Fly ash supported calcium oxide as recyclable solid base catalyst for Knoevenagel condensation reaction

A new type of solid base catalyst has been prepared by loading of CaO on thermally activated fly ash, with the aim of being used as heterogeneous catalyst for fine chemical production. The prepared fly ash supported calcium oxide catalyst (FAC) was characterized by FT-IR spectroscopy, X-ray diffraction analysis, Scanning Electron Microscopy and atomic absorption spectroscopy. The catalytic activity of FAC was evaluated by Knoevenagel condensation of benzaldehyde and ethyl cyanoacetate as model test reaction under optimized conditions. The catalyst gave very high conversion (87%) of benzaldehyde to desired product ethyl (E)-α-cyanocinnamate with high purity. The catalyst was completely recyclable without significant loss in activity up to three reaction cycles, which confers its stability during reaction unlike commercial catalysts. Moreover this catalyst shows a promising future in providing environmentally clean process for the industrial sector.     

Catalytic applications of sulfonic acid functionalized mesoporous organosilicas with different fraction of organic groups in the pore wall

Organosulfonic acid functionalized mesoporous organosilicas with different fraction of organic groups in the pore wall was synthesized in the presence of P123 (EO₂₀PO₇₀EO₂₀) by controlling the molar ratio of tetramethoxysilane (TMOS) to 1,2-bis(trimethoxysilyl)ethane (BTME) in the initial mixture during the co-condensation process of silane precursors in acidic medium. Structural characterizations (X-ray diffraction, nitrogen sorption analysis, and transmission electron microscopy) show that all materials have ordered hexagonal mesoporous structure with large pore diameter (7–9 nm). The existence of ethane and sulfonic acid groups in the material was verified by ²⁹Si MAS and ¹³C CP MAS NMR and X-ray photoelectron spectroscopy (XPS). The mesoporous solid acids can adsorb both water and hexane (the adsorption capacity for water and hexane is 240 and 600 mg/g, respectively) due to the existence of surface hydroxyl groups, propyl sulfonic acid group, and the ethane moiety. These mesoporous solid acids are efficient catalysts for the dehydration of 1-butanol and the hydration of propylene oxide (PO).     

含磺酸基的介孔分子筛SO3H-SBA-15催化合成油酸丁酯

采用水热法直接合成了含磺酸基的介孔分子筛SO3H-SBA-15.以油酸与正丁醇为原料催化合成油酸丁酯,进行了不同催化剂的对比实验以及反应条件包括催化剂用量、反应温度、反应时间、酸醇摩尔比的考察.得到最佳反应条件为：催化剂质量分数为10%,反应温度120 ℃,反应时间3 h,酸醇摩尔比1∶2.     

Baeyer–Villiger-oxidation of cyclopentanone with aqueous hydrogen peroxide by acid heterogeneous catalysis

Using aqueous hydrogen peroxide containing 30% H₂O₂, solid acid catalysts were compared in their performance as catalysts for the transformation of cyclopentanone to δ-valerolactone. It could be shown that organic ion exchange resins with sulphonic acid groups providing acid functionality are promising catalysts for this reaction. The variation of several reaction parameters was studied in more detail. The obtained results were compared to investigations of zeolites and Nafion^® composite materials.     

Novel NaY zeolite-supported nanoscale zero-valent iron as an efficient heterogeneous Fenton catalyst

NaY zeolite-supported nanoscale zero-valent iron (NZVI/NaY) was synthesized by in-situ reduction of exchanged iron ions. Composition and structural characterization showed that α-Fe nanoparticles (50–100 nm) were supported on the surface of NaY zeolite. Catalytic efficiency of the composite powders was tested in degradation of potassium acid phthalate (KHP) solution (425 mg/L). At pH 3.5, the chemical oxygen demand (COD) removal ratio reached 79%. The NZVI/NaY exhibited efficient catalytic activity close to that of iron homogeneous catalyst but with less than 50% leaching of iron cations. Further, it performed well under much wider pH range (pH 1.7–5) compared to classic Fenton reagent, providing potential alternative as a novel heterogeneous Fenton catalyst for environmental remediation.     

Environmentally friendly, heterogeneous acid and base catalysis for the methylation of catechol: Chances for the control of chemo-selectivity

The properties of catalysts with (i) Brønsted-type acidity (H-mordenite and Al/P mixed oxide), (ii) Lewis-type acidity (Al trifluoride) or (iii) basic characteristics (Mg/Fe mixed oxide) were investigated in the gas-phase methylation of catechol. When methanol was used as the methylating agent, H-mordenite and AlF₃ gave high selectivities to guaiacol (the product of O-methylation) under mild reaction conditions, that is at very low catechol conversions. An increase in temperature led to the transformation of guaiacol to phenol and cresols, and to considerable catalyst deactivation. The basic catalyst Mg/Fe/O also favored an extensive degradation of guaiacol to phenol. On the mildly acidic catalyst Al/P mixed oxide a stable catalytic performance and a high selectivity to guaiacol at 40% catechol conversion were obtained. When methylformate, a more reactive methylating agent, was used with AlF₃ and Mg/Fe mixed oxide as catalysts, higher catechol conversions and slower deactivation rates could be achieved under mild reaction conditions, with a low extent of guaiacol degradation. However, methylformate rapidly decomposed when temperatures above 350 °C were used. Finally, tests were made by reacting catechol and diethoxymethane with acid catalysts, with the aim of synthesizing methylenedioxybenzene. The latter product was obtained with high selectivity, but with very low yield, due to both catalyst deactivation and decomposition of diethoxymethane.     

Sulfonic acid functionalized mesoporous SBA-15 for one-pot synthesis of substituted aryl-14H-dibenzo xanthenes and bis(indolyl) methanes

The comparative catalytic activity studies of biologically and industrially important compounds such as Xanthenes and bis (indolyl) methanes were evaluated over propylsulfonic acid functionalized SBA-15/SO₃H. The material was characterized via standard characterization techniques such as Powder X-ray diffraction, FTIR, Temperature programmed desorption studies of NH₃. The catalytic performance of SBA/SO₃H under environmentally benign conditions results in high yield of xanthenes compared to bis (indolyl) methanes and finally the mechanism for both the reactions were proposed.     

Selective oxidation of alcohols using novel crystalline Mo-V-O oxide as heterogeneous catalyst in liquid phase with molecular oxygen

Catalytic selective oxidation of benzyl alcohol with molecular oxygen under mild conditions was carried out over novel crystalline Mo-V-O oxide. The present research is focused on investigation of recycling, reusability and stability of the crystalline oxide in the liquid-phase reaction. The Mo-V-O oxide catalyst was used at least four times with comparable activities to that of fresh catalyst. The separation of the catalyst from reaction medium can stop the conversion of benzyl alcohol, and the addition of the catalyst to the reaction medium can trigger the reaction immediately. The catalytic oxidation of 2,3,6-trimethylphenol as a reference reaction suggested that there were no leached active species in the reaction mixture. The results of the ICP–MS analysis, XRD, and SEM characterization confirmed that the structure and composition of the catalyst were stable. Besides, the Mo-V-O oxide can catalyze the oxidation of a series of alcohols with high selectivities for corresponding carbonyl compounds.     

Stability and performance of silica gel-supported triphenylpyrylium cation as heterogeneous photocatalyst

Pyrylium salts are known to be good photocatalysts in aqueous solutions, able to achieve the photodegradation of several phenolic pollutants. Nevertheless, they exhibit a limited stability in these media. The rate of the hydrolytic reaction depends on the pH of the solution, the intensity of irradiation and the pyrylium concentration. Silica gel plates have been employed as inorganic support of the pyrylium cation in order to improve its stability and performance as a heterogeneous catalyst. The resulting material has been tested using ferulic acid as a model compound. Important degradation yields have been achieved (up to 80% after 6 h of solar irradiation). The catalyst is stable under these conditions and can be easily recovered for further use.     

Absence of expected side-reactions in the dehydration reaction of fructose to HMF in water over niobic acid catalyst

The catalytic dehydration of fructose (FRU) to 5-hydroxymethylfurfural (HMF) usually runs with the formation of several side products. Among these, levulinic acid (LA) is often reported as the product of a consecutive reaction of HMF re-hydration. In this work, side reactions of the dehydration of FRU performed in very green conditions (water as solvent and niobic acid as solid catalyst) are taken into account. Experimental evidences are given that, in the used conditions: i) HMF is a final stable product, ii) no formation of LA, either deriving from a consecutive reaction of HMF or directly from FRU transformation, was observed, and iii) LA does not react to give condensation products with any other chemical species present in the reaction mixture.     

对甲苯磺酸催化合成丁酸正戊酯

以对甲苯磺酸为催化剂,正丁酸与正戊醇为原料催化合成丁酸正戊酯。较系统地研究了酸醇量比、催化剂用量、带水剂用量及反应时间等条件对收率的影响。结果表明：在固定正丁醇用量为0.2mol的情况下,在n（正丁酸）：n（正戊醇）=1：1.4,催化剂占反应物料总量2.5%,带水剂环己烷的用量为6mL,反应时间2.5h的优化条件下,产品收率可达83.3%。     

Nb/HUSY as a highly active catalyst for the direct transformation of fructose to methyl lactate

One-pot conversion of biomass-based carbohydrates to methyl lactate (MLA), a versatile platform chemical for the production of food additives as well as the starting material of pharmaceutical industry, is an attractive green process. In this study, the Nb/HUSY catalysts with highly catalytic performance are successfully synthesized and used for the production of MLA from fructose. Remarkably, when using 2%Nb/HUSY as catalyst, the highest MLA yield of 56.1% is obtained with complete conversion of fructose under optimal conditions (140 °C for 6 h). The introduction of niobium into HUSY enhances the Lewis acid properties, which facilitates the stepwise process, involving the retro-aldol condensation and dehydration reactions. The as-prepared catalysts have shown promising potential for conversion of fructose to MLA and effectively inhibited the formation of by-products. More importantly, the catalyst exhibits superior stability and could be reused for at least four cycles.     

Chemical surface functionalization of bulk poly (p-phenylene sulfide) yields a stable sulfonic acid catalyst

Catalytic materials are important in industrial chemistry; these materials must be inexpensive and easy to process as well as resistant to chemicals, heat and structural loads. Poly (p-phenylene sulfide) (PPS) is a widely used and exceptionally resistant thermoplast. We demonstrate that the superficial regions of polymerized bulk PPS can be sulfonated using either SO₃ or acetyl sulfate, yielding a solid core of unaltered PPS with a sulfonic acid-functionalized surface. The SO₃ method was the most efficient and achieved 0.9 mmol H⁺ per gram of polymer. We show that the sulfonated surfaces function as durable solid acid catalysts for the dehydration of ethanol to diethyl ether. We also develop a simple method for the formation of porous PPS structures based on compression molding and porogen leaching. Based on these results, we suggest that surface functionalization of bulk PPS can be used to develop a novel class of moldable, easily produced and durable heterogeneous catalysts.     

Esterification of lauric acid with isopropyl alcohol by tricaprylylmethylammonium chloride as a catalyst in a liquid-liquid heterogeneous system

Experiments were performed on the esterification of lauric acid with isopropyl alcohol by tricaprylylmethylammonium chloride in a stirred vessel with a flat liquid-liquid interface. The observed initial rate of reaction was used to analyze the reaction mechanism combined with the catalyst, and to evaluate the several kinds of reaction rate constant, from which equilibrium constants were expressed as a function of reaction temperature. The analysis of reaction kinetics indicated that the reaction was between a very slow and slow reaction regime.     

Oxovanadium (IV) Schiff base complex immobilized on CPS microspheres as heterogeneous catalyst for aerobic selective oxidation of ethyl benzene to acetophenone

In this work, chloromethylated crosslinked polystyrene microspheres (CMCPS microspheres) were used as starting carrier, and a new immobilized bidentate Schiff base oxovanadium (IV) complex catalyst was prepared. The chloromethyl groups of CMCPS microspheres were first transformed into aminomethyl groups via Delepine reaction with hexamethylene tetramine (HMTA) as reagent, obtaining aminomethylated (AM) microspheres AMCPS. And then the Schiff base reaction between the primary amino group of AMCPS microspheres and salicylaldehyde (SA) was allowed to be conducted, resulting in Schiff base-type resin microspheres, SAAM-CPS, on which bidentate Schiff base ligand SAAM were chemically anchored. Subsequently, the coordination reaction between the ligand SAAM of SAAM-CPS microspheres and vanadyl sulfate (VOSO₄) was carried out, obtaining a new immobilized bidentate Schiff base-type oxovanadium (IV) complex, CPS-[VO(SAAM)₂] microspheres, namely a new heterogeneous oxovanadium (IV) complex catalyst was prepared. On the basis of fully characterizing the microspheres CPS-[VO(SAAM)₂], they were used in the catalytic oxidation of ethyl benzene with molecular oxygen. The experimental results show that in the oxidation reaction of ethylbenzene with molecular oxygen as oxidant, the heterogeneous oxovanadium (IV) complex catalyst, CPS-[VO(SAAM)₂], has high catalytic activity and excellent catalytic selectivity. Under the mild conditions such as at ordinary pressure of dioxygen and at a relatively low temperature of 110 °C, ethyl benzene can be transformed to acetophenone as a single product with a yield of 43%. It was found that the reaction temperature and the used amount of the solid catalyst effect on the oxidation reaction greatly. The catalyst CPS-[VO(SAAM)₂] has excellent recycle and reuse property.     

Kinetics and mechanism of liquid-phase alkylation of 3-methylthiophene with 2-methyl-2-butene over a solid phosphoric acid

Drastic regulations concerning sulfur content in fuels require the development of new processes in the refineries. In the case of gasoline, AOTS process based on the alkylation of thiophene by butenes was proposed. In the present work, we attempted to describe the mechanism of such a reaction with model molecules. Liquid-phase alkylation of 3-methylthiophene with 2-methyl-2-butene was performed on supported phosphoric acid. It is shown that this reaction is mainly selective to monoalkylation products. The kinetics is following an Eley–Rideal law and the reaction intermediate seems to be an ester of phosphoric acid or polyphosphate.     

离子液体相转移催化氧化苯甲醛制备苯甲酸

以N-甲基咪唑、四氟硼酸铵、正丁醇、溴化钠为主要原料合成了1-正丁基-3-甲基咪唑四氟硼酸咪唑盐型离子液体。以该离子液体作相转移催化剂研究了双氧水氧化苯甲醛制备苯甲酸的反应。结果表明,该氧化反应中加入离子液体可起到溶剂及相转移催化剂的作用,当反应5 h时,苯甲醛可达最大转化率88%。反应后离子液体可回收再利用。     

离子液体/氯化亚锡催化合成聚乳酸的研究

以离子液体氯化1-丁基-3-甲基咪唑盐([Bmim]Cl)和氯化亚锡(SnCl_2)的复盐为催化剂,L-乳酸为原料,采用直接溶液缩聚法制备聚乳酸(PLA);探讨了催化剂用量、反应温度及反应时间对PLA相对分子质量的影响,借助红外光谱和核磁共振氢谱对聚合物进行了表征。结果表明:当反应体系真空度约1 kPa,[Bmim]Cl/SnCl_2催化剂质量分数为反应物的0.7%,[Bmim]Cl与SnCl_2的摩尔比为1:2,反应温度170℃,反应时间12 h时,制备的PLA的粘均相对分子质量为3.5×10~4。