A reusable polymer‐supported copper(I) catalyst for triazole click reaction on water: An experimental and computational study

In the search for establishing a clickable copper‐catalysed (3 + 2) Huisgen azide–alkyne cycloaddition (CuAAC) reaction under strict conditions, in particular in terms of preventing the presence of copper particles/traces in reaction products and using an environmentally benign medium such as water, we describe here the synthesis of an aminomethyl polystyrene‐supported copper(I) catalyst (Cu(I)‐AMPS) and its characterization by means of Fourier transform infrared and energy‐dispersive X‐ray spectroscopies and scanning electron microscopy. Cu(I)‐AMPS was found to be highly active in the CuAAC reaction of various organic azides with alkynes affording the corresponding 1,4‐disubstituted 1,2,3‐triazoles in a regioselective manner in air at room temperature and using water as solvent. The insolubility and/or partial solubility of the organic azide and alkyne precursors as well as the heterogeneous Cu(I)‐AMPS catalytic system points to the occurrence of the cycloaddition at the organic–water interface ‘on water’ affording quantitative yields of water‐insoluble 1,2,3‐triazoles. A mechanistic study was performed using density functional theory aiming at explaining the observed reactivity and selectivity of the Cu (I)‐AMPS catalyst in CuAAC reactions.     

基于超重力技术开展Co-N-CNTs催化剂制备及其氧还原性能的研究

开发高效的非贵金属氧还原(ORR)催化剂是促进燃料电池商业化进程的关键。本研究利用超重力技术制备了一种优良的非贵金属ORR催化剂Co-N-CNTs。物理表征表明,通过超重力技术可以使作为活性位点的金属Co纳米颗粒均匀分布在Co-N-CNTs催化剂表面,X射线光电子能谱(XPS)揭示Co-N-CNTs催化剂中的N元素不仅可以和碳纳米管(CNTs)中的C元素形成吡咯氮和石墨氮,还可以形成具有更高氧还原活性的吡啶氮结构。电化学测试结果表明,通过超重力技术制备的Co-N-CNTs催化剂的起始电位和半波电位与商业Pt/C催化剂相当;而且,Co-N-CNTs催化剂展现出优良的抗甲醇性能。     

CuI‐functionalized halloysite nanoclay as an efficient heterogeneous catalyst for promoting click reactions: Combination of experimental and computational chemistry

Amine‐functionalized halloysite nanotubes (HNTs‐2 N) were prepared and further modified by introduction of salicylaldehyde and formation of imine functionality (HNTs‐2 N‐Sal). The latter was subsequently used for immobilization of CuI and formation of CuI@HNTs‐2 N‐Sal, which could effectively promote click reactions of terminal alkynes, sodium azide and α‐haloketones or alkyl halides in aqueous media and under mild reaction conditions to afford 1,2,3‐triazoles in relatively short reaction times. Notably, the catalyst could be recycled in up to six reaction runs with negligible loss of catalytic activity and CuI leaching. Also, the geometry of CuI adsorption on the modified HNTs surface was explored by molecular simulation with density functional theory. Furthermore, topographic steric maps of possible coordination modes were obtained using the recently released SambVca2 web application tool. Based on obtained results, a catalytic site with superior performance was suggested.     

Palladium chloride anchored on organic functionalized MCM‐41 as a catalyst for the Heck reaction

Palladium chloride was grafted to amino‐functionalized MCM‐41 to prepare heterogeneous catalysts. XRD, N₂ adsorption–desorption isotherms, IR, ¹³C and ²⁹Si cross‐polarization magic‐angle spinning NMR spectroscopy and XPS techniques were employed to characterize the catalytic materials. The heterogeneous palladium catalyst exhibited excellent catalytic activity for the Heck vinylation of iodobenzene with methyl acrylate, giving 92% yield of methyl cinnamate in the presence of N‐methylpyrrolidone (NMP) and triethylamine (Et₃N). The stability of the heterogeneous catalyst was also studied in detail. The catalytic tests showed that the palladium leaching correlated to solvent, base and palladium loading. The heterogeneous catalyst exhibited excellent stability towards loss of activity and palladium leaching was not observed during six recycles in the presence of toluene and Na₂CO₃. Copyright © 2007 John Wiley & Sons, Ltd.     

铜基催化剂上甲烷催化燃烧反应动力学特性研究

采用固定床微分反应器,在常压、450~500℃、甲烷体积分数10%~35%条件下,进行铜基催化剂上甲烷催化燃烧动力学特性研究。研究表明,甲烷分压对反应速率影响显著,而氧气分压的影响可以忽略。采用最小二乘法进行动力学模型参数估计,建立的反应动力学模型为-rCH4=1.61×107×e-108 000/RT×pCH40.5。检验结果表明,所建模型与实验数据良好相容,是适宜和可信的。根据实验结果推断甲烷催化燃烧分两步进行,首先氧气快速与铜基催化剂上活性空位点反应,形成吸附氧气分子;随后吸附氧气分子和甲烷分子反应,生成二氧化碳和水。     

Dicalcium phosphate dehydrate DCPD as a highly efficient and reusable catalyst for Knoevenagel condensation

We have described the catalytic activities of dicalcium phosphate dihydrate (DCPD) in the condensation reaction of various substituted benzaldehydes with active methylene compound malononitrile. The influences of reaction conditions on the corresponding catalytic behavior have been investigated. The results showed that the DCPD exhibited high catalytic activity and versatility and that it can be recycled without significant loss of its activity for the condensation reactions, which shows the material is a promising new type of heterogeneous catalyst for the condensation reactions. Meanwhile, the catalytic results of DCPD compared favorably with those of other materials for Knoevenagel reactions reported previously.     

A study of the kinetics of phenol oxidation on a fibrous catalyst

Kinetics of phenol oxidation was studied. The effect of the hydrogen peroxide concentration, temperature, acidity of the medium, and catalyst mass on the oxidation rate was examined. A mathematical relation for calculating the reaction rate of phenol oxidation was derived.     

Influence of diosgenin structure on the polymerization kinetics of acrylamide: An experimental and theoretical approach

The acrylamide polymerization in presence of diosgenin has been investigated by experimental and theoretical methods. NMR spectroscopy shows the absence of copolymerization. Viscosimetric and dilatometric experiments support the occurrence of transfer reactions that retard the polymerization. The mechanism was studied at the MPWB1K/6-31G(d,p)//B3LYP/6-31G(d,p) level of theory. Transfer, homopropagation, copolymerization and reinitiation reactions were considered either in gas or solution phase. According to results, the retardation seems to be originated by the formation of an allylic radical in the ring B of diosgenin that reinitiates acrylamide polymerization at slow rate.     

Polymer‐supported macrocyclic Schiff base palladium complex as an efficient catalyst for the Heck reaction

A polymer‐supported macrocyclic Schiff base palladium complex has been synthesized. In the Heck reaction of aryl iodides and bromides with ethyl acrylate or styrene, the complex has been proved to give the corresponding products in good to excellent yields. The reaction proceeded smoothly in the presence of 0.5 mol% of catalyst in DMF within 1–4 h. Recycling studies have shown that the catalyst can be readily recovered and reused for four cycles with only a slightly decrease in its activity. Copyright © 2011 John Wiley & Sons, Ltd.     

Palladium nanoparticles supported on cucurbit[6]uril: an efficient heterogeneous catalyst for the Suzuki reaction under mild conditions

A new NC palladacycle was synthesized and supported on cucurbit[6]uril (CB[6]). The CB[6]‐supported palladium was used as an efficient nanocatalyst for the Suzuki reaction. In these reactions various aryl halides were reacted with arylboronic acids in H₂O–EtOH at both room temperature and 40 °C. The obtained Pd nanocatalyst exhibited excellent reactivity and stability in C ? C bond formation, which confirms that the catalyst is a completely active heterogeneous species. The Pd nanocatalyst was characterized using X‐ray diffraction, scanning electron microscopy and transmission electron microscopy. Copyright © 2014 John Wiley & Sons, Ltd.     

NMR-spectroscopic evidence of intermediate-dependent pathways for acetic acid formation from methane and carbon monoxide over a ZnZSM-5 zeolite catalyst

Two ways: a Zn-modified ZSM-5 zeolite catalyst was developed for the reaction of methane with carbon monoxide to directly produce acetic acid under mild conditions (573-623 K), and two different intermediate-dependent reaction pathways were unambiguously identified for acetic acid formation by in situ solid-state NMR spectroscopy.     

Biodiesel production in the presence of heterogeneous catalyst of alumina: Study of kinetics and thermodynamics

In the current research, biodiesel production was investigated in the presence of solid catalysts of K₂CO₃/Al₂O₃ by transesterification of rapeseed oil. The specifications of produced fatty acid methyl esters like viscosity and flash point were studied, and it was noted that they complied with the requirements of ASTM D6751. In addition, the kinetic and thermodynamic parameters were explored considering the temperature changes between 318.15 and 348.15 K. Mass transfer resistance (external diffusion or internal diffusion) over the catalyst was neglected with regard to theWeisz-Prater criterion and Mears criterion. The kinetic models containing Eley-Rideal, Langmuir-Hinshelwood, pseudo–first-order, pseudo–second-order, and α-order models were investigated. Corrected Akaike information criterion was utilized to find the best model fitted with the experimental data. The greatest illustration for the K₂CO₃/Al₂O₃-catalyzed reaction was the nonlinear model with an order of α = 1.287 and the activation energy of 12.12 kJ/mol. Using transition state theory (Eyring-Polanyi equation), the activation Gibbs free energy, activation enthalpy, and activation entropy were calculated at different temperatures. The equilibrium thermodynamic properties depicted that this process is endothermic and spontaneous toward biodiesel production and tends to be irreversible.     

超声辅助萃取-钨丝电热原子吸收光谱法测定痕量镉

镉对人体和动植物而言是一种非必需的元素,当其含量超过一定浓度就会产生毒性.由于镉在生物体内的半衰期长达1年之久,一旦进入生物体就不易排出.因此,测定食物样品中的镉对保证人类和动物的健康有重要的意义[1].     

Influence of several experimental parameters on As and Se leaching from coal fly ash samples

Coal fly ash leaching process for As and Se is studied. Environmental parameters such as pH, temperature, solid-liquid ratio, particle size and leaching time are taken into account in order to simulate As and Se leaching process for disposal coal fly ash. Analysis of reference materials was carried out by using of hydride generation coupled to atomic fluorescence spectrometry. Plackett-Burman experimental design is used to know the significative parameters, and Box-Behnken experimental design is used to refine the results obtained for these significative parameters. pH and temperature shown a hardly influence in leaching process. Furthermore, leaching time was also significative. According our results, it may be assumed that percentage of As and Se leaching in experimental conditions tested is relatively low for acidic fly ashes.     

The MOF/GO-based derivatives with Co@CoO core-shell structure supported on the N-doped graphene as electrocatalyst for oxygen reduction reaction

The development of nonprecious catalyst for oxygen reduction reaction (ORR) is important for the commercialization of the alkaline fuel cells (AFCs). Herein, we prepared a kind of Co-based nanoparticles (NPs) with a core-shell (Co@CoO) structure supported on the N-doped graphene (Co@CoO/NG) as an efficient ORR catalyst via simply pyrolyzing the ZIF-67 anchored on the synthesized graphene oxide (GO). The catalytic activity for ORR of the obtained Co@CoO/NG is comparable with the state-of-art Pt/C catalyst in terms of the onset and half-wave potential in the alkaline solution. In addition, the Co@CoO/NG exhibited an excellent ORR durability and antimethanol activity compared to the commercial Pt/C. This research would provide a simple strategy to prepare the high-performance nonprecious metal-based catalysts for AFCs.     

电化学去合金化Pt(Pd)-Cu对氧的电催化还原活性的研究

应用电化学去合金法制备了表面覆盖有Pt(Pd)原子层的Pt(Pd)-Cu合金催化剂.研究该催化剂在0.1mol.L-1HClO4酸性溶液中对氧气电化学还原的催化活性,并采用同步辐射反常X-射线衍射法(Anomalous X-ray Diffraction,AXRD)和表面X-射线散射法(Surface X-ray Scattering,SXS)从原子尺度研究了去合金化后催化剂的结构.分析对比纳米颗粒、薄膜和单晶3种不同形式的去合金化Pt-Cu的结构和催化活性以及Pt-Cu和Pd-Cu两种不同合金薄膜的结构和催化活性.结果表明,表面应力是影响催化剂催化活性的关键因素,而应力大小则与去合金化后所形成的表面Pt(Pd)层的厚度相关,材料尺寸和组成元素等都影响表面Pt(Pd)层的厚度.提出可利用调控材料表面的应力来设计高催化活性的催化剂.     

AlCl3 as a powerful catalyst for the one-pot preparation of 1,1,3-triheteroaryl compounds

A general and efficient procedure for the synthesis of 1,1,3-triheteroaryl compounds in good to excellent yield at room temperature is developed. The reaction proceeds via mixed Michael and Friedel-Crafts reactions of α,β-enals or α,β-enones and indoles, 2-methylfuran or 2-methylthiophene in the presence of a catalytic amount of AlCl₃.