High Oxygen Storage Capacity and High Rates of CO Oxidation and NO Reduction Catalytic Properties of Ce1−xSnxO2 and Ce0.78Sn0.2Pd0.02O2-δ

Abstract

Ce1−xSnxO2 (x = 0.1−0.5) solid solution and its Pd substituted analogue have been prepared by a single step solution combustion method using tin oxalate precursor. The compounds were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and H2/temperature programmed redution (TPR) studies. The cubic fluorite structure remained intact up to 50% of Sn substitution in CeO2, and the compounds were stable up to 700 °C. Oxygen storage capacity of Ce1−xSnxO2 was found to be much higher than that of Ce1−xZrxO2 due to accessible Ce4+/Ce3+ and Sn4+/Sn2+ redox couples at temperatures between 200 and 400 °C. Pd2+ ions in Ce0.78Sn0.2Pd0.02O2-δ are highly ionic, and the lattice oxygen of this catalyst is highly labile, leading to low temperature CO to CO2 conversion. The rate of CO oxidation was 2 μmol g−1 s−1 at 50 °C. NO reduction by CO with 70% N2 selectivity was observed at ∼200 °C and 100% N2 selectivity below 260 °C with 1000−5000 ppm NO. Thus, Pd2+ ion substituted Ce1−xSnxO2 is a superior catalyst compared to Pd2+ ions in CeO2, Ce1−xZrxO2, and Ce1−xTixO2 for low temperature exhaust applications due to the involvement of the Sn2+/Sn4+ redox couple along with Pd2+/Pd0 and Ce4+/Ce3+ couples.

High Oxygen Storage Capacity and High Rates of CO Oxidation and NO Reduction Catalytic Properties of Ce_1−xSn_xO₂ and Ce_0.78Sn_0.2Pd_0.02O_2-δ

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