Recyclable Heterogeneous Catalyst Research Articles

Recycling of post-use starch-based plastic bags through pyrolysis to produce sulfonated catalysts and chemicals

Pyrolysis was explored as a technology for depolymerizing and charring starch-based plastic bags in a novel valorization perspective based on a chemical recycling strategy, alternative to anaerobic digestion or composting. The char obtained from the thermal treatment (420°C for 15 h) was sulfonated to give a highly active and recyclable heterogeneous acid catalyst (10 wt% yield based on starch-based plastic bags subjected to pyrolysis), comparable in terms of catalytic activity and reusability to the analog catalyst prepared from potato starch and tested on a model esterification reaction. From pyrolysis liquid of starch-based plastic bags, highly pure terephthalic acid (4 wt% yield) was isolated through self-precipitation, whereas the remaining pyrolysis liquid produced (21 wt%) was solvent-fractionated to give a polar fraction (7 wt% yield) enriched in levoglucosan, and a less polar fraction (14 wt% yield) enriched in monobutenyl adipate and terephthalate.

Ultrasound promoted and Kit‐6 mesoporous silica‐supported Fe3O4 magnetic nanoparticles catalyzed cyclocondensation reaction of 4‐hydroxycoumarin, 3,4‐methylenedioxyphenol, and aromatic aldehydes

A new effective approach to synthesize a series of 7‐aryl‐6H,7H‐[1]benzopyrano[4,3‐b][1,3]dioxolo[4,5‐g][1]benzopyran‐6‐ones was reported using Fe3O4@SiO2@Kit‐6 as heterogeneous catalyst at room temperature under ultrasonic irradiation in aqueous media. This procedure is of great value due to its short reaction time, high yields, simple processing, and the use of easily available and magnetically recyclable heterogeneous catalyst.

A recyclable self-supported nanoporous PdCu heterogeneous catalyst for aqueous Suzuki-Miyaura cross-coupling.

Nanoporous PdCu (NP-PdCu) was prepared by the dealloying strategy from a PdCuAl ternary alloy precursor and characterized systematically using SEM, TEM, XRD, and XPS. NP-PdCu was demonstrated to be a competent self-supported heterogenous catalyst for Suzuki-Miyaura cross-coupling, affording a series of synthetically valuable biaryl compounds in good to excellent yields. This catalyst could be easily separated from the product via centrifugation and reused several times without obvious loss of catalytic performance.

High yield and greener C–H difluoromethylation reactions using copper iodide nanoparticles/boron nitride nanosheets as a versatile and recyclable heterogeneous catalyst

The 3 wt% CuI/BNNS catalyst exhibited high efficiency for C–H difluoromethylation reactions and enabled greener synthesis at high yields using cyrene as a solvent. Furthermore, the catalyst could be easily recovered and recycled for at least five cycles.

Direct synthesis of amides and imines by dehydrogenative homo or cross-coupling of amines and alcohols catalyzed by Cu-MOF

Oxidative dehydrogenative homo-coupling of amines to imines and cross-coupling of amines with alcohols to amides was achieved with high to moderate yields at room temperature in THF using Cu-MOF as an efficient and recyclable heterogeneous catalyst under mild conditions. Different primary benzyl amines and alcohols could be utilized for the synthesis of a wide variety of amides and imines. The Cu-MOF catalyst could be recycled and reused four times without loss of catalytic activity.

A ruthenium-inserted hydrotalcite (Ru-HT) heterogeneous catalyst: kinetic studies on the selective hydrogenation of carbon dioxide to formic acid

Kinetic studies have been carried out for an effective and recyclable heterogeneous Ru-HT catalyst for CO2 hydrogenation to formic acid without a base. A TON of 11 389 was successfully achieved in 24 h at 60 °C and 60 bar pressure in a MeOH:H2O mixed solvent.

A novel superparamagnetic powerful guanidine-functionalized γ-Fe2O3 based sulfonic acid recyclable and efficient heterogeneous catalyst for microwave-assisted rapid synthesis of quinazolin-4(3H)-one derivatives in Green media.

The novel organic–inorganic nanohybrid superparamagnetic (γ-Fe2O3@CPTMS–guanidine@SO3H) nanocatalyst modified with sulfonic acid represents an efficient and green catalyst for the one-pot synthesis of quinazolin-4(3H)-one derivatives via three-component condensation reaction between anthranilic acid, acetic anhydride and different amines under microwave irradiation and solvent-free conditions (4a–q). XRD, FT-IR, FE-SEM, TGA, VSM and EDX were used to characterize this new magnetic organocatalyst. Outstanding performance, short response time (15–30 min), simple operation, easy work-up procedure, and avoidance of toxic catalysts can be regarded as its significant advantages. Moreover, it can be easily separated from the reaction solution through magnetic decantation using an external magnet, and recycled at least six times without notable reduction in its activity.

A new 3D luminescent Ba-organic framework with high open metal sites: CO2 fixation, luminescence sensing, and dye sorption

A new synthesized 3D luminescent Ba-organic framework (1) may be used as a recyclable heterogeneous catalyst for fixation of CO2 and has excellent response and sensitivity for pollutant ions. Moreover, 1 exhibits the particular selective sorption towards Congo red (CR) dye.

Multi-purpose heterogeneous catalyst material from an amorphous cobalt metal–organic framework

We describe a unique amorphous cobalt metal–organic framework derived material that acts both as a recyclable heterogeneous catalyst for organic transformations and as a trifunctional electrocatalyst.

Biomass waste-derived recyclable heterogeneous catalyst for aqueous aldol reaction and depolymerization of PET waste

Eco-friendly biomass waste-derived recyclable heterogeneous catalyst for aldol reaction in water and for methanolysis of PET waste.

Ni–rGO–zeolite nanocomposite: an efficient heterogeneous catalyst for one-pot synthesis of triazoles in water

A Ni-based ternary nanocomposite, Ni–rGO–zeolite, has been developed as an efficient and recyclable heterogeneous catalyst for on-water regioselective azide alkyne cycloaddition.

A novel two-dimensional metal-organic framework as a recyclable heterogeneous catalyst for the dehydrogenative oxidation of alcohol and the N-arylation of azole compounds.

A novel metal–organic framework (MOF) with two-dimensional (2D) crystal structure was developed using Cu(NO3)2·3H2O and 2,2′,5,5′-tetramethoxy-[1,1′-biphenyl]-4,4′-dicarboxylic acid. Further, its structure was characterized using infrared spectroscopy, thermogravimetry, X-ray diffraction, and X-ray crystallography. The activated Cu-MOF was used to catalyze the dehydrogenative oxidation of alcohol and N-arylation of azole compounds. Furthermore, it could be easily recovered and reused.

POSS and imidazolium-constructed ionic porous hypercrosslinked polymers with multiple active sites for synergistic catalytic CO2 transformation.

In this work, we reported a facile one-pot approach to construct polyhedral oligomeric silsesquioxane (POSS) and imidazolium-based ionic porous hypercrosslinked polymers (denoted as iPHCPs) with multiple active sites towards efficient catalytic conversion of carbon dioxide (CO2) to high value-added cyclic carbonates. The targeted iPHCPs were synthesized from a rigid molecular building block octavinylsilsesquioxane (VPOSS) and a newly-designed phenyl-based imidazolium ionic crosslinker through the AlCl3-catalyzed Friedel-Crafts reaction. The desired multiple active sites come from the mixed anions including free Cl- and Br- anions, and in situ formed Lewis acidic metal-halogen complex anions [AlCl3Br]- within imidazolium moieties and POSS-derived Si-OH groups during the synthetic process. The typical polymer iPHCP-12 possesses a hierarchical micro-/mesoporous structure with a high surface area up to 537 m2 g-1 and shows a fluffy nano-morphology. By virtue of the co-existence of free nucleophilic Cl- and Br- anions, the metal complex anion [AlCl3Br]- with both electrophilic and nucleophilic characters and electrophilic hydrogen bond donor (HBD) Si-OH groups, iPHCP-12 is regarded as an efficient recyclable heterogeneous catalyst for synergistic catalytic conversion of CO2 with various epoxides into cyclic carbonates under mild conditions. The present work provides a succinct one-pot strategy to construct task-specific ionic porous hypercrosslinked polymers from easily available modules for the targeted catalytic applications.

Environmentally Benign Oxidation of Primary and Secondary Alcohols Catalyzed by Stabilized Gold Nanoparticles on Α-Hydroxy Amide-Functionalized Graphene Oxide

Multi-functionalized graphene oxide has been synthesized through an isocyanide-based multi-component reaction started by aminated graphene oxide and utilized as a support for the stabilization of gold nanoparticles. This composite has been used as a multifunctional, efficient and recyclable heterogeneous catalyst for the oxidation of various primary and secondary aliphatic and aromatic alcohols to the corresponding aldehydes and ketones in water under mild conditions in good to excellent yields.

Glycolysis of Poly(Ethylene Terephthalate) Using Biomass-Waste Derived Recyclable Heterogeneous Catalyst.

Plastic production has increased by almost 200-fold annually from 2 million metric tons per year in 1950s to 359 million metric tons in 2018. With this rapidly increasing production, plastic pollution has become one of the most demanding environmental issues and tremendous efforts have been initiated by the research community for its disposal. In this present study, we reported for the first time, a biomass-waste-derived heterogeneous catalyst prepared from waste orange peel for the depolymerisation of poly(ethylene terephthalate) (PET) to its monomer, bis(2-hydroxyethyl terephthalate) (BHET). The prepared orange peel ash (OPA) catalyst was well-characterised using techniques such as IR, inductively coupled plasma (ICP)-OES (Optical Emission Spectrometry), XRD, X-ray fluorescence (XRF), SEM, energy-dispersive X-ray spectroscopy (EDX), TEM, BET (Brunauer-Emmett-Teller) and TGA. The catalyst was found to be composed of basic sites, high surface area, and a notable type-IV N2 adsorption–desorption isotherm indicating the mesoporous nature of the catalyst, which might have eventually enhanced the rate of the reaction as well as the yield of the product. The catalyst completely depolymerises PET within 90 min, producing 79% of recrystallised BHET. The ability of reusing the catalysts for 5 consecutive runs without significant depreciation in the catalytic activity and its eco- and environmental-friendliness endorses this protocol as a greener route for PET recycling.

Fe3O4@L‐lysine‐Pd(0) organic–inorganic hybrid: As a novel heterogeneous magnetic nanocatalyst for chemo and homoselective [2 + 3] cycloaddition synthesis of 5‐substituted 1H‐tetrazoles

An efficient and sustainable synthetic protocol has been presented to synthesis and 5‐substituted 1H‐tetrazole privileged heterocyclic substructures. The synthetic protocol involves two‐component reaction between aryl nitriles and NaN3 in water using complex of L‐lysine‐palladium nanoparticles (NPs) modified Fe3O4 nanoparticles as magnetically separable, recyclable, and reusable heterogeneous catalyst. Magnetically retrievable L‐lysine‐Pd(0) modified Fe3O4 nanoparticles were applied in [2 + 3] cycloaddition synthesis of 5‐substituted 1H‐tetrazoles. The advantages of this strategy include easy recovery and efficient reusability of the expensive Pd NPs, obtaining high yields of [2 + 3] cycloaddition, short reaction times, and all of the reported synthetic strategies are being performed in water as green solvent for a wide range of substrates.

Catalytic and Aerobic Oxidative Biaryl Coupling of Anilines Using a Recyclable Heterogeneous Catalyst for Synthesis of Benzidines and Bicarbazoles.

In this study, a heterogeneous rhodium-catalyzed oxidative homocoupling reaction of anilines utilizing molecular oxygen as the sole oxidant is reported. Employing a commercially available and recyclable Rh/C catalyst enabled the oxidative dimerization of various anilines, including N,N-disubstituted and N-monosubstituted anilines, as well as diarylamines, triarylamines, and carbazoles. Additionally, the catalytic protocol was extended to the ortho-ortho coupling of anilines, affording 2,2'-diaminobiphenyls with high regioselectivity. Notably, the developed approach provides rapid access to diversely functionalized benzidines and diaminobiphenyls in an operationally simple, practical, and environmentally friendly manner.

Rh Particles Supported on Sulfated g-C3N4: A Highly Efficient and Recyclable Heterogeneous Catalyst for Alkene Hydroformylation

The hydroformylation of alkenes with CO and H2 to manufacture aldehydes is one of the most large-scale chemical reactions. However, an efficient and recyclable heterogeneous catalyst for alkene hydroformylation is extremely in demand in academia and industry. In this study, a sulfated carbon nitride supported rhodium particle catalyst (Rh/S-g-C3N4) was successfully synthesized via an impregnation-borohydride reduction method and applied in the hydroformylation of alkenes. The catalysts were characterized by XRD, FTIR, SEM, TEM, XPS, and nitrogen adsorption. The influence of the sulfate content, pressure of syngas, temperature, and reaction time, as well as the stability of Rh/S-g-C3N4, on the hydroformylation was examined in detail. The delocalized conjugated structure in g-C3N4 can lead to the formation of electron-deficient aromatic intermediates with alkenes. The sulphate g-C3N4 has a defected surface owing to the formation of oxygen vacancies, which increased the adsorption and dispersion of RhNPs on the surface of g-C3N4. Therefore, Rh/S-g-C3N4 exhibited an outstanding catalytic performance for styrene hydroformylation (TOF = 9000 h−1), the conversion of styrene could reach 99.9%, and the regioselectivity for the branched aldehyde was 52% under the optimized reaction conditions. The catalytic properties of Rh/S-g-C3N4 were also studied in the hydroformylation of various alkenes and displayed an excellent catalytic performance. Furthermore, the reuse of Rh/S-g-C3N4 was tested for five recycling processes, without an obvious decrease in the activity and selectivity under the optimum reaction conditions. These findings demonstrated that Rh/S-g-C3N4 is a potential catalyst for heterogeneous hydroformylation.

Sulfonic acid-functionalized core-shell Fe3O4@carbon microspheres as magnetically recyclable solid acid catalysts

Green and recyclable solid acid catalysts are in urgent demand as a substitute for conventional liquid mineral acids. In this work, a series of novel sulfonic acid-functionalized core-shell Fe3O4@carbon microspheres (Fe3O4@C-SO3H) have been designed and synthesized as an efficient and recyclable heterogeneous acid catalyst. For the synthesis, core-shell Fe3O4@RF (resorcinol-formaldehyde) microspheres with tunable shell thickness were achieved by interfacial polymerization on magnetic Fe3O4 microspheres. After high-temperature carbonization, the microspheres were eventually treated by surface sulfonation, resulting in Fe3O4@C-x-SO3H (x stands for carbonization temperature) microspheres with abundant surface SO3H groups. The obtained microspheres possess uniform core-shell structure, partially-graphitized carbon skeletons, superparamagnetic property, high magnetization saturation value of 10.6 emu/g, and rich SO3H groups. The surface acid amounts can be adjusted in the range of 0.59–1.04 mmol/g via sulfonation treatment of carbon shells with different graphitization degrees. The magnetic Fe3O4@C-x-SO3H microspheres were utilized as a solid acid catalyst for the acetalization reaction between benzaldehyde and ethylene glycol, demonstrating high selectivity (97%) to benzaldehyde ethylene glycol acetal. More importantly, by applying an external magnetic field, the catalysts can be easily separated from the heterogeneous reaction solutions, which later show well preserved catalytic activity even after 9 cycles, revealing good recyclability and high stability.

Synthesis of novel aromatic polyamides containing cardo groups and triphenylphosphine oxide structures by a heterogeneous palladium-catalyzed carbonylation and condensation reaction

New aromatic polyamides containing cardo groups and triphenylphosphine oxide structures were synthesized by a heterogeneous palladium-catalyzed carbonylation and condensation of bis(4-(3-iodophenoxy)phenyl)phenylphosphine oxide (BIPPO), aromatic diamines bearing cardo groups, and carbon monoxide. Polycondensations were carried out in N,N-dimethylacetamide under 1 atm of CO at 120 °C in the presence of a magnetically recyclable heterogeneous palladium catalyst and 1,8-diaza-bicyclo[5,4,0]-7-undecene (DBU) and afforded novel aromatic polyamides with inherent viscosities between 0.72 and 0.76 dL/g. All the polyamides were quite soluble in dipolar aprotic solvents and pyridine and could be converted into transparent, flexible, and tough polyamide films by casting from DMAc solutions. These polymers exhibited high thermal and thermooxidative stability with the glass transition temperatures of 237 °C–256 °C, the temperatures at 5% weight loss of 448 °C–465 °C in air. All the phosphorus-containing polyamides self-extinguished as soon as the flame was removed, and the limited oxygen indices (LOIs) of these polymers were in the range of 39%–44%. The polymer films also showed good mechanical properties and high optical transparency.