Effect of Bi 2O 3 content on characteristics of Bi 2O 3–GDC systems for direct methane oxidation

Abstract

Ceramic systems of Bi 2O 3 and gadolinia-doped ceria (GDC) solid mixture were prepared as catalysts for direct methane oxidation. These systems were characterized by temperature-programmed reduction using hydrogen and carbon monoxide, temperature-programmed reaction of methane, fixed-temperature direct methane oxidation, and X-ray diffraction analysis. Adding Bi 2O 3 to GDC promotes both hydrogen and CO oxidation activities, because of the presence of surface Bi 2O 3 and the high content of mobile oxygen in Bi 2O 3. The reactivity of CO with surface lattice oxygen is enhanced to a higher extent than that of H 2, and this enhanced extent shows a maximum in Bi 2O 3 content. Such a maximum also exists for the catalytic activity of direct methane oxidation. A synergistic effect occurs due to a combination of the high methane reactivity of GDC and the high content of mobile oxygen in Bi 2O 3. The CO 2 selectivity of direct methane oxidation can be modulated by varying the Bi 2O 3 content. The mixing of Bi 2O 3 with GDC also increases the self-de-coking capability of the catalyst during direct methane oxidation, which stabilizes the activity.