Hybrid Heterogeneous Catalyst Research Articles

Magnetite nanoparticles immobilized on hydrophilic polyelectrolyte-grafted carbon nanotube as efficient organic–inorganic hybrid heterogeneous catalyst for Knoevenagel condensation in aqueous medium

In this work, a novel organic–inorganic hybrid heterogeneous catalyst was fabricated for Knoevenagel condensation. First, the surface of carbon nanotube (CNT) was covalently functionalized with poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) polyelectrolyte (i.e., organic polybase) through the surface-initiated atom transfer radical polymerization (SI-ATRP) method. Subsequently, magnetic iron oxide nanoparticles (Fe3O4 NPs) (i.e., inorganic Lewis acid) are densely and homogeneously grown on the CNT surface using the CNT-g-PDMAEMA template. The as-prepared acid–base bifunctional catalyst (i.e., CNT-g-PDMAEMA/Fe3O4NPs) was investigated in the model reaction, i.e., Knoevenagel condensation between naphthol, malononitrile and benzaldehyde. The CNT-g-PDMAEMA/Fe3O4NPs catalyst shows high catalytic activity in the Knoevenagel condensation between naphthol, malononitrile and benzaldehyde due to its unique structure and specific chemical constitution. In addition, this acid–base bifunctional catalyst can be readily recovered with an applied magnetic field and reused with negligible loss in the catalytic activity even after six cycles.

Controlled Immobilization of a Palladium Complex/Laccase Hybrid into a Macrocellular Siliceous Host.

This study investigates the site-directed immobilization of a hybrid catalyst bearing a biquinoline-based-Pd(II) complex (1) and a robust laccase within cavities of a silica foam to favor veratryl alcohol oxidation. We performed the grafting of 1 at a unique surface located lysine of two laccase variants, either at closed (1⊂UNIK157 ) or opposite position (1⊂UNIK71 ) of the enzyme oxidation site. After immobilization into the cavities of silica monoliths bearing hierarchical porosity, we show that catalytic activity is dependent on the orientation and loading of each hybrid, 1⊂UNIK157 being twice as active than 1⊂UNIK71 (203 TON vs 100 TON) when operating under continuous flow. These systems can be reused 5 times, with an operational activity remaining as high as 40 %. We show that the synergy between 1 and laccase can be tuned within the foam. This work is a proof of concept for controlling the organization of a heterogeneous hybrid catalyst using a Pd/laccase/silica foam.

Phosphonic acid tagged carbon quantum dots encapsulated in SBA-15 as a novel catalyst for the preparation of N-heterocycles with pyrazolo, barbituric acid and indole moieties

Herein, we have presented a new insight for the synthesis of a hybrid heterogeneous catalyst. For this purpose, phosphonic acid tagged carbon quantum dots of CQDs-N(CH2PO3H2)2 encapsulated and assembled in channels of SBA-15 using a post-modification strategy. The mesoporous catalyst of functionalized carbon quantum dots (CQDs) was characterized by several techniques. CQDs-N(CH2PO3H2)2/SBA-15 as an excellent catalyst was applied for the preparation of novel pyrazolo[4′,3′:5,6]pyrido[2,3-d]pyrimidine derivatives by using pyrazole, barbituric acid and indole moieties at 100 °C under the solvent-free condition. The present work shows that a significant increase in the catalytic activity can be achieved by a rational design of mesoporous SBA-15 modified with CQDs for the synthesis of biological active candidates. The synthesized compounds did not convert to their corresponding pyridines via an anomeric-based oxidation mechanism.

Thiazolo[5, 4-d]thiazole based dye modified microspheres as metal nanoparticle reactor template and hybrid catalyst

2,5-di(pyridin-4-yl)thiazolo[5,4-d]thiazole (Py2TTz) molecule was synthesized and used to modify poly(4-vinyl benzylchloride) microparticles (PVBC-MPs) thanks to its superior interaction with 4-vinyl benzyl chloride monomer containing active –Cl atom. PVBC spherical microparticles were successfully synthesized by suspension polymerization method and they were modified via two different approaches as in-situ and post-modification. Monodispersity of particles via in-situ modification is a challenging approach due to the low solubility of Py2TTz. Therefore, post-modification of PVBC microparticles with Py2TTz dye was carried out. The particles act as metal nanoreactor in the absence of any reducing agent both at room temperature and 50 °C. The particle morphology was determined with electron microscopies before and after reduction process. Metal nanoparticles (MNP) on MPs were characterized via XRD analysis. Gold, silver and platinum nanoparticles (AuNP, AgNP and PtNP) decorated microparticles were successfully synthesized. According to the ICP-MS results, 25.6% Ag, 24.7% Pt and 0.33% Au were found in the microparticles treated with metal cations. These MNP decorated MPs were used as hybrid heterogeneous catalyst for 4-nitrophenol reduction into 4-aminophenol. The highest catalytic efficiency was obtained with AgNPs decorated MPs as also consistent with the ICP-MS data. The catalytic activities of the MNP decorated MPs were determined with time dependent absorption measurents via UV–Vis spectrophotometer.

Mechanism and practical application of homogeneous–heterogeneous hybrid catalysts in electrolytic system for high COD chemical waste acid treatment

Treatment of organic contaminants in waste acid via electrochemical oxidation process has drawn sustained attention. Inspired by the electro-generation of persulfate from homogeneous sulfate (SO42-) in waste acid and the catalytic activity of heterogeneous tourmaline, this study aimed to investigate the feasibility of in-situ persulfate electro-generation and activation via utilizing homogeneous–heterogeneous hybrid catalysts system (SO42-/tourmaline) for organic contaminants removal in high chemical oxygen demand (COD) sulfate-containing waste acid. p-Aminodiphenylamine (RT-Base) was selected as a model organic contaminant to explore the mechanism of electrolysis/SO42-/tourmaline system. No RT-Base was detected after 60 min reaction in electrolysis/SO42-/tourmaline system. The formation of •OH and SO4•− in electrolysis/SO42-/tourmaline system made contributions to the RT-Base degradation. Degradation intermediates of RT-Base were identified and possible degradation pathway was proposed. Additionally, the application of electrolysis/SO42-/tourmaline system in treating the real RT-Base waste acid, which contained high COD and SO42-, was explored. Results showed that the COD removal rate was 67.94% under the optimal conditions, and the electrolysis/SO42-/tourmaline system could enhance the biodegradability of RT-Base waste acid. Furthermore, the electrolysis/SO42-/tourmaline system followed by the activated sludge process achieved a high COD removal efficiency (99.09%). Microbial DNA analysis suggested that Bacteroidetes, Proteobacteria, and Actinobacteria were the dominant bacterial phyla in the activated sludge; and metabolism was the predominant microbial function. In-situ electro-generation of persulfate/SO4•− for organics degradation achieved efficient utilization of waste sulfate. Electrochemical oxidation process with activated sludge process as a post-treatment showed great potential in the treatment of organics in high-sulfate waste acid.

Synthesis of Pd supported on 3,4-diaminobenzoic acid functionalized Fe3O4 nanoparticles as a magnetic catalyst for synthesis of 2-methoxy-2-phenylacetonitrile derivative via a strecker-type reaction under ambient and solvent-free conditions

Pd supported on 3,4-diaminobenzoic acid functionalized Fe3O4 magnetic nanoparticles as an organic-inorganic hybrid heterogeneous catalyst was fabricated and characterized by FT-IR, XRD, SEM, TEM, TGA, VSM, EDX, and ICP-AES techniques. The catalytic activity of the magnetic catalyst was probed through a Strecker-type reaction for one-pot synthesis of 2-methoxy-2-phenylacetonitrile derivatives under ambient and solvent-free conditions. Simple procedure, high yields, short reaction time, and environmentally benign method are advantages of this protocol. The catalyst was readily separated using an external magnet and reusable without significant loss of its catalytic efficiency.

A 5-(2-Pyridyl)tetrazolate Complex of Molybdenum(VI), Its Structure, and Transformation to a Molybdenum Oxide-Based Hybrid Heterogeneous Catalyst for the Epoxidation of Olefins

There is a considerable practical interest in discovering new ways to obtain organomolybdenum heterogeneous catalysts for olefin epoxidation that are easier to recover and reuse and display enhanced productivity. In this study, the complex salt (H2pytz)[MoO2Cl2(pytz)] (1) (Hpytz = 5-(2-pyridyl)tetrazole) has been prepared, structurally characterized, and employed as a precursor for the hydrolysis-based synthesis of a microcrystalline molybdenum oxide/organic hybrid material formulated as [MoO3(Hpytz)] (2). In addition to single-crystal X-ray diffraction (for 1), compounds 1 and 2 were characterized by FT-IR and Raman spectroscopies, solid-state 13C{1H} cross-polarization (CP) magic-angle spinning (MAS) NMR, and scanning electron microscopy (SEM). Compounds 1 and 2 were evaluated as olefin epoxidation catalysts using the model reaction of cis-cyclooctene (Cy8) with tert-butyl hydroperoxide (TBHP), at 70 °C, which gave 100% epoxide selectivity up to 100% conversion. While 1 behaved as a homogeneous catalyst, hybrid 2 behaved as a heterogeneous catalyst and could be recovered for recycling without showing structural degradation or loss of catalytic performance over consecutive reaction cycles. The substrate scope was broadened to monoterpene DL-limonene (Lim) and biobased unsaturated fatty acid methyl esters, methyl oleate (MeOle), and methyl linoleate (MeLin), which gave predominantly epoxide products.

Synthesis and characterization of Pd supported on methane diamine (propyl silane) functionalized Fe3O4 nanoparticles as a magnetic catalyst for synthesis of α-aminonitriles and 2-methoxy-2-phenylacetonitrile derivative via Strecker-type reaction under ambient and solvent-free conditions

Pd supported on methane diamine (propyl silane) functionalized Fe3O4 magnetic nanoparticles as an organic–inorganic hybrid heterogeneous catalyst was fabricated and characterized by FT-IR, XRD, SEM, TEM, TGA, VSM, EDX, and ICP-AES techniques. The catalytic activity of the magnetic catalyst was probed through the Strecker-type reaction for one-pot synthesis of α-aminonitriles and 2-methoxy-2-phenylacetonitrile derivatives under ambient and solvent-free conditions. Simple procedure, high yields, short reaction time, and the environmentally benign method are advantages of this protocol. The catalyst was readily separated using an external magnet and reusable without significant loss of its catalytic efficiency.

Interfacial engineering for ultrafine Co3O4 confined in graphene macroscopic microspheres with boosting peroxymonosulfate activation

BackgroundAs an alternative to homogenous metal-catalyst for peroxymonosulfate activation, heterogeneous hybrid catalysts such as metal-doped graphene catalysts are highly desired due to their remarkable catalytic performance and ease of recovery. MethodIn this work, ultrafine Co3O4 confined in graphene macroscopic microspheres (Co3O4@rGO) were fabricated via coordination-driven interfacial self-assembly, followed by annealing in air. A series of characterizations and experiments verified that this kind of conductive and adsorptive graphitic structure facilitated the elimination of pollutants via a synergistic “adsorption-driven-catalysis’’ process. Significant findingsTherefore, almost 100% tetracycline (TC, 0.271 min−1) was eliminated after 30 min, which was far higher than those of reported catalysts. Besides, X-ray photoelectron spectroscopy (XPS) analysis, electron paramagnetic resonance (EPR), and quenching experiments demonstrated that confined cobalt species and oxygen vacancies as highly exposed active sites. The reactive oxygen species (ROS) follow a contribution order: SO4·− ˃ 1O2 ˃ O2·− ˃ ·OH More significantly, a fluidized-column catalytic unit enabled almost zero discharge of TC in continuous sewage treatment system. Overall, this work provided a generally applicable approach to fabricate removable and highly efficient heterogeneous catalysts for environmental remediation.

Assembly of SBA‐15 Derived Hybrid Heterogeneous Catalysts for Liquid Phase Cyclopentene Epoxidation

AbstractThree two‐dimensional SBA‐15‐based hybrid materials, SBA‐15‐ImCl‐PF6, SBA‐15‐NH(PO3H2), and SBA‐15‐N+, were synthesized employing a post‐synthetic functionalization strategy, and peroxo‐W and PW species were successfully immobilized on the surface of the corresponding organic moieties‐modified SBA‐15 via electrostatic interaction or covalent linking. The TEM and XRD results presented that the structure and morphology of SBA‐15 were maintained after multiple transformations. The final catalysts SBA‐15‐ImCl‐PF6‐W, SBA‐15‐NH(PO3H2)‐W, and SBA‐15‐N+(PW4O24)3− all showed considerable activity for the epoxidation of cyclopentene to cyclopentene oxide using H2O2 as the oxygen source without any co‐solvent. It was noteworthy that SBA‐15‐ImCl‐PF6‐W catalyst with increased hydrophobicity via altering counteranions of imisazolium ions exhibited excellent cyclopentene oxide selectivity (99 %), but a good cycle performance (10 times) was achieved via SBA‐15‐NH(PO3H2)‐W owing robust covalent bonds. Besides, the use of a low dose of heterogeneous catalyst (W=20 μmol) and a green oxidant of H2O2, along with the absence of co‐solvent or other additives make cyclopentene epoxidation reaction an environmenttally benign chemical process.

Non-hydrolytic sol–gel as a versatile route for the preparation of hybrid heterogeneous catalysts

The tools of sol–gel chemistry allow synthesizing a plethora of functional materials in a controlled bottom-up fashion. In the field of heterogeneous catalysis, scientists utilize sol–gel routes to design solids with tailored composition, texture, surface chemistry, morphology, dispersion, etc. A field of investigation which shows great promises is that of hybrid heterogeneous catalysts. Examples are flourishing to show that catalysts featuring a combination of inorganic and organic components often display improved activity, selectivity, or even chemical stability as compared to the purely inorganic counterparts. Yet, classic sol–gel methods face some well-known limitations—related to the different reactivity of the precursors and to the high surface tension of water—which complicate the tasks of chemists, specifically for the synthesis of hybrid catalysts. Non-hydrolytic sol–gel (NHSG) chemistry appears as a pertinent alternative. Being realized in the absence of water, NHSG routes allow reaching an excellent control over the solid properties and on the distribution of the organic and inorganic components at the nano- and microscales. In this review, we briefly recapitulate the main types of non-hydrolytic sol–gel routes and we present the modified protocols to hybrid materials. Then, we present an overview of the non-hydrolytic sol–gel approaches that have been proposed to synthesize hybrid heterogeneous catalysts. For both Class I and Class II hybrids, we discuss how the NHSG technique has allowed tailoring the key properties that command catalytic performance. From this panorama, we argue that NHSG has a prominent role to play for the development of advanced hybrid heterogeneous catalysts.

Preparation and Characterization of a Novel Magnetic Nano Catalyst for Synthesis and Antibacterial Activities of Novel Furan-2(5H)-Ones Derivatives

Sulfamic acid 2-Aminobenzothiazole-6-carboxylic acid functionalized Fe3O4 nanoparticles as a novel organic-inorganic hybrid heterogeneous catalyst were manufactured and characterized by FT-IR, XRD, TGA, SEM, TEM, and VSM techniques. The catalytic activity of the magnetic catalyst was investigated through the one-pot synthesis of novel 3,4,5-trisubstituted furan-2(5H)-ones derivatives from aryl aldehydes, 4-amino pyridine, and dimethyl acetylenedicarboxylate. The structure of all the new synthesized derivatives was determined by FT-IR, 1H-NMR, and 13C-NMR. The synthetic compounds exert moderate activity against both Gram-positive and Gram-negative bacteria and their effectiveness is higher against Bacillus subtilis. This green nano catalytic procedure has good reversibility and provides clean production in a short reaction time. These characters make the method practical and economical for researchers.

Incorporation of homogeneous organometallic catalysts into metal–organic frameworks for advanced heterogenization: a review

The heterogenization of homogeneous organometallic catalysts by incorporation into MOFs using different strategies, MOF selection, OMC selection, and the use of hybrid heterogeneous catalysts OMC@MOFs in catalytic applications are summarized and discussed.

Si-Gly-CD-PdNPs as a hybrid heterogeneous catalyst for environmentally friendly continuous flow Sonogashira cross-coupling

We have reported a waste-minimized protocol for the Sonogashira cross-coupling exploiting the safe use of a CPME/water azeotropic mixture and the utilization of a heterogeneous hybrid palladium catalyst supported onto a silica/β-cyclodextrin matrix in continuous flow.

Synthesis and characterization of a novel Pyrrole-2-carboxylic acid functionalized magnetic Fe3O4 as a nanocatalyst for synthesis and antibacterial activities of novel isoxazolo[4,3-e]indazole derivatives

Pyrrole-2-carboxylic acid functionalized Fe3O4 nanoparticles as a novel organic–inorganic hybrid heterogeneous catalyst was manufactured and characterized by X-ray diffraction (XRD) analysis, Fourier transform infrared (FT-IR), Transmission Electron Microscopy (TEM), Thermogravimetric analysis (TGA), Scanning electron microscope (SEM), Vibrating sample magnetometer (VSM) techniques. The catalytic activity of the nanomagnetic catalyst was investigated in the new heterocyclic system isoxazolo[4,3-e]indazole was synthesized via the nucleophilic substitution of a hydrogen in 5-nitro-1-p-tolyl-1H-indazole with different 2-phenylacetonitrile derivatives in basic medium. The synthetic compounds exert moderate activity against both Gram positive and Gram negative bacteria and their effectiveness is higher against Bacillus subtilis. This green magnetic nanocatalytic procedure has a good reversibility and provides clean production in a short reaction time.

Decorated palladium nanoparticles on mesoporous organosilicate as an efficient catalyst for Sonogashira coupling reaction

Reforming mesoporous silica was provided by the reaction of SBA‐15 with (3-aminopropyl)triethoxysilane, the product of which was treated with furfural to give SBA-propyl-imine-furan. In the next step, palladium chloride was attached to the functionalized SBA‐15, so Pd nanoparticles immobilized on the mentioned catalyst for providing an applicable catalyst to use in the Sonogashira cross-coupling reaction. The high stability and performance of functionalized heterogeneous hybrid catalyst of Pd@SBA-Pr-imine-furan in overall were highly essential. The nano-structured Pd@SBA-Pr-imine-furan catalyst was studied for Sonogashira cross-coupling reaction by phenylacetylene and various aryl halides under reflux conditions with a small amount of catalyst. In comparison with the earlier reports, this paper offered several benefits such as short reaction times, high yields of products, catalyst stability, quick recovery, and catalytic activity for at least seven continuous runs.

Synthesis and characterization of silica‐coated Fe3O4 nanoparticle@silylpropyl triethylammonium polyoxometalate as an organic–inorganic hybrid heterogeneous catalyst for the one‐pot synthesis of tetrahydrobenzimidazo[2,1‐b]quinazolin‐1(2H)‐ones

In this study, silica‐coated Fe3O4 nanoparticle@silylpropyl triethylammonium polyoxometalate catalyst was fabricated and characterized using atomic absorption, inductively coupled plasma optical emission spectrometry, elemental analysis, thermogravimetric analysis, Fourier‐transform infrared, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, and vibrating sample magnetometry analyses. The activity of this catalyst was examined in the synthesis of tetrahydrobenzimidazo[2,1‐b]quinazolin‐1(2H)‐ones. The bonding of the polyoxometalate to the surface of the nanoparticles exhibited excellent catalytic activity in this synthesis. Besides, the catalyst showed good reusability and recovery from the reaction mixture. Tetrahydrobenzimidazo[2,1‐b]quinazolin‐1(2H)‐ones were synthesized in high yields in the presence of inexpensive supported solid acid catalysts under classical heating conditions.

Nanoconfined (Bio)Catalysts as Efficient Glucose‐Responsive Nanoreactors

AbstractHerein, the design, synthesis, and characterization of bifunctional hybrid nanoreactors used for concurrent one‐pot chemoenzymatic reactions are shown. In the design, the enzyme, glucose oxidase, is wrapped with a peroxidase‐mimetic catalytic polymer. Hemin, the organic catalyst, is linked to the flexible polymeric scaffold through coordination to the imidazole groups that hang out the network. This spatial arrangement, which works as a metabolic channel, is optimized for cooperative chemoenzymatic reactions in which the enzyme catalyzes first. A deep characterization of the integrated nanoreactors demonstrates that the confinement of two distinct catalytic sites in the nanospace is very effective in one‐pot reactions. Moreover, besides its role as scaffold material, the polymeric mantel protects both the biocatalyst and the chemical catalyst from degradation and inactivation in the presence of organic solvents. Furthermore, the polymeric environment of the nanoreactors can be tailored in order to trigger the assembly of those into highly active heterogeneous hybrid catalysts. Finally, the new nanoreactors are applied to the efficient degradation of organic aromatic compounds using glucose as the only fuel.

Syntheses, structures, and immobilization of ruthenium(II) complexes with alkoxysilane groups functionalized N,N′-diamine and phosphine ligands

Treatment of [RuCl2(PPh3)3] with N-(β-aminoethyl)-γ-aminopropylmethylbimethoxysilane (L1) in tetrahydrofuran at room temperature gave a mononuclear ruthenium(II) complex [Ru(PPh3)2Cl2 (κ2-N,N-L1)] (1). Condensation of γ-aminopropyltriethoxysilane and potassium diphenylphosphine in the molar ratio of 1:1 in tetrahydrofuran afforded phosphine (PPh2)(CH2)3Si(OEt)3 (L2) with ethoxysilane groups. Reaction of [Ru(η6-p-cymene)Cl2]2 with L2 in refluxing tetrahydrofuran afforded a ruthenium(II) phosphine complex [Ru(η6-p-cymene)Cl2(κ-P-L2)] (2). Complexes 1 and 2 were systematically characterized by microanalyses, FT-IR, and NMR spectroscopies. Their structures have been unambiguously established by single-crystal X-ray diffraction. Immobilization of 1 and 2 on SBA-15 and characterization of these hybrid heterogeneous catalysts were studied by transmission electron microscopy (TEM), FT-IR, and low-pressure N2 adsorption/desorption measurements. Transfer hydrogenation of acetophenone was also briefly investigated with the heterogeneous catalysts.

Highly effective cellulose supported 2-aminopyridine palladium complex (Pd(II)-AMP-Cell@Al2O3) for Suzuki-Miyaura and Mizoroki–Heck cross-coupling

In the present work, a novel, highly efficient, retrievable organo–inorganic hybrid heterogeneous catalyst (Pd(II)-AMP-Cell@Al2O3) has been prepared by covalent grafting of 2-aminopyridine on chloropropyl modified cellulose-alumina composite followed by complexation with palladium acetate. The catalyst was characterized by techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), inductive coupled plasma-atomic emission spectroscopy (ICP-AES) and thermo gravimetric analysis (TGA). The catalyst has been successfully employed in Suzuki-Miyaura as well as Mizoroki–Heck cross-coupling reactions. The reactions proceed smoothly resulting in the high yields of cross-coupling products (81 to 95%) within short reaction times. The catalyst can be efficiently recovered by simple filtration and reused for multiple cycles without considerable loss in the catalytic activity. The key-features of the present protocol include mild reaction conditions, simple work-up procedure, high stability of the catalyst, high turnover number (TON) and frequency (TOF), ease recovery and reusability of the catalyst.