Synthesis and characterization of sintering-resistant silica-encapsulated Fe_3O_4 magnetic nanoparticles active for oxidation and chemical looping combustion

摘要

A nanocomposite catalyst composed of ferromagnetic magnetite cores (15.5 2.0nm) and silica shells with a thickness of 4.5 1.0nm (Fe_3O _4@SiO_2) was prepared by a two-step microemulsion-based synthesis. X-ray photoelectron spectroscopy and Raman spectroscopy after oxidation support the presence of a stable Fe_3O_4 core and a surface phase of γ-Fe_2O_3. The nanocomposite structure exhibited 100% conversion of CO in oxygen at a residence time of 0.1s at 310 °C. When pre-oxidized, the Fe_3O_4@SiO _2 catalyst is shown to be a suitable solid oxygen carrier for chemical looping combustion of methane at 700 °C. The nanocomposites retain their magnetism following the reaction which provides the potential for use of magnetic separation and capture in moving bed reactor applications. The core magnetite within the silica shell is resistant to sintering and a bulk phase transition to temperatures as high as 700 °C. These catalysts can be of use in applications of high temperature applications where catalyst recovery by magnetic separation may be required.