Abstract
The dynamic oxygen mobility and oxygen storage capacity (OSC) on three-model three-way catalysts of Pt/CeO 2–ZrO 2 (CZ-O, CZ-D and CZ-R) was characterized by the 18 O/ 16 O isotopic exchange (IE) reaction combined with CO oxidation. The measured oxygen surface and bulk diffusion coefficients, OSC, and oxygen release rates were correlated with XRD spectra, surface areas, metal dispersions and the other physical parameters. We found that the oxygen mobility was parallel to the structural homogeneity of Zr introduction into the CeO 2 framework, decreasing as CZ-R > CZ-D > CZ-O. The oxygen diffusion coefficients over CeO 2–ZrO 2 oxides hinted us that oxygen species are mobile in the oxide support. In addition to the contribution to the space effect, we proposed a new insight to the role of zirconium atoms as carriers for the oxygen transfer, although further investigation is necessary. These results showed that the combined IE reaction could be counted as a reliable technique for qualifying the oxygen mobility, the OSC and oxygen release rates, and is expected to be a direct probe into the nature of CeO 2–ZrO 2 oxygen storage materials and further development of more efficient oxygen storage materials.
Highlights
Automotive exhaust is regarded as a major source to the atmospheric pollution
Through the combination with CO oxidation, 18O/16O isotopic exchange reaction had been upgraded to a compact technique for quantifying the oxygen migration on the surface and in the bulk of the oxides, the efficient oxygen storage capacity (OSC) and the oxygen release rate of the oxygen storage materials
The measured oxygen surface and bulk diffusivity, oxygen storage capacity and the oxygen release rates showed a good consistency with the homogeneity of the Zr distribution into the oxide framework, as CZ-R > CZ-D > CZ-O
Summary
Automotive exhaust is regarded as a major source to the atmospheric pollution. Along with the more stringent environmental regulations imposed on the automobile industry, more efficient catalysts are necessary to detoxify the harmful exhaust, and increasing efforts are being investigated to optimize the efficiency of three-way catalysts. In 1987, Duprez and coworkers developed a method of isotopic exchange for the study of surface mobility, and systematically studied the supported metal catalysts and some mixed oxides [9–13]. In order to establish a characterization method to quantify the oxygen mobility or spillover rates from the metal to the surface of the support and from the surface to the bulk, we applied 18O/16O isotopic exchange (IE) reaction technique onto three catalysts of Pt/CeO2–ZrO2, which have the same Ce/Zr ratio of 1:1 but different structures. The obtained results hopefully give us some hints for the actual catalyst formulation and maximize the efficient oxygen storage capacity of some certain oxygen storage material to the theoretical limit, to develop more efficient automotive three-way catalysts. Thereafter, Pt (1.0 wt.%) was supported by conventional impregnation using Pt (NH3)2(NO2) as platinum precursor and calcinations at 500 ◦C for 3 h in air
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