Supercritical CO2-facilitating large-scale synthesis of CeO2 nanowires and their application for solvent-free selective hydrogenation of nitroarenes

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Abstract
Ceria nanowires were synthesized on a large scale by a simple, efficient, and environmentally benign strategy using supercritical (SC) CO2 expanded ethanol as reaction medium. Morphological characterization by SEM and TEM showed that most of the nanowires were bundles composed of individuals oriented parallel to each other throughout the whole length of the nanowires. Statistical data from AFM measurements showed that approximately 10% ceria nanowires (bundles/individuals) were ultrafine ones with diameters less than 5 nm. The effects of precursor concentration, reaction time and CO2 pressure on the formation of nanowires were studied, and it was found that SC CO2 played a key role in the evolution of the nanowires. As such, a possible formation mechanism for the as-prepared nanowires was provided. Moreover, the synthesis strategy was proved to be applicable to other rare earth oxide (La2O3, Eu2O3) nanowire preparation. Additionally, we successfully decorated ceria nanowires with ultrafine Pt nanoparticles via a sonication-facilitating deposition method. The as-prepared Pt-CeO2 showed superior catalytic activity and good selectivity for the solvent-free hydrogenation of nitrobenene and o-chloronitrobenzene.

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