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Commercial micro/mesoporous activated carbons were utilized as metal-free catalysts for the desulfurization of a model fuel, i.e. 4,6-dimethyldibenzothiophene (4,6-DMDBT) in hexadecane under ambient conditions. Both adsorption and catalytic oxidation were investigated as means of 4,6-DMDBT removal. The effect of chemical modification/oxidation of the carbon surface via treatment with two different acids (HNO3 or H2SO4) aiming to introduce additional functional groups was also investigated. The catalysts were characterized by FT-IR spectroscopy, N2 porosimetry, potentiometric titration, Boehm titration, and SEM-EDX, while adsorption and catalytic oxidation activity towards sufloxides and sulfones were assessed by GC-MS and UV-Vis analysis. The surface chemistry of the carbons, expressed by the density of the acidic functional groups, was found to be the most critical parameter with regard to adsorption or to catalytic oxidative performance. The surface modification of carbons by oxidation had a positive impact on the catalytic oxidation activity, leading to a 100% conversion of 4,6-DMDBT towards the corresponding sulfoxide and sulfone, compared to 67% with the parent non-oxidized carbon. Reusability tests showed that the oxidation activity of the carbons can be maintained for at least 5 cycles. [ABSTRACT FROM AUTHOR]

Abstract: Furfural takes an important position in hemicelluloses biorefinery platforms. It can be converted into a wide range of chemicals. One important valorization route is the catalytic hydrogenation. Whereas molecular hydrogen is mostly used in industrial hydrogenation processes, recent studies also showed that alcohols can be used as reductants from which hydrides can be transferred catalytically to furfural. This process is often assisted by the formation of significant amounts of side products, in despite of high yields to the hydrogenolysis product 2‐methylfuran. The present work explores the catalytic behavior in batch and continuous flow of mono‐ and bimetallic nickel catalysts supported on activated carbon for the catalytic transfer hydrogenation of furfural in isopropanol. [ABSTRACT FROM AUTHOR]

[Display omitted] • Microwave-assisted alkyl levulinates production. • Furfuryl alcohol (FA) as starting material for batch production of alkyl levulinates. • Commercial activated carbon is an efficient acid catalyst system for the synthesis of alkyl levulinates. • The non stability of the activated carbon permitted to transfer heterogeneous catalysis to homogeneous catalysis. • Application to other alcohols than methanol gave lower yield of the corresponding alkyl levulinates. A cheap and commercially available non-metal activated carbon (AC) as an efficient catalyst for the alcoholysis of furfuryl alcohol (FA) to alkyl levulinate (AL) under microwave assistance was firstly investigated. The catalyst gave an impressive methyl levulinate (ML) yield of 78% in only 5 min at 170 °C in the presence of FA (0.2 M, 3 mL) and AC (100 mg). Various reaction parameters in dependence of time such as temperature, catalyst and feedstock loadings as well as solvent types have been optimized. The re-utilization experiments of the catalyst showed that the activity related to the acidic groups of the catalysts, and the deactivation was due to the leaching of acidic specie, which was easily extracted by the solvent. Note that extremely low concentration of the active species extracted from AC (less than 1 wt %) could also give 62% ML yield. The present study provided a promising way for AL synthesis over cheap, commercially available and environmentally benign catalyst. [ABSTRACT FROM AUTHOR]

The efficiency for deep desulfurization (removal of dibenzothiophene, DBT) of a benchmark commercial activated porous carbon (BAX) and its chemically modified counterparts was evaluated both by dynamic (fixed-bed column) and batch experiments. Oxidation of BAX led to alteration of various key physicochemical features, namely textural parameters and surface chemistry heterogeneity. These alterations affected controversially the desulfurization efficiency/capacity, since the effect was positive for batch tests but slightly negative for column tests. The oxidized sample BAX-O4 was the only one capable to decrease the initial concentration of sulfur from 20 to less than 10 ppmwS at the batch experiments. In case of the dynamic tests, even though a slightly faster exhaustion was observed for the oxidized samples, the adsorption kinetics were faster. It was also shown that oxidation of BAX resulted in denser column packing. Thus, a higher amount of adsorbent material per unit volume (bed density) can be achieved which will lead to increment of the column's desulfurization efficiency. Analysis of the breakthrough data by curve modeling showed that carbon-beds operated smoothly under equilibrium conditions. By detailed analysis and comparisons of the physicochemical features of the initial and exhausted samples as well as considering the fitting of the adsorption results at various kinetic models, it was feasible to determine the key removal mechanisms and the involved interfacial phenomena occurring during the adsorption. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Deep desulfurization starting from 20 ppmwS is affected by specific physicochemical features of carbon. • Oxidation of commercial carbons led to elevated deep desulfurization efficiencies. • Mixed model fuels were tested containing DBT, 4,6-DMDBT, benzene and naphthalene simultaneously. • DBT and 4,6-DMDBT compete against each other only at specific adsorption sites. • π-π stacking is the predominate mechanism for the adsorption of the thiophenic compounds. The main novel objective of this work is the evaluation of the adsorptive "deep" desulfurization efficiency under ambient conditions and studying in detail the effects arisen from the presence of competitors as in real fuels. Towards this direction, several activated carbons (commercially available and chemically modified/oxidized counterparts) were examined using a (diesel) model fuel containing initially 20 ppmwS of 4,6-dimethyldibenzothiophene (4,6-DMDBT) and 20 ppmwS of dibenzothiophene (DBT), as well as mono- and di-aromatic competitors, namely benzene and naphthalene, in hexadecane. To gain better insights regarding the adsorption sites, the involved mechanisms, and the impact/antagonistic effect arisen by the presence of the aromatics in high concentration, simpler model fuels were also utilized while emphasis was also given on exploring which physicochemical features, textural (N 2 adsorption) or surface chemistry (Boehm titration and surface pH measurements), play a key role. In all cases, the oxidation treatment enhanced the adsorption capacity of the carbons, despite a decrease on the porosity, by introducing additional surface functional groups, indicating that surface chemistry plays a vital role in adsorptive desulfurization and that difference in chemical nature adsorption sites exists. The best performing oxidized carbon (SX PLUS-ox) presented a 92.1% (5.2 mgS/g capacity) removal of DBT in hexane and a 67.7% 4,6-DMDBT removal (4.0 mgS/g) in pure hexadecane. In the case of 4,6-DMDBT in hexadecane, the addition/co-presence of the aromatics in low concentration led to slightly lower desulfurization of 57.8% (3.6 mgS/g), revealing the limited antagonistic effect due to the aromatics. When DBT was also present, the 4,6-DMDBT removal was 51.2% (3.5 mgS/g) while the DBT removal 50.9 % (3.6 mgS/g), leading to a high total thiophenic adsorption capacity of 7.1 mgS/g. Even with the addition of the mono- and di-aromatics with concentrations as in real diesel fuel, the best performing carbons after oxidation demonstrated a superior desulfurization performance, since >10 ppmwS can still be removed from the model fuel. The results designate that the oxidation of porous activated carbon can be considered as an effective materials design strategy in adsorptive deep desulfurization, since different oxygen containing surface functional groups that can act as adsorption sites are created and have a crucial selectivity towards thiophenes compared to the aromatics. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sunflower-derived adsorbents were efficiently applied against toxic elements in water. • Crucial adsorption parameters (pH, contact time) were discussed. • The equilibrium isotherm and kinetic modeling were analyzed. • Maximum adsorption capacity varied from 3.3 to 252.5 mg/g. • Enthalpy-entropy compensation effect was observed. In recent years, adsorption is assumed to be one of the most widely used and efficient, user-friendly, and low-cost (waste) water purification technique to remove a wide range of pollutants. From that scope, commercial activated carbons, are commonly used as adsorbents. However, due to some crucial disadvantages (e.g. high cost and incomplete regeneration) their use is limited. Agricultural waste/biomass/residues have attracted interest as alternative and efficient adsorbents because they can be utilized without any or after chemical treatment, or can be used as precursors to fabricate activated carbon or biochar. Moreover, agricultural wastes are renewable, inexpensive and abundantly available, essentially non-toxic, and environmentally friendly, thus satisfying the concept of Green or Sustainable Chemistry. This review article emphasizes on the utilization of sunflower-derived adsorbents to remove potentially toxic elements (PTEs) from aqueous media. The effect of crucial adsorption parameters (effect of initial pH, contact time etc.) is discussed in detail. Data obtained from adsorption experiments, thermodynamic and kinetic modeling, and desorption studies are presented and analyzed. The maximum adsorption capacity values obtained for sunflower adsorbents vary between 3.28 and 252.52 mg/g for PTEs, indicating that these materials could be satisfactorily used as alternative adsorbents. [ABSTRACT FROM AUTHOR]