Manganese oxide nanoparticles supported on graphene oxide as an efficient nanocatalyst for the synthesis of 1,2,4-oxadiazoles from aldehydes

The easy synthesis of graphene oxide (GO)-supported manganese dioxide (MnO₂) nanoparticles as a stable heterogeneous nanocatalyst (MnO₂@GO) is described. This catalyst was investigated in the synthesis of 1,2,4-oxadiazoles from amidoximes and aldehydes via a cyclization and oxidation process. The nanocomposite was prepared and characterized using various techniques. The catalytic application of the nanocomposite was examined in the reaction of a variety of aldehydes with aliphatic and aromatic amidoximes. The stable and robust catalyst was recycled for seven consecutive runs without a significant decrease in the catalytic activity.     

Selective oxidation of alcohols over copper zirconium phosphate

The catalytic activity of copper zirconium phosphate (ZPCu) in the selective oxidation of alcohols to their corresponding ketones or aldehydes, using H₂O₂ as an oxidizing agent, was studied. The oxidation reaction was performed without any organic solvent, phase-transfer catalyst, or additive. Steric factors associated with the substrates influenced the reaction. The catalyst was characterized using X-ray diffraction, inductively coupled plasma atomic emission spectroscopy, energy-dispersive X-ray spectroscopy, and scanning electron microscopy. It was shown that the interlayer distance increased from 0.74 to 0.80 nm and the crystallinity was reduced after Cu²⁺ intercalation into the layers. This catalyst can be recovered and reused three times without significant loss of activity and selectivity.     

Fe–Co/sulfonated polystyrene as an efficient and selective catalyst in heterogeneous Baeyer–Villiger oxidation reaction of cyclic ketones

A highly efficient catalyst Fe–Co/sulfonated polystyrene (Fe–Co/SPS) was introduced and synthesized, which catalyzed BV oxidation of ketones with aqueous hydrogen peroxide to give the corresponding lactones in high yield and selectivity. Solid acid catalyst of Fe–Co/SPS has been prepared by using the 98-wt% sulfuric acid as the sulfonating agent and CoCl₂ combined FeCl₃ as sources of metal ions. Various physical–chemical characterizations including FT-IR, XRD, SEM and TGA, revealed that bimetallic ions Fe³⁺–Co²⁺ species in the sulfonated polystyrene framework were responsible for the catalytic activities. The BV reaction catalyzed by Fe–Co/SPS highlighted the special effects between metal ions and protonic acids as well as solvent-free heterogeneous catalytic oxidation with excellent conversion.     

Synthesis, characterization and investigation of catalytic activity of a highly sulfonated carbon solid acid in the synthesis of dihydropyrimidinones under solvent-free conditions

A highly sulfonated carbon as an efficient, recyclable, nontoxic and green solid acid catalyst was synthesized readily by simultaneous sulfonation, dehydration and carbonization of sucrose C¹²H²²O¹¹ in sulfuric acid and was characterized with Fourier transform infrared spectroscopy (FT-IR), thermal gravimetric and differential thermal gravimetric analysis (TG-DTG), X-ray diffraction (XRD), carbon-hydrogen-nitrogen-sulfur analysis (CHNS), neutralization potentiometric titration and scanning electron microscopy (SEM). This new catalyst was used in one pot three-component condensation reaction of various aromatic aldehydes with ??-ketoester and urea under solvent-free conditions to afford the corresponding dihydropyrimidinones (DHPMs). This catalyst can be reused several times without loss of its activity.     

超临界二氧化碳中功能化聚乙二醇稳定的钯纳米粒子催化醇的选择氧化反应

 以超临界二氧化碳 (scCO2)/聚乙二醇 (PEG) 两相为反应介质, 双齿氮配体功能化聚乙二醇稳定的 Pd 纳米颗粒作为催化剂, 进行了醇的需氧氧化反应. 系统研究了催化剂制备条件和反应条件对苯甲醇需氧氧化反应的影响. 结果表明, 以氢气为还原剂制备的 Pd 纳米粒子的催化活性最高. 反应结束后, 可以利用 scCO2 直接进行原位萃取得到产物, 实现了催化剂与产物的有效分离和催化剂的循环使用. 反应中没有检测到钯的流失. 催化剂经过 5 次循环利用后转化率仍可达 98%.     

Efficient and selective oxidation of alcohols with <Emphasis Type="Italic">tert</Emphasis>-BuOOH catalyzed by a dioxomolybdenum(VI) Schiff base complex under organic solvent-free conditions

The catalytic activity of dioxidobis{2-[(E)-p-tolyliminomethyl]phenolato}molybdenum(VI) complex was studied, for the first time, in the selective oxidation of various primary and secondary alcohols using tert-BuOOH as oxidant under organic solvent-free conditions at room temperature. The effect of different solvents was studied in the oxidation of benzyl alcohol in this catalytic system. It was found that, under organic solvent-free conditions, the catalyst oxidized various primary and secondary alcohols to their corresponding aldehyde or ketone derivatives with high yield. The effects of other parameters such as oxidant and amount of catalyst were also investigated. Among different oxidants such as H₂O₂, NaIO₄, tert-BuOOH, and H₂O₂/urea, tert-BuOOH was selected as oxygen donor in the oxidation of benzyl alcohol. Also, it was found that oxidation of benzyl alcohol required 0.02 mmol catalyst for completion. Dioxomolybdenum(VI) Schiff base complex exhibited good catalytic activity in the oxidation of alcohols with tert-BuOOH under mild conditions. In this catalytic system, different primary alcohols gave the corresponding aldehydes in good yields without further oxidation to carboxylic acids.     

Characterization of new catalysts based on uranium oxides

Catalysts based on uranium oxides were systematically studied for the first time. Catalysts containing various amounts of uranium oxides (5 and 15%) supported on alumina and mixed Ni-U/Al₂O₃ catalysts were synthesized. The uranium oxide catalysts were characterized using the thermal desorption of argon, the low-temperature adsorption of nitrogen, X-ray diffraction analysis, and temperature-programmed reduction with hydrogen and CO. The effects of composition, preparation conditions, and thermal treatment on physicochemical properties and catalytic activity in the reactions of methane and butane oxidation, the steam and carbon dioxide reforming of methane, and the partial oxidation of methane were studied. It was found that a catalyst containing 5% U on alumina calcined at 1000°C was most active in the reaction of high-temperature methane oxidation. For the Ni-U/Al₂O₃ catalysts containing various uranium amounts (from 0 to 30%), the introduction of uranium as a catalyst constituent considerably increased the catalytic activity in methane steam reforming and partial oxidation.     

Cr掺杂的丙烷选择氧化制丙烯酸高效催化剂

在丙烷选择氧化制丙烯酸催化剂MoVTeNbOx的活性相M1基础上掺杂一定量的Cr,当Cr/Nb摩尔比为0.002时,催化剂具有很高的丙烯酸选择性(78.3%)和收率(50.7%);并采用X射线衍射、X射线光电子能谱、程序升温还原、O2程序升温脱附、NH3程序升温脱附和异丙醇氧化等手段对催化剂的构效关系进行了探讨.结果表明,适量Cr的添加可调节催化剂表面Mo6+,V5+和Te4+等物种含量,提高催化剂的氧化能力,使丙烷转化率增加.同时,适量Cr的添加使得催化剂表面酸强度下降,酸性位点数量减少,从而抑制丙烯酸的深度氧化,提高了丙烯酸选择性.     

Enhanced electro-oxidation of formic acid by a PdPt bimetallic catalyst on a CeO2-modified carbon support

PdPt bimetallic catalysts that employ CeO2-modified carbon black as a support have been prepared using an organic colloidal method.PdPt/CeO2-C shows excellent performance toward the anodic oxidation of formic acid.The effects of varying both Pd to Pt ratio and CeO2 content have been investigated.The optimal Pd to Pt atomic ratio is 15,indicating that addition of small amounts of Pt can significantly enhance the activity of the catalyst.When the CeO2 content in the catalyst reaches as high as ～15 wt.%,the catalyst shows the maximum activity.Adding CeO2 not only enhances the catalytic activity of the material,but may also change the mechanism of its catalysis of the anodic oxidation of formic acid.Pd15Pt1/15CeO2-C exhibited 60% higher activity than Pd/C,and had a negative shift in onset potential of more than 0.1 V.Based on characterization by X-ray diffraction,X-ray photoelectron spectroscopy,thermogravimetric analysis and transmission electron microscopy,the interactions between the components are revealed and discussed in detail.     

Selective photocatalytic oxidation of alcohols to aldehydes in water by TiO2 partially coated with WO3

Semiconductor TiO₂ particles loaded with WO₃ (WO₃/TiO₂), synthesized by impregnation of tungstic acid followed by calcination, were used for photocatalytic oxidation of alcohols in water with molecular oxygen under irradiation at λ>350 nm. The WO₃/TiO₂ catalysts promote selective oxidation of alcohols to aldehydes and show higher catalytic activity than pure TiO₂. In particular, a catalyst loading 7.6 wt % WO₃ led to higher aldehyde selectivity than previously reported photocatalytic systems. The high aldehyde selectivity arises because subsequent photocatalytic decomposition of the formed aldehyde is suppressed on the catalyst. The TiO₂ surface of the catalyst, which is active for oxidation, is partially coated by the WO₃ layer, which leads to a decrease in the amount of formed aldehyde adsorbed on the TiO₂ surface. This suppresses subsequent decomposition of the aldehyde on the TiO₂ surface and results in high aldehyde selectivity. The WO₃/TiO₂ catalyst can selectively oxidize various aromatic alcohols and is reusable without loss of catalytic activity or selectivity.     

Fibroin-functionalized magnetic carbon nanotube as a green support for anchoring silver nanoparticles as a biocatalyst for A3 coupling reaction

Novel and powerful fibroin-functionalized magnetic carbon nanotube–supported silver nanoparticles (CNT–Fe₃O₄–fibroin–Ag) were successfully synthesized as a nontoxic and inexpensive biocatalyst. The structure of the organic–inorganic hybrid bionanocomposite was characterized by various techniques such as Fourier transform infrared spectroscopy, thermogravimetric analysis, energy-dispersive X-ray, field emission-scanning electron microscopy, transmission electron microscopy, X-ray diffraction, vibrating sample magnetometry, atomic absorption spectroscopy, and inductively coupled plasma-optical emission spectrometry. Then, the catalytic activity of synthesized bionanocomposite was evaluated in the three-component A³ coupling reaction under solvent-free conditions with good to excellent yields. Several propargylamine derivatives were synthesized by the reaction of different aldehydes with amines and phenylacetylene. Biodegradability, biocompatibility, availability, easy synthesis, high stability, high-throughput, cost-effectiveness, and efficient magnetic separation are some advantages of this catalyst that make it economically justified and sustainable. Moreover, the catalyst can be recycled for several runs without appreciable loss in its catalytic activity.     

Recyclable CuMgAl hydrotalcite for oxidative esterification of aldehydes with alkylbenzenes

A series of hydrotalcite-like compounds with various Cu:Mg:Al molar ratios were prepared by the co-precipitation method. The catalytic performance for oxidative esterification of aldehydes was investigated. X-ray diffraction, N₂ adsorption–desorption (BET), hydrogen temperature-programmed reduction (H₂-TPR), X-ray photoelectron spectroscopy, the scanning electron microscope (SEM), the transmission electron microscope and atomic absorption spectrometry were used to characterize the catalysts. The results showed that the benzyl benzoate product was obtained in good to excellent yield using tert-butyl peroxybenzoate as oxidant at 90°C under air atmosphere over Cu₂Mg₁Al₁-LDH catalyst. The catalyst can be recovered and used with 45% conversion after recycling five times. The oxidative esterification reaction in the heterogeneous system is environmentally friendly.

The Cu₂Mg₁Al₁-LDH catalyst prepared by co-precipitation method showed high catalytic activity for oxidative esterification of aldehydes. 81.0% yield of benzyl benzoate with benzaldehyde and toluene as reactants was obtained using tert-butyl peroxybenzoate as oxidant at 90°C under air atmosphere over Cu₂Mg₁Al₁-LDH catalyst. The catalyst can be recovered and used with 45% conversion after recycling five runs. The oxidative esterification reaction in the heterogeneous system is environmentally friendly.     

Novel ferrocene-based ionic liquid supported on silica nanoparticles as efficient catalyst for synthesis of naphthopyran derivatives

We report synthesis of silica nanospheres containing ferrocene-tagged imidazolium acetate (SiO₂@Im-Fc[OAc]) as efficient heterogeneous nanocatalyst for synthesis of naphthopyran derivatives under solvent-free conditions, based on modification of nano SiO₂ by ionic liquid with ferrocene tags and subsequent anion metathesis reaction. The synthesized novel nanocatalyst (SiO₂@Im-Fc[OAc]) was systematically characterized using Fourier-transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction analysis, and field-emission scanning electron microscopy. The catalytic activity of (SiO₂@Im-Fc[OAc]) was tested in one-pot three-component reaction of aromatic aldehydes, malononitrile, and 2-naphthol for facile synthesis of naphthopyran derivatives. To achieve high catalytic efficacy, the effects of various reaction parameters such as temperature, amount of catalyst, type of solvent, etc. were investigated. Furthermore, recovery and reuse of the nanocatalyst several times was demonstrated without appreciable loss in catalytic activity. The presented protocol offers several advantages, including green and ecofriendly nature, operational simplicity, higher yield, and easy recovery and reuse of the nanostructured catalyst. The workup of these very clean reactions involves only recrystallization of the product from ethanol and recovery of the catalyst by filtration.     

Magnetic core–shell Fe3O4@C-SO3H nanoparticle catalyst for hydrolysis of cellulose

Catalytic hydrolysis of cellulose over solid acid catalysts is one of efficient pathways for the conversion of biomass into fuels and chemicals. High catalytic activity and easy separation from reaction media are two important factors for evaluating the performance of the solid acid catalysts for the cellulose hydrolysis. In this study, we report a core–shell Fe₃O₄@C-SO₃H nanoparticle with a magnetic Fe₃O₄ core encapsulated in a sulfonated carbon shell, as recyclable catalyst for the hydrolysis of cellulose. The sulfonated carbon shell shows a good activity, presenting 48.6 % cellulose conversion with 52.1 % glucose selectivity under the moderate conditions of 140 °C after 12 h reaction. Importantly, the magnetic Fe₃O₄ core makes the catalysts easily separated from reaction mixtures by using the externally applied magnetic field. In addition, the Fe₃O₄@C-SO₃H nanoparticle catalyst shows a high stability in the activity and magnetization during recycling tests, suggesting it a promising solid acid catalyst for the hydrolysis of cellulose.     

Neat synthesis of octahydroxanthene-1,8-diones,catalyzed by silicotungstic acid as an efficient reusable inorganic catalyst

In this article, the first use of silicotungstic acid (H₄SiW₁₂O₄₀) as a catalyst for the synthesis of octahydroxanthene-1,8-diones by the reaction of 5,5-dimethylcyclohexane-1,3-dione (dimedone) with various aldehydes under thermal solvent-free conditions is described. The obtained results showed that the catalyst has a high catalytic activity, and the desired products were obtained in high yields. Moreover, the catalyst was found to be reusable, and a considerable catalytic activity still could be achieved after the fifth run. Easy work-up and avoidance of using harmful organic solvents are the other advantages of this simple procedure.     

Electrodeposited PdNi2 alloy with novelly enhanced catalytic activity for electrooxidation of formic acid

Bimetallic palladium–nickel (PdNi₂) alloy catalyst has been prepared for the electrooxidation of formic acid through a simple electrodepositing approach. Scanning Electron Microscopy and X-ray Diffraction revealed that the particle morphology and the crystalline lattice of PdNi₂ alloy were highly different from those of Pd. Although the PdNi₂ catalyst had less noble Pd content, the cyclic voltammetry and chronoamperometry results clearly demonstrated that its catalytic activity was significantly higher than that of Pd. The novel enhancement of catalytic activity was mainly ascribed to the weak absorption strength of intermediates on Pd through the interaction between Pd and additive Ni, which facilitated the formic acid oxidation through direct pathway.     

Synthesis of highly dispersed Pd/C electro-catalyst with high activity for formic acid oxidation

In this study, we present a simple process to obtain highly dispersed palladium nanoparticles on Vulcan XC-72R carbon support without any protective agent. To obtain high metal loading Pd/C catalyst without any surfactant, we modified the polyol process by employing NH₃ species as a mediation to control the reaction pathway to avoid the precipitation of Pd(OH)₂, and hence the agglomeration of Pd nanoparticles. The obtained Pd/C sample was characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM) techniques. The results show that highly dispersed Pd/C catalyst with an average diameter of 3.0 nm could be obtained in this novel process. The activity of formic acid oxidation on this Pd/C catalyst was examined via cyclic voltammetry technique and it is found that the catalytic activity is greatly enhanced due to the reduced particle size and the improved dispersion of palladium nanoparticles on the carbon surface.     

Synthesis and characterization of sulfamic acid supported on Fe3O4 nanoparticles: A green,versatile and magnetically separable acidic catalyst for oxidation reactions and Knoevenagel condensation

Sulfamic acid immobilized on diethylenetriamine functionalized Fe₃O₄ nanoparticles (SA‐DETA‐Fe₃O₄) was successfully prepared and characterized by X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FT‐IR), vibrating sample magnetometer (VSM), thermo gravimetric analysis (TGA), X‐Ray diffraction (XRD) and scanning electron microscopy (SEM). The sulfamic acid was found as a magnetically separable and highly active catalyst for the oxidative coupling thiols, oxidation of sulfides. Furthermore, the SA‐DETA‐Fe₃O₄ showed the high catalytic activity in Knoevenagel condensation of aromatic aldehydes with active methylene compounds (malononitrile and ethyl cynoacetate). The nanosolid catalyst could be easily recovered by a simple magnetic separation and reused for many cycles without deterioration in catalytic activity.     

Multi-wall carbon nanotube-supported manganese(III) porphyrin: An efficient and reusable catalyst for the oxidation of alkenes with H2O2 under ultrasonic irradiation

A manganese complex of meso-tetrakis(p-hydroxyphenyl)porphyrin immobilized onto functionalized multi-wall carbon nanotubes has been synthesized and characterized. The catalytic activity of this heterogeneous catalyst was investigated in the oxidation of various olefins with hydrogen peroxide under ultrasonic irradiation. The role of the stoichiometric amounts of acetic anhydride/or acetic acid as an activator that introduces in situ peracetic acid is discussed. This heterogeneous catalyst was highly reusable in the oxidation reactions and reused several times without significant loss of its catalytic activity.     

Design and characterization of Dendrimer of MNPs as a novel,heterogeneous and reusable nanomagnetic organometallic catalyst for one‐pot synthesis of hydroxyl naphthalene‐1,4‐dione derivatives under solvent‐free conditions

A novel super acidic magnetic nanoparticle as catalyst was successfully synthesized. The preparation of this dendrimer sulfonic acid functionalized γ‐Fe₂O₃ magnetic core‐shell silica nanoparticles as a new recoverable and heterogeneous nanocatalyst was described. The new catalyst was characterized using various techniques such as scanning electron microscopy (SEM), energy dispersive spectrum (EDS), and thermo gravimetric synthesis (TGA). Moreover, we have examined the catalytic activity of the catalyst for one‐pot, efficient and facile synthesis of 2‐hydroxy‐1,4‐naphthoquinone derivatives via a three‐component condensation reaction of 2‐hydroxynaphthalene‐1,4‐dione, aromatic aldehydes and aniline derivatives. High yields of products, short reaction times, waste‐free, mild, ambient and solvent‐free reaction conditions are advantages of this protocol. Also, the catalyst can be easily recovered by an external magnetic and reused several times without significant loss of its catalytic activity.