Distinctive size effects of Pt nanoparticles immobilized on Fe3O4@PPy used as an efficient recyclable catalyst for benzylic alcohol aerobic oxidation and hydrogenation reduction of nitroaromatics

Abstract

Fe₃O₄@PPy composite microspheres have been synthesized using Fe₃O₄ microspheres as a chemical template in an ultrasonic treatment process. Pt nanoparticles (NPs) were immobilized on Fe₃O₄@PPy by using ethylene glycol (EG) and NaBH₄ as reducing agents. The information on the morphologies, sizes, and dispersion of Pt NPs of the as-prepared catalysts was verified by TEM, XRD, FTIR and XPS. As expected, the chemical reduction methods remarkably affected the size of Pt NPs (∼2.5 nm and ∼5.5 nm) and the prepared catalysts exhibited high catalytic activities as well as awesome stabilities for aerobic oxidation of benzylic alcohols and hydrogenation reduction of nitroaromatics. It was highlighted that size effects for the catalytic properties of the two reactions were found to be quite different. Fe₃O₄@PPy–Pt (2.5 nm) afforded a higher conversion for benzylic alcohol aerobic oxidation, while the selectivities toward benzaldehyde over these two catalysts were similar. However, they showed almost the same catalytic performance for hydrogenation reduction of a majority of nitroaromatics. What is more, Fe₃O₄@PPy–Pt (5.5 nm) gave better activities than several nitroaromatics, which were relatively difficult to be hydrotreated under the same conditions. In addition, the EG reduced Fe₃O₄@PPy–Pt catalyst exhibited slightly poorer stability than the NaBH₄ reduced Fe₃O₄@PPy–Pt catalyst in the recycle tests, which might be due to the agglomeration of small Pt NPs.