1,721,009 research outputs found
Synthesis of isopropyl levulinate from furfural: Insights on a cascade production perspective
No full textThe present work explores the production of isopropyl levulinate from furfural by a two-step microwave assisted cascade process. Furfural is a versatile biomass-derived industrial feedstock with high annual production volume. Alkyl levulinates are promising bio-based molecules with several applications in many sectors, in particular, as biofuels, blended with transportation fuels including biodiesel, these compounds can significantly reduce the formation of soot in engines. Thus, in the first step, the catalytic transfer hydrogenation of furfural to furfuryl alcohol was studied employing a simply "ad hoc" synthesized magnetically recoverable Cu catalyst and 2-propanol as H-donor. Subsequently, the alcoholysis of the previously obtained liquors rich in furfuryl alcohol or of neat furfuryl alcohol solutions to isopropyl levulinate was investigated using commercial solid acid catalysts such as niobium phosphate and Amberlyst sulfonic resins (A15 and A70).The cascade process resulted feasible leading to good furfuryl alcohol yields in the transfer hydrogenation process with Cu-Fe3O4 magnetic catalyst using much lower Cu to furfural molar ratios than commonly reported. The subsequent alcoholysis step of furfuryl alcohol-rich liquors was highly efficient with A70 resin even in presence of unreacted furfural from the first step
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
Orthogonal assisted tandem reactions for the upgrading of bio-based aromatic alcohols using chitin derived mono and bimetallic catalysts
Full text linkThe upgrading of a benzyl-type alcohols was explored via an orthogonal tandem sequence comprised of a first oxidative step producing the corresponding aldehydes, and a subsequent reductive amination to achieve both secondary and tertiary amines. To the scope, acetonitrile (ACN) was used as a solvent and a source/precursor of reactant amines, and different heterogeneous catalysts based on Rh and Mo, were designed as mono- and bi-metallic systems in the form of metal nanoparticles dispersed on a chitin-derived N-doped carbons. A parametric analysis carried out separately for the oxidation and the reductive amination allowed to choose the best performant catalyst for both the reactions of the tandem process. A one-pot two-step protocol was implemented accordingly: as an example, benzyl alcohol was quantitatively and selectively oxidised to benzaldehyde (>99%) which in turn, was converted to N-benzylethanamine (66%) or N-benzyl-N-ethylethanamine (60%) in the presence of [Rh(5%)-N/C-Mo(5%)]-N/C or [Rh(3%)-N/C-Mo(5%)]-N/C as catalysts, respectively. The tandem sequence proved successful also for other bio-based benzyl-type alcohols that afforded the corresponding secondary/tertiary amines in yields up to 53-93%. Overall, the study proved the viability of an innovative method aimed not only at process intensification for multistep synthesis, but also at the valorization of substrates (alcohols) and biopolymers (chitin) derived from biomass
Solar-simulated light response of Au nanoparticles supported on TiO2 in the CO photo-oxidation in H2-rich stream
No full textHighly Efficient Solar-Light-Driven Photodegradation of Metronidazole by Nickel Hexacyanoferrate Nanocubes Showing Enhanced Catalytic Performances
Full text linkEnvironmental pollution is a complex problem that threatens the health and life of animal and plant ecosystems on the planet. In this respect, the scientific community faces increasingly challenging tasks in designing novel materials with beneficial properties to address this issue. This study describes a simple yet effective synthetic protocol to obtain nickel hexacyanoferrate (Ni-HCF) nanocubes as a suitable photocatalyst, which can enable an efficient photodegradation of hazardous anthropogenic organic contaminants in water, such as antibiotics. Ni-HCF nanocubes are fully characterized and their optical and electrochemical properties are investigated. Preliminary tests are also carried out to photocatalytically remove metronidazole (MDZ), an antibiotic that is difficult to degrade and has become a common contaminant as it is widely used to treat infections caused by anaerobic microorganisms. Under simulated solar light, Ni-HCF displays substantial photocatalytic activity, degrading 94.3% of MDZ in 6 h. The remarkable performance of Ni-HCF nanocubes is attributeto a higher ability to separate charge carriers and to a lower resistance toward charge transfer, as confirmed by the electrochemical characterization. These achievements highlight the possibility of combining the performance of earth-abundant catalysts with a renewable energy source for environmental remediation, thus meeting the requirements for sustainable development
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)
Promoting effect of rhodium on Co/ZnAl2O4 catalysts for the catalytic combustion of hydrocarbons
No full textZinc aluminate (ZnAl) was used as support to obtain a series of rhodium-modified Co-ZnAl catalysts for the catalytic oxidation of propane and naphthalene. The catalysts were characterized by various techniques including N2 adsorption (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR), diffuse reflectance spectroscopy (DRS), FTIR and X-ray photoelectron spectroscopy (XPS), to correlate chemical and physical characteristics with catalytic properties. TPR and XPS techniques show the presence of segregated cobalt compounds, as well as cobalt species interacting with the support. Segregated cobalt species are considered responsible for the catalytic activity, due to their high reducibility. The addition of Rh promotes the reducibility of the cobalt compounds yielding to an increase in the surface content of Co2+. For propane oxidation, the best activity shown by the Rh(0.5)Co(5)-ZnAl sample could be associated with a synergic effect between rhodium and cobalt species. No specific effects were revealed due to the addition rhodium for the naphthalene oxidation
TIO2 Nanorods-Supported Gold Nanoparticles as Photocatalysts foe the CO Preferential Oxidation
No full textTitanium dioxide is a robust, nontoxic and inexpensive semiconductor that presents unique and remarkable photocatalytic properties. A wide range of semiconductors have been evaluated, but a general consensus of the current literature is that only TiO2 satisfies the key criteria demanded for a good photocatalyst, even though it possesses activity only under UV light excitation, owing to the quite wide band gap, and a rapid electron-hole pair recombination. The above mentioned limitations of TiO2 can be overcome to some extent by depositing on its surface noble metal nanoparticles, such as gold, and exploiting their localized surface plasmon resonance (LSPR). It is generally agreed that the catalytic activity of Au based catalysts depends on the size of the gold particles, but also the morphology/shape of nano-scale titania supports can exhibit significant effects on the performance of noble metal based catalysts [1].
Due to their unique photophysical and chemical properties, one-dimensional TiO2 nanorods seem to play a cooperative effect with Au-NPs.
This type of catalysts can be photoactive in the preferential oxidation of CO to CO2 in excess of H2 (CO-PROX). This reaction, usually carried out in the temperature range 40-200°C, is one of the most economical and efficient approaches to reduce the CO content of the on-board H2-rich gas streams produced by reforming of alcohols or hydrocarbons down to ppm level, before entering the proton exchange membrane fuel cell (PEMFC) for automative applications.
In the present work we report on the photo-response behaviour of a series of Au-NPs/TiO2 nanorods systems in the CO-PROX reaction under solar-spectrum irradiation at r.t. and atmospheric pressure.
Au nanoparticles (1.0 wt% nominal loading) were precipitated-deposited on TiO2 nanorods, previously synthesized by different procedures to obtain rutile/anatase pure phases and thermally treated at different temperatures to obtain mixed polymorph compositions.
The impact of the Au loading and the calcination temperatures of the nanorods on the structural, physico-chemical and photocatalytic properties of Au-TiO2 catalysts were investigated by means of ICP-OES, N2 physisorption, XRD, HRTEM, DRIFT UV-visible and XPS. Catalytic tests showed differences in activity and stability among the prepared catalysts.
Au/TiO2 nanorods appeared active, stable and selective in the photo-PROX, making this class of materials, coupled with solar-spectrum irradiation, a novel feasible approach to remove the trace amount of CO in H2-rich stream at low temperature
CO2 hydrogenation over Ru hydrotalcite-derived catalysts
Full text linkThe hydrogenation of CO2 over Ru catalysts is structure sensitive, the selectivity of the process can be driven either to the production of CH4 or CO depending on Ru particles and support features. Herein, Ru-based MgAl-HT (HT=hydrotalcite) derived catalysts with different Ru loadings (0.5, 1.0 and 2.0 wt%) and promoted with La3+ were prepared, characterized, and tested for CO2 methanation at high Gas Hourly Space Velocity values (480 L/gcat h) feeding a CO2/H2/N2 = 1/4/1 v/v mixture. The MgAlOx mixed oxide obtained after calcination at 600 °C and reduction provided weak, medium and mainly strong basic sites, able to activate the CO2 molecule, and hosted very small Ru nanoparticles (1–3 nm). However, the catalysts displayed a low activity in the low temperature range and a poor selectivity to CH4. The addition of La3+, despite contributing to the basicity, did not have any significant effect on performance. In a comparison between Ru- and Ni-HT-derived catalysts, tested under similar reaction conditions, Ni largely overperformed Ru
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