Aluminum-based Catalysts Research Articles

Robust, Thermally Stable and Impurity-Tolerant Aluminum-Based Catalyst System for Polylactide Production under Industrial Conditions

Robust, Thermally Stable and Impurity-Tolerant Aluminum-Based Catalyst System for Polylactide Production under Industrial Conditions

Understanding the Effect of M(III) Choice in Heterodinuclear Polymerization Catalysts.

The ring-opening copolymerization (ROCOP) of epoxides with CO2 or anhydrides is a promising strategy to produce sustainable polycarbonates and polyesters. Currently, most catalysts are reliant on scarce and expensive cobalt as the active center, while more abundant aluminum and iron catalysts often suffer from lower activities. Here, two novel heterodinuclear catalysts, featuring abundant Al(III), Fe(III), and K(I) active centers, are synthesized, and their performance in the polymerization of four different monomer combinations is compared to that of their Co(III) analogue. The novel Al(III)K(I) catalyst exhibits outstanding activities in the cyclohexane oxide (CHO)/CO2 ROCOP, and at 1 bar CO2 pressure it is the fastest aluminum-based catalyst reported to date. The M(III) site electronics for all three catalysts, Al(III)K(I), Fe(III)K(I), and Co(III)K(I), are measured using IR and NMR spectroscopy, cyclic voltammetry, and single crystal X-ray diffraction. A correlation between M(III) electron density and catalytic activity is revealed and, based on the established structure-activity relationship, recommendations for the future catalyst design of abundant Al(III)- and Fe(III)-based catalysts are made. The catalytic performances of both Al(III)K(I) and Fe(III)K(I) are further contextualized against the relative elemental abundance and cost. On the balance of performance, abundance, and cost, the Al(III)K(I) complex is the better catalyst for the carbon dioxide/epoxide ROCOP, while Fe(III)K(I) is preferable for anhydride/epoxide ROCOP.

Atomically Dispersed p-Block Aluminum-Based Catalysts for Oxygen Reduction Reaction.

The main group metals are commonly perceived as catalytically inert in the context of oxygen reduction reactions (ORR) due to the delocalized valence orbitals. Regulating the local environment and structure of metal center coordinated by nitrogen ligands (M-Nx) is a promising approach to accelerate catalytic dynamics. Herein, we, for the first time, report the atomically dispersed Al catalysts coordinated with N and C atoms for 4-electron ORR. The axial coordinated pyrrolyl N group (No) is constructed in the Al-N4-No moiety to regulate the p-band structure of Al center, effectively steering the local environment and structure of the square planar Al-N4 sites, which typically exhibit too strong interaction with ORR intermediates. The dynamic covalency competition of axial Al-No and Al-O bonding could endow the Al center with moderate hybridization between Al 3p orbital and O 2p orbital, alleviating the binding energy of ORR intermediates. The as-prepared Al-N4-No electrocatalyst exhibits excellent ORR activity, selectivity, and durability, along with the rapid kinetics as demonstrated by in situ Raman spectroscopy. This work offers a fundamental comprehension of the fine regulation on p-band and guides the rational design of main-group metal-based single atom catalysts.

Controlled ring-opening (co)polymerization of macrolactones: a pursuit for efficient aluminum-based catalysts

This work reports on the search for highly efficient aluminum-based complexes for the synthesis of high molar mass polymacrolactones and their well-defined block copolymers with small ring lactones, ε-caprolactone and l-lactide.

Aluminum-based catalysts prepared in the presence of pectin for low-energy biodiesel production

Materials containing aluminum oxides were prepared in the presence and absence of pectin and used as catalysts for biodiesel production. The material prepared in the presence of the biopolymer and calcinated at 600 °C (ALP-6) was the most promising one, yielding 95 % of biodiesel at 3 wt% of the catalyst after 1 h using methanol: oil molar ratio of 21:1. For comparison, the material prepared in the absence of pectin, ALR-6, yields only 27 % biodiesel in the same conditions. The reusability of the material was evaluated with 5 runs, obtaining more than 50 % of yield in the fifth run. SEM, TEM, FT-IR, TGA, XRD, N2 adsorption/desorption, and CO2-TPD analysis gathered insights about the catalytic behavior. The results reveal that adding pectin results in smaller particles with enhanced basicity due to the formation of sodium aluminate when compared to the material prepared in its absence, demonstrating that this biopolymer is a promising agent for catalyst preparation.

Unveiling the mechanisms of epoxide polymerization with N–Al adduct catalysts: a comprehensive experimental and theoretical investigation

Combining theory and experiments, the full mechanism has been determined for the polymerization of functional epoxides with aluminum-based catalysts.

Efficient 5-hydroxymethylfurfural synthesis from carbohydrates and food wastes in aqueous-natural deep eutectic solvent (A-NADES) with robust Al2O3 or Al(OH)3

As one of the essential building blocks for bio-chemicals and bio-fuels, the 5-Hydroxymethylfurfural (HMF) production is still challenging in a green and cheap way. This work developed a bio-derived aqueous-natural deep eutectic solvent (A-NADES) to synthesize HMF using α-Al2O3 or Al(OH)3 as robust catalysts, obtaining high yields of 67.1% and 63.6% HMF from glucose under mild reaction reactions, respectively. Different kinds of starches and starchy food waste also exhibited high conversion efficiency in the A-NADES system. The mechanistic study indicated that the in-situ formed Al (III) site of α-Al2O3 during the reaction was critical for converting glucose-based carbohydrates. A-NADES could be effectively reused six times with a more convenient direct reuse method without significant activity loss. This study suggested a novel A-NADES reaction media in the synergistic reaction with robust aluminum-based catalysts for HMF synthesis, and proposed a novel process of food waste utilization in green solvents.

MIL-53(Al) catalytic synthesis of poly(ethylene terephthalate).

Poly(ethylene terephthalate) (PET) is one of the world's five major engineering plastics and is widely used in various fields. At present, the main catalysts used in the synthesis of PET are antimony, titanium, and aluminum metal compounds. Among them, antimony-based catalysts are poisonous and the titanium-based catalyst products are relatively yellow in hue. The aluminum-based catalyst has the advantages of low price and environmental friendliness, but current research shows that the organoaluminum catalyst has the problem of hydrolysis, and MIL-53 (Al) has good stability and will not affect the environment, so we add a catalyst before the esterification reaction, and uses thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscope (SEM), and N2 low-temperature physical adsorption characterizes the thermal stability and structure of MIL-53(Al). At the same time, the effects of different content, polycondensation time, before and after activation and polycondensation temperature on the properties of PET were investigated. The research results show that when the molar content of catalyst is 0.05% and the reaction temperature is 280 °C for 150 min, the product obtained is relatively excellent. The catalytic activity has almost no effect before and after activation, indicating that the polycondensation reaction is carried out on the surface of the catalyst. Therefore, MIL-53 (Al) has great potential in PET industrial catalysis.

Isospecific Group-Transfer Polymerization of Diethyl Vinylphosphonate and Multidimensional NMR Analysis of the Polymer Microstructure

Control of stereoregularity is an integral part of a precision polymerization method and for the development of functional materials. Yttrium- and aluminum-based catalysts are known for converting diethyl vinylphosphonate (DEVP) into its stimuli-responsive polymer in a precise but stereoirregular way. Herein, we present Y- and Al-based constrained geometry complexes (CGCs) to induce isotacticity without losing control over other macromolecular parameters. After having established convenient synthesis routes and detailed structural analyses, these CGCs showed exceedingly high turn-over frequencies (up to 45 000 h–1) in the group-transfer polymerization of DEVP. The initiator efficiencies (≤99%) and dispersities (≤1.02) strongly depended on the substitution pattern of the applied ligands. An analysis of the microstructure using multidimensional NMR (1H–1H and 1H–13C(−31P)) correlation experiments demonstrated significant disparities for the stereospecificity of the CGCs and enabled a reliable signal assignment. The yttrium catalysts produced highly isotactic poly(diethyl vinylphosphonate), likely following a chain-end control mechanism, whereas the aluminum complexes produced less defined polymers.

Mechanism of Glucose–Fructose Isomerization over Aluminum-Based Catalysts in Methanol Media

The catalytic isomerization of glucose to fructose has been deemed a vital step in biorefinery, while the isomerization mechanism in alcoholic media still remains ambiguous. Hereby, density functional theory (DFT) calculations were carried out to investigate the isomerization mechanism of glucose over aluminum-based catalysts in methanol media. Al3+ was apt to coordinate with methanol and cyclic β-d-glucose (CDG) to form various complexes. It was found that [Al(CH3O)2(CH3OH)2]+ was the most stable one in +1 charge complexes based on the DFT calculations and ESI-MS experiments. Furthermore, the four-coordination complex [(η2O4,O6-CDG)Al(CH3O)2]+ was predicted to be the most preferable. Ionic species formed between Al3+ and the solvent can further assemble with glucose to catalyze the isomerization. The isomerization proceeds mainly by three steps, including ring-opening, hydride shift, and ring-closing with the migration of H from the C2–H to the O1–H bond (hydride shift) as the rate-determining step. The ...

Impact of catalyst load, chemical oxygen demand and nitrite on disinfection and removal of contaminants during catalytic ozonation of wastewater

Calcium-silicate mineral Polonite® and aluminum-based catalyst (AL-1010S), previously identified as promising materials for catalytic ozonation, were used as catalysts to investigate the impact of some operating conditions (ratio ozone feed concentration to catalyst load) and wastewater characteristics (chemical oxygen demand - COD and nitrite - NO2 concentration) on the disinfection and removal of contaminants of emerging concern (CECs) during catalytic ozonation of wastewater. Tests conducted in synthetic wastewater using two different ozone gas concentration (4 and 8 g (nm3)) and 6 different catalyst loads provided ratios of 0.08, 0.11, 0.16, and 0.32. Results from the experiments indicated that the ratio of 0.11 was optimal and reached residual disinfection below 2 MPN mL−1 from the initial concentration of 5 ± 2 × 105 MPN mL−1 and removal of atrazine (ATZ) above 80% from the initial concentration of 100 ± 10 μg L−1 for an ozone dose of 41–45 mg L−1. Catalytic ozonation with the selected materials enhanced disinfection and ATZ removal from synthetic wastewater (SWW) in comparison to non-catalytic ozonation by making the treatment performance less sensitive to increased chemical oxygen demand (COD) and nitrite (NO2) in the matrix. Validation of the results in real wastewater effluents confirmed that catalytic ozonation enhanced disinfection. Catalytic ozonation using Polonite® and AL-1010S provided residual bacteria level of 0.6 ± 0.42 MPN mL−1 and 0.29 ± 0.41 MPN mL−1, while non-catalytic ozonation lead to an average residual bacteria level of 1.26 ± 0.09 MPN mL−1 for the same range of transferred ozone dose. However, under the conditions tested, a limited number of CECs were extracted at levels above the limits of quantification and further validation work required to evaluate the performance of catalytic ozonation for the removal of CECs.

Bifunctional aluminum catalyst for CO2 fixation: regioselective ring opening of three-membered heterocyclic compounds.

Regioselective ring opening of three-membered heterocyclic compounds (epoxides or N-substituted aziridines) at various temperatures was observed in coupling reactions with CO2 by the use of an aluminum-salen catalyst in conjunction with intramolecular quaternary ammonium salts as cocatalysts, affording the corresponding five-membered cyclic products with complete configuration retention at the methine carbon. Notably, this bifunctional aluminum-based catalyst exhibited nearly 100% regioselectivity for the ring opening at the methylene C-O bond for various terminal epoxides. This was true for those bearing an electron-withdrawing group, such as styrene oxide or epichlorohydrin, thereby affording the synthesis of various enantiopure cyclic carbonates that have previously been obtained only rarely by other methods. An intramolecular cooperative catalysis is suggested to contribute to the high activity and excellent stereochemistry control observed. Surprisingly, the highly selective ring opening at the methine carbon of N-substituted aziridines was found in the coupling with CO2, predominantly giving 5-substituted oxazolininones with retention of configuration as a result of double inversion at the methine carbon.

Alkylation of p-cresol with camphene in the presence of aluminum-containing catalysts

Alkylation of p-cresol with camphene was studied in the presence of aluminum-based catalysts (i-PrO)3Al, AlH3, AlCl3, (i-Bu)2AlH, EtAlCl2, and LiAlH4. Aluminum isopropylate was a selective catalyst for the preparation of ortho-isobornylphenol, its activity being close to that of aluminum phenolate.

Highly Efficient Aluminum-Catalyzed Ring-Opening Polymerization of Cyclic Carbonates, Lactones, and Lactides, Including a Unique Crystallographic Snapshot of an Intermediate

The synthesis of a new well-defined aluminum-based catalyst (1) for the ring-opening polymerization of cyclic carbonates, lactones, and lactides is described. Compound 1 is supported by a cheap and...

Isopropoxyaluminum 1,1′-Biphenyl-2-oxy-2′-perfluorooctanesulfonamide as a Catalyst for Tishchenko Reaction.

Abstract Isopropoxyaluminum 1,1′-biphenyl-2-oxy-2′-perfluorooctanesulfonamide ( 3 ) has been evaluated as an aluminum-based catalyst for the Tishchenko reaction. Compound 3 was found to exert high catalytic activity in the reaction with aliphatic aldehydes and also enabled smooth dimerization of enolizable aldehydes. This advantage was highlighted by the quantitative formation of ethyl acetate from acetaldehyde by the present system.

Isopropoxyaluminum 1,1′-biphenyl-2-oxy-2′-perfluorooctanesulfonamide as a catalyst for Tishchenko reaction

Isopropoxyaluminum 1,1′-biphenyl-2-oxy-2′-perfluorooctanesulfonamide (3) has been evaluated as an aluminum-based catalyst for the Tishchenko reaction. Compound 3 was found to exert high catalytic activity in the reaction with aliphatic aldehydes and also enabled smooth dimerization of enolizable aldehydes. This advantage was highlighted by the quantitative formation of ethyl acetate from acetaldehyde by the present system.

General computational strategy to study polymerization reactions at aluminum‐based catalysts

AbstractFollowing our previous work, we have tested an effective computational strategy to study olefin polymerization at Al systems. The proposed protocol rests on a combined use of post–Hartree‐Fock and density functional theory (DFT) methods, to obtain the best ratio between accuracy and resource demand. Several Al systems have been treated, selected so as to explore different electronic and structural environments around the metal site. Our results confirm that termination reactions involving hydrogen transfer cannot be reliably described at the DFT level, but this problem can be overridden by our combined approach. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003

The asymmetric Meerwein-Schmidt-Ponndorf-Verley reduction of prochiral ketones with iPrOH catalyzed by Al catalysts.

Efficient and practical: An aluminum-based catalyst system for the asymmetric Meerwein–Schmidt–Ponndorf–Verley reduction of aromatic ketones is reported. By using iPrOH as the achiral hydride source and BINOL-type chiral ligands (see scheme), chiral secondary aromatic alcohols (up to 83 % ee) can be obtained in good yields.

Modeling Polymerization Reactions at Aluminum-Based Catalysts: Is DFT a Reliable Computational Tool?

A large number of DFT approaches, including classical GGA approximations, hybrid HF/DFT approaches, and more recent τ-dependent functionals, have been tested for olefin polymerization reactions at a cationic aluminum system, and their results have been compared with refined post-HF methods. The results show that hybrid density functional methods always outperform classical GGA approaches, and more recent τ-dependent functionals are not yet competitive, providing nonsystematic errors in the energy evaluations. The effect of the lengthening of the polymer chain from the “standard” ethyl group to a butyl group was found to be significant and hence has to be taken into account when predicting the molecular weight of polymers. A computational strategy to study olefin polymerization at Al systems is proposed.

Mechanistic alternatives in Lewis acid-catalyzed acyl halidealdehyde cyclocondensations

An investigation of the operative reaction mechanisms in Lewis acid-catalyzed acyl halidealdehyde cyclocondensations is presented. Aluminum-based catalysts promote cyclocondensation via a ketene-dependent reaction pathway while acyl halide enolates are implicated as reactive intermediates in Ti(IV)-catalyzed reactions.