Transmission electron microscopic observation on reduction process of copper–iron spinel catalyst for steam reforming of dimethyl ether

The reduction process of copper–iron spinel oxide, which is active for steam reforming of dimethyl ether after mixing with alumina, has been investigated by a transmission electron microscope (TEM), scanning TEM (STEM), and energy dispersive X-ray (EDX) analyzer. The catalyst preparation was started from formation of well-sintered CuFe2O4 by calcination in air at 900 °C. After reduction of CuFe2O4 with hydrogen at 250 °C, metallic copper grains were developed on reduced spinel surface by the phase separation from the oxide. Strong chemical interaction between deposited Cu and reduced spinel oxide was expected from their intimate interfacial contact and lattice matching. The reduced sample contained metallic Cu, reduced spinel, and spinel oxide with super-lattice structure. Partial elimination of Cu and lattice oxygen resulted in formation of pores in and between the oxide grains. The size of the deposited Cu particle and Cu grain was largely distributed. After heating at higher temperature of 350 °C, the large spinel oxide particles are decomposed into small particles via formation of cracks. The resultant catalyst powder was very porous and consisted of very small particles of Cu, iron oxide, and spinel oxide. STEM–EDX analyses clarified the phase separation process of metallic Cu and iron oxide from host CuFe2O4 upon reduction.