生物质炭基固体酸催化剂的制备

 以生物质木粉为原料, 采用炭化-磺化法制备了炭基固体酸催化剂, 并用于油酸与甲醇的酯化反应, 考察了制备条件对炭基固体酸催化剂活性的影响. 采用 X 射线衍射、红外光谱、热重分析、高分辨透射电子显微镜及元素分析等手段对催化剂进行了表征. 结果表明, 由生物质木粉制备的炭基固体酸催化剂具有较高催化酯化反应活性, 在 400 oC 下炭化 0.5 h, 135 oC 下磺化 1 h 制备的炭基固体酸催化剂在精馏分水连续酯化装置中催化油酸与甲醇的酯化反应 2 h 时, 酯化转化率达到 96%. 采用炭化-磺化法制备的生物质炭基固体酸催化剂具有蠕虫状的无序乱层炭结构, 磺酸基 (－SO3H) 含量高达 13.25%, 并且在 220 oC 以下时具有良好的热稳定性.     

Bio-Inspired Aerobic-Hydrophobic Janus Interface on Partially Carbonized Iron Heterostructure Promotes Bifunctional Nitrogen Fixation

Competition from hydrogen/oxygen evolution reactions and low solubility of N₂ in aqueous systems limited the selectivity and activity on nitrogen fixation reaction. Herein, we design an aerobic-hydrophobic Janus structure by introducing fluorinated modification on porous carbon nanofibers embedded with partially carbonized iron heterojunctions (Fe₃C/Fe@PCNF-F). The simulations prove that the Janus structure can keep the internal Fe₃C/Fe@PCNF-F away from water infiltration and endow a N₂ molecular-concentrating effect, suppressing the competing reactions and overcoming the mass-transfer limitations to build a robust “quasi-solid–gas” state micro-domain around the catalyst surface. In this proof-of-concept system, the Fe₃C/Fe@PCNF-F exhibits excellent electrocatalytic performance for nitrogen fixation (NH₃ yield rate up to 29.2 μg h⁻¹ mg⁻¹_cat. and Faraday efficiency (FE) up to 27.8 % in nitrogen reduction reaction; NO₃⁻ yield rate up to 15.7 μg h⁻¹ mg⁻¹_cat. and FE up to 3.4 % in nitrogen oxidation reaction).     

Preparation, characterization, and theoretical studies of azelaic acid derived from oleic acid by use of a novel ozonolysis method

Environmentally friendly manufacture of organic compounds has been intensively reexamined in recent years. Many excellent methods have been devised to produce organic compounds from renewable resources. Azelaic acid has been produced by ozonolysis of oleic acid. The reaction was performed in a Bach bubbling reactor, with fine bubbles, at high temperature (150 °C) without utilizing any catalyst or any solvent. Yield of the reaction was 20% after 2 h. Production of azelaic acid was confirmed by use of FT-IR and ¹H NMR spectroscopic data and high-performance liquid chromatography of both synthesized and reference azelaic acid. A theoretical study was performed to obtain quantum chemical data for azelaic acid and to optimize the molecule’s geometry.     

Silica iminopyridine-functionalized nanomaghemite enhances the oxygenation activity and durability of simple Co(II) salophen complex

A novel magnetically recoverable catalyst was produced by coordinative attachment of Co(II) salophen complex to silica iminopyridine (SIPy)-functionalized-γ-Fe₂O₃ magnetic nanoparticles (SMNP@SIPy/Co(II) salophen). The vibration spectra and compositional data provided sufficient evidences for the structural integrity of as-prepared organic–inorganic nanohybrid. The magnetic nanocatalyst proved to be an efficient and selective heterogeneous catalyst for oxidation of different benzylic alcohols and featured higher catalytic activity and stability than that of homogenous counterpart. A TOF of 151 h⁻¹ and TON of more than 322 were obtained for oxidation of 4-cholrobenzyl alcohol in this catalytic system. The supported catalyst could easily be recovered from the reaction mixture by an external magnetic field and reused for subsequent experiments with consistent catalytic activity.     

Modulation of Self-Separating Molecular Catalysts for Highly Efficient Biomass Transformations

The energetically viable fabrication of stable and highly efficient solid acid catalysts is one of the key steps in large-scale transformation processes of biomass resources. Herein, the covalent modification of the classical Dawson polyoxometalate (POMs) with sulfonic acids (-SO₃H) is reported by grafting sulfonic acid groups on the POM's surface followed by oxidation of (3-mercaptopropyl)trimethoxysilane. The acidity of TBA₆-P₂W₁₇-SO₃H (TBA=tetrabutyl ammonium) has been demonstrated by using ³¹P NMR spectroscopy, clearly indicating the presence of strong Brønsted acid sites. The presence of TBA counterions renders the solid acid catalyst as a promising candidate for phase transfer catalytic processes. The TBA₆-P₂W₁₇-SO₃H shows remarkable activity and selectivity, excellent stability, and great substrate compatibility for the esterification of free fatty acids (FFA) with methanol and conversion into biodiesel at 70 °C with >98 % conversion of oleic acid in 20 min. The excellent catalytic performance can be attributed to the formation of a catalytically active emulsion, which results in a uniform catalytic behavior during the reaction, leading to efficient interaction between the substrate and the active sites of the catalyst. Most importantly, the catalyst can be easily recovered and reused without any loss of its catalytic activity owing to its excellent phase transfer properties. This work offers an efficient and cost-effective strategy for large-scale biomass conversion applications.     

Janus纳米金稳定的Pickering乳液界面催化氧化性能

Janus纳米粒子的结构设计和简易合成是Pickering乳液界面催化的关键. 本文通过在Pickering乳液保护法中操纵共轭亚油酸的自组装、 自交联性和弱还原性, 合成了Janus型自交联吸附胶束修饰的纳米Fe₃O₄ (SCA-Fe₃O₄), 并在其表面原位还原金后, 合成了Janus型催化剂Au-SCA-Fe₃O₄, 考察其同时作为乳化剂和催化剂在乳液界面催化苯甲醇氧化生成苯甲醛的性能. 结果表明, 该Janus纳米粒子的金修饰量(质量分数)仅为0.66%, 兼具乳化性、 催化性和磁响应性. Au-SCA-Fe₃O₄可制备外观稳定(100 μm)和热稳定(90 ℃)的苯甲醇/水型Pickering乳液, 可显著提高互不相溶反应物与催化剂间的接触面积, 使其催化活性达到均匀纳米催化剂的2倍和非乳液催化时的3倍, 其在界面的不可转动性使苯甲醛的选择性高于99.9%, 避免了苯甲醛被过度氧化成苯甲酸.     

Oxidation of allylic alcohols, amines, and sulfides mediated by assembled triphase catalyst of phosphotungstate and non-cross-linked amphiphilic copolymer

A novel catalyst PWAA, an assembled complex of phosphotungstic acid (H₃PW₁₂O₄₀) and a non-cross-linked copolymer of N-isopropylacrylamide with an ammonium, was developed. It is an amphiphilic, cross-linked, and supramolecular insoluble complex and showed catalytic activity on oxidation with aqueous hydrogen peroxide. PWAA, used in 2.7×10⁻⁵-2.0×10⁻³ mol equiv., catalyzed oxidation of allylic alcohols, amines, and sulfides efficiently. The turnover number (TON) of PWAA reached up to 35,000. PWAA showed a good stability in organic/aqueous media and was reused three to five times.     

Catalytic wet air oxidation of oleic acid on ceria-supported platinum catalyst.effect of pH

Summary Catalytic wet air oxidation (CWAO) of oleic acid was carried out in a batch reactor on platinum supported ceria catalyst (Pt/CeO₂). Oleic acid is a water insoluble linear unsaturated fatty acid of 18 carbon atoms. To increase the homogeneity of the solution by saponification, the influence of NaOH additions in oleic acid CWAO mechanism and catalyst performances have been investigated. The oxidation of such molecule occurs by two types of mechanisms: successive carboxy-decarboxylation which leads essentially to CO₂and/or C-C bonds splitting in the alkyl chain inducing a high formation of acetic acid. With or without NaOH, the 5%Pt/CeO₂catalyst is active in the conversion of oleic acid and selective to carbon dioxide. In alkaline medium, oleic acid is initially saponified which increases the solubility of the reactant before it to be oxidized. Finally the oxidation is slightly delayed by the presence of NaOH. The catalyst characterizations show no significant difference before and after reaction.</o:p>     

Breaking Local Charge Symmetry of Iron Single Atoms for Efficient Electrocatalytic Nitrate Reduction to Ammonia

The electrochemical conversion of nitrate pollutants into value-added ammonia is a feasible way to achieve artificial nitrogen cycle. However, the development of electrocatalytic nitrate-to-ammonia reduction reaction (NO₃⁻RR) has been hampered by high overpotential and low Faradaic efficiency. Here we develop an iron single-atom catalyst coordinated with nitrogen and phosphorus on hollow carbon polyhedron (denoted as Fe−N/P−C) as a NO₃⁻RR electrocatalyst. Owing to the tuning effect of phosphorus atoms on breaking local charge symmetry of the single-Fe-atom catalyst, it facilitates the adsorption of nitrate ions and enrichment of some key reaction intermediates during the NO₃⁻RR process. The Fe−N/P−C catalyst exhibits 90.3 % ammonia Faradaic efficiency with a yield rate of 17980 μg h⁻¹ mg_cat⁻¹, greatly outperforming the reported Fe-based catalysts. Furthermore, operando SR-FTIR spectroscopy measurements reveal the reaction pathway based on key intermediates observed under different applied potentials and reaction durations. Density functional theory calculations demonstrate that the optimized free energy of NO₃⁻RR intermediates is ascribed to the asymmetric atomic interface configuration, which achieves the optimal electron density distribution. This work demonstrates the critical role of atomic-level precision modulation by heteroatom doping for the NO₃⁻RR, providing an effective strategy for improving the catalytic performance of single atom catalysts in different electrochemical reactions.     

Efficient and Bio‐inspired Conversion of Cellulose to Formic Acid Catalyzed by Metalloporphyrins in Alkaline Solution

A bio‐inspired approach for efficient conversion of cellulose to formic acid (FA ) was developed in an aqueous alkaline medium. Metalloporphyrins mimicking cytochrome P450 exhibit efficiently and selectively catalytic performance in catalytic conversion of cellulose. High yield of FA about 63.7% was obtained by using sulfonated iron(III ) porphyrin as the catalyst and O₂ as the oxidant. Iron(III )‐peroxo species, TSPPFe^IIIOO ⁻, was involved to cleave the C‐C bonds of gluconic acid to FA in this catalytic system. This approach used relatively high concentration of cellulose and ppm concentration of catalyst. This work may provide a bio‐inspired route to efficient conversion of cellulose to FA .     

Catalytic vapor-phase oxidation of 2,2,2-trifluoroethanol

The synthesis of trifluoroacetaldehyde by vapor-phase oxidation of 2,2,2-trifluoroethanol using supported vanadium catalysts was studied. Significant differences were observed in the reaction outcomes resulting from different types of catalysts. The ZrO₂- and Al₂O₃-supported catalyst demonstrated both high catalytic activity and selectivity. The addition of co-catalysts such as MoO₃ or SnO₂ improved catalytic performance (Selectivity: up to 91%; S.T.Y.: >200 g L⁻¹ h⁻¹). The experimental results on catalyst lifetime showed a marked decrease in the activity of the Al₂O₃-supported catalyst within tens of hours, while the ZrO₂-supported catalyst showed little, if any, performance alterations for 2000 h.     

Kinetics of osmium(VIII) catalyzed oxidation of allyl alcohol by potassium bromate in aqueous acidic medium‐autocatalysis in catalysis

The kinetics of oxidation of allyl alcohol with potassium bromate in the presence of osmium(VIII) catalyst in aqueous acid medium has been studied under varying conditions. The active species of oxidant and catalyst in the reaction were understood to be Bro₃⁻ and H₂OsO₅, respectively. The autocatalysis exhibited by one of the products, that is, Br⁻, was attributed to complex formation between bromide and osmium(VIII). A composite scheme and rate law were possible. Some reaction constants involved in the mechanism have been evaluated. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 583–589, 1999     

Asymmetric Aza-Diels–Alder Reaction with Ion-Paired—Iron Lewis Acid—Brønsted Acid Catalyst

The development and use of a multiple-activation catalyst with ion-paired Lewis acid and Brønsted acid in an asymmetric aza-Diels–Alder reaction of simple dienes (non-Danishefsky-type electron-rich dienes) was achieved by utilizing the [FeBr₂]⁺[FeBr₄]⁻ combination prepared in situ from FeBr₃ and chiral phosphoric acid. Synergistic effects of the highly active ion-paired Lewis acid [FeBr₂]⁺[FeBr₄]⁻ and a chiral Brønsted acid are important for promoting the reaction with high turnover frequency and high enantioselectivity. The multiple-activation catalyst system was confirmed using synchrotron-based X-ray absorption fine structure measurements, and theoretical studies. This study reveals that the developed catalyst promoted the reaction not only by the interaction offered by the ion-paired Lewis acid and the Brønsted acid but also noncovalent interactions.     

One-Pot Synthesis of Heterobimetallic Metal–Organic Frameworks (MOFs) for Multifunctional Catalysis

A one-pot synthesis of bimetallic metal–organic frameworks (Co/Fe-MOFs) was achieved by treating stoichiometric amounts of Fe and Co salts with 2-aminoterephthalic acid (NH₂-BDC). Monometallic Fe (catalyst A) and Co (catalyst F) were also prepared along with mixed-metal Fe/Co catalysts (B–E) by changing the Fe/Co ratio. For mixed-metal catalysts (B–E) SEM energy-dispersive X-ray (EDX) analysis confirmed the incorporation of both Fe and Co in the catalysts. However, a spindle-shaped morphology, typically known for the Fe-MIL-88B structure and confirmed by PXRD analysis, was only observed for catalysts A–D. To test the catalytic potential of mixed-metal MOFs, reduction of nitroarenes was selected as a benchmark reaction. Incorporation of Co enhanced the activity of the catalysts compared with the parent NH₂-BDC-Fe catalyst. These MOFs were also tested as electrocatalysts for the oxygen evolution reaction (OER) and the best activity was exhibited by mixed-metal Fe/Co-MOF (Fe/Co batch ratio=1). The catalyst provided a current density of 10 mA cm⁻² at 410 mV overpotential, which is comparable to the benchmark OER catalyst (i.e., RuO₂). Moreover, it showed long-term stability in 1 m KOH. In a third catalytic test, dehydrogenation of sodium borohydride showed high activity (turnover frequency=87 min⁻¹) and hydrogen generation rate (67 L min⁻¹ g⁻¹ catalyst). This is the first example of the synthesis of bimetallic MOFs as multifunctional catalysts particularly for catalytic reduction of nitroarenes and dehydrogenation reactions.     

Carbon-Based Electron Buffer Layer on ZnOx−Fe5C2−Fe3O4 Boosts Ethanol Synthesis from CO2 Hydrogenation

The conversion of CO₂ into ethanol with renewable H₂ has attracted tremendous attention due to its integrated functions of carbon elimination and chemical synthesis, but remains challenging. The electronic properties of a catalyst are essential to determine the adsorption strength and configuration of the key intermediates, therefore altering the reaction network for targeted synthesis. Herein, we describe a catalytic system in which a carbon buffer layer is employed to tailor the electronic properties of the ternary ZnO_x−Fe₅C₂−Fe₃O₄, in which the electron-transfer pathway (ZnO_x→Fe species or carbon layer) ensures the appropriate adsorption strength of −CO* on the catalytic interface, facilitating C−C coupling between −CH_x* and −CO* for ethanol synthesis. Benefiting from this unique electron-transfer buffering effect, an extremely high ethanol yield of 366.6 g_EtOH kg_cat⁻¹ h⁻¹ (with CO of 10 vol % co-feeding) is achieved from CO₂ hydrogenation. This work provides a powerful electronic modulation strategy for catalyst design in terms of highly oriented synthesis.     

Magnetic Solid Base Catalyst Fe3O4@Gly Used as Acid‐Resistant Catalyst for Biodiesel Production

Fe₃O₄@Gly nanoparticles were synthetized by coprecipitation and studied in the transesterification of soybean oil and methanol to determine its performance for biodiesel synthesis. The magnetism and catalytic performance of Fe₃O₄@Gly alkaline catalyst were investigated in detail. With a catalyst dosage 1.5 wt %, methanol/soybean oil ratio of 15:1, reaction temperature of 65 °C, and a reaction time of 3 h, the highest yield of biodiesel was 95.8%. The strong base catalyst CaO was used as comparison, from which it was seen that Fe₃O₄@Gly was more hydrophobic than the former. Moreover, because of the complete dissolution of oleic acid in methanol, Fe₃O₄@Gly could make better contact with oleic acid, which made it perform far better than pure CaO in oleic acid. In addition, after four times recycling, the yield of biodiesel was still 86.6%. The results show that Fe₃O₄@Gly possesses excellent properties of acid resistance and recyclability. The catalyst can be a high‐efficiency alkaline heterogeneous catalyst for biodiesel production.     

The effect of encapsulated Zn-POM on the catalytic activity of MIL-101 in the oxidation of alkenes with hydrogen peroxide

Zinc monosubstituted Keggin heteropolyanion [PZnMo₂W₉O₃₉]^5? was electrostatically bound to nanocages of MIL-101 polymer matrix. The Zn-POM@MIL-101 catalyst was characterized by XRD, N₂ adsorption, atomic absorption (AAS), and FT-IR spectroscopic methods. The catalytic activity of the new composite material, Zn-POM@MIL-101, was assessed in the oxidation of alkenes using aqueous hydrogen peroxide as oxidant. Zn-POM@MIL-101/H₂O₂ catalytic system demonstrated good catalytic activity in the oxidation reactions. Zn-POM@MIL-101 was reusable for three catalytic cycles. While the MIL-101 matrix is an active catalyst in these oxidation reactions, the presence of Zn-POM significantly changed the selectivity and reaction times.     

Influence of the reaction parameters on the Pd—HCl catalysed synthesis of phenylacetic acid derivatives via reduction of mandelic acid derivatives with carbon monoxide

The catalytic system Pd/C—HCl is highly active in the reduction of mandelic acid derivatives to phenylacetic acid derivatives with carbon monoxide when the aromatic ring is para-substituted with a hydroxy group. Typical reaction conditions are: 70–110 °C, 20–100 atm of carbon monoxide, benzene—ethanol as reaction medium, substrate/Pd=10²–10⁴/1, HCl/substrate=0.3–0.8/1. [Pd] = 10⁻² −10⁻⁴ M. When the catalytic system is used in combination with PPh₃ a slightly higher activity is observed. Comparable results are observed when using a Pd(II) catalyst precursor such as PdX₂, in combination with PPh₃, or PdX₂(PPh₃)₂ (XCl, AcO). When operating at 110 °C, decomposition to metallic palladium occurs. Pd(II) complexes with diphosphine ligands, such as diphenylphosphinemethane, -ethane, -propane or -butane, do not show any catalytic activity and are recovered unchanged. These observations suggest that Pd(0) complexes play a key role in the catalytic cycle. The proposed catalytic cycle proceeds as follows: the chloride ArCHClCOOR, formed in situ upon reaction of ArCHOHCOOR with hydrochloric acid, oxidatively adds to a Pd(0) species with formation of a catalytic intermediate having a Pd—[CH(Ar)COOR] moiety, which inserts a CO molecule, yielding an acyl intermediate of the type Pd—[COCH(Ar)COOR]. The nucleophilic attack of H₂O on the carbon atom of the carbonyl ligand gives back the Pd(0) complex to the catalytic cycle and yields a phenylmalonic acid derivative, which produces the final product, ArCH₂COOR, upon CO₂ evolution. Alternatively, protonolysis of the intermediate having a Pd—[CH(Ar)COOR] moiety yields directly the final product and a Pd(II) species, which is then reduced by CO to Pd(0). Moreover, no catalytic activity is observed when the Pd/C—HCl system is used in combination with any one of the above diphosphine ligands, probably because these ligands block the sites on the catalyst able to promote the catalytic cycle or because they prevent the reduction of Pd(II) to Pd(0). The influence of the following reaction parameters has been studied: concentration of HCl, PPh₃, palladium and substrate, pressure of carbon monoxide, the temperature, reaction time and solvent. The results are compared with those obtained in the carbonylation of aromatic aldehydes to phenylacetic acid derivatives catalyzed by the same system, for which it has been proposed that the catalysis occurs via carbonylation of the aldehyde to a mandelic acid derivative as an intermediate, which is further reduced with CO to yield the final product.     

Kinetics of vanadium (V) catalyzed oxidation of gallic acid by potassium bromate in acid medium

The kinetics of oxidation of gallic acid with potassium bromate in the presence of vanadium(V) catalyst in aqueous acid medium has been studied under varying conditions. The active species of catalyst and oxidant in the reaction were understood to be HBrO₃ and VO₂⁺. The autocatalysis exhibited by one of the products, i.e. Br⁻, was attributed to complex formation between bromide and vanadium(V). A composite scheme and rate law were possible, some reaction constants involved in the mechanism have been evaluated. © 1996 John Wiley & Sons, Inc.     

Synthesis of ceria nanoparticles for the catalytic activity of cyclohexene epoxidation and selective detection of nitrite

Based on a few noteworthy features, cerium oxide nanoparticles have gained significance in nanotechnology. The effective microwave combustion method (MCM) and the conventional sol–gel (CRSGM) technologies are used in this study to successfully generate the crystalline CeO₂ nanoparticles (NPs). Additionally, using a variety of spectroscopic and analytical methods, the synthesized CeO₂ NPs are examined to assess to understand their structure and morphology. The XRD patterns of CeO₂ NPs show that the structure exhibits a face-centered cubic lattice. Then, with demonstrated good conversion and selectivity, the impact of the epoxidation reaction of cyclohexene was examined. Finally, it can be said that using CeO₂ nanoparticles is an efficient strategy to increase the catalytic activity toward the epoxidation reaction of cyclohexene. In the presence of acetonitrile as a solvent and H₂O₂ as an oxidant, the catalyst samples utilized in the cyclohexene epoxidation reaction were examined. In this study, the CeO₂ catalyst outperformed all other catalysts in terms of cyclohexene maximal conversion and selectivity. After six prolonged cycles, the conversion of cyclohexene oxidation using CeO₂ NPs shows reasonable recyclability and conversion efficiency, making it the best catalyst for an industrial production application.Additionally, the upgraded CeO₂ nanoparticle electrode for nitrite detection has a linear concentration range (0.02–1200 M), a low detection limit (0.22 M), and a higher sensitivity (1.735 A M⁻¹ cm⁻²). CeO₂ NPs, on the other hand, have a quick response time, excellent sensitivity, and high selectivity. Additionally, the manufactured electrode is used to find nitrite in various water samples. Finally, it can be said that using CeO₂ NPs is an efficient strategy to increase the catalytic activity toward cyclohexene oxidation and nitrite.