydration properties of the catalysts.