Egg-like magnetically immobilized nanospheres: A long-lived catalyst model for the hydrogen transfer reaction in a continuous-flow reactor

A novel egg-like nanosphere was designed as a long-lived catalyst and is described as Fe₃O₄@nSiO₂-NH₂-Fe₂O₃·xBi₂O₃@mSiO₂. The catalyst was prepared using a modified Stöber method with template-free surface-protected etching. The catalyst particle consists of a magnetic Fe₃O₄ core as the "yolk", an inner silica shell bearing active Fe₂O₃·xBi₂O₃ species as the "egg white", and outer mesoporous silica as the "egg shell". It exhibits an excellent performance in the catalytic reduction of nitro aromatics to corresponding anilines in a fixed-bed continuous-flow reactor. The reaction could be performed at 80 ℃ and could reach complete conversion in less than 1 min with only a 7% excess of hydrazine hydrate. The catalyst bed could be easily shifted between different substrates without cross-contamination because of the uniformity of the catalyst particles. This catalyst exhibited very good stability in the continuous-flow protocol. In the long-term reduction of p-nitrophenol with 0.5 mmol·min^-1 productivity, it worked for more than 1, 500 cycles without any catalytic activity loss.