Role of rare-earth dopants in nanophase zirconia catalysts for automotive211 emission control

摘要

Rare earth (RE) modification of automotive catalysts (e.g., ZrO(sub 2)) for211u001eexhaust gas treatment results in outstanding improvement of the structural 211u001estability, catalytic functions and resistance to sintering at high temperatures. 211u001eOwing to the low redox potential of nonstoichiometric CeO(sub 2), oxygen release 211u001eand intake associated with the conversion between the 3+ and 4+ oxidation states 211u001eof the Ce ions in Ce-doped ZrO(sub 2) provide the oxygen storage capacity that is 211u001eessentially to effective catalytic functions under dynamic air-to-fuel ratio 211u001ecycling. Doping tripositive RE ions such as La and Nd in ZrO(sub 2), on the other 211u001ehand, introduces oxygen vacancies that affect the electronic and ionic 211u001econductivity. These effects, in conjunction with the nanostructure and surface 211u001ereactivity of the fine powders, present a challenging problem in the development 211u001eof better ZrO(sub 2)-containing three-way catalysts. We have carried out in-situ 211u001esmall-to-wide angle neutron diffraction at high temperatures and under controlled 211u001eatmospheres to study the structural phase transitions, sintering behavior, and 211u001eCe(sup 3+) (leftrightarrow) Ce(sup 4+) redox process. We found substantial 211u001eeffects due to RE doping on the nature of aggregation of nanoparticles, defect 211u001eformation, crystal phase transformation, and metal-support interaction in ZrO(sub 211u001e2) catalysts for automotive emission control.