Current Catalysis - Volume 7, Issue 3, 2018

Background: Graphene and its composites with various transition metals and their oxides are widely studied for their applications in electrochemical energy conversion and storage devices. Graphene, a two-dimensional single atomic layer of the carbon atoms, has a high conductivity and high surface area. For these reasons, it has attracted considerable interest in electrochemical devices, such as batteries and supercapacitors. This review aims at identifying these electrocatalysts. Methods: Peer-reviewed research papers were scavenged using various bibliographic databases with graphene as one of the keywords. Research papers with good quality data were screened, analysed and the findings of the papers were summarized using a conceptual framework. Results: All together 80 research articles which have used graphene and/or its nanocomposite are included in the review. These bifunctional electrocatalysts are studied in a metal-oxygen battery which is a hybrid system of a Li-ion battery and a H2-O2 fuel cell. Several metal-oxygen (Zn-O2, Li-O2, Na-O2, K-O2, Ca-O2, Mg-O2, etc.) batteries are known in the literature. Li-O2 battery is another potential device for future electrical vehicles applications with its energy density being about 8 times higher than the state-of-the-art Li-ion battery. Current research works aim to improve the performance of existing metal- oxygen systems and explore the possibilities of using cheaper Na and K as anodes. Two types of reactions occur at the cathode in a metal-oxygen battery and electrocatalysts are employed to improve the kinetics of these reactions for better performance. Conclusion: Several research articles on graphene and its composites with transition metals and their oxides based nanocatalysts claim to improve the oxygen reaction kinetics and cycle life of the batteries. In this review, recent articles of graphene-based nanocatalysts for metal-oxygen batteries are summarized which give the present scenario of research in the field and scope of future work.

Intoduction: A highly efficient protocol for the one pot synthesis of 4(3H)-quinazolinones from anthranilic acid, ortho esters and various amines using a magnetically separable solid acid catalyst, nano sulfated TiO2 encapsulated Fe3O4 with microwave irradiation, is described. The plausible reaction mechanism for the synthesis of 4(3H)-quinazolinone, catalyzed by sulfated TiO2 encapsulated magnetic nanomaterial is also described. Conclusion: The developed process has been successfully applied for the synthesis of diverse 4(3H)- quinazolinones with variable functionality. This approach overcomes many of the drawbacks of the existing methods and provides an environmentally benign process.

Background: Solid acids and superacids based on supported heteropoly acids have become very popular. Use of mesoporous materials such as mesocellular silica foam (MCF) was made in this work for its superior textural properties and stability. Methods: MCF was used as a support for cesium substituted dodecatungstophosphoric acid (DTP). 20% (w/w) Cs2.5H0.5PW12O40 (Cs-DTP)/MCF was used as a superacidic heterogeneous catalyst for acetylation of p-anisyl alcohol. p-Anisyl acetate is widely used as fragrance and perfumery agent in a number of formulations. The catalyst was fully characterized by various techniques before and after use. Results: The catalysts selected for comparison were MCF, bulk Cs-DTP, commercial catalyst Amberlyst- 15, and 20% (w/w) Cs-DTP/MCF. Among all 20% (w/w) Cs-DTP/MCF was found to be the best catalyst with 57.6% conversion of p-anisyl alcohol with 100% selectivity in 90 min at 313 K. Reaction parameters were optimized through a systematic study. Langmuir-Hinshelwood-Hougen-Watson (LHHW) model with weak adsorption of all species was fitted leading to overall second order kinetics. Apparent activation energy is 13.4 kcal/mol. Conclusion: 20% (w/w) Cs2.5H0.5PW12O40 (Cs-DTP)/MCF was found to be the most active, selective and reusable catalyst under mild condition for the acetylation of p-anisyl alcohol to p-acetyl acetate.

In this work, the catalytic performance of cobalt oxide supported on activated carbon was studied during the oxidation reaction of several aliphatic/aromatic primary or secondary alcohols. Good results for benzyl alcohol and benzyl alcohol derivatives conversion and selectivity were obtained, while aliphatic, primary, and secondary alcohols in the study exhibited low conversions. The influence of the use of sonication during the impregnation of cobalt species was also evaluated. The particle size, distribution and dispersion of cobalt oxide (Co3O4) were compared with the catalyst prepared conventionally. These results are essential for understanding more about the activity of this type of catalysts in the synthesis of aldehydes and ketones. Methods: Two powdered activated carbons, RX3 Extra provided by NORIT and G60 provided by Aldrich, were used as support of the catalysts. Cobalt oxide particles were deposited on the supports by means of the incipient wetness technique. A portion of this preparation was manually stirred (i), while another portion was subjected to sonication by 20 min (ii). The catalysts so synthetized were called: Co/RX and Co/G60 as item (i); while Co/RX-s and Co/G60-s for item (ii). The performance and characterization of synthetized catalysts was studied with N2 physisorption, AA (Atomic Absorption), SEM (Scanning Electron Microscopy) and H2-TPR (Temperature Programmed Reduction). Alcohols oxidation reaction was carried out at 80°C using 0.2 mmol of each alcohol, a mass of catalyst (0.1 g, 0.09 mol%) and 20 mL of toluene as solvent. Different types of alcohols were used: benzyl alcohol, 1-phenylethanol, 4-chlorobenzyl alcohol, cyclohexanol, 2-phenylethanol, 2-octanol, 1-heptanol, 1-octanol, 3-phenyl-1-propanol. Results: Co3O4 particles supported on activated carbon catalysts were prepared through incipient wetness method. According to the characterization results, the use of sonication is an important factor if used in the impregnation process. G60 and RX supports and Co/G60, Co/RX, Co/G60-s,Co/RX-s catalysts have a very high surface area (500-1900 m2 g-1). No differences were found on surface area between catalysts either using or not the sonication treatment. Cobalt loading by AA technique in each support showed a slight variation with the synthesis method. The cobalt content for Co/G60 and Co/RX catalysts was 9.5 and 9.6 % wt Co, respectively; while Co/G60-s and Co/RX-s was 9 % wt Co, indicating that ultrasound affects interaction between precursor and support. SEM analysis showed uniform distribution on the catalysts, when ultrasound is used during the synthesis. It is evidenced that the synthesized catalysts without the sonication treatment have more agglomerations, and consequently the particles are less distributed on the support surface. Excellent results were obtained in the oxidation of aromatic alcohols such as benzyl alcohol and benzyl alcohol derivatives, showing higher conversion and selectivity with Co/G60-s and Co/RX-s (100 % conversion and 99 % selectivity at 3 hours of reaction). It is believed that their chemical properties permit good dehydrogenation and the subsequent oxidation. On the contrary, the aliphatic primary and secondary alcohols by their structural and chemical characteristics do not demonstrate good conversions. Conclusion: Cobalt oxide-based catalysts supported on activated-carbon (Co/AC) showed good catalytic activity and selectivity during the alcohol oxidation. The use of sonication is an important factor if used in impregnation step, because it causes physicochemical changes by the cavitation and implosion processes, changing the nucleation and agglomeration of the active phase on support. This favors the catalytic development of the system mainly involved in quantity, dispersion and particle size. Excellent results were obtained in the oxidation of aromatic alcohols such as benzyl alcohol and benzyl alcohol derivatives, showing higher conversion and selectivity with this type of catalyst (Co/AC). The effect of sonication on the preparation of this type of catalysts might contribute to the study of the green oxidation reaction of alcohols with O2 as oxidizing agent.

Background: Imidazoles are important class of heterocyclic compounds showing biological activities. Several methods have been investigated till today for the synthesis of triaryl imidazoles. Some of these classical as well as nonclassical methods experiences drawbacks for instance elongated reaction time, expensive catalyst, low yield of product etc. Hence improvement of a competent method is still necessary. This paper reveals greener protocol for the synthesis of triaryl imidazoles by cyclocondensation of aromatic aldehydes, benzil and ammonium acetate in existence of fly ash as an efficient heterogeneous catalyst by means of microwaves. Methods: Heterogeneous catalyst fly ash was prepared by simple thermal activation method. The catalyst was systematically characterized through wet chemical analysis, XRD, FT-IR, SEM and EDS. The structural analysis was done using XRD and IR. Morphological study was performed using SEM and elemental composition studied by EDS technique. This activated fly ash catalyst was applied in the synthesis of trisubstituted imidazoles. The progress of reaction was checked by TLC and the synthesized compounds were further confirmed by FT-IR, 1H-NMR and 13C-NMR spectroscopy. Results: To check feasibility of activated fly ash for trisubstituted imidazole synthesis, reactions under microwave irradiation employed. The products were obtained in higher yield (92-98%). Conclusion: The fly ash was found to be highly effective in the synthesis of trisubstituted imidazoles under microwave irradiation. The significant features of this protocol are rate enhancement, uncomplicated work up process, high yields and employ of ecofriendly catalyst.

Background: A versatile, facile, one-pot multi-component protocol for the synthesis of 4Hbenzochromenes using L- valine as organocatalyst in aqueous medium has been developed. Methods: Superior catalytic performance of L- valine, operational simplicity, easy workup procedure and recyclability of the catalyst are the key strengths of reported strategy. Results: Therefore, it is a green alternative to the existing protocols. Conclusion: This method offers mild reaction conditions, the use of easily available cheap reagents, short reaction times, excellent yields and high atom economy.

Background: In this work, we aimed to synthesize gold nanoparticles stabilized with Nacetyl- L-cysteine and study their catalytic activity towards the benzaldehyde oxidation as well as the formation of imines. Methods: N-acetyl-L-cysteine stabilized gold nanoparticles were prepared and the catalyst was characterized via spectroscopic techniques such as UV-VIS spectrophotometry and SERS. Gold nanoparticles dimensions were evaluated through DLS and SEM. After having the catalytic system set, the oxidation of benzaldehyde and the one-pot reaction for the synthesis of imines were proceeded. All the products were characterized via NMR spectroscopy. Results: Regarding the nanoparticles dimensions, a diameter of approximately 25 nm was achieved. Firstly, gold nanoparticles were effective towards the benzaldehyde oxidation, with a conversion of 97%. Furthermore, we investigated a one-pot formation of imines and it was noticed through NMR analysis a carboxylic acid as intermediate. Finally, a substrate scope with different aldehydes and amines was created and products were obtained with up 99%. Conclusion: N-acetyl-L-cysteine modified gold nanoparticles are effective support-free catalyst for the chemoselective aldehyde oxidation/amine coupling to imine under mild conditions. Aromatic aldehydes were consumed to form benzoic acids and went under an amine coupling reaction giving a wide range of imines. This consists the first example in which there is a support-free catalyst capable of synthesize imines from aldehydes through carboxylic acids with good to excellent yields.

Introduction: A one-pot approach for the synthesis of 2,3-dihydroquinazolin-4(1H)-ones in the reaction between 2-aminobezamide and aromatic aldehydes in the presence of highly available carboxylic acids such as benzilic acid, phthalic acid and salicylic acid has been reported. Material and Methods: Carboxylic acids such as benzilic acid, phthalic acid and salicylic acid, used as efficient catalysts for the synthesis of 2,3-dihydroquinazolin-4(1H)-ones, are structurally stable compounds. Synthesized compounds were characterized by 1H NMR and IR spectroscopy and their melting points are in good agreement with previous reports. Results: Results show that carboxylic acids such as benzilic acid, phthalic acid and salicylic can act as effective catalysts in the synthesis of 2,3-dihydroquinazolin-4(1H)-ones without any side products in acceptable reaction time. Conclusion: In conclusion, we use a simple one-pot process for the synthesis of 2,3- dihydroquinazolin-4(1H)-ones by using carboxylic acids which has some advantages such as low cost, nontoxic solvents and simple separation of products.

Introduction: Titanium dioxide (TiO2) nanorod and nanowire structure are an important material in photocatalytic and photoelectrocatalytic application. But, photocatalytic performance of TiO2 nanostructure was limited by electron-hole recombination. The surface adsorbed hydroxyls on TiO2 surface play an important role in photocatalytic and energy applications. It increases the trapping site for electron and hole and prevents its recombination. Materials and Methods: Herein, TiO2 nanorod array (NRA) was synthesized on FTO substrate with the facile hydrothermal method. The existence of the surface adsorbed hydroxyl group on the TiO2 surface was studied by performing different calcination treatment on synthesized TiO2 NRA. Results: X-ray diffraction (XRD) revealed that synthesized TiO2 NRA has only rutile phase. Field emission scanning electron microscopy (FE-SEM) showed that the morphology of nanorods array is grown on FTO substrate. The optical properties of TiO2 NRA were studied using UV-Visible spectrophotometer and Photoluminescence (PL). The existence of surface hydroxyl group was estimated by X-ray photoelectron spectroscopy (XPS). The photocatalytic efficiency of the obtained TiO2 NRA was investigated by the photodegradation of methylene blue under UV light irradiation. Conclusion: The effect of calcination and growth time of as-synthesized TiO2 NRA and its photocatalytic activity were also studied. The TiO2 NRA treated with low calcination temperature showed higher photocatalytic activity.