Sulfur-based thermochemical cycles, such as the hybrid sulfur-ammonia (HySA) cycle, offer a valuable approach in which hydrogen is produced by exploiting sulfur dioxide (potentially pollutant ...emissions) through the electrochemical oxidation of aqueous sulfite. In this study, the effect of pH on electrooxidation rate was assessed by comparing different reaction scenarios. Then, a Central Composite Design (CCD) combined with a Response Surface Methodology (RSM) was used to optimize batch electrooxidation of ammonium sulfite at near-neutral pH. Results show that the use of an anion exchange membrane (AEM) greatly improves sulfite electrooxidation rate while pH is effectively stabilized. Furthermore, a second-order model that relates applied potential and sulfite concentration with the normalized half-life of the reaction was obtained and verified experimentally at long-term batch electrooxidations. A good agreement between the model and experimental tests, adequate hydrogen recoveries and low sulfur crossover through the membrane demonstrate practical robustness of this approach.
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•Batch electrooxidation of ammonium sulfite is optimized at slightly alkaline media.•pH is stabilized in an electrochemical reactor by means of an anion exchange membrane.•A second-order model for electrooxidation rate estimation is obtained.•Long-term electrooxidation tests demonstrate robustness of the approach.
Thermochemical water splitting cycles (TWSCs) are processes with the potential for large-scale production of carbon-free hydrogen. Among these, the sulfur-family thermochemical cycles are considered ...the most promising due to both, the use of readily affordable chemical reagents and the temperature required to thermally decompose oxygenated sulfur compounds, which is achievable by solar means. Indeed, solar heat assisted metal sulfate decomposition is a key step, where catalysis can be employed to reduce decomposition temperature. Here we present a green route to synthesize Ag-Pd and Fe-Pd intermetallic alloy catalysts supported over γ-Al2O3 and Si-C by a microwave-assisted method using glycerol both as a solvent and as a reducing and stabilizing agent. The obtained supported catalysts were physicochemically characterized. Fe-Pd/Al2O3 catalyst exhibited the best performance, abating the zinc sulfate decomposition temperature by ca. 85 °C in comparison with other reported catalysts.
•Green supported catalysts for metal sulfate thermal decomposition were synthesized.•Glycerol proved to be an effective solvent, reducing and stabilizing agent.•FePd/Al2O3 is an economic and effective catalyst to be used in sulfur-family cycles.
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•Cu2O nanoclusters using onion waste extract (Allium cepa) were synthesized.•Heterojunction between “green” Cu2O and TiO2 exhibited a bandgap of 2.80 eV.•Green Cu2O/TiO2 showed ...superior performance to catalyze glycerol photoreforming.•Green heterojunction chemically stable, even after recycling no Cu2+ was evident.
A rapid and sustainable route for synthesizing a green photocatalyst based on nanometric Cu2O clusters dispersed on TiO2 (≈ 2 wt%) was developed. These nanoclusters were synthesized using reducing sugars (0.85 wt%) from aqueous onion waste (Allium cepa) as reducing and stabilizing agent. All this under microwave irradiation. Green photocatalysts produced hydrogen through glycerol photoreforming, ca. 4.7 mmol H2/gcat. The recyclability and reusability of these materials were demonstrated and the achieved heterojunction between Cu2O and TiO2 exhibited a bandgap within the visible spectrum at 2.80 eV, showing potential feasibility to solarize this process.
Recientemente, la modificación de aceites vegetales para obtener ésteres metílicos de ácidos grasos (FAMEs) o biodiesel ha emergido como una alternativa para la sustitución de los derivados del ...petróleo, esto debido a los problemas ambientales y de salud que genera su uso. Debido a su estructura química es posible epoxidar estas moléculas y usarlas directamente para producir plastificantes o lubricantes. Sin embargo, éstas también pueden ser sujetas a modificaciones para mejorar sus propiedades y el de servir como intermediarias para la síntesis de poliuretanos. Puesto que los métodos convencionales para la producción de epóxidos también son una fuente potencial de contaminación, se ha sugerido el uso de catalizadores enzimáticos como una alternativa sostenible o “Verde” para su preparación, ya que permiten obtener productos con alta pureza y mejores rendimientos. Este artículo presenta una revisión de la literatura disponible centrándose en la epoxidación enzimática de los FAMEs, así como sus principales aplicaciones.
Background
Malathion (
R,S
)-diethyl-2-(dimethoxyphosphorothioyl)sulfanylbutanedioate is a chiral organophosphorus compound used widely as pesticide for suppression of harmful insects such as ...mosquitoes. It is well known that in biological systems (
R
)-malathion is the active enantiomer, therefore a sustainable approach could be the use of only the biologically active enantiomer. The resolution of the commercial racemic mixture to obtain the pure active enantiomer combined with a recycling of the undesired enantiomer through a racemization process could be an attractive alternative to reduce the environmental impact of this pesticide. Thus, this work evaluates the use of four commercially available lipases for enantioselective hydrolysis and separation of malathion enantiomers from the commercial racemic mixture.
Results
Several lipases were methodologically assessed, considering parameters such as enzyme concentration, temperature and reaction rates. Among them,
Candida rugosa
lipase exhibited the best performance, in terms of enantioselectivity,
E
= 185 (selective to the (
S
)-enantiomer). In this way, the desired unreacted (
R
)-enantiomer was recovered in a 49.42 % yield with an enantiomeric excess of 87 %. The monohydrolized (
S
)-enantiomer was recovered and racemized in basic media, followed by esterification to obtain the racemic malathion, which was recycled. In this way, an enantioenriched mixture of (
R
)-malathion was obtained with a conversion of 65.80 % considering the recycled (
S
)-enantiomer.
Conclusion
This work demonstrated the feasibility of exploiting
Candida rugosa
lipase to kinetically resolve racemic malathion through an environmentally friendly recycling of the undesired (
S
)-enantiomer.
Graphical Abstract
Lipase catalyzed enantioselective resolution of (R)-malathion in aqueous solvent.
The sulfur-ammonia (SNH3) cycle uses the entire solar radiation spectrum to split water. It uses the UV radiation to promote the photolytic oxidation of ammonium sulfite to produce hydrogen and ...ammonium sulfate. Here, Raman and inelastic neutron scattering spectra of (NH4)2SO3·H2O at 20 K are discussed, supported by density functional theory (DFT) calculations. The feasibility of photolytic oxidation of this monohydrate to produce hydrogen at room temperature was also demonstrated.
Synopsis: Raman and inelastic neutron scattering spectra of (NH4)2SO3·H2O were discussed, DFT calculations were carried to support vibrational modes assignments. Feasibility to produce hydrogen through photolytic oxidation of such monohydrate was also demonstrated. Display omitted
•Photolytic oxidation of ammonium sulfite monohydrate in solid state was proven.•Vibrational modes of (NH4)2SO3, (NH4)2SO4, Na2SO3 were assigned.•INS spectrum of Na2SO3 was accurately reproduced by density functional theory.
A short and practical preparation of
α
-asarone was developed using the inexpensive methylisoeugenol as a starting material. The utilization of a sequence of tribromination, debromination, and ...copper-mediated aromatic substitution enabled the stereoselective formation of only the E-isomer of
α
-asarone in good yield.
A short and practical preparation of α-asarone was developed using the inexpensive methylisoeugenol as a starting material. The utilization of a sequence of tribromination, debromination, and ...copper-mediated aromatic substitution enabled the stereoselective formation of only the E-isomer of α-asarone in good yield.
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