A review on convenient synthesis of substituted coumarins using reuseable solid acid catalysts

Due to growing concern about chemicals and their impact on the environment, cleaner reaction conditions are needed to be incorporated into chemical synthetic procedures. Recently, the use of heteropolyacid catalysts, mainly reuseable solid acid catalysts, has gained a leading role in organic synthesis due to their environmental and economic considerations and industrial utilization. The high catalytic activity, moisture sensitivity, reusability and inexpensive makes solid supported reagents attractive substituents to conventional Lewis acids. Nowadays synthesis of coumarins and their derivatives has attracted considerable attention from organic and medicinal chemists for many years as a large number of natural products contain this heterocyclic nucleus. In continuation with our investigations into the synthesis of substituted coumarins and due to several advantages of heterogeneous catalysts viz. cost-effective, no side products, high yield of desired products and no toxic waste material, here we report a new approach for the synthesis of substituted coumarins using solid acid catalysts.

Due to growing concern about chemicals and their impact on the environment, cleaner reaction conditions are needed to be incorporated into chemical synthetic procedures.     

Precursor accumulation on nanocarbons for the synthesis of LaCoO3 nanoparticles as electrocatalysts for oxygen evolution reaction

Oxygen evolution reaction (OER) is a key step in energy storage devices. Lanthanum cobaltite (LaCoO₃) perovskite is an active catalyst for OER in alkaline solutions, and it is expected to be a low-cost alternative to the state-of-the-art catalysts (IrO₂ and RuO₂) because transition metals are abundant and inexpensive. For efficient catalysis with LaCoO₃, nanosized LaCoO₃ with a high surface area is desirable for increasing the number of catalytically active sites. In this study, we developed a novel synthetic route for LaCoO₃ nanoparticles by accumulating the precursor molecules over nanocarbons. This precursor accumulation (PA) method for LaCoO₃ nanoparticle synthesis is simple and involves the following steps: (1) a commercially available carbon powder is soaked in a solution of the nitrate salts of lanthanum and cobalt and (2) the sample is dried and calcined in air. The LaCoO₃ nanoparticles prepared by the PA method have a high specific surface area (12 m² g⁻¹), comparable to that of conventional LaCoO₃ nanoparticles. The morphology of the LaCoO₃ nanoparticles is affected by the nanocarbon type, and LaCoO₃ nanoparticles with diameters of less than 100 nm were obtained when carbon black (Ketjen black) was used as the support. Further, the sulfur impurities in nanocarbons significantly influence the formation of the perovskite structure. The prepared LaCoO₃ nanoparticles show excellent OER activity owing to their high surface area and perovskite structure. The Tafel slope of these LaCoO₃ nanoparticles is as low as that of the previously reported active LaCoO₃ catalyst. The results strongly suggest that the PA method provides nanosized LaCoO₃ without requiring the precise control of chemical reactions, harsh conditions, and/or special apparatus, indicating that it is promising for producing active OER catalysts at a large scale.

A simple synthetic process for LaCoO₃ nanoparticles based on the accumulation of precursors on nanocarbon supports was presented. The LaCoO₃ nanoparticles showed excellent OER activity owing to their high surface area and perovskite structure.     

Hybrids based on borate-functionalized cellulose nanofibers and noble-metal nanoparticles as sustainable catalysts for environmental applications

Polymeric supports from renewable resources such as cellulose nanomaterials are having a direct impact on the development of heterogenous sustainable catalysts. Recently, to increase the potentiality of these materials, research has been oriented towards novel functionalization possibilities. In this study, to increase the stability of cellulose nanofiber films as catalytic supports, by limiting the solubility in water, we report the synthesis of new hybrid catalysts (HC) based on silver, gold, and platinum nanoparticles, and the corresponding bimetallic nanoparticles, supported on cellulose nanofibers (CNFs) cross-linked with borate ions. The catalysts were prepared from metal precursors reduced by the CNFs in an aqueous suspension. Metal nanoparticles supported on CNFs with a spherical shape and a mean size of 9 nm were confirmed by TEM, XRD, and SAXS. Functionalized films of HC-CNFs were obtained by adding a borate solution as a cross-linking agent. Solid-state ¹¹B NMR of films with different cross-linking degrees evidenced the presence of four different boron species of which the bis-chelate is responsible for the cross-linking of the CNFs. Also, it may be concluded that the bis-chelate and the mono-chelates modify the microstructure of the film increasing the water uptake and enhancing the catalytic activity in the reduction of 4-nitrophenol.

We report the synthesis of supported noble metal nanoparticles on cellulose nanofibers cross-linked with borate as highly efficient sustainable catalysts.     

Synthesis and characterization of an efficient and stable Al/Fe pillared clay catalyst for the catalytic wet air oxidation of phenol

A facile method for synthesizing Al/Fe pillared clays (PILCs) from natural bentonite clay, by using ultrasonic treatment during the aging and intercalation steps, has been established. Single metal (Fe-PILCs and Al-PILCs) and mixed metal (Al/Fe-PILCs, with varying compositions of the pillaring precursors) pillared clays were prepared and characterized with a combination of chemical and instrumental methods. The pillared clays were evaluated as catalysts in the catalytic wet air oxidation (CWAO) of phenol and the mixed metal pillared clay catalysts, especially with an Al/Fe ratio of 3 : 1, were found to be highly active and stable, with superior properties such as surface areas, basal spacing, high porosity and thermal stability. The catalysts could also be reused several times without significant loss of activity. The results of the study show that Al/Fe-pillared clay catalysts are effective catalysts for the oxidation of phenol and removal of TOC in aqueous solutions. The main intermediate products in the CWAO of phenol were hydroquinone, pyrocatechol, and benzoquinone and oxalic, formic, malonic, oxalic, malonic and maleic acids.

A facile method for synthesizing Al/Fe pillared clays (PILCs) from natural bentonite clay, by using ultrasonic treatment during the aging and intercalation steps, has been established.     

Magnetically recoverable catalysts for the preparation of pyridine derivatives: an overview

Magnetically recoverable nano-catalysts can be readily separated from the reaction medium using an external magnet. In recent years, chemistry researchers have employed them as catalysts in chemical reactions. The high surface area, simple preparation, and modification are among their major advantages. Pyridine derivatives are an important category of heterocyclic compounds, which show a wide range of excellent biological activities, including IKK-β inhibitors, anti-microbial agents, A2A adenosine receptor antagonists, inhibitors of HIV-1 integrase, anti-tumor, anti-inflammatory, and anti-Parkinsonism. Recently, the catalytic activity of magnetic nanoparticles was investigated in multicomponent reactions in the synthesis of pyridine derivatives, which is discussed in this review.

Magnetically recoverable nano-catalysts can be readily separated from the reaction medium using an external magnet.     

A ZrO2-RGO composite as a support enhanced the performance of a Cu-based catalyst in dehydrogenation of diethanolamine

The sintering resistance of supported Cu nanoparticle (NP) catalysts is crucial to their practical application in the dehydrogenation of diethanolamine (DEA). In this paper, co-precipitation, hydrothermal synthesis, and sol–gel condensation are used to form a new support material through chemical bonding between graphene oxide and ZrO₂. The composite carriers prepared by the three methods are mixed with copper nitrate and ground using a ball mill. A series of Cu/ZrO₂-reduced graphene oxide (RGO) composites were prepared by calcination under nitrogen at 450 °C for 3 h and hydrogen reduction at 250 °C for 4 h. The conversion of DEA to iminodiacetic acid (IDA) reached 96% with the Cu/ZrO₂-RGO catalyst prepared by hydrothermal synthesis. The conversion rate of DEA is more than 80% following the reuse of the CZG-2 catalyst for twelve cycles. The various physicochemical characterization techniques show that the Cu/ZrO₂-RGO layered and wrinkled nanostructures can improve catalytic stability and suppress the sintering of the supported Cu NPs during the catalytic dehydrogenation of diethanolamine. A synergistic effect between the RGO and the Cu nanoparticles is observed. The Cu nanoparticles with RGO have a better dispersibility, and a new nano-environment is created, which is the key to improving the efficiency of diethanolamine dehydrogenation. These new Cu/ZrO₂-RGO catalysts show increased durability compared to commercially produced Cu/ZrO₂ catalysts and show promise for practical applications involving diethanolamine dehydrogenation.

A Cu/ZrO₂-RGO catalyst prepared by hydrothermal synthesis of a ZrO₂-RGO carrier has highly dispersed Cu nanoparticles and resistance to sintering.     

Expedient approach for trans-esterification of β-keto esters under solvent free conditions using silica supported boric acid (SiO2–H3BO3) as a recyclable catalyst

A highly efficient trans-esterification of β-keto methyl/ethyl esters with primary, secondary, allylic, benzylic and chiral alcohols has been carried out in excellent yields under solvent-free conditions using silica supported boric acid as a heterogeneous catalyst. The surface morphology of the silica-boric acid catalyst (fresh and recycled) has been characterized by SEM and EDX techniques. This sustainable protocol resulted in a remarkable enhancement in the synthetic efficiency (87–95% yield) with high purity and eliminating the use of an environmentally toxic solvent. The work up procedure is very simple and the catalyst has been successfully recovered and recycled. The present methodology is also applicable for trans-esterification with chiral alcohols on a multi-gram scale without compromising the yield. Noteworthy features of this protocol are simple operational procedure, minimizing production of chemical waste, mild reaction conditions, easy preparation of the catalyst and its recyclability up to five cycles without any appreciable loss of catalytic activity.

A simple, mild, high yielding and minimizing chemical waste procedure for trans-esterification of β-keto methyl/ethyl esters with alcohol groups was developed under solvent-free condition using silica-boric acid as recyclable heterogeneous catalyst.     

Solventless synthesis of cerium oxide nanoparticles and their application in UV protective clear coatings

Colloidal dispersions of cerium oxide nanoparticles are of importance for numerous applications including as catalysts, chemical mechanical polishing agents and additives for UV protective and anticorrosion coatings. Here, concentrated oleate-coated cerium oxide nanoparticles (CeO₂ NPs) with a uniform size have been produced by solventless thermolysis of cerium-oleate powder under low pressure at 320 °C and subsequently dispersed in hexane. Unlike any previously reported colloidal synthesis process for ceria nanoparticles, this process does not involve any toxic high boiling point organic solvent that requires subsequent removal at high cost. Although the process is very simple, highly concentrated cerium oxide nanoparticles with more than 17 wt% solid content and 70% of the theoretical yield can be easily obtained. Moreover, the size, shape and crystallinity of cerium oxide nanoparticles can be tailored by changing the thermal decomposition temperature and reaction time. Moreover, the new synthesis route developed in this study allows the synthesis of clean and dispersible ceria nanoparticles at a relatively low cost in a single step. The prepared ceria nanoparticles have an excellent UV absorption property and remain transparent to visible light, thus having the potential to replace potentially hazardous organic compounds in UV absorbing clear coatings. As a proof of concept, the prepared dispersions of cerium oxide nanoparticles in hexane were formulated into a solvent borne binder base to develop clear UV protecting coatings for light sensitive substrates. The general synthesis strategy presented in this study is generally applicable for the low-cost production of a concentrated dispersion of metal oxide nanoparticles with minimal environmental impact.

Solventless synthesis of metal oxide nanoparticles.     

Ultrafine Pt nanoparticles supported on a dendrimer containing thiol groups: an efficient catalyst for the synthesis of benzimidazoles and benzothiazoles from benzyl alcohol derivatives in water

A novel and unique platform was prepared based on a dendrimer containing thiol groups supported on nanosilica (nSTDP), and ultrafine platinum nanoparticles were synthesized and immobilized on the thiol decorated branches of nSTPD. The new catalyst, (Pt_np@nSTDP), was characterized by different techniques such as FE-SEM, TEM, ICP, XPS and DR UV-vis. This heterogeneous catalyst presented an outstanding performance for the synthesis of benzimidazole and benzothiazole derivatives through a reaction between benzyl alcohol derivatives and 2-aminothiophenol or 1,2-phenylenediamine. No requirement for the pre-reduction of catalysts and using water as a green solvent make it an individual catalyst for these reactions. Furthermore, the catalyst can be easily recovered and reused five consecutive times in the production of benzimidazoles and benzothiazoles without significant leaching of Pt and loss of its activity which illustrated the chemical stability of the catalyst during the reaction.

A new heterogeneous reusable catalyst containing ultrafine Pt nanoparticles was synthesized and applied for the synthesis of benzimidazoles and benzothiazoles in water as a green solvent.     

Transition metal oxide (NiO,CuO, ZnO)-doped calcium oxide catalysts derived from eggshells for the transesterification of refined waste cooking oil

This paper reports the synthesis of new transition metal oxide-modified CaO catalysts derived from eggshells for the transesterification of refined waste cooking oil. CaO is a well-known base catalyst for transesterification. However, its moderate basicity and low surface area have restricted its catalytic performance. Therefore, a new attempt was made to modify the CaO catalyst with transition metal oxides, including Ni, Cu and Zn oxides, via simple wetness impregnation method. The catalytic performance of the resulting modified CaO-based catalysts was evaluated through the transesterification reaction using refined waste cooking oil. The results showed that the NiO/CaO(10 : 90)(ES) catalyst calcined at 700 °C, demonstrated being highly potential as a catalyst. It gave the highest biodiesel production (97.3%) at the optimum conditions of 1 : 18 oil-to-methanol molar ratio, 6 wt% catalyst loading and 180 minutes reaction time as verified by response surface methodology (RSM). The high catalytic activity of NiO/CaO(10 : 90)(ES)(700 °C) was attributed to its high basicity (8.5867 mmol g⁻¹) and relatively large surface area (7.1 m² g⁻¹). The acid value and free fatty acids of the biodiesel produced under optimal process conditions followed the EN 14214 and ASTM D6751 limit with 0.17 mg KOH per g (AV) and 0.09 mg KOH per g (FFA), respectively.

This paper reports the synthesis of new transition metal oxide-modified CaO catalysts derived from eggshells for the transesterification of refined waste cooking oil.     

Difference in the deactivation of Au catalysts during ethanol transformation when supported on ZnO and on TiO2

Au nanoparticles of different sizes were supported by the deposition–precipitation method on two metal oxides: ZnO and TiO₂. The resulting catalysts were tested in the ethanol catalytic transformation reaction. Both metal oxide support materials exerted a different influence on the achieved Au particle size as well as on the behavior of the subsequent catalyst, with regard to their initial conversion values, product distribution and stability. While TiO₂ favors the formation of smaller nanoparticles, ZnO offers larger Au particle sizes when prepared under similar conditions. At the same time, TiO₂ produced catalysts which displayed higher initial conversions in comparison with AuZnO catalysts, even when observing catalysts of each series with similar particle sizes. At the same time, catalysts supported on ZnO exhibited higher resistance to deactivation caused by coke formation. These results were evidenced employing different characterization techniques on both used and fresh catalyst samples. The decline in deactivation was generally accompanied by an increase in the carbon content on the catalyst''s surface.

Au NPs of different sizes were supported on two metal oxides: ZnO and TiO₂. Differences in ethanol transformation for Au of similar particle size reveal that TiO₂ support induces condensation products while ZnO only gives place to dehydrogenation.     

A convenient and efficient precursor transformation route to well-dispersed,stable, and highly accessible supported Au nanocatalysts with excellent catalytic hydrogenation performances

A new, convenient, and efficient precursor transformation route for the synthesis of supported Au nanocatalysts was reported. In this strategy, [Au(en)₂]³⁺-riched titanate nanospheres (en: ethylenediamine) with hierarchical flower-like architecture were pre-synthesized via “ammonia etching-ion exchange” processes and then used as the precursors of the objective catalysts. Direct pyrolysis of these precursors, varying in amount of [Au(en)₂]³⁺, led to the formation of Au nanoparticles (AuNPs) with different contents uniformly supported on highly crystalline titania nanoflowers (fTiO₂). The fTiO₂-supported AuNPs nanocomposites possessed highly open porous structures with large surface areas (142.3–149.3 m² g⁻¹), which could allow guest molecules to diffuse in and out easily. More interestingly, the formed AuNPs with small size (∼3.8 nm) were well-dispersed and partially embedded into the nanosheets of fTiO₂, which was beneficial for achieving high activity while avoiding their detachment from the support during application. Accordingly, the AuNPs/TiO₂ catalysts exhibited superior catalytic properties for 4-nitrophenol hydrogenation with significantly higher catalytic efficiencies than many previously reported heterogeneous catalysts. Moreover, the catalytic activity could remain almost unchanged after being recycled several times, demonstrating their high stability. These findings open up a new possibility for rational design and synthesis of supported catalysts for diverse catalytic applications.

Synthesis of well-dispersed, stable, and highly accessible supported Au nanocatalysts was achieved via a new and efficient precursor transformation route.     

Construction of stable bio-Pd catalysts for environmental pollutant remediation

It has been reported that Pd nanoparticles were a little weak to bind to the dried microbial (yeast) surface, leading to the poor stability of the bio-supported catalysts. The objectives of the study are to construct stable Pd nanocatalysts supported on the dried yeast surface with the help of a tiny amount (<0.1 wt%) of reduced graphene oxide (Pd/yeast/rGO) and apply the catalysts in environmental pollutant remediation. The characterizations of the as-obtained Pd/yeast/rGO catalysts showed that reduced GO could cover Pd/yeast materials and prepare 15–21 nm Pd nanoparticles under acid and base media. The catalytic performance of the Pd/yeast/rGO catalyst was compared with that of control Pd/yeast catalysts without GO. The results revealed the kinetic constant K_app in the reduction of 4-nitrophenol of Pd/yeast/rGO catalysts could reach 3.6 × 10⁻² s⁻¹ without stirring during the reaction, which was 2.4 times higher than that of Pd/yeast catalysts, and the Pd/yeast/rGO catalysts kept a good stability even after being reused in seven cycles. Furthermore, the catalysts also showed quite good catalytic activities on CO oxidation and decolorization of dye methylene blue (MB). Thus, Pd/yeast/rGO catalysts were proven to be highly active and stable for environmental remediation and have the advantage that they can prevent the loss of noble metals and be prepared conveniently from discarded microorganisms.

Stable bio-supported Pd/yeast/rGO catalysts were prepared by covering with a tiny amount (<0.1 wt%) of GO based on a non-enzyme reduction method.     

Structure and characterisation of hydroxyethylcellulose–silica nanoparticles

Functionalising nanoparticles with polymers has gained much interest in recent years, as it aids colloidal stability and manipulation of surface properties. Here, polymer-coated thiolated silica nanoparticles were synthesised by self-condensation of 3-mercaptopropyltrimethoxysilane in the presence of hydroxyethylcellulose. These nanoparticles were characterised by dynamic light scattering, small angle neutron scattering, Nanoparticle Tracking Analysis, Raman spectroscopy, FT-IR spectroscopy, thermogravimetric analysis, Ellman''s assay, transmission electron microscopy and cryo-transmission electron microscopy. It was found that increasing the amount of hydroxyethylcellulose in the reaction mixture increased the nanoparticle size and reduced the number of thiol groups on their surface. Additionally, by utilising small angle neutron scattering and dynamic light scattering, it was demonstrated that higher concentrations of polymer in the reaction mixture (0.5–2% w/v) resulted in the formation of aggregates, whereby several silica nanoparticles are bridged together with macromolecules of hydroxyethylcellulose. A correlation was identified between the aggregate size and number of particles per aggregate based on size discrepancies observed between DLS and SANS measurements. This information makes it possible to control the size of aggregates during a simple one-pot synthesis; a prospect highly desirable in the design of potential drug delivery systems.

Polymer-coated thiolated silica nanoparticles were synthesised by self-condensation of 3-mercaptopropyltrimethoxysilane in the presence of hydroxyethylcellulose.     

Recent advances and future perspectives of sol–gel derived porous bioactive glasses: a review

The sol–gel derived porous bioactive glasses have drawn worldwide attention by virtue of the convenience and flexibility of this versatile synthesis method. In this review, the recent advances in sol–gel processed porous bioactive glasses in biomedical fields, especially for bone tissue regeneration applications have been comprehensively reviewed. Generally, it is envisaged that the morphology and chemical compositions of sol–gel derived porous bioactive glasses significantly affect their biological properties. Therefore, the controlled synthesis of these porous glasses is critical to their effective use in the biomedical fields. With this context, the first part of the review briefly describes the fundamentals of the sol–gel technique. In the subsequent section, different approaches frequently used for the sol–gel synthesis of porous glasses such as microemulsion and acid-catalyzed based synthesis have been reviewed. In the later part of the review, different types of sol–gel derived bioactive glasses namely silica, phosphate and silica–titania based glasses along with organic–inorganic hybrids materials have been discussed. The review also discusses the chemical, surface, mechanical and biological properties and further highlights the strategies to control the pore structure, shape, size and compositions of sol–gel derived bioactive glasses. Finally, the review provides a detailed discussion about the bone tissue regeneration application of different types of sol–gel derived bioactive glasses and presents future research perspectives.

Sol–gel derived bioactive glasses have been extensively explored as a promising and highly porous scaffold materials for bone tissue regeneration applications owing to their exceptional osteoconductivity, osteostimulation and degradation rates.     

Magnetization of graphene oxide nanosheets using nickel magnetic nanoparticles as a novel support for the fabrication of copper as a practical,selective, and reusable nanocatalyst in C–C and C–O coupling reactions

Catalyst species are an important class of materials in chemistry, industry, medicine, and biotechnology. Moreover, waste recycling is an important process in green chemistry and is economically efficient. Herein, magnetic graphene oxide was synthesized using nickel magnetic nanoparticles and further applied as a novel support for the fabrication of a copper catalyst. The catalytic activity of supported copper on magnetic graphene oxide (Cu–ninhydrin@GO–Ni MNPs) was investigated as a selective, practical, and reusable nanocatalyst in the synthesis of diaryl ethers and biphenyls. Some of the obtained products were identified by NMR spectroscopy. This nanocatalyst has been characterized by atomic absorption spectroscopy (AAS), scanning electron microscopy (SEM), wavelength dispersive X-ray spectroscopy (WDX), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), and vibrating sample magnetometer (VSM) techniques. The results obtained from SEM shown that this catalyst has a nanosheet structure. Also, XRD and FT-IR analysis show that the structure of graphene oxide and nickel magnetic nanoparticles is stable during the modification of the nanoparticles and synthesis of the catalyst. The VSM curve of the catalyst shows that this catalyst can be recovered using an external magnet; therefore, it can be reused several times without a significant loss of its catalytic efficiency. The heterogeneity and stability of this nanocatalyst during organic reactions was confirmed by the hot filtration test and AAS technique.

Catalytic activity of supported copper on magnetic graphene oxide was investigated as a selective and reusable nanocatalyst in the synthesis of diaryl ethers and biphenyls.     

An efficient multicomponent synthesis of 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted imidazoles catalyzed by a magnetic nanoparticle supported Lewis acidic deep eutectic solvent

A mild and highly efficient reaction for the synthesis of 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted imidazoles catalyzed by a magnetically supported Lewis acidic deep eutectic solvent on magnetic nanoparticles (LADES@MNP) has been developed via one-pot multicomponent processes under solvent-free sonication. These reactions have good to excellent yields, mild conditions, and work-up simplicity. This method represents a new method for the preparation of 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted imidazoles. More importantly, LADES@MNP can be easily recovered by magnetic separation and reused five times without significant loss of catalytic activity.

A mild and highly efficient method for the synthesis of 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted imidazoles catalyzed by a Lewis acidic deep eutectic solvent on magnetic nanoparticles (LADES@MNP).     

Fe3O4/SO3H@zeolite-Y as a novel multi-functional and magnetic nanocatalyst for clean and soft synthesis of imidazole and perimidine derivatives

In this study, SO₃H@zeolite-Y was synthesized by the reaction of chlorosulfonic acid with zeolite-NaY under solvent-free conditions, which was then supported by Fe₃O₄ nanoparticles to give SO₃H@zeolite-Y (Fe₃O₄/SO₃H@zeolite-Y) magnetic nanoparticles. Several techniques were used to evaluate the physical and chemical characterizations of the zeolitic nanostructures. Fe₃O₄-loaded sulfonated zeolite was applied as a novel multi-functional zeolite catalyst for the synthesis of imidazole and perimidine derivatives. This efficient methodology has some advantages such as good to excellent yield, high purity of products, reusability of nanocatalyst, simple reaction conditions, environmental friendliness and an economical chemical procedure from the viewpoint of green chemistry.

Fe₃O₄/SO₃H@zeolite-Y was applied as a novel, effective and environmentally friendly magnetic nanocatalyst for the synthesis of imidazole and perimidine scaffolds.     

Tuning the metal-support interaction in the thermal-resistant Au–CeO2 catalysts for CO oxidation: influence of a mild N2 pretreatment

Pretreatment is very important for altering the catalytic properties of the supported noble metal catalysts in many heterogeneous reactions. In this study, a simple and mild pretreatment with N₂ has been reported to re-activate the Au–CeO₂ catalysts that were prepared by a deposition–precipitation method followed by calcination at 600 °C. Upon N₂ pretreatment at 200 °C, the metal-support interaction between Au nanoparticles (NPs) and CeO₂ was observed with the evidence of particular coverage of Au nanoparticles by CeO₂, electronic interactions and changes in CO adsorption ability. As a result, the CO oxidation activity of the pretreated Au–CeO₂ catalysts largely improved compared with those without any pretreatment and even with those subjected to H₂ and O₂ pretreatments. N₂ pretreatment also makes the Au NPs more resistant to sintering at high temperature. Furthermore, this mild pretreatment strategy can provide a potential approach to improve the thermal stability of other supported noble metal catalysts.

The degree of encapsulation for Au–CeO₂ catalysts was identical to the catalysts exhibiting metal-support interaction, which improved the CO oxidation activity.     

Enhanced stability and ultrahigh activity of amorphous ripple nanostructured Ni-doped Fe oxyhydroxide electrode toward synergetic electrocatalytic water splitting

The development of high-performance catalysts for oxygen-evolution reaction (OER) is paramount for cost-effective conversion of renewable electricity to fuels and chemicals. Here we report, highly efficient, ultra-durable and earth-abundant Ni@Fe-NP electrocatalysts developed by solvothermal method for oxygen evolution reaction (OER). The newly developed oxygen electrode show prolonged stability and high catalytic-activity in line with water oxidation keeping alkaline condition which requires overpotential of only 211 mV at current density of 10 mA cm⁻². Collectively, the as-prepared amorphous Ni@Fe-NP rippled nanostructured electrode is the most effective oxygen evolution electrode in alkaline solution. Therefore, this study will offer exciting new avenues for designing self-supported electrode materials towards water splitting and other applications.

The development of high-performance catalysts for oxygen-evolution reaction (OER) is paramount for cost-effective conversion of renewable electricity to fuels and chemicals.