1,720,972 research outputs found
Metal‐Free Carbonaceous Catalytic Materials: Biomass Feedstocks for a Greener Future
No full textMetal-free catalytic systems (MFCS) have emerged as sustainable and cost-efficient heterogeneous catalysts, particularly in the case of carbonaceous materials with oxygen, nitrogen, boron, sulfur or phosphorus functionalities. This contribution aims to provide a general overview of the recent advances on the design of such materials, with emphasis on those derived from biomass waste and on the relationship between their structure and their activity. The opportunities of using MFCS in different areas of catalysis, including thermo-, electro-, and photo-catalysis, will be addressed for applications towards the upgrading of renewable feedstocks. This analysis will describe sustainable approaches not only with respect to the nature of catalyst but also for the employment of non-toxic and sustainable precursors, and for the efficiency of the synthetic protocol and its carbon footprint
Insights into the Selective Oxidation of 5-Hydroxymethylfurfural to 5-Hydroxymethyl-2-furancarboxylic Acid Using Silver Oxide
No full textThis contribution reports the oxidation of HMF to 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) employing Ag2O, a relatively cheap and commercially available catalyst, to achieve an impressive HMFCA yield of 98% (60 min, 90 °C). Various reaction parameters including type of catalyst, base, quantities of base and catalyst, hydrogen peroxide concentration, and reaction temperature in function of reaction time have been optimized. Microwave batch conditions provided optimum yields, with quantitative HMF conversion with 97% HMFCA yield in only 24 min reaction (30 W). Reusability studies revealed catalyst deactivation, most likely associated with the reduction of silver oxide to metallic silver and nanoparticles sintering after the catalytic reaction
Isosorbide: Recent advances in catalytic production
No full textThis article focuses on the state-of-the-art advancements on the production of isosorbide, a furanic diol exclusively produced via a two-steps dehydrocyclisation of sorbitol; polyol acquired from the catalytic reduction of glucose. Generally, the compound is formed admixed with various types of monocyclic ethers called sorbitans. During the past half century, many researchers tried to explore the underlying mechanistic and kinetic aspects of the reactions involved in its formation with the main objective to increase the selectivity thus avoiding the formation of 2,5-sorbitan by-product. In the intervening years, new energy-saving and environmental-friendly methods have been developed, especially those that involve heterogeneous catalysts or acidic ionic liquids. In order to improve the catalytic activities of catalysts, it is imperative to measure the impact of their intrinsic acidity strength, porosity and surface hydrophobicity on each stage of the formation of bicyclic furanic compound. Additionally, comparative advantageous features of simple protocols involving acidic deep eutectic solvent employed as catalyst in solvent-free microwave-assisted reaction, are highlighted
Metal-Free N-Doped Carbons for Solvent-Less CO2 Fixation Reactions: A Shrimp Shell Valorization Opportunity
Full text linkHigh anthropogenic CO2 emissions are among the main causes of climate change. Herein, we investigate the use of CO2 for the synthesis of organic cyclic carbonates on metal-free nitrogen-doped carbon catalysts obtained from chitosan, chitin, and shrimp shell wastes, both in batch and in continuous flow (CF). The catalysts were characterized by N-2 physisorption, CO2-temperature-programmed desorption, X-ray photoelectron spectroscopy, scanning electron microscopy, and CNHS elemental analysis, and all reactivity tests were run in the absence of solvents. Under batch conditions, the catalyst obtained by calcination of chitin exhibited excellent performance in the conversion of epichlorohydrin (selected as a model epoxide), resulting in the corresponding cyclic carbonate with 96% selectivity at complete conversion, at 150 degrees C and 30 bar CO2, for 4 h. On the other hand, in a CF regime, a quantitative conversion and a carbonate selectivity >99% were achieved at 150 degrees C, by using the catalyst obtained from shrimp waste. Remarkably, the material displayed an outstanding stability over a reaction run time of 180 min. The robustness of the synthetized catalysts was confirmed by their good operational stability and reusability: ca. (75 +/- 3)% of the initial conversion was achieved/retained by all systems, after six recycles. Also, additional batch experiments proved that the catalysts were successful on different terminal and internal epoxides
Controlled alcohol oxidation reactions by supported non-noble metal nanoparticles on chitin-derived N-doped carbons
No full textA series of catalysts based on non-noble metal nanoparticles supported on chitin-derived N-doped carbons was prepared through a one-step protocol in the presence of EDTA as a ligand. Both the complexing properties of EDTA and the interaction of metal precursors with the nitrogen sites on the support surface allowed a good dispersion and a homogeneous distribution of the metal active sites. The synthesized materials were tested in the catalytic oxidation of alcohols to aldehydes and ketones. Particularly, the model reaction of oxidation of benzyl alcohol showed that iron- and even more molybdenum-based materials exhibited the best performance. At 130 degrees C and 20 bar, in the presence of air as an oxidant, the Mo-N/C-catalyzed reactions proceeded with excellent conversion and selectivity, both above 90%, towards the product of partial oxidation, benzaldehyde, and the catalytic performance was retained over 5 recycling runs without any loss of activity. The Mo-based system proved effective also for the conversion of some representative benzyl- and furyl-type alcohols bearing primary and secondary hydroxyl functions to the corresponding aldehydes/ketones, though the oxidation of aliphatic substrates was unsuccessful. All catalysts together with the Mo-N/C sample recovered after its use were fully characterized following a multi-technique approach involving XRD, N-2-physisorption, XPS, and HRTEM-EDX analyses. Textural, morphological and chemical properties were thus compared and related to the observed trend of catalytic activity
Upcycling of Chitin to Cross-Coupling Catalysts: Tailored Supports and Opportunities in Mechanochemistry
Full text linkIn this study chitin derived from shrimp shells was used in the design of heterogeneous Pd-based catalysts for Heck and Suzuki-Miyaura cross-coupling reactions. The synthesis of Pd nanoparticles supported on N-doped carbons was performed through different approaches, including a sustainable mechanochemical approach, by using a twin-screw extruder. All catalytic systems were characterized by a multitechnique approach and the effect of nanoparticles size, N-doping on the support, and their synergistic interactions were elucidated. Specifically, Kelvin Probe Atomic Force Microscopy provided valuable insights on charge transfer and metal-support interactions. The catalytic behaviour of the samples was investigated in cross-coupling reactions under batch conditions and under semi-continuous flow solvent-free conditions, respectively obtaining a quantitative yield and a noteworthy productivity of 8.7 mol/(gPdh)
Catalytic screening of the cascade reductive amination reaction of furfural and acetonitrile
No full textThe reductive amination reaction of furfural with acetonitrile has been explored employing various catalytic systems based on supported Rh, Ru, Pt and Pd nanoparticles. The synthesis of Rh and Ru nanoparticles supported on titania was accomplished following an environmentally friendly two step-protocol, based on the microwave assisted preparation of TiO2 and its subsequent functionalization by an impregnation/chemical reduction method. Commercial Pd/C, Pt/C and Ru/C were additionally evaluated to get insights into the effect of the metal component into the reaction progress and the products selectivity. Interestingly, the metal component resulted to have a drastic influence into the selectivity of the reaction. In particular, catalytic materials based on rhodium supported on TiO2, led to the selective formation of the reductive amination products, namely towards the secondary and tertiary amines, derived from the hydrogenated furfural ring. In turn, ruthenium-based materials drove the reaction progress towards the hydrogenation of the carbonyl functionality and did not favor the hydrogenation of the furan ring, similar to the behavior observed for platinum system. Furthermore, palladium-based catalyst favored the hydrogenation of the aldehyde group and, moreover, led to the hydrogenation of the furan ring. Products characterization was carried out by GC-MS and NMR spectroscopies. Outstanding conversion (>99%) and selectivity (76%) values towards the N-ethyl-N-((tetrahydrofuran-2-yl)methyl)ethanamine were reached for the TiO2-Rh1% catalyst
Sustainable production of pharmaceutical, nutraceutical and bioactive compounds from biomass and waste
Full text linkThe aim of this tutorial review is to provide a general overview of processes, technologies and challenges in the production of pharmaceutical and bioactive compounds from food waste and lignocellulosic residues. Particular attention is given to benign-by-design processes instinctively devoted to environmental sustainability for the recovery of bioactive compounds from food waste as well as for the production of alcohols, acids, polyols, furans and aromatic compounds from lignocellulosic residues. At the same time, novel green synthetic routes for the production of active pharmaceutical ingredients and the development of novel bioactive compounds are discussed. Recent success industrial stories on the use of food waste and lignocellulosic residues for pharmaceutical and nutraceutical applications are also discussed. This journal i
Metal-Free N-Doped Carbons for Solvent-Less CO2 Fixation Reactions: A Shrimp Shell Valorization Opportunity
Full text linkHigh anthropogenic CO2 emissions are among the main causes of climate change. Herein, we investigate the use of CO2 for the synthesis of organic cyclic carbonates on metal-free nitrogen-doped carbon catalysts obtained from chitosan, chitin, and shrimp shell wastes, both in batch and in continuous flow (CF). The catalysts were characterized by N-2 physisorption, CO2-temperature-programmed desorption, X-ray photoelectron spectroscopy, scanning electron microscopy, and CNHS elemental analysis, and all reactivity tests were run in the absence of solvents. Under batch conditions, the catalyst obtained by calcination of chitin exhibited excellent performance in the conversion of epichlorohydrin (selected as a model epoxide), resulting in the corresponding cyclic carbonate with 96% selectivity at complete conversion, at 150 degrees C and 30 bar CO2, for 4 h. On the other hand, in a CF regime, a quantitative conversion and a carbonate selectivity >99% were achieved at 150 degrees C, by using the catalyst obtained from shrimp waste. Remarkably, the material displayed an outstanding stability over a reaction run time of 180 min. The robustness of the synthetized catalysts was confirmed by their good operational stability and reusability: ca. (75 +/- 3)% of the initial conversion was achieved/retained by all systems, after six recycles. Also, additional batch experiments proved that the catalysts were successful on different terminal and internal epoxides
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