Fabrication of a metal free catalyst for chemical reactions through decoration of chitosan with ionic liquid terminated dendritic moiety

Chitosan pyrolysis in the presence of a ZnCl2/NaCl salts for carbons with electrocatalytic activity in oxygen reduction reaction in alkaline solutions

The one-step carbonization of low cost and abundant chitosan biopolymer in the presence of salt eutectics ZnCl2/NaCl results in nitrogen-doped carbon nanostructures (8.5 wt.% total nitrogen content). NaCl yields the spacious 3D structure, which allows external oxygen to easily reach the active sites for the oxygen reduction reaction (ORR) distinguished by their high onset potential and the maximum turnover frequency of 0.132 e site⁻1 s⁻1. Data show that the presence of NaCl during the synthesis exhibits the formation of pores having large specific volumes and surface (specific surface area of 1217 m2 g-1), and holds advantage by their pores characteristics such as their micro-size part, which provides a platform for mass transport distribution in three-dimensional N-doped catalysts for ORR. It holds benefit over sample pre-treated with LiCl in terms of the micropores specific volume and area, seen as their percentage rate, measured in the BET. Therefore, the average concentration of the active site on the surface is larger.

Chitosan bead containing metal-organic framework encapsulated heteropolyacid as an efficient catalyst for cascade condensation reaction

Using cyclodextrin and chitosan that are bio-based compounds, a novel bi-functional catalytic composite is designed, in which metal-organic framework encapsulated phosphomolybdic acid was incorporated in a dual chitosan-cyclodextrin nanosponge bead. The composite was characterized via XRD, TGA, ICP, BET, NH₃-TPD, FTIR, FE-SEM/EDS, elemental mapping analysis and its catalytic activity was examined in alcohol oxidation and cascade alcohol oxidation-Knoevenagel condensation reaction. It was found that the designed catalyst that possess both acidic feature and redox potential could promote both reactions in aqueous media at 55 °C and various substrates with different electronic features could tolerate the aforementioned reactions to furnish the products in 75-95% yield. Furthermore, the catalyst could be readily recovered and recycled for five runs with slight loss of the catalytic activity. Notably, in this composite the synergism between the components led to high catalytic activity, which was superior to each component. In fact, the amino groups on the chitosan served as catalysts, while cyclodextrin nanosponge mainly acted as a phase transfer agent. Moreover, measurement of phosphomolybdic acid leaching showed that its incorporation in metal-organic framework and bead structure could suppress its leaching, which is considered a drawback for this compound. Other merits of this bi-functional catalyst were its simplicity, use of bio-based compounds and true catalysis, which was proved via hot filtration.

Heteroployacid on the composite of boehmite and polyionic liquid as a catalyst for alcohol oxidation and tandem alcohol oxidation Knoevenagel condensation reactions

Using boehmite as an available and low-cost natural compound, a bi-functional catalytic composite is prepared through vinyl-functionalization of boehmite, followed by polymerization with the as-prepared bis-vinylimidazolium bromide ionic liquid and supporting of phosphotungstic acid. The catalyst was characterized via ICP, XRD, TGA, FTIR, SEM/EDS and elemental mapping analysis and applied for promoting alcohol oxidation reaction and one-pot tandem alcohol oxidation/Knoevenagel condensation reaction in aqueous media under mild reaction condition. The results indicated high catalytic activity of the catalyst for both reactions. This protocol showed high generality and aliphatic, aromatic and heterocyclic alcohols could be applied as substrates to furnish the corresponding products in high to excellent yields. Furthermore, hot filtration test confirmed true heterogeneous nature of the catalysis. The catalyst could also be recovered readily and reused for at least five runs of the reaction with low loss of the activity and phosphotungstic acid leaching upon each run.

Pd on cyclotriphosphazen-hexa imine decorated boehmite as an efficient catalyst for hydrogenation of nitro arenes under mild reaction condition

Cyclotriphosphazen-hexa imine ligand was prepared through successive reactions of phosphonitrilchloride trimer with 4-hydroxybenzaldehyde and (3-aminopropyl) triethoxy silane. The as-prepared ligand was then covalently grafted on boehmite to furnish an efficient support for the immobilization of Pd nanoparticles and synthesis of a novel heterogeneous catalyst for hydrogenation of nitro arenes. The catalytic tests revealed that the catalyst had excellent catalytic activity for hydrogenation of various nitro arenes with different steric and electronic features under mild reaction condition in aqueous media. Noteworthy, the catalyst was highly selective and in the substrates with ketone or aldehyde functionalities, reduction of nitro group was only observed. The catalyst was also recyclable and only slight loss of activity was detected after each recycling run. Hot filtration test also approved true heterogeneous nature of catalysis.

Pd on thermo-responsive composite of silica-coated carbon nanotube and 1-vinyl-3-butylimidazolium-based ionic liquid copolymers as an efficient catalyst for hydrogenation of nitro compounds

In this work, an ionic liquid-containing thermo-responsive heterogeneous catalyst with utility for promoting hydrogenation of nitro-compounds in aqueous media is developed. To prepare the catalyst, silica-coated carbon nanotubes were synthesized and vinyl-functionalized. The resulted compound was then polymerized with 1-viny-3-butylimidazolium bromide and N-isopropylacrylamide. The obtained ionic liquid-containing thermo-responsive composite was palladated via wet-impregnation method to give the final catalyst. Study of the performance of the catalyst confirmed high catalytic activity of the catalyst at temperature above the lower critical solution temperature. Furthermore, the catalyst was highly recyclable and showed negligible Pd leaching upon recycling. Broad substrate scope and selectivity of the catalyst towards reduction of nitro functionality were also confirmed. Furthermore, hot filtration test implied the heterogeneous nature of the catalysis. The comparison of the activity of Pd/CNT-P with some control catalysts approved the importance of hybridization of P and CNT and the presence of ionic liquid for the catalytic activity.

Halloysite Nanoclay with High Content of Sulfonic Acid-Based Ionic Liquid: A Novel Catalyst for the Synthesis of Tetrahydrobenzo[b]pyrans

One of the main drawbacks of supported ionic liquids is their low loading and consequently, low activity of the resultant catalysts. To furnish a solution to this issue, a novel heterocyclic ligand with multi imine sites was introduced on the surface of amino-functionalized halloysite support via successive reactions with 2,4,6-trichloro-1,3,5-triazine and 2-aminopyrimidine. Subsequently, the imine sites were transformed to sulfonic acid-based ionic liquids via reaction with 1,4-butanesultone. Using this strategy, high loading of ionic liquid was loaded on halloysite nanoclay. The supported ionic liquid was then characterized with XRD, SEM, TEM, EDS, FTIR, BET, TGA and elemental mapping analysis and utilized as a metal-free Brønsted acid catalyst for promoting one-pot reaction of aldehydes, dimedone and malononitrile to furnish tetrahydrobenzo[b]pyrans. The catalytic tests confirmed high performance of the catalyst. Moreover, the catalyst was stable upon recycling.