Simple but efficient synthesis of novel substituted benzimidazoles over ZrO2-Al2O3

Solid-acid catalytic materials such as ZrO₂-Al₂O₃ containing 80?mol% of ZrO₂ were prepared by the solution combustion method (SCM) using different fuels such as urea, hexamethylene tetramine, glycine, and sucrose. All the prepared solid acid catalytic materials were characterized for their physico-chemical properties like crystalinity, acidity, functionality and morphology. These materials were evaluated for their catalytic activity in the synthesis of a series of novel substituted benzimidazoles. The reaction conditions were optimized by varying the solvents, reaction temperature, weight of solid acid catalyst, molar ratio of the reactants, and reaction time. The ZrO₂-Al₂O₃ solid acid catalytic material prepared by urea as a fuel was found to be highly active, recyclable, and reusable in the synthesis of benzimidazoles. A possible reaction mechanism for the synthesis of benzimidazoles is also proposed.     

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.     

Esterification of acetic acid with n-Butanol using vanadium oxides supported on γ-alumina

Esterification of acetic acid with n-Butanol has been studied in a heterogeneous reaction system using two γ-alumina-supported vanadium oxide catalysts with different V loadings, which were prepared by the impregnation of a precipitated alumina. The alumina support and the supported catalysts were characterized using X-ray diffraction, N₂ adsorption, EDX analysis and NH₃-TPD techniques. The effects of the reaction time, of the molar ratio of the reactants, of the speed of agitation and of the mass fraction of the catalyst on the catalytic properties were studied. In the presence of the supported catalyst containing 10 wt % V₂O₅ (10V-Al₂O₃ sample) the conversion reached 87.7% after 210 min of reaction at 100 °C with an n-Butanol-to-acetic acid mole ratio equal to one. The conversion as well as the total acidity measured by TPD of NH₃ increased in the following order: Al₂O₃ < 5V-Al₂O₃ (5 wt % V₂O₅/Al₂O₃) < 10V-Al₂O₃. In all cases the reaction was completely selective to n-butyl acetate. Nevertheless, a loss in catalytic activity after three reaction cycles with 10 V₂O₅–Al₂O₃ catalyst was observed.     

A study of Pt–Pd/γ-Al2O3 catalysts for methane oxidation resistant to deactivation by sulfur poisoning

The catalytic oxidation of methane was studied over calcined and reduced Pt–Pd/γ-Al₂O₃ catalysts, in the presence and the absence of SO₂ in the CH₄–O₂ reaction feed. The effect of sulfation (SO₂ + O₂ for 4 h at 500 °C) was also studied on the catalyst resistance to deactivation by sulfur poisoning. Sulfating the calcined Pt–Pd/γ-Al₂O₃ catalysts resulted in a strong deactivation for the CH₄–O₂ reaction. However, the catalytic activity of the reduced-sulfated Pt–Pd/γ-Al₂O₃ catalyst for CH₄–O₂ reaction remained rather unaffected in the presence and in the absence of SO₂ in the reaction feed. XPS analysis revealed, over reduced-sulfated Pt–Pd/γ-Al₂O₃ catalysts, the presence of Pt(0) metallic surface species on which SO₂ interactions may be faster related to Pd surface species. The presence of Pt(0) may be necessary to prevent the interactions between SO₂ and Pd surface species. Long time catalytic tests showed that the activity of a reduced Pt–Pd/γ-Al₂O₃ catalysts for CH₄–O₂ reactions remained rather unaffected despite the presence of SO₂ in the reaction feed.     

Catalytic dehydrogenation of propane to propylene over highly active PtSnNa/γ-Al_2O_3 catalyst

This paper reports a new fabrication method of the PtSnNa/γ-Al₂O₃ catalyst through ball milling, which is more stable and active than the commercial catalyst.     

Highly active Pd-Fe/α-Al_2O_3 catalyst with the bayberry tannin as chelating promoter for CO oxidative coupling to diethyl oxalate

A novel Pd-Fe/α-Al_2O_3 catalyst was synthesized by incipient-wetness impregnation method with bayberry tannin as chelating promoter and commercial hollow column Raschig ring a-Al_2O_3 as support for the synthesis of diethyl oxalate from CO and ethyl nitrite.A variety of characterization techniques including N_2 physical adsorption,optical microscopy,scanning electron microscopy and energy dispersive system(SEM-EDS),inductively coupled plasma optical emission spectroscopy(ICP-OES),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),transmission electron microscopy(TEM),were employed to explore the relationship between the physicochemical properties and activity of catalysts.It indicated that a large number of phenolic hydroxyl groups in bayberry tannin can efficiently anchor the active component Pd,reduce the particle size and make the active Pd as a multi-ring distribution on the commercial a-Al_2O_3 suppo rt,which we re beneficial to improve the catalytic activity for the production of diethyl oxalate from CO and ethyl nitrite.0.3 wts Pd-Fe/α-Al_2O_3 showed excelle nt catalytic activity and selectivity in a continuous flow,fixed-bed reactor with the loading amount of 10 mL catalysts,Under the mild reaction conditions,the space-time yield of diethyl oxalate was 978 g L ~1 h ~1 and CO conversion was 44% with the selectivity to diethyl oxalate of 95.5%.     

Some aspects of metal-support strong interactions in Rh/Al2O3 catalyst under oxidising and reducing conditions

The aim of the Letter is to elucidate the nature of metal-support interaction in the 2 wt% Rh/Al₂O₃ catalyst obtained by annealing Rh–O–Al xerogel at 1113 K in air.XPS, HRTEM, and XRD results reveal that during the Rh–O–Al xerogel annealing in air, rhodium incorporates into forming alumina, which results mostly in Rh⁴⁺/δ-Al₂O₃ solid solution formation.However, in the course of the catalyst reduction at 773 with H₂ and at 823 K with CH₄ the Rh⁴⁺/δ-Al₂O₃ solid solution transforms into Rh–Al alloy. The islands of rhodium form on the surface of the Rh–Al alloy nanocrystallites if the reduction is slow enough.     

Embedding of Al nanoparticle in Al2O3 matrix by electron beam

Embedding structures of a metal nanoparticle in an oxide matrix were first achieved by electron beam irradiation. In the system of Al/α-Al₂O₃. Al nanoparticles derived from θ-Al₂O₃ migrated and embedded in α-Al₂O₃ matrix having epitaxy relation, {1 1 2̄ 0}α-Al₂O₃//{2 0 0} Al. The driving force of the embedding is momentum transfer from electrons or ions to Al atoms of nanoparticles in the pole piece of transmission electron microscopy.     

Study of CuZnMOx oxides (M = Al,Zr, Ce,CeZr) for the catalytic hydrogenation of CO2 into methanol

CuO–ZnO–Al₂O₃ catalysts were synthesized by two methods, sol–gel and co-precipitation syntheses. Al₂O₃ was then substituted with other supports, such as ZrO₂, CeO₂ and CeO₂–ZrO₂ in order to have a better understanding of the support's effect. These catalysts containing 30 wt% of Cu were then tested for CO₂ hydrogenation into methanol. The effect of reaction temperature and GHSV on the catalytic behaviour was also investigated. The best results were obtained with a 30 CuO–ZnO–ZrO₂ catalyst synthesized by co-precipitation and calcined at 400 °C. This catalyst presents a good CO₂ conversion rate (23%) with 33% of methanol selectivity, leading to a methanol productivity of 331 g_MeOH.kg_cata⁻¹·h⁻¹ at 280 °C under 50 bar and a GHSV of 10,000 h⁻¹.     

Core-shell zirconia-coated magnetic nanoparticles offering a strong option to prepare a novel and magnetized heteropolyacid based heterogeneous nanocatalyst for three- and four-component reactions

A new type of magnetically-separable nanocatalyst was prepared through the immobilization of phosphomolybdic acid (H₃PMo₁₂O₄₀) in 10–30 wt.% on the surface of core-shell zirconia-coated magnetite nanoparticle (nano-Fe₃O₄@ZrO₂). The developed heterogeneous nano-sized acid catalyst named nano-Fe₃O₄@ZrO₂ supported PMA (or n-Fe₃O₄@ZrO₂/PMA) was characterized using several techniques such as FT-IR, XRD, FE-SEM, VSM, EDX, TEM and TGA. The characterization data derived from FT-IR spectroscopy exhibited that H₃PMo₁₂O₄₀ species on the support retained their Keggin structures. Additionally, the potentiometric titration with n-butylamine was employed to measure the acidity content of the as-obtained catalyst. Surprisingly, this novel active solid acid catalyst displayed to have a higher number of surface active sites compared to its homogeneous analogues. Besides, the catalytic activity of the catalyst was evaluated in multicomponent reactions (MRCs) for the rapid and efficient one-pot synthesis of 2, 4, 5-trisubstituted and 1, 2, 4, 5-tetrasubstituted imidazoles in high yields and selectivity. The sample of 20 wt.% displayed higher acidity content which led to its enhanced activity in the catalytic transformation. Moreover, the catalyst could be easily reused without deactivation after five runs, which made it a promising catalyst for practical and large-scale applications. This outstanding reusability was ascribed to the strong attachment of PMA molecules on the n-Fe₃O₄@ZrO₂ support material.     

Al含量对Pt-SO2-4 /ZrO2-Al2O3固体超强酸催化

通过向SO^2-₄ /ZrO₂催化剂中同时引入适量的Pt和Al₂O₃, 制备出了具有较高催化性能和稳定性的Pt-SO^2-₄ /ZrO₂-Al₂O₃型固体超强酸催化剂. 以正戊烷异构化反应为探针, 考察了Al含量对催化剂性能的影响; 并采用X射线衍射(XRD)、比表面积测定(BET)、红外(IR)光谱、程序升温还原(TPR)、热重-差热分析(TG-DTA)和氨-程序升温脱附(NH₃-TPD)手段对催化剂进行了表征. 结果表明, Al能够提高ZrO₂的晶化温度, 抑制硫的分解, 增加催化剂的比表面积, 增强硫氧键的结合, 提高催化剂的还原性能, 增加催化剂的酸强度和酸总量. 当Al₂O₃含量(质量分数, w)为5.0%时, Pt-SO^2-₄ /ZrO₂-Al₂O₃固体超强酸催化剂的催化活性最好, 在100 h内异戊烷收率可稳定在52.0%以上, 选择性在98.2%以上.     

Methane-fueled SOFC with traditional nickel-based anode by applying Ni/Al2O3 as a dual-functional layer

Novel γ-Al₂O₃ supported nickel (Ni/Al₂O₃) catalyst was developed as a functional layer for Ni–ScSZ cermet anode operating on methane fuel. Catalytic tests demonstrated Ni/Al₂O₃ had high and comparable activity to Ru–CeO₂ and much higher activity than the Ni–ScSZ cermet anode for partial oxidation, steam and CO₂ reforming of methane to syngas between 750 and 850 °C. By adopting Ni/Al₂O₃ as a catalyst layer, the fuel cell demonstrated a peak power density of 382 mW cm^?2 at 850 °C, more than two times that without the catalyst layer. The Ni/Al₂O₃ also functioned as a diffusion barrier layer to reduce the methane concentration within the anode; consequently, the operation stability was also greatly improved without coke deposition.     

Preparation and application in oil–water separation of ZrO2/α-Al2O3 MF membrane

The composite tubular membranes were prepared by applying suspensions of zirconia particles to form separation top-layers on two different porous α-alumina supports and heating the coated supports to partly sinter the particles of top-layers. The conditions of synthesizing the ZrO₂/α-Al₂O₃ membranes were investigated systematically. The mean pore diameter of zirconia membrane was about 0.2 μm by gas bubble pressure method, and the pure water flux was about 400 and 1500 l/(m² h bar) for ZrO₂ membrane on symmetric and asymmetric Al₂O₃ support, respectively. Zirconia membrane and three different alumina membranes were applied to separate oil–water emulsion obtained from steelworks to evaluate the permeability and separation characteristics, the ZrO₂/α-Al₂O₃ MF membrane in this work was the preferred membrane.     

Heterogeneous catalysts based on B/P/O for the monoetherification of 1,2-dihydroxybenzene in the gas phase

Boron–phosphorus mixed oxides were tested as heterogeneous catalysts for the gas-phase etherification of catechol (1,2-dihydroxybenzene) with methanol, aimed at the production of guaiacol (1-methoxyphenol). This reaction represents an alternative to the etherification processes which makes use of homogeneous catalysts in the liquid phase. The activity of the catalysts was found to depend considerably on the B/P atomic ratio. A catalyst having B/P = 1.0, made of BPO₄, exhibited the best results in terms of (i) conversion of catechol, (ii) selectivity to guaiacol, and (iii) steadiness of performance with time-on-stream. Characterisation of the catalyst using TPD of NH₃ evidenced that this catalyst has the optimal surface acidity, which makes the undesired reactions of tar formation and ring-alkylation slower. Supporting the B/P/O catalysts on α-Al₂O₃ resulted in lower activity, but the catalytic performance was less dependent on the B/P ratio. Doping with potassium resulted in a lowering of the number of acid sites; however, small amounts of dopant led to an increase in activity, possibly due to a co-operation effect between basic and acid sites.     

Bulky diarylammonium arenesulfonates as mild and extremely active dehydrative ester condensation catalysts

More environmentally benign alternatives to current chemical processes, especially large-scale, fundamental reactions like ester condensations, are highly desirable for many reactions. Bulky diarylammonium pentafluorobenzenesulfonates and tosylates serve as extremely active dehydration catalysts for the ester condensation reaction of carboxylic acids with equimolar amounts of sterically demanding alcohols and acid-sensitive alcohols. Typically, the esterification reaction is performed in heptane by heating at 80 °C in the presence of 1 mol% of the catalyst without removing water. Esterification with primary alcohols proceeds without solvents even at room temperature. Furthermore, 4-(N-mesitylamino)polystyrene resin-bound pentafluorobenzenesulfonate can be recycled more than 10 times without a loss of activity.     

A theoretical and experimental XAS study of monolayer dispersive supported CuO/γ-Al2O3 catalysts

The local structures of supported CuO/γ-Al₂O₃ monolayer dispersive catalysts with different CuO loadings have been investigated by EXAFS and multiple scattering XANES simulations. The EXAFS results show that the first nearest neighbors around the Cu atoms in the CuO/γ-Al₂O₃ catalysts are similar to that of the polycrystalline CuO powder, which is independent of the CuO loadings. Moreover, the Cu K-XANES FEFF8 calculations for CuO reveal that the monolayer-dispersed CuO species are of small distorted (CuO₄)_mⁿ⁺ clusters, which is mainly composed of a distorted CuO₆ octahedron incorporated in the surface octahedral vacant sites of the γ-Al₂O₃ support. We consider that the CuO species for the CuO/γ-Al₂O₃ catalysts with loadings of 0.4 and 0.8 mmol/100 m² are distorted (CuO₄)_mⁿ⁺ clusters composed mainly of a distorted CuO₆ octahedron incorporated in the surface octahedral vacant sites of the γ-Al₂O₃ support after calcinations at high temperature in air for a few hours. On the contrary, for the CuO/γ-Al₂O₃ with loading of 1.2 mmol/100 m², the local structure of Cu atoms in CuO/γ-Al₂O₃ is similar to that of polycrystalline CuO powder.     

ZrO2- and Li2ZrO3-stabilized spinel and layered electrodes for lithium batteries

Strategies for countering the solubility of LiMn₂O₄ (spinel) electrodes at 50 °C and for suppressing the reactivity of layered LiMO₂ (M=Co, Ni, Mn, Li) electrodes at high potentials are discussed. Surface treatment of LiMn₂O₄ with colloidal zirconia (ZrO₂) dramatically improves the cycling stability of the spinel electrode at 50 °C in Li/LiMn₂O₄ cells. ZrO₂-coated LiMn_0.5Ni_0.5O₂ electrodes provide a superior capacity and cycling stability to uncoated electrodes when charged to a high potential (4.6 V vs Li⁰). The use of Li₂ZrO₃, which is structurally more compatible with spinel and layered electrodes than ZrO₂ and which can act as a Li⁺-ion conductor, has been evaluated in composite 0.03Li₂ZrO₃ · 0.97LiMn_0.5Ni_0.5O₂ electrodes; glassy Li_xZrO_2 + x/2 (0<x⩽2) products can be produced from colloidal ZrO₂ for surface coatings.     

Enantioselective hydrogenation of ethyl pyruvate catalyzed by alumina support rhodium modified with quinine

Alumina supported rhodium catalyst using cinchonidine as a stabilizer exhibited excellent performance in the asymmetric hydrogenation of ethyl pyruvate with the addition of quinine. Quinine as a chiral modifier can not only induce the enantioselectivity, but also greatly accelerate the reaction. Under the optimum conditions: 293 K, 7.0 MPa of hydrogen pressure and 4.6 × 10⁻³ mol/L of quinine concentration in THF, TOF of Rh/2(cinchonidine)-γ-Al₂O₃ as catalyst and ee value of (R)-ethyl lactate can achieve 894 h⁻¹ and 71.6% ee, respectively.     

Nickel-catalyzed decarboxylative coupling of an alkynyl carboxylic acid with aryl iodides

A decarboxylative coupling reaction with an alkynyl carboxylic acid and aryl iodides in the presence of a nickel catalyst was developed. When the reaction was conducted with NiCl₂ (10 mol%), Xantphos (15 mol%), Mn (1.0 equiv), and Cs₂CO₃ (1.5 equiv), the desired diaryl alkynes were formed in moderated to good yields. Furthermore, this method does not produce the diyne, which is formed in the homocoupling of alkynyl carboxylic acids.     

Base-catalyzed cross coupling of secondary alcohols and aryl-aldehydes with concomitant oxidation of alcohols to ketones: An alternative route for synthesis of the Claisen-Schmidt condensation products

Base-catalyzed C–C cross coupling of secondary alcohols and aryl-aldehydes was achieved, when an alcoholic solution of an aryl-aldehyde was stirred under reflux for 45 h in the presence of a catalytic (20 mol%) amount of K₂CO₃. The consistent formation of α,α′-bis-(benzylidene) alkanones was obtained in moderate to good yields using various secondary alcohols and substituted aryl-aldehydes. Herein, α,α′-bis-(benzylidene)alkanones, which are the classical products of Claisen-Schmidt (cross aldol) condensation, have been synthesized via an alternative strategy using secondary alcohols. Bis-(benzylidene) alkanones are an integral part of various drug regimes and the production of bis-(benzylidene) alkanones without using any precious metal is a major outcome of the present reaction.