Neutron studies of rare earth-modified zirconia catalysts and yttrium-doped barium cerate proton-conducting ceramic membranes

Abstract

The techniques of neutron scattering were applied to characterize two rare-earth containing ceramic systems: oxide-based automotive three-way catalysts and proton-conducting cerate-perovskite-based hydrogen-separation membranes. High-surface-area zirconias are widely used as catalytic support of noble metals in automotive three-way catalytic converters for exhaust gas treatment. Doping these oxides with rare-earth elements provides an important means in tailoring their properties for better catalytic performance. We have carried out in situ small-to-wide angle neutron diffraction at high temperatures and under controlled atmospheres to study the sintering behavior and the Ce 3+ ↔ Ce 4+ redox process in Ce x Zr 1− x O 2− δ solid solutions dispersed with Pt nanoparticles. We found substantial effects due to RE-doping on the nature of aggregation of nanoparticles, defect formation, crystal phase transformation, and metal-support interaction. Y-doped BaCeO 3 exhibits significant proton conductivity under a hydrogen-containing atmosphere at high temperatures. This system has high potential for applications as fuel-cell electrolytes, gas sensors, and ceramic membranes for hydrogen separation. We have performed in situ neutron diffraction to obtain information regarding the crystal phase evolution that permits dissolution of hydrogen and proton migration through the lattice. Neutron quasielastic- and inelastic-scattering experiments were carried out to investigate the proton dynamics from local vibrations to long-range diffusion.