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•Stable Ru@C replica using β-CD with different substitution patterns were prepared.•Cyclodextrins were used as carbon precursors and metal complexing agents.•HP-β-CD-assisted ...catalysts afforded higher dispersion and reducibility of Ru species.•Ru@MC-HP catalysts displayed much higher hydrogenation activities than controls.•Enhanced activities attributed to a good balance between Ru dispersion and H2 spillover.
The present study is concerned with the preparation of ordered mesoporous carbons containing uniform dispersions of ruthenium nanoparticles by a hard-template method, based on the use of RuCl3 and cyclodextrin as respective sources of metal and carbon. The influence of chemical structure of the parent CD randomly methylated-β-CD (RAME-β-CD) and 2-hydroxypropyl-β-CD (HP-β-CD) and loading of the ruthenium source are studied in detail. The catalysts are carefully characterized by N2-adsorption, TEM, XRD, CO pulse chemisorption, TG-MS and H2-TPR. The most outstanding effect is obtained when HP-β-CD is used, allowing to stabilize small and reactive Ru particles (1–2 nm) in the carbon matrix, with a good compromise between immobilization, surface availability and hydrogen spillover effect. The catalytic systems prepared from HP-β-CD display remarkably high catalytic activities in the liquid-phase hydrogenation of various substrates while their reusability and robustness are also demonstrated.
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•Ru catalysts were prepared on different O- and N-containing carbon materials.•Different synthesis methods on active carbon and mesoporous carbon replica.•Surface properties greatly ...influence the rate of HMF oxidation to FDCA in water.
Different oxygen- and nitrogen-containing carbons were studied as supports of ruthenium catalysts for the alkaline aqueous-phase oxidation of 5-hydroxymethylfurfural (HMF) to the corresponding diacid 2,5-furandicarboxylic acid FDCA. The surface properties of catalyst support (active carbon or mesoporous carbon replicated from mesostructured silica) were suggested to be a key factor deeply influencing the oxidation rates of the different steps of this reaction of ruthenium nanoparticles. The results highlight that the HMF oxidation reaction in water does not well tolerate O-functional groups, which strongly adsorb water and then block access of the substrate to the active metal sites and decrease the reaction rates. N-containing carbons were anticipated to be beneficial for the acceleration of the first step of ruthenium-alcoholate species formation. The result was the opposite, with a detrimental effect on the reaction rate when the Ru precursor was reacted with the amine-functionalized surface.
•5-HMF was synthesized from glucose using niobium oxide/phosphate-carbon composites.•Cyclodextrins (native and modified) were used as raw materials in the HTC process.•Catalyst prepared from randomly ...methylated β-CD in low H2O volume are more efficient.•Performance depends on strategic positioning of catalyst in biphasic reaction medium.
Direct conversion of glucose to 5-hydroxymethylfurfural was studied in a biphasic system, with phosphated niobium oxide-carbon catalysts. We developed a facile approach to generate Nb-based composites with high metal loadings (∼ 20 %) through hydrothermal carbonization (HTC), followed by calcination and H3PO4 adsorption. Attention has been paid to the nature of oligosaccharide and amount of water used upon HTC. Catalysts were characterized by XRD, N2 adsorption, NH3-TPD, SEM-EDS and XPS. NbP@C-RB30 and NbP@C-RB15 prepared from randomly methylated β-CD in low volumes were found to be more efficient for HMF production, with yields of 32-34 % attained after 3 h in biphasic NaCl-water/methyl isobutyl ketone media. Notably, HTC route provided appropriate conditions for forming acidic Nb2O5 nanoparticles, dispersed and maintained over carbon microspheres, and enriched with surface P–OH. These features played an important role for an adequate distribution of the catalyst in the reaction medium composed of two immiscible solvents.
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Removal of heavy metals (Cu(II), Pb(II) and Zn(II)) from aqueous solution was investigated using native or saponified chicory pulp biomass. Firstly, carbohydrates constituted about 70% of pulp dried ...matter. The pectic fraction represented 12–14% of dried matter and about 51% of these pectic units were esterified by methanol. The pH of the zero net proton charge of the pulp ranged from 4.5 to 5. Native pulp contained numerous surface functional groups and their cation exchange capacity is 0.566 meq g⁻¹. After saponification of chicory pulp, the cation exchange capacity reached 0.959 meq g⁻¹ due to the demethylation of carboxylic groups from pectic polymers. Then, the kinetics and equilibrium of sorption were examined. A pseudo second-order kinetic model was used to correlate experimental data and to determine the kinetic parameters. The equilibrium sorption data fitted well with the Langmuir model and showed the following affinity order of the materials: Pb²⁺>Cu²⁺>Zn²⁺. The maximum adsorption capacities ranged from 0.215 to 0.315 mmol g⁻¹ for native pulp and from 0.341 to 0.507 mmol g⁻¹ for saponified pulp. Finally, competitive effects were observed in multi-metallic solution adsorption experiments.
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► Adsorption equilibrium studies of selected cyclodextrins on activated carbons. ► Activated carbons could spontaneously adsorb high contents of cyclodextrins. ► Use of modified ...cyclodextrins may improve the dispersion of the carbon particles. ► New insights into the role of cyclodextrins in the dispersion of carbon suspensions.
We have investigated the adsorption equilibrium of selected cyclodextrins onto activated carbons. A number of parameters were examined including the type of carbon material, the size of macrocyclic cavity, and the chemical nature of the oligosaccharide (e.g., neutral, anionic, or cationic cyclodextrin). Adsorption isotherm studies revealed that the maximum amount of cyclodextrin immobilized on the carbon surface is obtained for the native β-CD, while the adsorption capacity of the ionic cyclodextrins derivatives strongly depends on the net surface charge of the activated carbon. The affinity of cyclodextrins for activated carbons was further utilized to prepare modified activated carbons containing controlled amounts of cyclodextrins through an adsorption process. The resulting materials were characterized by N2 adsorption–desorption volumetric measurements, FTIR and Raman spectroscopy, while the quantitative determination of the oligosaccharide content on activated carbons was performed by gravimetric measurements. On the basis of the Turbiscan results, it was found that the chemical structure of cyclodextrins, which are incorporated in the carbon framework, had significant influence on the dispersibility and stabilization of the solid particles in water. Agglomeration and precipitation of the carbon particles were markedly suppressed with substituted cyclodextrins whose hydroxyl groups were partially substituted by methyl or alkylammonium groups.
Hydroxyapatite Ca
10
(PO
4
)
6
(OH)
2
, Ca-HA, is the emblematic mineral phase of bones, and is known for its complexity and difficult to reproduce chemical synthesis. Among the routes developed for ...obtaining this calcium phosphate, the so-called double-decomposition method is well described and often utilized. However, the Ca-HA synthesized by this way forms a larger mass of ammonium nitrate by-product than the desired product itself. Pure Ca-HA for orthopedic or dental applications usually uses thermal treatment to eliminate residual nitrogen compounds by releasing them in the atmosphere. Contemporary sol–gel methods currently in fashion produce even more degradation products including solvents and precursor organics. We now report on a green synthesis procedure which makes pure Ca-HA with minimum by-product. The synthesis calls for reacting phosphoric acid with calcium carbonate in water suspension to form a Ca-HA gel of fine particles. This gel can be filtered and the solids recovered, dried, and sintered, but can also be used as-is for environmental applications such as heavy metal ions or textile dye removal from polluted waste streams. This green Ca-HA has been used to trap heavy metals in flue gases and in municipal waste water treatment plants. This low-cost and low-environmental impact material can be developed for medical use because of its absence of impurities, and in catalytic productions for remediation of many environmental problems. Recent results show Ca-HA can also serve in reforming biogas compositions into useful products, after deposition of selected metal elements. Some of these results will be communicated in this paper.
BRIEFS Sulfonated mesoposous carbons efficiently catalyze the glycosylation of various monosaccharides with alkyl alcohols.
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•Sulfonated mesoporous carbons exhibit high catalytic ...performances in the glycosylation of glucose with fatty alcohols.•Mesoporous channel improved the glycosylation rate of carbohydrates, thus limiting the side formation of humins.•Limiting the formation of humins concomitantly limit the deactivation rate of the catalyst which was successfully recycled.•Sulfonated mesoporous carbons was found applicable from different carbohydrates and different alkyl alcohols.•Space time yields of the Fischer glycosylation reactions are in line with the industrial requirements of the field.
Herein we investigated the catalytic performances of sulfonated mesoporous carbons in the glycosylation of carbohydrates with alkyl alcohols. Catalytic performances were compared to common solid acid catalysts previously reported for this reaction. Under optimized conditions, the targeted alkyl glycosides were obtained in 85% yield, together with a turn over frequency and a space time yield higher than those of the best heterogeneous catalysts reported so far in such reaction. Furthermore, the presence of mesoporous channels significantly lowered the deactivation rate of the catalyst in comparison to a non-porous sulfonated carbon.
Coal combustion in power plant produces fly ash. Fly ash may be used in water treatment to remove mercury (Hg
2+) from water or to immobilize mercury mobile forms in silts and soils. Experiments were ...carried out on two kinds of fly ashes produced by two circulating fluidized bed plants with different chemical composition: silico-aluminous fly ashes and sulfo-calcic fly ashes. For the two kinds of fly ashes, adsorption equilibrium were reached in 3 days. Furthermore, removal of mercury was increased with increasing pH. Sulfo-calcic fly ashes allow us to remove mercury more efficiently and more steady. The chemical analysis of fly ash surface was carried out by electron spectroscopy. The results show that mercury is bound to ash surface thanks to several chemical reactions between mercury and various oxides (silicon, aluminium and calcium silicate) of the surface of the ashes.
The objective of this study is to optimize experimental conditions of sorbent preparation from sewage sludge using experimental design methodology. Series of carbonaceous sorbents have been prepared ...by chemical activation with sulfuric acid. The sorbents produced were characterized, and their properties (surface chemistry, porous and adsorptive properties) were analyzed as a function of the experimental conditions (impregnation ratio, activation temperature and time). Carbonaceous sorbents developed from sludge allow copper ion, phenol and dyes (Acid Red 18 and Basic Violet 4) to be removed from aqueous solution as well as VOC from gas phase. Indeed, according to experimental conditions, copper adsorption capacity varies from 77 to 83 mg
g
−1, phenol adsorption capacity varies between 41 and 53 mg
g
−1 and VOC adsorption capacities (acetone and toluene) range from 12 to 54 mg
g
−1. Each response has been described by a second-order model that was found to be appropriate to predict most of the responses in every experimental region. The most influential factors on each experimental design response have been identified. Regions in which optimum values of each factor were achieved for preparation of activated carbons suitable for use in wastewater and gas treatments have been determined using response surfaces methodology. In order to have a high mass yield and to minimize the energetic cost of the process, the following optimal conditions, 1.5 g of H
2SO
4 g
−1 of sludge, 700 °C and 145 min are more appropriate for use of activated carbon from sludge in water and gas treatments.
The pyrolysis of impregnated wood for the production of activated carbon is investigated. Laboratory experiments are performed in a TG for heating rates of 10
°C/min and 20
°C/min and a mathematical ...model for the kinetics of the pyrolysis process is developed and validated. The effect of the temperature and of the time duration of the pyrolysis process on the specific surface of the activated carbon is examined on the basis of experiments conducted in a crossed bed reactor. Results indicate that the temperature and the residence time in the pyrolysis reactor may be optimised. Indeed, it is found that the maximum specific surface of the end product is obtained for pyrolysis processes conducted at a temperature of 400
°C for a time period of 1
h.
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