镁基固体催化剂催化酯交换反应制备生物柴油研究进展

生物柴油是一种重要的可再生能源,非均相催化甘油酯酯交换反应制备生物柴油是当前的研究热点,而高活性的非均相催化剂则是非均相催化工艺的核心。镁基催化剂由于其原料来源广泛、价格低廉,受到了广泛关注。综述近年来镁基催化剂催化酯交换反应制备生物柴油的研究进展,重点介绍了镁基催化剂制备方法、组成、结构、反应条件等对催化酯交换反应活性的影响,并探讨了镁基催化剂目前存在的不足以及今后的发展方向。     

Synthesis and characterization of hierarchical ZSM-5 zeolite containing Ni nanoparticles for one-pot reductive amination of aldehydes with nitroarenes

In this paper, we wish to report the synthesis and characterization of nickel nanoparticles supported on acidic form of ZSM-5 zeolite (Ni/H-mZSM-5) with microporous/mesoporous hierarchical structure. This catalyst was effectively employed as novel acid-metal bi-functional heterogeneous catalyst for direct one-pot reductive amination of aldehydes with nitroarenes in the presence of NaBH₄ as a mild reducing agent. Excellent yields at room temperature and short reaction time in aqueous media conditions were obtained.     

HClO4–SiO2 as a novel and recyclable catalyst for the synthesis of 2,4,6-triarylpyridines under solvent-free conditions

A simple and efficient synthesis of 2,4,6-triarylpyridines using a variety of aromatic and heteroaromatic aldehydes in the presence of solid-supported perchloric acid (HClO₄–SiO₂) as a heterogeneous catalyst at 120 °C under solvent-free conditions. The present methodology offers several advantages such as excellent yields, simple procedure, shorter reaction times (4–6 h), milder conditions and the catalyst exhibited remarkable reusable activity.     

相转移催化剂TEBAB的合成研究及催化活性测试

相转移催化剂可改善反应条件,提高收率,使反应慢、产率低的非均相反应正常进行。但是合成成本高,很难实现工业化生产。根据季铵盐类相转移催化剂的烷基化合成原理,设计并合成出未见文献报道的新型季铵盐类相转移催化剂三乙基丁基溴化铵(TEBAB),以降低成本,提高市场竞争力。该合成以三乙胺和溴代正丁烷为原料,DMF为反应溶剂进行反应,考查了配料比、反应温度、反应时间等条件对产物产率的影响,应用三因素三水平的正交实验法确定该合成的最佳工艺条件为:配料比为1.0∶1.5,反应温度102℃,反应时间1h。经过熔点测定和傅立叶变换红外光谱仪对其进行结构表征确认,产品的熔点为99.6℃~102.4℃,红外谱图分析确认所合成产品为目的物。最后,通过诺氟沙星衍生物合成的相转移催化反应实验验证了其催化活性。     

Solventless synthesis of cyclic carbonates from carbon dioxide and epoxides catalyzed by silica-supported ionic liquids under supercritical conditions

A silica-supported ionic liquid proved to be an efficient heterogeneous catalyst for solventless synthesis of cyclic carbonates from epoxides and carbon dioxide under supercritical conditions, which requires no additional organic solvents either for the reaction or for the separation of product. The effects of reaction time, temperature and other reaction parameters on the reaction are investigated. High yields with excellent selectivity were obtained. The purity of product separated directly by filtration from the reaction mixture, reached 99% without further purification process. Moreover, the catalyst can be easily recovered by filtration and reused over four times with slight loss of its catalytic activity. The process represents a simple, ecologically safer, cost-effective route to cyclic carbonates with high product quality, as well as easy product recovery and catalyst recycling.     

Comparison of supports for the direct synthesis of hydrogen peroxide from H2 and O2 using Au–Pd catalysts

The direct synthesis of hydrogen peroxide from H₂ and O₂ using a range of supported Au–Pd alloy catalysts is compared for different supports using conditions previously identified as being optimal for hydrogen peroxide synthesis, i.e. low temperature (2 °C) using a water–methanol solvent mixture and short reaction time. Five supports are compared and contrasted, namely Al₂O₃, -Fe₂O₃, TiO₂, SiO₂ and carbon. For all catalysts the addition of Pd to the Au only catalyst increases the rate of hydrogen peroxide synthesis as well as the concentration of hydrogen peroxide formed. Of the materials evaluated, the carbon-supported Au–Pd alloy catalysts give the highest reactivity. The results show that the support can have an important influence on the synthesis of hydrogen peroxide from the direct reaction. The effect of the methanol–water solvent is studied in detail for the 2.5 wt% Au–2.5 wt% Pd/TiO₂ catalyst and the ratio of methanol to water is found to have a major effect on the rate of hydrogen peroxide synthesis. The optimum mixture for this solvent system is 80 vol.% methanol with 20 vol.% water. However, the use of water alone is still effective albeit at a decreased rate. The effect of catalyst mass was therefore also investigated for the water and water–methanol solvents and the observed effect on the hydrogen peroxide productivity using water as a solvent is not considered to be due to mass transfer limitations. These results are of importance with respect to the industrial application of these Au–Pd catalysts.     

Synthesis of cenosphere supported heterogeneous catalyst and its performance in esterification reaction

A heterogeneous catalyst has been developed from cenosphere, a byproduct generated in thermal power plant. The performance of catalyst was investigated in the esterification of propionic acid and ethanol. The catalyst was characterized by FTIR, X-ray diffraction, field emission scanning electron microscope, and Brunauer–Emmett–Teller surface area and surface acidity analysis. The response surface methodology (RSM) with the Box–Behnken design was employed to design the experiments as well as to optimize the various process parameters such as catalyst loading, alcohol/acid molar ratio, and reaction temperature. The characterization revealed that the cenosphere supported catalyst possessed increased amounts of silica content, surface hydroxyl groups, surface area as well as surface acidity as compared with that of pristine cenosphere. The catalyst showed an excellent activity in the esterification reaction with a maximum conversion up to 91%. The RSM model well fitted the experimental data and predicted optimal conditions which were validated experimentally with a good agreement. The recyclability study showed a significant catalytic stability up to three reaction cycles. This study reveals that the cenosphere supported catalyst can be used as a potential catalyst in the esterification reaction may replace the conventional homogeneous acid catalyst.     

Nuclear magnetic resonance imaging of an operating gas–liquid–solid catalytic fixed bed reactor

This work reports our pioneering application of the nuclear magnetic resonance imaging (MRI) technique to the dynamic in situ studies of gas–liquid–solid reactions carried out in a catalytic trickle bed reactor at elevated temperature. The major advance of these studies is that MRI experiments are performed under reactive conditions. We have applied MRI to map the distribution of liquid phase inside a catalyst pellet as well as in a catalyst bed in an operating trickle-bed reactor. In particular, our studies have revealed the existence of the oscillating regimes of the heterogeneous catalytic hydrogenation reaction caused by the oscillations of the catalyst temperature and directly demonstrated the existence of the coupling of mass and heat transport and phase transitions with chemical reaction. The existence of the partially wetted pellets in a catalyst bed which are potentially responsible for the appearance of hot spots in the reactor has been also visualized. The combination of NMR spectroscopy with MRI has been used to visualize the spatial distribution of the reactant-to-product conversion within an operating reactor.     

A simulation study on gas-to-liquid (natural gas to Fischer–Tropsch synthetic fuel) process optimization

A simulation study on gas-to-liquid (natural gas to Fischer–Tropsch synthetic fuel) process was carried out in order to find optimum reaction conditions for maximum production of synthetic fuel. Optimum operating condition for GTL (gas-to-liquid) process was determined by changing reaction variable such as temperature. During the simulation, overall synthetic process was assumed to proceed under steady-state conditions. It was also assumed that physical properties of reaction medium were governed by RKS (Redlich–Kwong–Soave) equation. ATR (auto-thermal reforming) in synthesis gas production unit and slurry phase reaction over Co-based catalyst in FTS (Fischer–Tropsch synthesis) unit were considered as reaction models for GTL process. The effect of reaction temperature on CO conversion and C₅–C₂₀ hydrocarbon yield in FTS unit was mainly examined. Simulation and experimental results showed that optimum reaction temperature in FTS unit was 255 °C. Simulation results were also compared to experimental results to confirm the reliability of simulation model. Simulation results were reasonably well matched with experimental results.     

High-throughput synthesis and screening of V–Al–Nb and Cr–Al–Nb oxide libraries for ethane oxidative dehydrogenation to ethylene

High-throughput synthesis and screening of mixed metal oxide libraries for ethane oxidative dehydrogenation to ethylene have been developed. A 144-member catalyst library was prepared on a 3 in. quartz wafer. An apparatus for screening catalytic activity and selectivity of a 144-member catalyst library consists of a reaction chamber, where each member can be heated individually by a CO₂ laser and reactant gases can be delivered locally to each member. The reaction products, ethylene and CO₂, are detected by photothermal deflection spectroscopy and by mass spectrometry. A 144-member catalyst library can be screened in slightly more than 2 h. V–Al–Nb oxide and Cr–Al–Nb oxide libraries are illustrated as examples. V–Al–Nb oxide catalysts are high temperature catalysts and Nb did not affect the catalytic activity of the V–Al oxides in contrast to the effect of Nb found in Mo–V–Nb oxides. However, for the Cr–Al–Nb oxide library, the most active catalyst contains about 4% Nb. These results suggest that a fine composition mapping is necessary for discovery of new heterogeneous catalysts in those ternary systems.     

一步酯交换法合成碳酸二甲酯催化剂研究进展

综述了一步酯交换法合成碳酸二甲酯催化剂的研究进展,阐述了所用催化剂的组成、性质和催化活性,从反应产物分析推测了反应机理。适宜孔径的碱性沸石分子筛等多孔材料将是合成多相催化剂载体的首选材料。制备高活性、高选择性、高稳定性的多相催化剂将是今后催化剂研究的方向。     

Synthesis and characterization of poly(4-vinylpyridine)/MCM-48 catalyst for one-pot synthesis of substituted 4H-chromenes

In this paper, we wish to report the synthesis and characterization of poly(4-vinylpyridine) supported on MCM-48 by in situ polymerization of 4-vinylpyridine in the presence of MCM-48. This catalyst was effectively employed as a novel heterogeneous basic catalyst for the one-pot synthesis of 4H-chromenes in aqueous medium. This catalyst was easily prepared, and showed considerable level of reusability.     

Continuous Transesterification Reaction of Residual Frying Oil with Pressurized Ethanol Using KF/Clay as Catalyst

The efficiency of a heterogeneous potassium fluoride (KF)/clay catalyst in continuous ester production from residual frying oil using pressurized ethanol is evaluated. Reactions without catalysts are conducted to determine the effect of the catalyst on ester yield. To verify the performance of the catalyst, the reactions are conducted for 3 h with determination of the ester yield every 30 min and characterization of the catalyst after each reaction. The influence of the temperature, catalyst mass used in the catalytic bed, and the residence time are evaluated. KF/clay is found to be efficient in ester synthesis and provides better results compared with non‐catalytic reactions and the formation of esters is favored on increasing the temperature. The ester yields remain stable over time at 275 and 300 °C but at 225 and 250 °C the yields decrease by 48.42% and 38.40%, respectively. This may be due to the lower diffusion coefficient at these temperatures, implying that the reaction occurs preferentially at the catalyst surface. There is an increase in yield with an increase in the catalyst mass up to 2 g. The catalyst maintains its morphological characteristics after the reaction and the average mass loss in each reaction is <8%. Practical Applications: Transesterification at high temperature under pressurized conditions has great potential in biodiesel production, due to the efficiency in obtaining esters in short reaction times. In addition, the use of inexpensive and easily obtained clay‐based catalysts contributes to higher yields and allows milder operating conditions. These factors make it possible to obtain biodiesel using a low‐cost raw material (residual frying oil), under pressurized conditions, which will be of interest worldwide due to the various benefits linked to its use.     

二氧化碳和甲醇直接合成碳酸二甲酯研究进展

从均相及多相催化剂体系和反应条件等方面,综述了近年来二氧化碳和甲醇直接合成碳酸二甲酯的研究开发最新进展。介绍了均相催化剂体系包括有机金属烷氧基化合物、碱土金属烷氧基化合物、碱性催化剂和乙酸盐催化剂;多相催化剂体系包括负载型金属催化剂、负载型固体碱催化剂和氧化物催化剂。对催化剂及反应体系的设计、光催化剂、杂多酸催化剂、离子液体体系、助催化剂及吸水剂的使用、微波加热、膜反应器以及超临界二氧化碳溶剂体系进行了评述。     

Selectivity enhancement in the catalytic heterogeneous hydrogenation of limonene in supercritical carbon dioxide by an ionic liquid

Ionic liquids as coated catalysts or additives tremendously alter the selectivity pattern of the heterogeneous solid catalyst in the selective hydrogenation of limonene. The conventional monometallic ruthenium over alumina catalyst combined with an ionic liquid enables the one-pot synthesis of the intermediate p-menthene through limonene hydrogenation in supercritical carbon dioxide. Among eight screened imidazolium ILs, [C₁₀mim]NTf₂ was employed as additive, or as the coating agent of ruthenium catalyst in the reaction under supercritical conditions.The coating of the heterogeneous catalyst allows the selective production of p-menthene and increases the conversion level of limonene (>99%) compared to the conversion of limonene in the reaction carried out in the presence of an ionic liquid as an additive. Results of the catalyst recycling indicate that there is no depletion of catalyst reactivity even after four successive cycles of operation under the studied reaction conditions. Further hydrogenation of p-menthene is strongly inhibited by employing an ionic liquid. The solubility of limonene or p-menthene in an ionic liquid governs the selective hydrogenation of limonene towards p-menthene.     

An efficient method for the synthesis of 2-aminothiazoles using silica chloride as a heterogeneous catalyst

This article describes a facile and efficient synthesis of 2-aminothiazoles under mild reaction conditions with quantitative yields using silica chloride as an effective heterogeneous catalyst.     

以碳酸钾为高效非均相催化剂合成2-氨基-3-氰基-4,5,6,7-四氢苯并[b]噻吩

提出了一种以碳酸钾为非均相固体碱催化剂的通过三组分Gewald反应一锅法简易高效合成2-氨基-3-氰基-4,5,6,7-四氢苯并[b]噻吩的新方法。考察了催化剂用量、反应时间和溶剂类型对目标产物收率的影响,确定最佳反应条件如下:催化剂用量为20%(摩尔分数),反应时间为3.0h,溶剂为乙醇。该方法具有催化剂价廉高效、分离纯化简单、反应时间短以及产物收率高等优点。     

Hydrothermal synthesis of pure AlPO4-5 without fluoride medium: synthesis, characterization and application as a support

Hydrothermal synthesis of pure AlPO₄-5 crystals using various reaction gels is reported. The influence of synthesis conditions on the purity of the AlPO₄-5 has been studied by changing Al sources and factors affecting the pH of the starting gel. It was observed that the additive acid to adjust the gel pH value has strongly influenced both the crystallinity and purity of the resulting AlPO₄-5 crystals. The crystals were characterized by XRD, FT-IR, TGA, BET, SEM and TPD techniques. The resulting microporous AlPO₄-5 was used as an efficient support for a functional polymer to produce an efficient heterogeneous basic nanocomposite catalyst. The catalytic activity of this novel nanocomposite was tested for Knoevenagel reaction under solvent-free conditions at room temperature. The catalyst showed a considerable degree of reusability besides very good activity.     

非热等离子体催化转化C1分子及其催化剂研究进展

非热等离子体催化具有反应条件温和、启动快和反应器结构紧凑等特点,在C₁分子催化转化领域（如CO₂加氢、甲烷活化、水煤气变换反应和甲醇重整制氢）有着广阔的应用前景。具体来说,等离子体特有的高能电子可在气相中快速活化稳定性极强的C₁分子并生成活性物质,接着与催化剂结合发生表面化学反应,从而实现常温常压下C₁分子的高效转化。然而,等离子体与催化剂之间的协同作用机制以及催化机理极为复杂,仍有待进一步研究。本综述简单介绍了非热等离子体催化转化C₁分子的近期研究进展,重点探讨了适用于非热等离子 体的催化剂研究以及催化机理的高级原位表征。最后,提出了非热等离子体催化转化C₁分子的未来发展方向：①设计并构筑适用于非热等离子体催化的高效催化剂,并研究其构效关系;②发展高级原位表征技术,揭示活性物质的作用机理以及催化机理;③设计并构建高效的等离子体催化反应器,并建立反应器的理论模型和数值模拟方法,科学指导等离子体反应器的设计、优化和放大。     

Heteropolyanions based catalysts for paraffins isomerization

n-Hexane isomerization was carried over Cs_xH_3−xPW₁₂O₄₀ catalysts promoted with Pt by mechanical mixing with a Pt on alumina catalyst. Different parameters as caesium and platinum content in the catalyst, temperature and atmosphere of heteropolyacids pre-treatment were optimized. The catalytic performances of the best catalyst were compared with those of industrial Pt promoted mordenite. 0.3 wt.% Pt-promoted Cs₂H₁PW₁₂O₄₀ pre-treated under hydrogen flow at 473 K showed the highest conversion and selectivity. Its performances are very close to those of the industrial zeolitic catalyst in the same reaction conditions. The gain in dibranched isomers selectivity is really promising for the future. With this catalyst, the reaction proceeds by a non-ideal bifunctional mechanism resulting from the superposition of a monofunctional acid and a bifunctional metal–acid mechanism.