Synthesis and characterization of iron-impregnated porous carbon spheres prepared by ultrasonic spray pyrolysis

Porous carbon microspheres impregnated with iron-based nanoparticles are prepared in a single step, continuous process using ultrasonic spray pyrolysis (USP). Precursor solutions containing a carbon source, an inorganic salt, and an iron salt are ultrasonically aerosolized and pyrolyzed. Solutions containing nitrate or chloride salts are examined. During pyrolysis, sucrose is dehydrated to carbon, and the metal salt is converted to crystalline or non-crystalline iron species, depending on processing conditions. The product's porosity is generated from: (1) aromatization of carbon around an in situ template, (2) in situ gasification of isolated carbon, or (3) in situ chemical activation of the carbon precursor. Porous carbon spheres (0.5-3 μm diameter) containing well-dispersed iron oxide nanoparticles (4-90 nm diameter), referred to here as Fe-C, are prepared. Iron loadings between 1 and 35 wt.% are achieved while maintaining well-dispersed Fe nanoparticles with as-produced surface areas up to 800 m²/g. Post-pyrolysis heat and hydrogen treatments increase the surface area of the materials while reducing iron species. USP Fe-C materials may have useful catalytic applications due to their potential for high-loading of well-dispersed metal nanoparticles. Despite negligible surface Fe content, chromium reduction tests indicate that internal Fe sites are catalytically active.