(CoFeMnCuNiCr)₃O₄ High-Entropy Oxide Nanoparticles Immobilized on Reduced Graphene Oxide as Heterogeneous Catalysts for Solvent-Free Aerobic Oxidation of Benzyl Alcohol

Abstract

The development of noble metal-free heterogeneous catalysts holds promise for the solvent-free and selective aerobic oxidation of organic compounds. However, the moderate activity of these catalysts under atmospheric conditions limits their industrial use. In this work, the synthesis of noble metal-free (CoFeMnCu-NiCr) 3 O 4 high-entropy oxide (HEO) nanoparticles and their grafting on reduced graphene oxide (rGO) to produce a HEO− rGO nanocomposite is detailed. X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman and Mossbauer spectroscopy analyses confirm the formation of the spinel HEO phase. HEO−rGO nanocomposites are used for aerobic and solvent-free oxidation of benzyl alcohol, displaying excellent catalytic performance. Up to 10.36% conversion and 78.5% selectivity of benzaldehyde can be achieved in only 4 h. An extensive analytical study shows that the excellent performance of HEO−rGO nanocomposites is attributed to the synergistic effect between the rGO active sites and the abundant oxygen vacancies within the HEO nanoparticles. Moreover, four robust machine learning models including Adaptive Boosting (AdaBoost), Categorical Boosting (CatBoost), Random Forest (RF), and eXtreme Gradient Boosting (XGBoost) are applied to predict the selectivity of the oxidation reactions. The XGBoost is demonstrated as the best-fitting model for all data with an error of less than 2.5%. Overall, both experimental and numerical data suggest the potential application of the HEO−rGO nanocomposites in chemical industries for the selective oxidation of alcohols to added-value products.

La(FeCuMnMgTi)O3 High-Entropy Oxide Nanoparticles as Highly Efficient Catalysts for Solvent-Free Aerobic Oxidation of Benzyl Alcohol

“…The Raman spectrum of the La­(FeCuMnMgTi)­O 3 HEO nanoparticles reveals a distinct broad asymmetric band at 493 cm –1 and a low-intensity band at 1307 cm –1 (Figure b). Moreover, the HEO showcases six main Raman bands at 125, 198, 336, 645, and 1307 cm –1 , providing compelling evidence of their consistency with similar structures . The presence of a 645 cm –1 band emphasizes the existence of distinct cubic units within the lattice structure.…”

“…This method often uses toxic solvents and has safety concerns . To align these oxidation reactions with green chemistry, it is essential to develop milder catalytic reaction processes that eliminate the need for harmful solvents and oxidizing agents, reducing their environmental impact and improving safety and economic feasibility. , Recent studies have demonstrated that metal heterogeneous catalysts can selectively oxidize alcohols without the need for additional oxidizing agents in a solvent-free manner under mild conditions. , In this regard, the development of high-performance heterogeneous catalysts for aerobic solvent-free oxidation of benzyl alcohol to key commercial raw materials is an important topic.…”

High Entropy Oxides: Mapping the Landscape from Fundamentals to Future Vistas

“…(j) Recyclability test of the HEO-rGO catalyst for the solvent-free oxidation of PhCH 2 OH. Panels (h–j) are adapted with permission from ref . Copyright 2024 American Chemical Society.…”

“…However, Mehrabi-Kalajahi et al’s study outlined the synthesis of noble metal-free NPs composed of (CoFeMnCu-NiCr) 3 O 4 HEO and their subsequent grafting onto reduced graphene oxide (rGO) to form a HEO-rGO composite material . The HEO-rGO nanocomposites exhibited exceptional performance in the aerobic and solvent-free oxidation of PhCH 2 OH.…”