Solid-supported Catalysts Research Articles

TiO2 supported pallidum-bipyridyl complex as an efficient catalyst for Suzuki–Miyaura reaction in aqueous-ethanol

Owing to their improved catalytic stability and ability to undergo repeated cycles, solid-supported catalysts show great potential for various catalytic reactions. In this study, we synthesized a catalyst comprising a palladium-2,2-bipyridine complex supported on TiO2 nanoparticles (TiO2@BDP-PdCl2) fully characterised and investigated its efficacy in Suzuki–Miyaura cross coupling reactions involving phenyl boronic acid with various aryl halides under mild reaction conditions. The 2,2′- bipyridine (bp) has shown excellent complexation properties for Pd (II) and it could be easily anchored onto functionalized TiO2 support by the bridging carboxylate ions. The composition and structure of the as-prepared catalyst was characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), Transmission Electron Microscope (TEM), X-ray photoelectron spectroscopy (XPS), and UV–Vis spectroscopy. The catalyst easily demonstrated separability, enhancing its practicality in catalytic processes. Subsequent utilization showed a consistent activity level, suggesting the stabilization of the aggregated catalyst species. This research sheds light on the importance of catalyst stability and maintenance during consecutive reaction cycles.

Hydrogenation of CO2 into Value-added Chemicals Using Solid-Supported Catalysts.

Reducing CO2 emissions is an urgent global priority. In this context, several mitigation strategies, including CO2 tax and stringent legislation, have been adopted to halt the deterioration of the natural environment. Also, carbon recycling procedures undoubtedly help reduce net emissions into the atmosphere, enhancing sustainability. Utilizing Earth's abundant CO2 to produce high-potential green chemicals and light fuels opens new avenues for the chemical industry. In this context, many attempts have been devoted to converting CO2 as a feedstock into various value-added chemicals, such as CH4, lower methanol, light olefins, gasoline, and higher hydrocarbons, for numerous applications involving various catalytic reactions. Although several CO2-conversion methods have been used, including electrochemical, photochemical, and biological approaches, the hydrogenation method allows the reaction to be tuned to produce the targeted compound without significantly altering infrastructure. This review discusses the numerous hydrogenation routes and their challenges, such as catalyst design, operation, and the combined art of structure-activity relationships for the various product formations.

Acetalization of Alkyl Alcohols with Benzaldehyde over Cesium Phosphomolybdovanadate Salts

In this work, vanadium-substituted cesium phosphomolybdate salts with general formulae Cs3+nPMo12−nVnO40 (n = 0, 1, 2, and 3) were synthesized and evaluated in the acetalization of benzaldehyde with alkyl alcohols. All the catalysts were characterized through Raman, infrared, and ultraviolet–visible spectroscopies, powder X-ray diffraction patterns, isotherms of N2 desorption/adsorption, and measurements of acidity strength. The catalytic activity of cesium phosphomolybdovanadate salts was evaluated in the acetalization reactions of benzaldehyde with alkyl alcohols. Among the salts tested, the Cs4PMo11V1O40 was the most active and selective catalyst in the conversion of benzaldehyde to methyl benzyl acetal and benzoic acid, which was obtained without the use of an oxidant agent. The impact of the main reaction parameters on the conversion and selectivity was evaluated by varying the content of vanadium per heteropolyanion, catalyst load, temperature, and alkyl alcohols. The greatest activity of the Cs4PMo11V1O40 salt was assigned to the highest Brønsted acidity strength, as demonstrated by the acidity measurements and analysis of their surface properties. This solid catalyst has advantages over traditional liquid homogenous catalysts, such as low corrosiveness, a minimum generation of residues and effluents, and easy recovery/reuse. In addition, its synthesis route is easier and quicker than solid-supported catalysts and comprises a potential alternative route to synthesize acetals.

Cesium Heteropolyacid Salts: Synthesis, Characterization and Activity of the Solid and Versatile Heterogeneous Catalysts

Keggin-type heteropolyacid cesium salts have been regarded as potential candidates for heterogeneous catalytic reactions. This review describes the success of Keggin-type heteropolyacids cesium salts (Cs-HPA salts) as efficient catalysts in various synthesis processes. The Cs-HPA catalysts can be synthesized as solid salts through the metathesis of a solution containing precursor HPA and another solution containing soluble Cs salt, which will give Cs-HPA salt as a solid precipitate. Alternatively, they can be also obtained from the commercial precursor HPA. In this review, all the routes to prepare the different cesium salts (i.e., saturated, lacunar, metal-doped) were described. These salts can be used in acid-catalyzed reactions (i.e., esterification, etherification, acetalization, dehydration) or oxidative transformations (oxidative esterification, oxidation, epoxidation). All of these reactions were addressed herein. Aspects related to the synthesis and characterization of these catalyst salts were discussed. This review aims to discuss the most pertinent heterogeneous catalytic systems based on Keggin HPA Cs salts. The focus was to correlate the physicochemical properties of these salts with their catalytic activity. Ultimately, the most recent advances achieved in the applications of these Cs-HPA salts as catalysts in the synthesis of industrial interest compounds were discussed. Cesium heteropoly salts are an alternative to the traditional soluble mineral acids as well as to solid-supported catalysts.

Biodiesel Additives Synthesis Using Solid Heteropolyacid Catalysts

Fossil additives are a primary energy source and their contribution is around 80% in the world. Therefore, bioadditives that reduce their impact are each very important. This article discusses the chemical transformation of glycerol to carbonate, ethers, esters, ketals, and acetals, compounds with high technological applications, especially in the fuel sector as bioadditives. Mainly, heterogeneous catalysts are important in the production of more than 80% of chemicals in the word. The focus is on demonstrating how the Keggin heteropolyacids (HPAs) are efficient catalysts in the reactions of syntheses of glycerol-derived bioadditives, either in homogeneous or heterogeneous phases. Although solid, HPAs have a low surface area and are soluble in polar solvents, hampering their use as heterogeneous catalysts. Alternatively, they have been successfully used supported on solid matrixes with a high surface area. Another option is converting the Keggin HPAs to insoluble salts simply by exchanging their protons with large cations like potassium, cesium, or ammonium-derivatives. Therefore, solid heteropoly salts have reduced the cost and the environmental impact of bioadditive synthesis processes, being an alternative to traditional mineral acids or solid-supported catalysts. This review describes the most recent advances achieved in the processes of synthesis of glycerol-derived bioadditives over solid-supported HPAs or their solid heteropoly salts.

Efficient and Recyclable Solid-Supported Pd(II) Catalyst for Microwave-Assisted Suzuki Cross-Coupling in Aqueous Medium.

Solid-supported catalysts play efficient and crucial roles in organic synthesis. A solid-supported palladium(II) complex based on chitosan was synthesized and fully characterized using all possible tools (Fourier transform infrared spectroscopy, thermogravimetry analysis, differential scanning calorimetry, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, inductively coupled plasma atomic emission spectrometry, scanning electron microscopy, transmission electron microscopy, and Brunauer–Emmett–Teller analysis). The catalytic activity of the solid-phase catalyst in Suzuki cross-coupling reactions was evaluated in aqueous solvents under both conventional heating and microwave irradiation conditions. The recyclability and thermal stability of the prepared catalyst were also examined, and the catalyst was found to be active till five consecutive runs without a notable loss of activity under the microwave condition, with the turnover number and turnover frequency values reaching 19,019 and 114,114 h–1, respectively.

Eosin Y: Homogeneous Photocatalytic In-Flow Reactions and Solid-Supported Catalysts for In-Batch Synthetic Transformations

In this paper, the most recent and significant applications of Eosin Y as an organo-photocatalyst will be discussed, focusing the attention on enabling technological aspects in homogeneous photochemical flow reactions, as well as on recent developments in solid-supported catalyst applications for batch synthetic transformations.

Expanded mesoporous silica-encapsulated ultrasmall Pt nanoclusters as artificial enzymes for tracking hydrogen peroxide secretion from live cells

Design of synthetic structures that possess the similar functions to natural enzymes held great promise in environmental detection and biomedical application. Herein, a new concept for the fabrication of solid-supported catalysts as peroxidase mimic have been proposed to realize high-catalytic activity and stability by utilizing expanded mesoporous silica (EMSN)-encapsulated Pt nanoclusters. Compared with PtNCs, the introduction of amino group modified EMSN would enrich H2O2 on the surface of PtNCs and increase the catalytic sites for H2O2 decomposition, which gave rise to the higher catalytic activity of EMSN-PtNCs over a broad pH range, especially in weakly acidic and neural solutions. This would facilitate their applications for real-time monitoring the secretion of H2O2 from living cancer cells stimulated by various anticancer drugs. Our findings not only pave the way to use porous matrix as the structural component for the design of the biomimetic catalysts, but also provide a simple and reliable platform to monitor H2O2 released from living cells in real time, which holds great potential for elucidating the biological roles of H2O2 and underlying molecular mechanisms of drug cytotoxicity as well as drug therapeutic effects.

Recyclable Solid-Supported Catalysts for Quaternary Ammonium Iodide-Catalyzed Living Radical Polymerization

Quaternary ammonium iodide (R4N+I–) catalysts immobilized on silica particles, Fe3O4 magnetic particles, and organic resin particles were developed for organocatalyzed living radical polymerization...

Catalytically sustainable, palladium-decorated graphene oxide monoliths for synthesis in flow

Continuous flow synthesis is an essential route towards high throughput manufacturing of fine chemical and pharmaceutical products. The mentioned chemistries are often catalyzed by solid-supported catalysts via packed beds which are characterized by multiple issues such as high pressure-drops, micro channeling through the bed, and leaching of the metallic catalyst into the product stream. These issues lower the overall process efficiency. Three dimensional (3D) structures, known as monoliths, with high porosity and mechanical robustness, offer the ideal properties to be used macroscopic supports for metallic catalyst particles. This approach has shown to alleviate several known issues with catalyst packed beds effectively.Herein centimeter-scale monolithic catalysts of palladium (Pd)-decorated, covalently-bonded graphene oxide (GO) layers have been prepared via a completely aqueous, one-pot system. These monolithic composite structures were designed for Suzuki cross-coupling reactions in flow. As highly engineered materials, monoliths’ properties such as oxygen content and Pd catalyst ionic species were tuned via microwave irradiation and ethanol vapor reduction treatments. The optimal monolithic catalysts showed over 5 h of operational longevity in flow, which was 300% higher than the conventional Pd on GO catalyst packed beds. As a proof of concept, the monolithic catalyst was successfully used as a model structure for nondestructive X-ray CT-scan elemental and porosity mapping in the centimeter scale.

Oxidation of secondary alcohols using solid-supported hypervalent iodine catalysts

Solid-supported catalysts for the oxidation of secondary alcohols are disclosed, featuring metal-free conditions, low catalyst loadings and easy reusability.

Lacunar Keggin Heteropolyacid Salts: Soluble, Solid and Solid-Supported Catalysts

Polyoxometalates are an important class of environmentally friendly catalysts. The Keggin heteropolyacids containing tungsten or molybdenum addenda atoms have received great attention because they have attractive acid and redox properties, which may be easily tunable through changes in their composition and structure. The replacement of their protons by large radium cations makes insoluble the Keggin heteropolyacids and increases their surface area. On the other hand, the removal of tungsten or molybdenum atoms from the Keggin heteropolyanion generates vacancies, which can activate different organic substrates. Therefore, solid lacunar heteropolyacid salts are potentially active catalysts and selective in a plethora of reactions. These catalysts are used either in homo- or heterogeneous conditions. In this review, we wish would highlight recent advances achieved in the chemistry of lacunar Keggin heteropolyacids. We describe their use as solid, soluble or solid-supported catalysts in reactions of oxidation of alcohols and olefins, oxidative desulfurization and acid-catalyzed reactions such as acetalization, esterification, and transesterification.

Synthesis of Medicinally Privileged Heterocycles through Dielectric Heating.

Heterocyclic compounds are intriguing part of modern drug discovery research. Ecofriendly syntheses of heterocycles, following green techniques, are privileged routes to protect Mother nature. Microwave-assisted synthesis of chemical compounds is considered as a major greener pathway, both in academia and industry. A total of 106 publications (including a few authentic web links) have been reviewed mainly to discuss (i) mechanism of microwave irradiation, (ii) abundance of commercial heterocyclic drugs, (iii) various synthetic procedures, and (iv) medicinal activity of the synthesized molecules. This review summarizes the potential application of microwave irradiation (dielectric heating) to synthesize biologically important heterocyclic small molecules in the recent past. A huge number of heterocyclic compounds are present in various natural sources like plant, marine microbe or other organisms and many of them possess unique biological activity. In addition to nature-derived heterocyclic compounds, a large number of synthetic heterocycles are being used as medicines. This review describes the relevant recent examples of microwave irradiation to accomplish various chemical transformations accelerated by a variety of catalysts which include, but not limited to, Lewis acids, other metal containing catalysts, organocatalysts, heterogeneous catalysts, phase-transfer catalysts, solid-supported catalysts, inorganic catalysts (bases, acids and salts) and so on. Although there are an increasing number of reports on application of dielectric heating in various other fields, this review is focused on a large number of new and novel strategies related to synthetic organic chemistry. The discussion is mostly organized by the disease type although some reactions/molecules can certainly be placed in multiple sections. Since green chemistry is an extremely emerging and comparatively new field of research, attempts to stimulate more activities on green medicinal chemistry are provided. Discussion related to the concurrent effect of microwaves, catalysts and/or solvents, supports to constitute expeditious and general route for the syntheses of medicinally important heterocyclic compounds and pharmacophores has also been included. The dielectric heating procedure to produce novel medicinally privileged heterocyclic scaffolds/ compounds is extremely promising and challenging. As a result, this green technique has been gaining increasing interest from the pharmaceutical world. A recent update has been presented. While every effort has been made to include all pertinent reports in this field, any omission is unintentional.

Synthesis of Cyclic Thiocarbonates from Thiiranes and CS2 with Silica-Immobilized Catalysts

The synthesis of cyclic thiocarbonates by the cycloaddition of carbon disulfide (CS2) to thiiranes in the presence of silica-immobilized amine catalysts was investigated. The catalytic activities of the silica-immobilized catalysts toward the synthesis of cyclic thiocarbonates were higher than the activities of their homogeneous counterparts. The silica-supported catalysts strongly accelerated the cycloaddition of CS2 to thiiranes, and the pseudo-first-order rate constant of the silica-immobilized catalyst was about 430 times larger than that of the corresponding homogeneous catalyst. The coexistence of the molecular catalyst species and the neighboring surface silanols on the catalyst support was found to be key to the reaction acceleration. In addition to providing improved catalytic activity, the solid-supported catalysts were also shown to be recyclable and reusable for at least five cycles.

Catalytic Oxidation of Chlorobenzene over MnxCe1-xO2/HZSM-5 Catalysts: A Study with Practical Implications.

Industrial-use catalysts usually encounter severe deactivation after long-term operation for catalytic oxidation of chlorinate volatile organic compounds (CVOCs), which becomes a "bottleneck" for large-scale application of catalytic combustion technology. In this work, typical acidic solid-supported catalysts of MnxCe1-xO2/HZSM-5 were investigated for the catalytic oxidation of chlorobenzene (CB). The activation energy (Ea), Brønsted and Lewis acidities, CB adsorption and activation behaviors, long-term stabilities, and surficial accumulation compounds (after aging) were studied using a range of analytical techniques, including XPS, H2-TPR, pyridine-IR, DRIFT, and O2-TP-Ms. Experimental results revealed that the Brønsted/Lewis (B/L) ratio of MnxCe1-xO2/HZSM-5 catalysts could be adjusted by ion exchange of H• (in HZSM-5) with Mnn+ (where the exchange with Ce4+ did not distinctly affect the acidity); the long-term aged catalysts could accumulate ca. 14 organic compounds at surface, including highly toxic tetrachloromethane, trichloroethylene, tetrachloroethylene, o-dichlorobenzene, etc.; high humid operational environment could ensure a stable performance for MnxCe1-xO2/HZSM-5 catalysts; this was due to the effective removal of Cl• and coke accumulations by H2O washing, and the distinct increase of Lewis acidity by the interaction of H2O with HZSM-5. This work gives an in-depth view into the CB oxidation over acidic solid-supported catalysts and could provide practical guidelines for the rational design of reliable catalysts for industrial applications.

Aldol condensation of benzaldehyde with heptanal using solid-supported caesium and potassium catalysts

In this work, the possibility of using different heterogeneous basic catalysts in the aldol condensation of benzaldehyde and heptanal was tested. The solid basic catalysts were magnesium and calcium oxide, and different zeolites (HY, NaY, USY). Other catalysts were prepared – caesium-modified zeolites and MCM-41 and potassium-modified alumina. The basic properties of the used catalysts were studied using acid–base titration and temperature programmed desorption of carbon dioxide. Several techniques (UV-Vis and infrared spectroscopy, X-ray diffraction, nitrogen physisorption) were used to characterise the catalysts. These catalysts were used in the aldol condensation of benzaldehyde and heptanal, to test the influence of catalyst type, solvent, ratio of reactants and temperature on the course of reaction. Caesium and potassium leaching from catalysts was also monitored using atomic absorption spectroscopy. The best results were obtained using magnesium oxide (96% heptanal conversion, 68% selectivity to jasmine aldehyde), but all caesium- or potassium-modified catalysts showed reasonable results as well (caesium-MCM-41 40% heptanal conversion, 31% selectivity to jasmine aldehyde; potassium-alumina 62% heptanal conversion, 34% selectivity to jasmine aldehyde).

Transmission and fluorescence X-ray absorption spectroscopy cell/flow reactor for powder samples under vacuum or in reactive atmospheres.

X-ray absorption spectroscopy is an element-specific technique for probing the local atomic-scale environment around an absorber atom. It is widely used to investigate the structures of liquids and solids, being especially valuable for characterization of solid-supported catalysts. Reported cell designs are limited in capabilities-to fluorescence or transmission and to static or flowing atmospheres, or to vacuum. Our goal was to design a robust and widely applicable cell for catalyst characterizations under all these conditions-to allow tracking of changes during genesis and during operation, both under vacuum and in reactive atmospheres. Herein, we report the design of such a cell and a demonstration of its operation both with a sample under dynamic vacuum and in the presence of gases flowing at temperatures up to 300 °C, showing data obtained with both fluorescence and transmission detection. The cell allows more flexibility in catalyst characterization than any reported.

Divergent Approach to a Family of Tyrosine-Derived Ru-Alkylidene Olefin Metathesis Catalysts.

A simple and generic approach to access a new family of Ru-alkylidene olefin metathesis catalysts with specialized properties is reported. This strategy utilizes a late stage, utilitarian Hoveyda-type ligand derived from tyrosine, which can be accessed via a multigram-scale synthesis. Further functionalization allows the catalyst properties to be tuned, giving access to modified second-generation Hoveyda-Grubbs-type catalysts. This divergent synthetic approach can be used to access solid-supported catalysts and catalysts that function under solvent-free and aqueous conditions.

Solid-Supported Iron Catalysts for C–H Functionalization Reactions

Solid-Supported Iron Catalysts for C–H Functionalization Reactions

Ru(II) impregnated Al2O3, Fe3O4, SiO2 and N-coordinate ruthenium(II) arene complexes: Multifunctional catalysts in the hydrogenation of nitroarenes and the transfer hydrogenation of aryl ketones

Six new [RuClL(p-cymene)]Cl (LN-arenesulfonyl-4,5-dichloro-o-phenylenediamines) complexes (6–10) were prepared from the starting complex [RuCl2(p-cymene)]2. Also, three novel Al2O3, Fe3O4, SiO2-[RuClL(p-cymene)]Cl materials (11–13) were synthesized by an impregnation method using (10) and were solid-supported. The structural elucidations of the complexes and materials were characterized by different methods such as 1H, 13C-NMR, FT-IR, elemental analysis, TG/DTA, nitrogen adsorption-desorption (BET), SEM and EDX. The 6–10 complexes and 11–13 materials were applied for the transfer hydrogenation (TH) of ketones in the presence of 2-propanol (as the hydrogen source). The TH experiments showed that all complexes are average catalytic precursors (6–10). In particular, {[N-4-chlorobenzenesulfonyl-4,5-dichloro-o-phenylenediamine]-(p-cymene)-chloro-ruthenium(II)}chloride (10) was found to be a good catalyst in comparison to the others giving the corresponding alcohols in a good turnover frequency value of 2192h−1. Additionally, the synthesized Al2O3, Fe3O4, SiO2-[RuClL(p-cymene)]Cl materials (11–13) obtained from the most active catalyst (10) were used as catalysts for the TH and their efficiency was screened in the hydrogenation of nitroarenes in aqueous media at ambient temperature in the presence of NaBH4 by UV–vis spectrophotometer. Furthermore, the Fe3O4-[RuClL(p-cymene)]Cl materials can be recovered by filtration and reused for four cycles for the reduction of 2-nitroaniline. This facile and environment-friendly approach provides a green way to effectively synthesize low cost solid-supported catalysts for the reduction of nitroarenes and is promising for the development of other useful materials.