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.     

Efficient Noble‐Metal‐Free γ‐Fe2O3@NiO Core–Shell Nanostructured Photocatalysts for Water Oxidation

Flowerlike noble‐metal‐free γ‐Fe₂O₃@NiO core–shell hierarchical nanostructures have been fabricated and examined as a catalyst in the photocatalytic oxidation of water with [Ru(bpy)₃](ClO₄)₂ as a photosensitizer and Na₂S₂O₈ as a sacrificial electron acceptor. An apparent TOF of 0.29 μmols^?1 m^?2 and oxygen yield of 51 % were obtained with γ‐Fe₂O₃@NiO. The γ‐Fe₂O₃@NiO core–shell hierarchical nanostructures could be easily separated from the reaction solution whilst maintaining excellent water‐oxidation activity in the fourth and fifth runs. The surface conditions of γ‐Fe₂O₃@NiO also remained unchanged after the photocatalytic reaction, as confirmed by X‐ray photoelectron spectroscopy (XPS).     

Novel electromagnetic functionalized γ‐Fe2O3/polypyrrole composite nanostructures with high conductivity

In general, the conductivity of polypyrrole (PPy) is reduced by addition of magnetic nanoparticles as the additives owing to insulating effect of magnetic nanoparticles. In this article, novel electromagnetic functionalized PPy composite nanostructures were prepared by a template‐free method associated with γ‐Fe₂O₃ nano‐needles as the hard templates in the presence of p‐toluene‐sulfonic acid (p‐TSA) and FeCl₃·6H₂O as the dopant and oxidant, respectively. It was found that the molar ratio of γ‐Fe₂O₃ to pyrrole monomer represented by [γ‐Fe₂O₃]/[Py] ratio strongly affected the morphology and the conductivity of the γ‐Fe₂O₃/PPy composite nanostructures. A growth mechanism for the composite nanostructures was proposed based on the variance of the morphology with the [γ‐Fe₂O₃]/[Py] ratio. Compared with previously reported γ‐Fe₂O₃/PPy composites, the as‐prepared novel composite nanostructures showed much higher conductivity (up to ～50 times higher). Moreover, the synthesized γ‐Fe₂O₃/PPy composite nanostructures displayed ferromagnetic behavior with a high coercive force. Explanations for these interesting observations were made in terms of the magnetic interaction between ferromagnetic γ‐Fe₂O₃ nano‐needles and spin‐polaron of PPy nanotubes. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4446–4453, 2009     

Location of the Spinel Vacancies in γ‐Al2O3

A non‐spinel model for the structure of γ‐Al₂O₃, with 25 % of the Al³⁺ cations at tetrahedral positions, has been the subject of wide interest. However, ¹⁷O NMR measurements and, more recently, ²⁷Al NMR measurements have shown that there are considerably more Al³⁺ cations at tetrahedral positions. This means that the Al³⁺ vacancies in γ‐Al₂O₃ are not at tetrahedral but at octahedral positions, as in isostructural γ‐Fe₂O₃ and in accordance with density functional theory predictions. This has consequences with regard to the surface structure of γ‐Al₂O₃, and thus, for catalysis.     

Palladium‐Catalyzed Cascade Annulation To Construct Functionalized β‐ and γ‐Lactones in Ionic Liquids

A highly efficient and mild palladium‐catalyzed, one‐pot, four‐step cascade annulation has been developed to afford functionalized β‐ and γ‐lactones in moderate to good yields with high regio‐ and diastereoselectivities in ionic liquids. The employment of ionic liquids under mild reaction conditions makes this transformation green and practical. Especially, this reaction provided a novel and convenient methodology for the construction of naturally occurring biologically active β‐ and γ‐lactones.     

Microporous Crystalline γ‐Al2O3 Replicated from Microporous Covalent Triazine Framework and Its Application as Support for Catalytic Hydrolysis of Ammonia Borane

Significant progress has been made on the synthesis and application of mesoporous γ‐alumina. To date, little attention has been paid to the synthesis of microporous crystalline alumina. Here, fabrication of microporous crystalline γ‐alumina using a microporous covalent triazine framework (CTF‐1) as a template is described. Microporous crystalline γ‐alumina with a micro‐meso binary pore system was replicated by infiltration of aluminum nitrate into the micropores of the CTF‐1 template through a NH₃/water‐vapor‐induced internal hydrolysis method, followed by thermal treatment, and subsequent removal of the CTF‐1 template with a 30 % H₂O₂ aqueous solution. The obtained crystalline γ‐alumina material exhibits a large surface area (349 m² g⁻¹) with micropore distribution centered at about 1.27 nm. Ru supported on microporous γ‐Al₂O₃ can be employed as catalyst for hydrolytic dehydrogenation of ammonia borane, and it exhibits high catalytic activity and good durability. This finding provides a new benchmark for preparing well‐defined crystalline microporous alumina materials by a template method, which can be applied in a wide range of fields.     

Biodegradable Gelatin as Template for the Preparation of Mesoporous Alumina

In this study, we propose a time‐ and energy‐saving method using biodegradable gelatin as a green template and a low‐toxicity inorganic aluminum salt (Al(NO₃)₃·9H₂O) as a low‐cost aluminum source for the preparation of mesoporous alumina (γ‐Al₂O₃). The effects of pH (pH 8.0–10.0), gelatin to aluminum source ratio (0–1.9), and the hydrothermal treatment time (0–72 h) are thoroughly explored. The gelatin can assemble with the aluminum species γ‐AlOOH via hydrogen bonding to prevent the self‐condensation of the γ‐AlOOH during the hydrothermal treatment. Distinctly, the mesoporous γ‐Al₂O₃ was obtained from the calcination of the resulting gelatin–γ‐AlOOH composites. Without gelatin, high‐crystallinity γ‐AlOOH formed after the hydrothermal treatment, which transformed into the nonporous γ‐Al₂O₃ with a small surface area (20 m²/g). Finally, it was found that with a gelatin/aluminum ratio of 0.81, reaction pH value of 8.0, and hydrothermal treatment time of 24 h, high‐surface‐area mesoporous γ‐Al₂O₃ (262 m²/g) with pore diameter of 6.3 nm could be synthesized.     

Fe K‐Edge X‐ray Absorption Fine Structure Determination of γ‐Al2O3‐Supported Iron‐Oxide Species

The structure of FeO_x species supported on γ‐Al₂O₃ was investigated by using Fe K‐edge X‐ray absorption fine structure (XAFS) and X‐ray diffraction (XRD) measurements. The samples were prepared through the impregnation of iron nitrate on Al₂O₃ and co‐gelation of aluminum and iron sulfates. The dependence of the XRD patterns on Fe loading revealed the formation of α‐Fe₂O₃ particles at an Fe loading of above 10 wt %, whereas the formation of iron‐oxide crystals was not observed at Fe loadings of less than 9.0 wt %. The Fe K‐edge XAFS was characterized by a clear pre‐edge peak, which indicated that the Fe?O coordination structure deviates from central symmetry and that the degree of Fe?O?Fe bond formation is significantly lower than that in bulk samples at low Fe loading (<9.0 wt %). Fe K‐edge extended XAFS oscillations of the samples with low Fe loadings were explained by assuming an isolated iron‐oxide monomer on the γ‐Al₂O₃ surface.     

Fine tuning the assembly and gel behaviors of PEGylated polypeptide conjugates by the copolymerization of l‐alanine and γ‐benzyl‐l‐glutamate N‐carboxyanhydrides

Tuning the secondary structure of polypeptide is an effective strategy to modulate the assembly behaviors of polypeptide‐based copolymers. In this study, ring‐opening polymerization of l ‐alanine (Ala) and γ‐benzyl‐l ‐glutamate (BLG) N‐carboxyanhydrides was adopted using mPEG‐NH₂ as the initiator to prepare mPEG‐poly(l ‐alanine‐co‐γ‐benzyl‐l ‐glutamate) (PEAB) copolymers with various Ala to BLG ratios. ¹H NMR spectra and GPC test confirmed their well‐defined chemical structures. FT‐IR spectra indicated that at the powder state, all copolymers adopted both β‐sheet and α‐helical conformations. With the content of PBLG increased, the crystallization temperature and melting points of PEAB copolymers first rose then fell indicated by DSC curves. The self‐assembly of PEAB copolymers in dilute aqueous solution studied by DLS, TEM and circular dichroism spectra showed that PEAB copolymers self‐assembled into nanostructures with diverse morphologies and sizes due to distinct polypeptide conformations. Rheological analysis indicated that the alteration of the polypeptide composition can effectively modulate the modulus of PEAB assemblies in concentrated solutions. In all, copolymerization of two hydrophobic amino acid N‐carboxyanhydrides into the polypeptide block maybe an effective approach for modulating the assembly properties of PEGylated polypeptide. Besides, nanosilver‐encapsulated PEA or PEAB hydrogel showed promising antibacterial effect against Staphylococcus aureus and Bacillus subtillis. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1512–1523     

Nano n‐propylsulfonated γ‐Al2O3: a new,efficient and reusable catalyst for synthesis of spiro[indoline‐3,4‐pyrazolo[3,4‐e][1,4]thiazepine]diones in aqueous media

Nano n‐propylsulfonated γ‐Al₂O₃ is easily prepared by the reaction of nano γ‐Al₂O₃ with 1,3‐propanesultone. This reagent can be used as an efficient catalyst for the synthesis of spiro [indoline‐3,4‐pyrazolo[3,4‐e][1,4]thiazepine]diones in aqueous media. This new method consistently has the advantages of excellent yields and short reaction times. Further, the catalyst can be reused and recovered several times. Copyright © 2013 John Wiley & Sons, Ltd.     

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.     

Synthesis and characterization of macroinitiator‐amino terminated PEG and poly(γ‐benzyl‐L‐glutamate)‐PEO‐poly(γ‐benzyl‐L‐glutamate) triblock copolymer

Macroinitiator‐amino terminated poly(ethylene glycol) (PEG) (NH₂‐PEO‐NH₂) was prepared by converting both terminal hydroxyl groups of PEG to more reactive primary amino groups. The synthetic route involved reactions of chloridize, phthalimide and finally hydrazinolysis. Furthermore, poly(γ‐benzyl‐L ‐glutamate)‐poly(ethylene oxide)‐poly(γ‐benzyl‐L ‐glutamate) (PBLG‐PEO‐PBLG) triblock copolymer was synthesized by polymerization of γ‐benzyl‐L ‐glutamate N‐carboxyanhydride (Bz‐L‐GluNCA) using NH₂‐PEO‐NH₂ as macroinitiator. The resultant NH₂‐PEO‐NH₂ and triblock copolymer were characterized by FT‐IR, ¹H‐NMR and gel permeation chromatography (GPC) techniques. The results demonstrated that the degree of amination of the NH₂‐PEO‐NH₂ could be up to 1.95. The molecular weight of the PBLG‐PEO‐PBLG triblock copolymer could be adjusted easily by controlling the molar ratio of Bz‐L ‐Glu NCA to the macroinitiator NH₂‐PEO‐NH₂. Copyright © 2004 John Wiley & Sons, Ltd.     

3D Porous Carbon Framework Stabilized Ultra‐Uniform Nano γ‐Fe2O3: A Useful Catalyst System

We present a novel strategy for the scalable fabrication of γ‐Fe₂O₃@3DPCF, a three‐dimensional porous carbon framework (PCF) anchored ultra‐uniform and ultra‐stable γ‐Fe₂O₃ nanocatalyst. The γ‐Fe₂O₃@3DPCF nanocomposites were facilely prepared with the following route: condensation of iron(III) acetylacetonate with acetylacetonate at room temperature to form the polymer precursor (PPr), which was carbonized subsequently at 800 °C. The homogeneous aldol condensation offered an ultra‐uniform distribution of iron, so that the γ‐Fe₂O₃ nanoparticles (NPs) were uniformly distributed in the 3D carbon architecture with the average size of approximate 20 nm. The Fe₂O₃ NPs were capped with carbon, so that the iron oxide maintained its γ‐phase instead of the more stable α‐phase. The nanocomposite was an excellent catalyst for the reduction of nitroarene; it gave >99 % conversion and 100 % selectivity for the reduction of nitroarenes to the corresponding anilines at 100 °C. The fabrication of the γ‐Fe₂O₃@3DPCF nanocatalyst represents a green and scalable method for the synthesis of novel carbon‐based metal oxide nanostructures.     

Highly dispersed palladium nanoclusters incorporated in amino‐functionalized silica spheres for the selective hydrogenation of succinic acid to γ‐butyrolactone

Highly dispersed palladium nanoclusters incorporated on amino‐functionalized silica sphere surfaces (Pd/SiO₂‐NH₂) were fabricated by a simple one‐pot synthesis utilizing 3‐(2‐aminoethylamino)propyltrimethoxysilane (AAPTS) as coordinating agent. Uniform palladium nanoclusters with an average size of 1.1 nm can be obtained during the co‐condensation of tetraethyl orthosilicate and AAPTS owing to the strong interaction between palladium species and amino groups in AAPTS. The palladium particle size can be controlled by addition of AAPTS and plays a significant role in the catalytic performance. The Pd/SiO₂‐NH₂ catalyst exhibits high catalytic activity for succinic acid hydrogenation with 100% conversion and 94% selectivity towards γ‐butyrolactone using 1,4‐dioxane as solvent at 240°C and 60 bar for 4 h. Moreover, the Pd/SiO₂‐NH₂ catalyst is robust and readily reusable without loss of its catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd.     

Environmentally Friendly γ‐MnO2 Hexagon‐Based Nanoarchitectures: Structural Understanding and Their Energy‐Saving Applications

Although about 200,000 metric tons of γ‐MnO₂ are used annually worldwide for industrial applications, the γ‐MnO₂ structure is still known to possess a highly ambiguous crystal lattice. To better understand the γ‐MnO₂ atomic structure, hexagon‐based nanoarchitectures were successfully synthesized and used to elucidate its internal structure for the present work. The structural analysis results, obtained from the hexagon‐based nanoarchitectures, clearly show the coexistence of akhtenskite (ε‐MnO₂), pyrolusite (β‐MnO₂), and ramsdellite in the so‐called γ‐MnO₂ phase and verified the heterogeneous phase assembly of the γ‐MnO₂ state, which violates the well‐known “De Wolff” model and derivative models, but partially accords with Heuer's results. Furthermore, heterogeneous γ‐MnO₂ assembly was found to be a metastable structure under hydrothermal conditions, and the individual components of the heterogeneous γ‐MnO₂ system have structural similarities and a high lattice matches with pyrolusite (β‐MnO₂). The as‐obtained γ‐MnO₂ nanoarchitectures are nontoxic and environmentally friendly, and the application of such nanoarchitectures as support matrices successfully mitigates the common problems for phase‐change materials of inorganic salts, such as phase separation and supercooling‐effects, thereby showing prospect in energy‐saving applications in future “smart‐house” systems.     

Spectroscopic and thermal characterization of the host–guest interactions between α‐, β‐ and γ‐cyclodextrins and vanadocene dichloride

Host–guest interactions between α‐, β‐ and γ‐cyclodextrins and vanadocene dichloride (Cp₂VCl₂) have been investigated by a combination of thermogravimetric analysis, differential scanning calorimetry, powder X‐ray diffraction and solid‐state and solution electron paramagnetic resonance (EPR) spectroscopy. The solid‐state results demonstrated that only β‐ and γ‐cyclodextrins form 1:1 inclusion complexes, while α‐cyclodextrin does not form an inclusion complex with Cp₂VCl₂. The β‐ and γ‐CD–Cp₂VCl₂ inclusion complexes exhibited anisotropic electron‐⁵¹V (I = 7/2) hyperfine coupling constants whereas the α‐CD–Cp₂VCl₂ system showed only an asymmetric peak with no anisotropic hyperfine constant. On the other hand, solution EPR spectroscopy showed that α‐cyclodextrin (α‐CD) may be involved in weak host–guest interactions in equilibrium with free vanadocene species. Copyright © 2008 John Wiley & Sons, Ltd.     

The Crystal Structure of ζ2‐Al3Cu4‐δ

The crystal structure of the ζ₂‐phase Al₃Cu_4‐δ was determined by means of X‐ray powder diffraction: a = 409.72(1) pm, b = 703.13(2) pm, c = 997.93(3) pm, space group Imm2, Pearson symbol oI24‐3.5, R_I = 0.0696. ζ₂‐Al₃Cu_4‐δ forms a distinctive a × √3a × 2c superstructure of a metal deficient Ni₂In‐type‐related structure. The phase is meta‐stable at ambient temperature. Between 400 °C and 450 °C it decomposes into ζ₁‐Al₃Cu₄ and η₂‐AlCu. Entropic contributions to the stability of ζ₂‐Al₃Cu_4‐δ are reflected in three statistically or partially occupied sites.     

A Copper(I)‐Catalyzed Enantioselective γ‐Boryl Substitution of Trifluoromethyl‐Substituted Alkenes: Synthesis of Enantioenriched γ,γ‐gem‐Difluoroallylboronates

The first catalytic enantioselective γ‐boryl substitution of CF₃‐substituted alkenes is reported. A series of CF₃‐substituted alkenes was treated with a diboron reagent in the presence of a copper(I)/Josiphos catalyst to afford the corresponding optically active γ,γ‐gem‐difluoroallylboronates in high enantioselectivity. The thus obtained products could be readily converted into the corresponding difluoromethylene‐containing homoallylic alcohols using highly stereospecific allylation reactions.     

Base‐Catalyzed Highly Stereoselective Conversion of γ‐Hydroxy‐α,β‐acetylenic Esters to γ‐Acetoxy Dienoates

A convenient route with high stereo control to γ‐acetoxy dienoates is provided by the reaction of methyl propiolate with aldehydes in the presence of ZnEt₂ and N‐methylimidazole at room temperature, followed by the catalytic conversion of the resulting γ‐hydroxy‐α,β‐acetylenic esters with p‐N,N‐dimethylaminopyridine (DMAP) in acetic anhydride (see scheme).

     

Towards Truly Sustainable Polymers: A Metal‐Free Recyclable Polyester from Biorenewable Non‐Strained γ‐Butyrolactone

The first effective organopolymerization of the biorenewable “non‐polymerizable” γ‐butyrolactone (γ‐BL) to a high‐molecular‐weight metal‐free recyclable polyester is reported. The superbase tert‐Bu‐P₄ is found to directly initiate this polymerization through deprotonation of γ‐BL to generate reactive enolate species. When combined with a suitable alcohol, the tert‐Bu‐P₄‐based system rapidly converts γ‐BL into polyesters with high monomer conversions (up to 90 %), high molecular weights (M_n up to 26.7 kg mol^?1), and complete recyclability (quantitative γ‐BL recovery).