(484b) Insights into Influencing Factors on Oxygen Storage Characteristics for Ceria-Zirconia Catalysts

Ceria systems have been investigated extensively in the field of automotive catalysis as oxygen storage materials in order to compensate for deviating stoichiometric operation during exhaust aftertreatment. The ability of ceria to cycle between Ce⁴⁺ and Ce⁺³provides an attractive characteristic desirable for reactions such as water-gas shift, hydrocarbon oxidation, and hydrocarbon reforming [1]. Often, an additional dopant is added into the ceria lattice in order to increase oxygen storage capacity (OSC) and oxygen mobility, with ceria zirconia (CZO) being the most common system used [2]. The oxygen release rate (ORR) by these materials can be further enhanced by depositing platinum group metal (PGM) such as Pd or Rh, which provides beneficial metal-support interface in order for rapid oxygen transfer to occur [3]. While these catalytic materials have been in use, additional fundamental insight in the mechanism of OSC and the effect of PGM dispersion, CZO surface area, material pre-treatment, and varying testing conditions on catalyst performance are explored in this study.

A series of Pd/CZO catalysts was prepared by incipient wetness impregnation with different loadings and aged in redox conditions at high temperatures. Characterization by BET, H₂ chemisorption, and XRD will be discussed. OSC measurements were conducted via lambda probes before and after the catalyst as a function of temperature, while ORR were evaluated by the production of CO₂ as measured by FTIR as a function of time. Structure-activity relationships were developed to determine what factors were most important in achieving high OSC and fast ORR, particularly after high temperature aging. In addition, catalysts were evaluated for CO oxidation and water-gas shift to establish the importance of OSC in either reaction. Results from this study will help provide guidelines in the design of future oxygen storage materials in order to meet future emission standards.

[1] R. Gorte, AIChE Journal 56 (2010) 1126-1135

[2] E. Mamontov, et al., J. Phys. Chem. B 104 (2000) 11110-11116

[3] H.W. Jen, et al., Catal. Today 50 (1999) 309-328