Immobilized glucose oxidase on magnetic silica and alumina: Beyond magnetic separation.

Here we report immobilization of glucose oxidase (GOx) on magnetic silica (Fe3O4-SiO2) and alumina (Fe3O4-Al2O3) functionalized with amino groups using glutaraldehyde as a linker. Magnetic support based biocatalysts demonstrate high catalytic activity in d-glucose oxidation to D-gluconic acid at pH 5-7.5 and temperature of 30-50 °C with the best activities of 95% and 91% for magnetic silica and alumina, respectively. A comparison of magnetic and non-magnetic alumina and silica shows a significant enhancement of the relative catalytic activity for magnetic supports, while the silica based biocatalysts show a higher activity than the biocatalysts based on alumina. A noticeably higher activity of GOx immobilized on magnetic supports is explained by synergy of the GOx inherent activity and enzyme-like activity of iron oxide nanoparticles, while the enhancement with silica based catalysts is most likely due to a larger pore size and stronger Brønsted acid sites. Excellent relative activity of Fe3O4-SiO2-GOx (95% of native GOx) in a tolerant pH and temperature range as well as high stability in a repeated use (6% relative activity loss after five catalytic cycles) makes this catalyst promising for practical applications.

Facile Synthesis of Magnetically Recoverable Pd and Ru Catalysts for 4-Nitrophenol Reduction: Identifying Key Factors.

This paper reports the development of robust Pd- and Ru-containing magnetically recoverable catalysts in a one-pot procedure using commercially available, branched polyethyleneimine (PEI) as capping and reducing agent. For both catalytic metals, ∼3 nm nanoparticles (NPs) are stabilized in the PEI shell of magnetite NPs, whose aggregation allows for prompt magnetic separation. The catalyst properties were studied in a model reaction of 4-nitrophenol hydrogenation to 4-aminophenol with NaBH4. A similar catalytic NP size allowed us to decouple the NP size impact on the catalytic performance from other parameters and to follow the influence of the catalytic metal type and amount as well as the PEI amount on the catalytic activity. The best catalytic performances, the 1.2 min-1 rate constant and the 433.2 min-1 turnover frequency, are obtained for the Ru-containing catalyst. This is discussed in terms of stability of Ru hydride facilitating the surface-hydrogen transfer and the presence of Ru4+ species on the Ru NP surface facilitating the nitro group adsorption, both leading to an increased catalyst efficiency. High catalytic activity as well as the high stability of the catalyst performance in five consecutive catalytic cycles after magnetic separation makes this catalyst promising for nitroarene hydrogenation reactions.