Characterization and Activity of Cu‐MnOx/γ‐Al2O3 Catalyst for Hydrogenation of Carbon Dioxide

The effect of manganese on the dispersion, reduction behavior and active states of surface of supported copper oxide catalysts have been investigated by XRD, temperature‐programmed reduction and XPS. The activity of methanol synthesis from CO₂/H₂ was also investigated. The catalytic activity over CuO‐MnO_x/γ‐Al₂O₃ catalyst for CO₂ hydrogenation is higher than that of CuO/γ‐Al₂O₃. The adding of manganese is beneficial in enhancing the dispersion of the supported copper oxide and make the TPR peak of the CuO‐MnK_x/γ‐Al₂O₃ catalyst different from the individual supported copper and manganese oxide catalysts, which indicates that there exists strong interaction between the copper and manganese oxide. For the CuO/γ‐Al₂O₃ catalyst there are two reducible copper oxide species; α and β peaks are attributed to the reduction of highly dispersed copper oxide species and bulk CuO species, respectively. For the CuO‐MnO_x/γ‐Al₂O₃ catalyst, four reduction peaks are observed, α peak is attributed to the dispersed copper oxide species; β peak is ascribed to the bulk CuO; γ peak is attributed to the reduction of high dispersed CuO interacting with manganese; δ peak may be the reduction of the manganese oxide interacting with copper oxide. XPS results show that Cu⁺ mostly existed on the working surface of the Cu‐Mn/γ‐Al₂O₃ catalysts. The activity was promoted by Cu with positive charge which was formed by means of long path exchange function between Cu? O? Mn. These results indicate that there is synergistic interaction between the copper and manganese oxide, which is responsible for the high activity of CO₂ hydrogenation.     

Praseodymium Oxide Modified CeO2/Al2O3 Catalyst for Selective Catalytic Reduction of NO by NH3

A series of CeO₂/Al₂O₃ catalysts was modified with praseodymium oxide using an extrusion method. The catalytic activities of the obtained catalysts were measured for the selective catalytic reduction of NO with NH₃ to screen suitable addition of praseodymium oxide. These samples were characterized by XRD, N₂‐BET, NH₃‐TPD, NO‐TPD, Py‐IR, H₂‐TPR, Raman spectra and XPS, respectively. Results showed the optimal catalyst with the Pr/Ce molar ratio of 0.10 exhibited more than 90% NO conversion in a wide temperature range of 290–425°C under GHSV of 5000 h^?1. The number of Lewis acid sites and the chemisorbed oxygen concentration of the catalysts would increase with the Pr incorporation, which was favorable for the excellent catalytic performance. In addition, the Pr incorporation inhibited growth of the Al₂O₃ crystal particles and led to the lattice expansion of CeO₂, which increased catalytic activity. The results implied that the higher chemisorbed oxygen concentrations and the more Lewis acid sites were conductive to obtain the excellent SCR activity.     

Novel Flower‐Like Ag‐SiO2‐MgO‐Al2O3 Material: Preparation,Characterization and Catalytic Application in Methanol Dehydrogenation

Catalytic direct dehydrogenation of methanol to formaldehyde was carried out over Ag‐SiO₂‐MgO‐Al₂O₃ catalysts prepared by sol‐gel method. The optimal preparation mass fractions were determined as 8.3% MgO, 16.5% Al₂O₃ and 20% silver loading. Using this optimum catalyst, excellent activity and selectivity were obtained. The conversion of methanol and the selectivity to formaldehyde both reached 100%, which were much higher than other previously reported silver supported catalysts. Based on combined characterizations, such as X‐ray diffraction (XRD), scanning electronic microscopy (SEM), diffuse reflectance ultraviolet‐visible spectroscopy (UV‐Vis, DRS), nitrogen adsorption at low temperature, temperature programmed desorption of ammonia (NH₃‐TPD), desorption of CO₂ (CO₂‐TPD), etc., the correlation of the catalytic performance to the structural properties of the Ag‐SiO₂‐ MgO‐Al₂O₃ catalyst was discussed in detail. This perfect catalytic performance in the direct dehydrogenation of methanol to formaldehyde without any side‐products is attributed to its unique flower‐like structure with a surface area less than 1 m²/g, and the strong interactions between neutralized support and the nano‐sized Ag particles as active centers.     

Vapor‐Phase Aldolization of n‐Butyraldehyde to 2‐Ethyl‐2‐Hexenal over Solid‐Base Catalysts

Vapor‐phase aldol condensation of n‐butyraldehyde to 2‐ethyl‐2‐hexenal was studied at 1 atm and 150～ 300°C in a fixed‐bed, integral‐flow reactor by using NaX, KX, γ‐Al₂O₃ and Na/NaOH/γ‐Al₂CO₃ catalysts. Ion exchange of NaX zeolite with potassium acetate solution results in a decrease of crystallinity and apparent lowering of surface area, whereas the basic strength is enhanced. Treatment of γ‐Al₂O₃ with NaOH and Na causes a large decrease of the surface area but strong enhancement of the catalyst basicity. The catalytic activity on the basis of unit surface area is in the order Na/NaOH/γ‐Al₂O₃ < KXU < KXW < NaX >γ‐Al₂O₃, in accordance with the relative catalyst basic strength. The molar ratio of trimeric to dimeric products increases with increasing the reaction temperature and the catalyst basic strength except for Na/NaOH/γ‐Al₂O₃. Very high selectivity of 2‐ethyl‐2‐hexenal (>98.5%) was observed for reactions over NaX zeolite at 150°C. Based on the FT‐IR and the catalytic results, the reaction paths are proposed as follows: self‐aldol condensation of n‐butyraldehyde, followed by dehydration produces 2‐ethyl‐2‐hexenal, which then reacts with n‐butyraldehyde and successively dehydrates to 2,4‐diethyl‐2,4‐octadienal and 1,3,5‐triethylbenzene. For the reaction over NaX, the calculated Arrhenius frequency factor and activation energy are 314 mol/g·h and 32.6 kJ/mol, respectively.     

Continuous Dehydrogenation of n‐Pentanol over a Cr Modified Cu/γ‐Al2O3‐La2O3 Catalyst

The oxidant‐free dehydrogenation of n‐pentanol over copper based catalysts was investigated in this paper. The effect of metal modification on the activity and stability of the copper catalyst supported on γ‐Al₂O₃ and La₂O₃ (Cu/γ‐Al₂O₃‐La₂O₃) was clarified and a Cr modified Cu/Al₂O₃‐La₂O₃ (Cu‐Cr/γ‐Al₂O₃‐La₂O₃) showed the best catalytic performance. The conversion of n‐pentanol was 70.0% and the selectivity for n‐pentanal increased to 97.1% over Cu‐Cr/γ‐Al₂O₃‐La₂O₃. X‐ray diffraction and temperature programmed reduction of H₂ indicated that the addition of Cr favors the formation and reduction of the copper oxide, and the dispersion of the active Cu⁰ species, accounting for the good activity and stability of this catalyst. Furthermore, the lower amount of acidic sites in Cu‐Cr/γ‐Al₂O₃‐La₂O₃ is suggested to suppress the dehydration in oxidant‐free dehydrogenation of n‐pentanol, accounting for the higher selectivity for n‐pentanal.     

Catalytic Stereoselective 1,4‐Addition Reactions Using CsF on Alumina as a Solid Base: Continuous‐Flow Synthesis of Glutamic Acid Derivatives

A novel methodology using CsF⋅Al₂O₃ as a highly efficient, environmentally benign, and reusable solid‐base catalyst was developed to synthesize glutamic acid derivatives by stereoselective 1,4‐addition of glycine derivatives to α,β‐unsaturated esters. CsF⋅Al₂O₃ showed not only great selectivity toward 1,4‐addtion reactions by suppressing the undesired formation of pyrrolidine derivations by [3+2] cycloadditions, but also offered high yields for the 1,4‐adduct with excellent anti diastereoselectivities. The catalyst was well characterized by using XRD, ¹⁹F MAS‐NMR and ¹⁹F NMR spectroscopy, FT‐IR, CO₂‐TPD, and XPS. And highly basic F from Cs₃AlF₆ was identified as the most probable active basic site for the 1,4‐addition reactions. Continuous‐flow synthesis of 3‐methyl glutamic acid derivative was successfully demonstrated by using this solid‐base catalysis.     

Synthesis of 3‐Methylindole from Glycerol Cyclization with Aniline over CuCr/Al2O3 Catalysts Modified by Alkali Earth Oxides

In the present work, CuCr catalysts supported on γ‐Al₂O₃ are prepared and modified with alkali earth elements by impregnation, characterized by N₂ adsorption–desorption, XRD, H₂‐TPR (temperature‐programmed reduction by H₂), CO₂‐TPD and NH₃‐TPD (temperature‐programmed desorption of NH₃ or CO₂), and applied in the synthesis of 3‐methylindole (3‐MI) with a N‐heterocycle from glycerol and aniline in the fixed‐bed reactor. The results show that the introduction of alkali earth elements into the CuCr/Al₂O₃ catalyst can improve the yield of target 3‐MI in the order of Mg < Ca < Sr < Ba. CuCr‐Ba/Al₂O₃ gives rise to a high 3‐MI yield of 39.09% and 65.17% in N₂ as a carrier gas and 20%H₂–N₂ mixture gas, respectively. According to catalysts characterization and catalytic tests, the reaction pathway of glycerol cyclization with aniline is proposed, the formation of 3‐MI and 3H‐indol‐3‐yl methanol is hypothesized to be through the aniline cyclization with 2,3‐hydroxypropanal from glycerol dehydrogenation over Cu⁰ centers and basic sites. The acidic sites mainly play a role on activating aniline, which interacts with glycerol to form 3‐MI or quinoline through cyclization and dehydration.     

Effect of Calcination Temperature and Pretreatment with Reaction Gas on Properties of Co/γ‐Al2O3 Catalysts for Partial Oxidation of Methane

The effects of calcination temperature and feedstock pretreatment on the catalytic performance of Co/γ‐Al₂O₃ catalysts were studied for partial oxidation of methane (POM) to synthesis gas, with emphasis on the role of feedstock pretreatment. The physicochemical properties of the catalysts were characterized by N₂ adsorption, X‐ray diffraction (XRD), transmission electron microscopy (TEM), H₂ temperature‐programmed reduction (H₂‐TPR), and Raman spectroscopy. The results showed that the pretreatment of the catalyst by reaction gas significantly improved the catalytic activity and stability for the POM reaction. On the other hand, the effect of calcination temperature was less significant. Although the initial activity was increased by an increased calcination temperature, the catalyst without the feedstock pretreatment suffered a rapid deactivation. The reaction‐atmosphere pretreatment was revealed as a process that mainly modified the surface structure of the catalyst. In that process, the formation of a CoAl₂O₄‐like compound led to high Co metal dispersion after reduction, and the transformation of the carrier into α‐Al₂O₃ occurred over the catalyst surface. Both the high dispersion of cobalt and the presence of α‐Al₂O₃ surface phase were assumed as the important factors resulting in an excellent catalytic performance in terms of high activity and high stability.     

A Novel Way to Prepare TiO2 and γ‐Al2O3 Supported Catalysts with Large Surface Areas

Several TiO₂ and γ‐Al₂O₃ supported catalyst systems were prepared by a novel way and characterized by X‐ray diffraction, Raman spectroscopy and BET surface area measurement. The results show: (1) all the samples, including MoO₃/TiO₂, WO₃/TiO₂, V₂O₅/TiO₂, FeSO₄/γ‐Al₂O₃, Al₂ (SO₄)₃/γ‐Al₂O₃, K₂CO₃/‐Al₂O₃ and so on, prepared by impregnating TiO₂·H₂O or pseudo‐boehmite AlO(OH) with the active components then calcining at a high temperature exhibit much larger surface areas than that of pure TiO₂ or γ‐Al₂O₃ calcined at the same temperature; (2) the surface area of the sample increases with the increase in the coverage of active component on the surface of the support; (3) when the content of active component reaches its utmost monolayer dispersion capacity, the surface area of the sample is the largest, and then decreases when the content of active component exceeds its dispersion threshold.     

A Magnetically Separable Catalyst for Synthesis of 1‐Phenoxy‐2‐propanol Via Atom‐economic Reaction

A magnetically separable catalyst Al₂O₃‐MgO/Fe₃O₄ was prepared by Al₂O₃‐MgO supported on magnetic oxide Fe₃O₄ and charactered by FT‐IR, XRD and SEM. The mixed oxides afforded high catalytic activity and selectivity for synthesis of 1‐phenoxy‐2‐propanol from phenol and propylene oxide with 80.3% conversion and 88.1% selectivity to 1‐phenoxy‐2‐propanol. Especially, facile separation of the catalyst by a magnet was obtained and the catalytic performance of the recovered catalyst was unaffected even at the forth run.     

The Use of Laser Induced Breakdown Spectroscopy (LIBS) to Study Catalyst Deactivation of V2O5/γ‐Al2O3 as Compared to Inductively Coupled Plasma Optical Emission Spectrometry

Laser Induced Breakdown Spectroscopy (LIBS) method is introduced as a novel approach in this work to study catalyst deactivation of V₂O₅/γ‐‐Al₂O₃ for gas‐phase dehydration of glycerol and producing acrolein. The LIBS results of V₂O₅/γ‐Al₂O₃ samples are compared with those data that are obtained by Inductively Coupled Plasma Optical Emission Spectrometry (ICP‐OES). Experimental data of LIBS data specify that line intensities of vanadium are decreased by deactivation of V₂O₅/γ‐Al₂O₃ catalyst. A comparison between the results of LIBS test as well as ICP‐OES analysis shows that the amount of vanadium is decreased in the catalyst. Moreover, coke formation changes the surface of the catalyst. The results of deactivation of V₂O₅/γ‐Al₂O₃ are also compared with Pd/C catalyst deactivation.     

Porous Organic Zirconium Phosphonate as Efficient Catalysts for the Catalytic Transfer Hydrogenation of Ethyl Levulinate to γ‐Valerolactone without External Hydrogen

Organic hybrid zirconium phosphonate materials (ZrATMP, ZrEDTMPS, ZrDTPMPA, and ZrHEDP) were synthesized through reaction of organic phosphonic acid sodium salt and ZrOCl₂ in water, which exhibited high catalytic activity on the conversion of ethyl levulinate (EL) to γ‐valerolactone (GVL) in the presence of isopropanol. The obtained catalysts were characterized by FT‐IR, TGA, XRD, BET, XPS, ICP‐AES, SEM, TEM, NH₃‐TPD, and CO₂‐TPD. The results demonstrate that the number of acid sites and basic sites between the layers of the catalysts play a very important role in promoting the conversion of EL to GVL and that the functional groups that exist in phosphates could regulate the number of acid and basic sites. Meanwhile, the catalysts could be easily separated from the reaction system and reused at least five times without any obvious decrease in activity or selectivity.     

Glycerol catalytic cyclocondensation with ethanediamine to pyrazinyl compounds over the modified SiO2‐Al2O3

The Fe, Zn, and Mn‐modified SiO₂‐Al₂O₃ catalysts for the glycerol vapor‐phase cyclocondensation with ethanediamine (ED) to 2‐pyrazinemethanol (2‐PMol) and 2‐methylpyrazine (2‐MP) in a fixed‐bed system were prepared by coprecipitation and characterized by N₂ adsorption–desorption, X‐ray powder diffraction, and NH₃ temperature‐programmed desorption (NH₃‐TPD) in the present work. The results showed that the Mn‐modified SiO₂‐Al₂O₃ catalyst with a SiO₂/Al₂O₃ molar ratio 15.84 and 6% Mn gave the highest catalytic activity for formation of 2‐PMol (53.1%) and 2‐MP (42.9%). Mn species could cause the modulation of the acidic species of catalysts, improving the glycerol cyclocondensation with ED to 2‐PMol, and also acted as the catalytic centers for the hydrodehydration of 2‐PMol to 2‐MP. However, too many strong acidic sites could lead to ED self‐cyclocondensation to form a by‐product pyrazine. The optimum temperature was tested to be 380°C for the cyclocondensation over a 6%Mn‐SiO₂‐Al₂O₃ catalyst. © 2012 Wiley Periodicals, Inc. Heteroatom Chem 23:377–382, 2012; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.21026     

Study on the mechanism of catalytic synthesis of dimethyldichlorosilane by AlCl3/MIL‐53(Al)@γ‐Al2O3

Dimethyldichlorosilane, one of the most consumed organosilicon monomers in the industry, can be prepared in a highly efficient and environmentally friendly synthesis method of disproportionating methylchlorosilanes. However, the internal mechanism of the reaction remains unclear. In this paper, the mechanism catalyzed by AlCl₃/MIL‐53(Al) and AlCl₃/MIL‐53(Al)@γ‐Al₂O₃ catalysts was calculated at B3LYP/6‐311++G(3df, 2pd) level by using the density functional theory (DFT). The results showed that although the two catalysts had similar active structures, the catalytic effects were significantly different. The Lewis acid center on the surface of γ‐Al₂O₃ in the core‐shell catalyst is complementary to the classic Lewis acid AlCl₃ through the spatial superposition effect, which greatly improves the Lewis acid catalytic activity of AlCl₃/MIL‐53(Al)@γ‐Al₂O₃.     

Efficient conversion of fructose to 5‐hydroxymethylfurfural by functionalized γ‐Al2O3 beads

Millimeter size γ‐Al₂O₃ beads were prepared by alginate assisted sol–gel method and grafting organic groups with propyl sulfonic acid and alkyl groups as functionalized γ‐Al₂O₃ bead catalysts for fructose dehydration to 5‐hydroxymethylfurfural (5‐HMF). Experiment results showed that the porous structure of γ‐Al₂O₃ beads was favorable to the loading and dispersion of active components, and had an obvious effect on the properties of the catalyst. The lower calcination temperature of γ‐Al₂O₃ beads increased the specific surface area, the hydrophobicity and the activity of catalysts. Competition between the reaction of alkyl groups and ‐SH groups with surface hydroxyl during the preparation process of the catalyst influenced greatly the acid site densities, hydrophobic properties and activity of the catalyst. With an increase in the alkyl group chain, the hydrophobicity of catalysts increased obviously and the activity of the catalyst was enhanced. The most hydrophobic catalyst C₁₆‐SO₃H‐γ‐Al₂O₃–650°C exhibited the highest yield of 5‐HMF (84%) under the following reaction conditions: reaction medium of dimethylsulfoxide/H₂O (V/V, 4:1), catalyst amount of 30 mg, temperature of 110°C and reaction time of 4 hr.     

Catalytic transfer hydrogenation of furfural into furfuryl alcohol over Ni–Fe‐layered double hydroxide catalysts

Layered double hydroxides (LDHs) and their derivatives have been reported to be widely used as heterogeneous catalysts in various reactions. Herein, Ni‐Fe LDHs with the controlled Ni/Fe molar ratios (2:1, 3:1, 4:1) were synthesized via an easy hydrothermal method, which were used to catalyze the selective reduction of biomass‐derived furfural into furfuryl alcohol using 2‐propanol as a H‐donor under autogenous pressure and characterized using FT‐IR, XRD, TGA, BET, SEM, NH₃‐TPD, and CO₂‐TPD. It was found that the LDH with a Ni/Fe molar ratio of 3:1 demonstrated the best catalytic activity among the LDHs with different Ni/Fe molar ratios, which showed 97.0% conversion of furfural and 90.2% yield of furfuryl alcohol at 140°C for 5 hr. This was attributable to the synergistic effect of acidic sites and basic sites of the catalyst.     

Perylene diimide‐modified magnetic γ‐Fe2O3/CeO2 nanoparticles as peroxidase mimics for highly sensitive colorimetric detection of Vitamin C

Perylene diimide‐modified magnetic γ‐Fe₂O₃/CeO₂ nanoparticles (γ‐Fe₂O₃/CeO₂‐PDI) were prepared and exhibited excellent peroxidase‐like activity. The samples were characterized by HR‐TEM, XRD, Raman, N₂ adsorption, magnetic strength and XPS. The obtained γ‐Fe₂O₃/CeO₂‐PDI had size of 10~20 nm with high specific surface area of 77 m²/g, and could be easily separated from the aqueous solution by using a magnet, which are in favor of its practical application. Due to the decoration of PDI, the γ‐Fe₂O₃/CeO₂‐PDI possessed more surface defects (Ce³⁺) and active oxygen species than that of γ‐Fe₂O₃/CeO₂, resulting in the outstanding catalytic performance. And the composite catalyst also showed highly sensitive and selectivity toward VC with a limit of detection of 0.45 μM. Based on the fluorescent results, a possible hydroxyl radical (?OH) catalytic mechanism was proposed. It is believed that the as‐prepared γ‐Fe₂O₃/CeO₂‐PDI nanoparticles are promising biosensors applied for biomedical and food analysis.     

Highly Selective Aldol Condensation Using Amine-functionalized SiO2-Al2O3 Mixed-oxide under Solvent-free Condition

A series of amine catalysts supported on mesoporous molecular sieves SiO₂/Al₂O₃ with trimethoxysilylpropylamine [(CH₃O)₃Si(CH₂)₃NH₂] loading varying from 3 mmol to 6 mmol were synthesized by impregnation method. The aldol condensation of various aromatic aldehydes and 1‐heptanal was used to test the acid‐base cooperativity of amine‐functionalized SiO₂/Al₂O₃. The effects of solvent, reaction temperature, benzaldehyde to 1‐heptanal molar ratio, different supports (SiO₂, Al₂O₃ and SiO₂‐Al₂O₃), catalyst amount and recyclability of the catalyst were investigated. Sample containing 5 mmol amine loaded showed highest benzaldehyde conversion (100%) and selectivity (97%) for jasminaldehyde.     

Production of 5‐Hydroxymethylfurfural from Fructose in Ionic Liquid Efficiently Catalyzed by Cr(III)‐Al2O3 Catalyst

A series of metal‐Al₂O₃ catalysts were prepared simply by the conventional impregnation with Al₂O₃ and metal chlorides, which were applied to the dehydration of fructose to 5‐hydroxymethylfurfural (HMF). An agreeable HMF yield of 93.1% was achieved from fructose at mild conditions (100°C and 40 min) when employing Cr(III)‐Al₂O₃ as catalyst in 1‐butyl‐3‐methylimidazolium chloride ([Bmim]Cl). The Cr(III)‐Al₂O₃ catalyst was characterized via XRD, DRS and Raman spectra and the results clarified the interaction between the Cr(III) and the alumina support. Meanwhile, the reaction solvents ([Bmim]Cl) collected after 1^st reaction run and 5^th reaction run were analyzed by ICP‐OES and LC‐ITMS and the results confirmed that no Cr(III) ion was dropped off from the alumina support during the fructose dehydration. Notably, Cr(III)‐Al₂O₃ catalyst had an excellent catalytic performance for glucose and sucrose and the HMF yields were reached to 73.7% and 84.1% at 120°C for 60 min, respectively. Furthermore, the system of Cr(III)‐Al₂O₃ and [Bmim]Cl exhibited a constant stability and activity at 100°C for 40 min and a favorable HMF yield was maintained after ten recycles.     

Thiourea dioxide‐grafted γ‐Fe2O3/HAp magnetic nanoparticles: Efficient,green and reusable nanocatalyst for synthesis of pyranopyridine derivatives

A novel t hiourea dioxide‐functionalized hydroxyapatite‐encapsulated hybrid core‐shell γ‐Fe₂O₃@HAp‐TUD nanoparticles (MNPs) were prepared and characterized by FT‐IR, EDX, SEM, XRD, TGA and VSM analytical methods. The catalytic activity of these MNPs was evaluated through one‐pot three‐component reactions between various substituted aldehydes, malononitrile and 3‐cyano‐6‐hydroxy‐4‐methyl‐pyridin‐2(1H )‐one to afford the corresponding pyrano[2,3‐b]pyridines in high yields under mild and solvent‐free conditions. The catalyst can be easily recycled in a magnetic field and reused in five consecutive runs without significant decrease of its catalytic activity.