RESUMEN

Alcohol groups and ß-O-4 (C-C) linkages are widespread in biomass feedstock that are abundant renewable resource for value-added chemicals. The development of sustainable protocols for direct oxidation or oxidative cleavage of feedstock materials in a controlled fashion, using open air as an oxidant is an intellectually stimulating task to produce industrially important value-added carbonyls. Further, the oxidative depolymerization of lignin into fine chemicals has evoked interest in recent times. Herein, we report the first example of a catalyst system that could activate molecular oxygen from atmospheric air for controlled oxidation and oxidative cleavage/depolymerization of feedstock materials such as alcohols, ß-O-4 (C-C) linkages and real lignin in water under open air conditions. The selectivity of carbonyl products is controlled by altering the pH between ~7.0 and ~12.0. The current strategy highlights the non-involvement of any external co-catalyst, oxidant, radical additives, and/or destructive organic solvents. The catalyst shows a wide substrate scope and eminent functional group tolerance. The upscaled multigram synthesis using an inexpensive catalyst and easily available oxidant evidences the practical utility of the developed protocol. A plausible mechanism has been proposed with the help of a few controlled experiments, and kinetic and computational studies.

RESUMEN

The synthesis of carbonyl derivatives from renewable feedstocks, by direct oxidation/functionalization of activated and unactivated C(sp3)-H bonds under a controlled and predictably selective fashion, especially in late stages, remains a formidable challenge. Herein, for the first time, cost-effective and widely applicable protocols for controlled and predictably selective oxidation of petroleum waste and feedstock ingredients like methyl-/alkylarenes to corresponding value-added carbonyls have been developed, using a surfactant-based oxodiperoxo molybdenum catalyst in water. The methodologies use hydrogen peroxide (H2O2) as an environmentally benign green oxidant, and the reactions preclude the need of any external base, additive, or cocatalyst and can be operated under mild eco-friendly conditions. The developed protocols show a wide substrate scope and eminent functional group tolerance, especially oxidation-liable and reactive boronic acid groups. Upscaled multigram synthesis of complex steroid molecules by late-stage oxidation proves the robustness and practical utility of the current protocol since it employs an inexpensive recyclable catalyst and an easily available oxidant. A plausible mechanism has been proposed with the help of few controlled experiments and kinetic and computational studies.

Asunto(s)

RESUMEN

Depolymerization of lignin biomass to its value-added chemicals and fuels is pivotal for achieving the goals for sustainable society, and therefore has acquired key interest among the researchers worldwide. A number of distinct approaches have evolved in literature for the deconstruction of lignin framework to its mixture of complex constituents in recent decades. Among the existing practices, special attention has been devoted for robust site selective chemical transformation in the complex structural frameworks of lignin. Despite the initial challenges over a period of time, oxidation and oxidative cleavage process of aromatic building blocks of lignin biomass toward the fine chemical synthesis and fuel generation has improved substantially. The development has improved in terms of cost effectiveness, milder reaction conditions, and purity of compound individuals. These aforementioned oxidative protocols mainly involve the breaking of C-C and C-O bonds of complex lignin frameworks. More precisely in the line with environmentally friendly greener approach, the catalytic oxidation/oxidative cleavage reactions have received wide spread interest for their mild and selective nature toward the lignin depolymerization. This mini-review aims to provide an overview of recent developments in the field of oxidative depolymerization of lignin under greener and environmentally benign conditions. Also, these oxidation protocols have been discussed in terms of scalability and recyclability as catalysts for different fields of applications.

Asunto(s)

RESUMEN

An advanced approach with DNA-mediated bismuth tungstate (Bi2WO6) one-dimensional (1-D) nanochain assemblies for hydrogen production with 5-fold enhanced photoelectrochemical (PEC) water splitting reaction is presented. The creation of new surface states upon DNA modification mediates the electron transfer in a facile manner for a better PEC process. The UV-Vis-DRS analysis results a red shift in the optical absorption phenomenon with the interference of DNA modification on Bi2WO6, and, thus, the band gap was tuned from 3.05 eV to 2.71 eV. The applied bias photon-to-current efficiency (ABPE) was calculated and shows a maximum for the Bi2WO6@DNA-2 (25.22 × 10-4%), compared to pristine Bi2WO6 (7.76 × 10-4%). Furthermore, the idea of practical utility of produced hydrogen from PEC is established for the first time with photocatalytic feedstock conversion to platform chemicals using cinnamaldehyde, 2-hydroxy-1-phenylethanone, and 2-(3-methoxyphenoxy)-1-phenylethanone in large scale by hydrogenation and/or hydrogenolysis reactions under eco-friendly green conditions with external hydrogen pressure in an aqueous mixture. Also, the recyclability experiment delivered good yields, which further confirm the robustness of the developed catalyst.

Asunto(s)

RESUMEN

Highly efficient and earth-abundant elements capable of water reduction by electrocatalysis and are attractive for the sustainable generation of fuels. Among the earth-abundant metals, copper is one of the cheapest but often the most neglected choice for the hydrogen evolution reaction (HER) due to its high overvoltage. Herein, for the first time we have tuned the overpotential of copper by tellurizing it by two different methodologies, viz. hydrothermal and wet chemical methods, which form copper telluride nanochains and aggregates. The application of copper telluride as an electrocatalyst for the HER gave fruitful results in terms of both activity and stability. The hydrothermally synthesized catalyst Cu2-xTe/hyd shows a low overpotential (347 mV) at 10 mA cm-2 toward the HER. In addition, the catalyst showed a very low charge transfer resistance (Rct) of 24.4 Ω and, as expected, Cu2-xTe/hyd exhibited a lower Tafel slope value of 188 mV/dec in comparison to Cu2-xTe/wet (280 mV/dec). A chronoamperometry study reveals the long-term stability of both catalysts even up to 12 h. The Faradaic efficiency of Cu2-xTe/hyd was calculated and found to be 95.06% by using gas chromatographic (GC) studies. Moreover, with the idea of utilizing produced hydrogen (H2) from electrocatalysis, for the first time we have carried out feedstock conversion to platform chemicals in water under eco-friendly green conditions. We have chosen cinnamaldehyde, 2-hydroxy-1-phenylethanone, 4-(benzyloxy)benzaldehyde, and 2-(3-methoxyphenoxy)-1-phenylethanone (ß-O-4) as model compounds for feedstock conversion by hydrogenation and/or hydrogenolysis reactions in aqueous medium using external hydrogen pressure. This protocol could also be scaled up for large-scale conversion and the catalyst is likely to find industrial application since it requires an inexpensive catalyst and an easily available, mild reducing agent. The robustness of the developed catalyst is proven by recyclability experiments and its possibility of use in real-life applications.

RESUMEN

A material with interdisciplinary properties is of wide interest for use in environmental applications. Currently, hydrogen generation by electrolysis and formation of carbonyl derivatives from alcohols are two different fields that focus on energy and environmental applications. In this work, a new material, Cobalt Tungsten Oxide Hydroxide Hydrate (CTOHH) on deoxyribonucleic acid (DNA) scaffold having chain-like morphology has been prepared for the first time by a facile microwave heating method. The same CTOHH was also prepared without the DNA scaffold and resulted in irregular aggregated molecular structures. Further, both CTOHH-DNA and CTOHH were converted into CoWO4-DNA and CoWO4, respectively by annealing them at a temperature of 600 °C. All the four catalysts were used for electrocatalytic oxygen evolution reaction (OER) and for oxidation of aromatic alcohols. In OER, CTOHH-DNA delivered fruitful results compared to all other electrocatalysts. For attaining a current density of 10 mA cm-2, it just required an overpotential of 355 mV with a Tafel slope value of 47.5 mV dec-1. Similarly, all four catalysts were also analyzed for selective and controlled oxidation of aromatic alcohols to their respective aldehydes and ketones using molecular oxygen as a green oxidant where CTOHH-DNA showed better results. Chemo-selectivity has been observed for CTOHH-DNA in the co-presence of hydroxyl and cyano functional groups. The durability of CTOHH-DNA was analyzed and it showed excellent catalytic activity retention up to five cycles.

Asunto(s)