Aluminum Alkoxide Research Articles

Silica–alumina/sepiolite nanoarchitectures

Novel silica–alumina/sepiolite nanoarchitectures have been prepared by an original approach based on sol–gel procedures. A commercial organo-sepiolite is used as a starting material whose organocations are provided by alkylchains that contribute to the controlled hydrolysis and polycondensation of silicon and aluminium alkoxides mixtures added to a non-aqueous suspension of that sepiolite. This procedure yields the coagulation of the alkoxides–organosepiolite suspension, resulting in the formation of a homogenous gel. After thermal treatment of the dried system, the organic matter is removed and the silica–alumina network consolidated. The characterization of the resulting materials reveals the formation of silica–alumina nanoparticles that remain anchored to the surface of sepiolite fibers through the silanol groups of the core silicate. These novel nanoarchitectures show specific surface areas in the range of 250–300 m2 g−1. The porosity of the resulting materials can be controlled depending on the nature of the oxide network generated. Thus, high silica contents generated microporous systems, whereas the incorporation of alumina enhances the mesoporous formation. The incorporation of a silica–alumina network on the surface sepiolite also permits the tuning of its surface acidity, typical values increasing from 0.1 to 1.4 mmol of acid sites per gram, according to the aluminium content. The acid–base properties of the new nanoarchitectures were evaluated as acid catalysts from the 2-propanol dehydration test. The catalytic behaviour is discussed in terms of the acidic properties of the involved solids.

Aluminum complexes incorporating symmetrical and asymmetrical tridentate pincer type pyrrolyl ligands: synthesis, characterization and reactivity study

A series of aluminum complexes incorporating substituted symmetrical and asymmetrical tridentate pyrrolyl ligands are synthesized conveniently and the treatment of the derivatives with small organic molecules are analyzed. The reaction of lithiated [C4H2NH(2-CH2NH(t)Bu)(5-CH2NR1R2)], where for 1, R1 = R2 = Me; 2, R1 = H, R2 = (t)Bu, with AlCl3 in diethyl ether affords Al[C4H2N(2-CH2NH(t)Bu)(5-CH2NMe2)]Cl2 (3) and Al[C4H2N(2,5-CH2NH(t)Bu)2]Cl2 (4), respectively, in high yields. Furthermore, subjecting 3 and 4 to reaction with one equiv. of LiNMePh in diethyl ether generates Al[C4H2N(2-CH2NH(t)Bu)(5-CH2NMe2)][NMePh]Cl (5) and Al[C4H2N(2,5-CH2NH(t)Bu)2][NMePh]Cl (6), respectively, while eliminating one equiv. of LiCl. The reaction between compound 4 with two equiv. of LiO-Ph-4-Me in diethyl ether yields the aluminum di-phenoxide compound Al[C4H2N(2,5-CH2NH(t)Bu)2](O-Ph-4-Me)2 (7) whereas the combination of 3 and two equiv. of LiNH(t)Bu, produces Al[C4H2N(2-CH2N(t)Bu)(5-CH2NMe2)](NH(t)Bu)(NH2(t)Bu) (8). Additionally, the mixing of 1 and one equiv. of AlMe3 renders Al[C4H2N(2-CH2NH(t)Bu)(5-CH2NMe2)]Me2 (9). Adding one more equiv. of AlMe3 with 9 affords {Al[C4H2N(2-CH2NH(t)Bu)(5-CH2NMe2)AlMe3]Me2} (10), which can also be obtained by treating 1 with two equiv. of AlMe3 directly. The treatment of 9 with one equiv. of 2,6-dimethylphenol in diethyl ether gives the aluminum alkoxide derivative, Al[C4H2N(2-CH2NH(t)Bu)(5-CH2NMe2)](O-C6H3-2,6-Me2)Me (11). Furthermore, the reaction between 9 and one equiv. of 1-ethyl-1-phenyl ketene, initiates the aluminum dimethyl complex Al{C4H2N[2-CH2CEtPh-C(=O)-NH(t)Bu](5-CH2NMe2)}Me2 (12) with a C-N bond breakage and a C-C bond formation. All the Al-derivatives are characterized by (1)H and (13)C NMR spectroscopy and the molecular structures are determined by single crystal X-ray diffractometry in solid state.

Mesoporous isocyanurate-containing organosilica–alumina composites and their thermal treatment in nitrogen for carbon dioxide sorption at elevated temperatures

Composite mesostructures consisting of organosilica with isocyanurate bridging groups and alumina have been synthesized using evaporation-induced self-assembly (EISA) in the presence of a triblock copolymer, Pluronic P123, in absolute ethanol solution. These mesostructures were prepared using aluminum isopropoxide and aluminum nitrate nonahydrate as alumina precursors and tris[3-(trimethoxysilyl)propyl]isocyanurate (ICS). The triblock copolymer was removed by extraction with 95% ethanol solution followed by additional thermal treatment of the extracted sample at 300 °C in flowing nitrogen; this process assured a complete removal of the polymeric template without degradation of the ICS bridging groups. The use of aluminum nitrate nonahydrate and a N-containing ICS precursor with a small amount of 3-aminopropyltriethoxysilane (AP) led to the hybrid materials with well-developed porosity and high specific surface area (200–450 m2 g−1). A controlled heating of these materials in nitrogen resulted in N-doped alumina–silica mesostructures showing high affinity towards CO2 at elevated temperatures. The use of inexpensive aluminum nitrate instead of aluminum alkoxides in the EISA synthesis had a significant impact on the pore structure, surface area and adsorption properties of the resulting composite materials.

Aluminum alkoxide complexes from highly substituted 3,4-epoxy alcohols: An NMR and computational study

The organoaluminum mediated epoxide ring opening of epoxy alcohols is a key step in the oxirane-based approach for polypropionate synthesis. However, this reaction has shown unanticipated regioselectivities when applied to 2-methyl-3,4-epoxy alcohols. In order to gain mechanistic insight into the factors controlling the epoxide ring opening process, diastereomeric 2-methyl-3,4-epoxy alcohols were reacted with triethylaluminum in order to identify the aluminum complexes formed by these systems. Different epoxide–aluminum complexes were calculated using ab initio HF/[13s7p/11s5p] and B3PW91/6-31G** gauge-including atomic orbital (GIAO) methods and compared to the experimental NMR data. The calculated and experimental data correlates with the aluminum dimer complex (TIPSOCH2CH(OAlEt2)CH(CH)3CHCH(O)(AlEt3))2 (VIII) for the systems favoring the nucleophilic attack at the external C4 epoxide carbon, while an unusual trialuminum species TIPSOCH2CH(OAlEt2)CH(CH)3CHCH(O)(AlEt3)2 (X) is consistent with the systems favoring the internal C3 attack. The 27Al NMR data established the tetracoordinated nature of the aluminum metal in all alkoxy aluminum intermediates, while the 13C NMR data provided insight into the aluminum-oxygen coordination. The formation of the complexes was dictated by the stereochemical disposition of the substituents. These complexes are different from the generally accepted bidentate intermediates proposed for 2,3-epoxy alcohols and simpler 3,4-epoxy alcohols. Copyright © 2012 John Wiley & Sons, Ltd.

Ultrathin highly porous alumina films prepared by alucone ABC molecular layer deposition (MLD)

Highly structured porous alumina thin films have many practical uses, including membrane applications and catalyst encapsulation. One route to synthesizing these films that offers exceptional control over film thickness to several angstroms starts with the molecular layer deposition (MLD) of an aluminum alkoxide (alucone) film. Oxidizing the alucone film removes the organic component and produces the desired nanoporous alumina. The pore size can be controlled by selection of the length of the carbon chain in the polymer film. In this study, 500nm silica nanoparticles were coated with 10–40cycles of alucone using a three-step ABC MLD process. Trimethylaluminum, ethanolamine, and maleic anhydride were used as precursors. The organic component of the alucone films was removed in air by calcination at elevated temperature or in water at room temperature. It is shown that the pore size of the porous films can be increased from 0.6 to 0.8nm by depositing an alucone film having longer carbon chains. Film surface area, composition, thickness, and pore size were measured, confirming that the ABC MLD process can produce high quality porous alumina films and provide a pathway to tune nanopore size in these films.

Facile solvent-deficient synthesis of mesoporous γ-alumina with controlled pore structures

We report a simple, one-pot, solvent-deficient process using different aluminum salts to synthesize mesoporous γ-alumina without external templates or surfactants. Samples prepared from aluminum inorganic salts have a close-packed morphology, where randomly stacked fibrous crystallites of γ-alumina are obtained when utilizing aluminum alkoxides. After calcination at 700°C for 2h, surface areas of these nanostructured γ-aluminas range from 210 to 320m2/g. The average pore diameters range from 6 to 18nm, the crystallite diameters range from 3 to 4nm, and pore volumes range from 0.4 to 1.7cm3/g. This synthetic method provides a facile route to synthesize stable, high surface-area mesoporous aluminas having a wide range of pore sizes and volumes.

Ubiquitous aluminum alkyls and alkoxides as effective catalysts for glucose to HMF conversion in ionic liquids

Metal halides (chlorides in particular) are employed almost exclusively as Lewis acid catalysts for the homogeneous conversion of glucose (or cellulose) to HMF (5-hydroxymethylfurfural) in ionic liquids (ILs), with CrCl2 being arguably the most effective benchmark catalyst. Reported herein is a discovery that ubiquitous aluminum alkyl or alkoxy compounds are very effective Lewis acid catalysts for the glucose-to-HMF conversion in ILs. Under the current reaction conditions (1-ethyl-3-methylimidazolium chloride [EMIM]Cl, 120°C, 6h), simple trialkyl and trialkoxy aluminum species such as AlEt3 and Al(OiPr)3, which are much cheaper than CrCl2 (by a factor of 5 for AlEt3 or 180 for Al(OiPr)3), are at least as effective as CrCl2 to catalyze this conversion process. The molecular structure of [EMIM]+[ClAlMe(BHT)2]−, formed upon mixing the alkylaryloxy aluminum MeAl(BHT)2 and the IL [EMIM]Cl, has been determined by X-ray diffraction; the structure simulates that of the metallate [EMIM]+[CrCl3]−, the proposed active species responsible for the effective glucose to HMF conversion by CrCl2 in [EMIM]Cl. Another significant finding is that a gradual substitution of the chloride ligand on aluminum by the alkyl ligand brings about a drastic enhancement on the HMF yield, from 1.6% by AlCl3 to 7.6% by MeAlCl2 to 17% by Et2AlCl and to 51% by AlEt3, thus showing approximately an overall 32-fold HMF yield enhancement going from AlCl3 to AlEt3.

Facile synthesis of hexagonally ordered mesoporous aluminum oxide thin films with high catalytic activity

Facile synthesis of hexagonally ordered mesoporous aluminum oxide thin films on glass has been reported using a modified aluminum alkoxide precursor and a triblock co-polymer (P123) in ambient condition. The fast hydrolysis rate of aluminum alkoxide can be effectively controlled using a complexing agent acetyl acetone (acac). The slow and controlled hydrolysis and condensation reactions of such partially acac complexed aluminum alkoxide in presence of P123 yielded well-organized mesostructures originating from the self-assembling of micelles in sols. The symmetry of mesopores, thermal stability and catalytic activity of these films were studied. X-ray diffraction studies and transmission electron microscopy (TEM) at different temperatures of these mesoporous films confirmed the ordered nature of mesopores with hexagonal p6mm symmetry and retention of the ordered arrangement up to a high temperature of 900°C where the transformation of amorphous to γ-alumina took place. The films heat-treated at 500°C with hexagonally ordered pore arrangement showed much better catalytic activity in the decomposition of toxic KMnO4 to MnO2 nanoparticles in aqueous solution compared to its disordered analogue of similar thickness and porosity.

Modification of Aluminium Alkoxide with Different Long-Chain Chelating Agent: Hydrolysis and Characterization of the Product

An aluminum alkoxide, [Al(OCH2CH2OCH2CH3)3] (O 1 ), was synthesized by alcohol exchange method and after characterization by 27Al NMR, 1H NMR, infrared spectroscopies and mass spectrometry was used as a precursor for the preparation of high quality γ-alumina. γ-aluminas also were prepared from [Al(OCH2CH2OCH2CH2OCH3)3] (O 2 ) and [Al(OCH2CH(CH3)CH3)3] (O 3 ) in an identical hydrolysis condition and their textural parameters compared to that of prepared from O 1 . The gels obtained from hydrolysis of aluminum alkoxides by sol–gel processing were characterized by X-ray powder diffraction, thermal analysis, scanning electron microscopy (SEM), and nitrogen adsorption–desorption analysis. The X-ray diffraction patterns showed the materials obtained from hydrolysis of O 1 , O 2 and O 3 are pseudoboehmite and converts to γ-alumina by calcinations at 800 °C. The alumina obtained from hydrolysis of O 3 showed higher surface area (SBET), slightly above 200 m2/g and lower particle size, about 40–50 nm, than aluminas prepared from the hydrolysis of O 1 and O 2 . SEM showed that morphology of alumina obtained from O 2 is different to a great extent than the ones obtained from other precursors. Moreover, a transparent monolith gel has been prepared from O 1 .

Aluminum Complexes Stabilized by Piperazidine‐Bridged Bis(phenolate) Ligands: Syntheses, Structures, and Application in the Ring‐Opening Polymerization of ε‐Caprolactone

AbstractThe synthesis and characterization of aluminum alkoxide and alkyl complexes stabilized by piperazidine‐bridged bis(phenolate) ligands are described. Treatment of ligand precursors H2[ONNO]1 {H2[ONNO]1=1,4‐bis(2‐hydroxy‐3‐tert‐butyl‐5‐methylbenzyl)piperazidine} and H2[ONNO]2 {H2[ONNO]2=1,4‐bis(2‐hydroxy‐3,5‐di‐tert‐butylbenzyl)piperazidine} with AlEt2(OCH2Ph) and AlEt2(OPr‐i), which were generated in situ by the reactions of AlEt3 with equivalent of the corresponding alcohols, in a 1:1 molar ratio in THF gave the corresponding aluminum alkoxide complexes [ONNO]1Al(OCH2Ph) (1) and [ONNO]2Al(OPr‐i) (2), respectively. The reaction of H2[ONNO]1 with AlEt2(OCH2Ph) in a 1:2 molar ratio in THF afforded a mixture of monometallic aluminum ethyl complex [ONNO]1AlEt (3) and complex 1, which can be isolated by stepwise crystallization. Similarly, H2[ONNO]2 reacted with AlEt2(OPr‐i) in a 1:2 molar ratio in THF to give a mixture of aluminum ethyl complex [ONNO]2AlEt (4) and complex 2. Complexes 1 and 2 were also available via treatment of complexes 3 and 4 with 1 equiv. of benzyl alcohol and isopropyl alcohol, respectively. All of these complexes were fully characterized including X‐ray structural determination. It was found that complexes 1 to 4 can initiate the ring‐opening polymerization of ε‐caprolactone, and complexes 1 and 2 showed higher catalytic activity in comparison with complexes 3 and 4.

Preparation and Characterization of Aluminum Alkoxides Coordinated on salen-Type Ligands: Highly Stereoselective Ring-Opening Polymerization of rac-Lactide

A series of salen-type ligands (L1H2–L6H2) with sterically bulky cumyl groups have been synthesized. Reaction of these ligands with AlMe3 yields the mononuclear aluminum complexes [LAlMe] (1–3) or dinuclear species [L2Al2Me4] (4–6), respectively. Further reaction of [LAlMe] (1–3) with benzyl alcohol produces [LAl(OBn)] (1a–3a), respectively. Solid-state structural studies reveal that complexes 1a and 2a are mononuclear; however, complex 6 is a dinuclear species. Aluminum alkoxides 1a–3a are highly stereoselective in the ROP of rac-lactide, producing polylactide (PLA) with 94–97% enantiomeric selectivity (Pm) at high conversion. Their high enantioselectivity leads to PLA with high Tm (205 °C). The polymerization of l-lactide by these complexes also shows good living features with narrow PDI values (Mw/Mn = 1.06–1.25) signaling less or no transesterification, which can be further verified by MALDI-TOF mass spectrometric analysis.

An environmentally friendly method for the synthesis of nano-alumina with controllable morphologies

The relatively high price of aluminum alkoxides as an alumina source and organic surfactants as morphology control or structure directing agents are less attractive for practical applications to the synthesis of nanostructured alumina. Moreover, some of these synthesis processes may generate large masses of salt by-products. A highly efficient synthesis of nano-alumina from ammonium carbonate aqueous solution and aluminum nitrate ethanol solution without the use of a template and complicated processes has been achieved. The Al(NO3)3·9H2O reagent can be completely converted to nano-alumina without a by-product and the ethanol solutions can be reused. In addition, the CO2 and NH3 produced can also be recycled to the reagent (NH4)2CO3. The nano-alumina synthesized is of γ-alumina structure. Moreover, the simple and environmentally friendly route described could enhance the synthesis technology for nano-alumina and its applications.

Iron-catalysed cross-coupling of halohydrins with aryl aluminium reagents: a protecting-group-free strategy attaining remarkable rate enhancement and diastereoinduction

Non-protected halohydrins are cross-coupled with aryl aluminium reagents to produce aryl alkanols in the presence of the iron-bisphosphine catalysts. Remarkable reaction rate enhancement and diastereoinduction are realized by the in situ generated aluminium alkoxides, offering a new method for the reactivity and selectivity control of the iron-catalysed cross-coupling reaction.

Synthesis of Stereoregular Polylactide

The paper studied polymerization of rac-lactide catalyzed by a diketiminato aluminum alkoxide complex. The aluminum alkoxide complex bearing bulky isopropyl ortho substituents showed moderate activity for the rac-lactide polymerization. Microstructural study of polymer generated with the aluminum catalyst reveals that syndiotactic polylactide were produced. Results have shown that the conversion of lactide depend on the monomer/catalyst feed ratio and the reaction temperature.

Stereoselective ring-opening polymerization of D,L-lactide, initiated by aluminum isopropoxides bearing tridentate nonchiral schiff-base ligands

Ring-opening polymerization of D,L-lactide was stereoselectively achieved using newly designed aluminum alkoxide complexes as initiators. These half-SALEN aluminum complexes bearing tridentate nonchiral Schiff-base ligands are racemates, which provide chirality in the aluminum centers, efficiently afforded a stereoblock copolymer of D,L-LA. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Molecular Layer Deposition of Aluminum Alkoxide Polymer Films Using Trimethylaluminum and Glycidol

Molecular layer deposition (MLD) of aluminum alkoxide polymer films was examined using trimethlyaluminum (TMA) and glycidol (GLY) as the reactants. Glycidol is a high vapor pressure heterobifunctional reactant with both hydroxyl and epoxy chemical functionalites. These two different functionalities help avoid "double reactions" that are common with homobifuctional reactants. A variety of techniques, including in situ Fourier transform infrared (FTIR) spectroscopy and quartz crystal microbalance (QCM) measurements, were employed to study the film growth. FTIR measurements at 100 and 125 °C observed the selective reaction of the GLY hydroxyl group with the AlCH(3) surface species during GLY exposure. Epoxy ring-opening and methyl transfer from TMA to the surface epoxy species were then monitored during TMA exposure. This epoxy ring-opening reaction is dependent on strong Lewis acid-base interactions between aluminum and oxygen. The QCM experiments observed linear growth with self-limiting surface reactions at 100-175 °C under certain growth conditions. With a sufficient purge time of 20 s after TMA and GLY exposures at 125 °C, the mass gain per cycle (MGPC) was 19.8 ng/cm(2)-cycle. The individual mass gains after the TMA and GLY exposures were also consistent with a TMA/GLY stoichiometry of 4:3 in the MLD film. This TMA/GLY stoichiometry suggests the presence of Al(2)O(2) dimeric core species. The MLD films resulting from these TMA and GLY exposures also evolved with annealing temperature to form thinner conformal porous films with increased density. Non-self-limiting growth was a problem at shorter purge times and lower temperatures. With shorter purge times of 10 s at 125 °C, the MPGC increased dramatically to 134 ng/cm(2)-cycle. The individual mass gains after the TMA and GLY exposures in the CVD regime were consistent with a TMA/GLY stoichiometry of 1:1. The MGPC decreased progressively versus purge time. This behavior was attributed to the removal of reactants that could lead to CVD and the instability of the surface species after the reactant exposures. These results reveal that the TMA and GLY reaction displays much complexity and must be carefully controlled to be a useful MLD process.

Introduction of Bridging and Pendant Organic Groups into Mesoporous Alumina Materials

Incorporation of organic functionalities into soft-templated mesoporous alumina was performed via organosilane-assisted evaporation induced self-assembly using aluminum alkoxide precursors and block copolymer templates. This strategy permits one to obtain mesoporous alumina-based materials with tailorable adsorption, surface and structural properties. Isocyanurate, ethane, mercaptopropyl, and ureidopropyl-functionalized mesoporous alumina materials were synthesized with relatively high surface area and large pore volume with uniform and wormhole-like mesopores. The presence of organosilyl groups within these hybrid materials was confirmed by IR or Raman spectroscopy and their concentration was determined by elemental analysis.

Sol–gel based alumina powders with catalytic applications

The sol–gel process provides a new approach to the preparation of oxide materials and offers many advantages for making catalysts. Since homogeneous mixing can be achieved at the molecular scale, the chemical reactivity of the oxide surface can be greatly enhanced; thus powders with high surface area and optimized pore size distribution can be obtained at low temperatures. In the present work NiO/Al 2O 3 sol–gel catalysts were obtained by simultaneous gelation of aluminium isopropoxide and nickel nitrate. A comparative study with pure sol–gel alumina was also realized. By physical–structural studies the changes induced by the introduction of the Ni precursor, before and after aluminium alkoxide hydrolysis were highlighted. The introduction of Ni at the beginning of the reaction favors γ-Al 2O 3 crystallization. When Ni is added at the end of reaction, it delays the alumina crystallization and induces the disorder of the lattice. The obtained Ni doped sol–gel derived alumina has been used as catalyst in the finished form for glycerol reforming to generate H 2 for fuel cell applications. Some evaluation results of Ni-doped alumina combined with TiO 2 in photocatalytic glycerol reforming reaction have been included.

Stabilization of Supported Metal Nanoparticles Using an Ultrathin Porous Shell

Supported Pt nanoparticles (<2 nm) were stabilized by a highly porous, alumina nanofilm that was deposited on the Pt and its high surface area silica support. The alumina film with subnanometer thickness control resulted from thermal decomposition of an aluminum alkoxide layer that was deposited by molecular layer deposition (MLD). A catalyst with a porous ultrathin alumina layer was much more stable to calcination in air, even at 800 °C. The alumina-coated Pt nanoparticles were less catalytically active, most likely because of the small size of the pores in the alumina layer.

Hierarchically structured meso-macroporous aluminosilicates with high tetrahedral aluminium content in acid catalysed esterification of fatty acids

A simple synthesis pathway has been developed for the design of hierarchically structured spongy or spherical voids assembled meso-macroporous aluminosilicates with high tetrahedral aluminium content on the basis of the aqueous polymerisation of new stabilized alkoxy-bridged single molecular precursors. The intimate mixing of an aluminosilicate ester (sec-BuO)2–Al–O–Si(OEt)3 and a silica co-reactant (tetramethoxysilane, TMOS) with variable ratios and the use of alkaline solutions (pH 13.0 and 13.5) improve significantly the heterocondensation rates between the highly reactive aluminium alkoxide part of the single precursor and added silica co-reactant, leading to aluminosilicate materials with high intra-framework aluminium content and low Si/Al ratios. The spherically-shaped meso-macroporosity was spontaneously generated by the release of high amount of liquid by-products (water/alcohol molecules) produced during the rapid hydrolysis and condensation processes of this double alkoxide and the TMOS co-reactant. It has been observed that both pH value and Al–Si/TMOS molar ratio can strongly affect the macroporous structure formation. Increasing pH value, even slightly from 13 to 13.5, can significantly favour the incorporation of Al atoms in tetrahedral position of the framework. After the total ionic exchange of Na+ compensating cations, catalytic tests of obtained materials were realised in the esterification reaction of high free fatty acid (FFA) oils, showing their higher catalytic activity compared to commercial Bentonite clay, and their potential applications as catalyst supports in acid catalysed reactions.