Cobalt-entrenched N-, O-, and S-tridoped carbons as efficient multifunctional sustainable catalysts for base-free selective oxidative esterification of alcohols
| Autor: | Pawan Kumar, Giorgio Zoppellaro, Manoj B. Gawande, Ondřej Tomanec, Claudia Aparicio, Rajender S. Varma, Martin Petr, Devaki Nandan, Ivo Medřík, Radek Zbořil |
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| Rok vydání: | 2018 |
| Předmět: |
inorganic chemicals
Reaction mechanism Carbonization chemistry.chemical_element 02 engineering and technology 010402 general chemistry 021001 nanoscience & nanotechnology 01 natural sciences Pollution Nanomaterial-based catalyst 0104 chemical sciences Catalysis chemistry.chemical_compound chemistry Benzyl alcohol Environmental Chemistry Organic chemistry 0210 nano-technology Cobalt oxide Carbon Cobalt |
| Zdroj: | Green Chemistry. 20:3542-3556 |
| ISSN: | 1463-9270 1463-9262 |
| Popis: | We report the synthesis of sustainable and reusable non-noble transition-metal (cobalt) nanocatalysts containing N-, O-, and S-tridoped carbon nanotube (Co@NOSC) composites. The expensive and benign carrageenan served as the source of carbon, oxygen, and sulfur, whereas urea served as the nitrogen source. The material was prepared via direct mixing of precursors and freeze-drying followed by carbonization under nitrogen at 900 °C. Co@NOSC catalysts comprising a Co inner core and outer electron-rich heteroatom-doped carbon shell were thoroughly characterized using various techniques, namely, TEM, HRTEM, STEM elemental mapping, XPS, BET, and ICP-MS. The utility of the Co@NOSC catalyst was explored for base-free selective oxidative esterification of alcohols to the corresponding esters under mild reaction conditions; excellent conversions (up to 97%) and selectivities (up to 99%) were discerned. Furthermore, the substrate scope was explored for the cross-esterification of benzyl alcohol with long-chain alcohols (up to 98%) and lactonization of diols (up to 68%). The heterogeneous nature and stability of the catalyst facilitated by its ease of separation for long-term performance and recycling studies showed that the catalyst was robust and remained active even after six recycling experiments. EPR measurements were performed to deduce the reaction mechanism in the presence of POBN (α-(4-pyridyl-1-oxide)-N-tert-butylnitrone) as a spin-trapping agent, which confirmed the formation of ˙CH2OH radicals and H˙ radicals, wherein the solvent plays an active role in a nonconventional manner. A plausible mechanism was proposed for the oxidative esterification of alcohols on the basis of EPR findings. The presence of a cobalt core along with cobalt oxide and the electron-rich N-, O-, and S-doped carbon shell displayed synergistic effects to afford good to excellent yields of products. |
| Databáze: | OpenAIRE |
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