The influence of κ-Ce2Zr2O8 content on three-way catalytic performance

Abstract

The CeO2-ZrO2 based oxide (CZ) with κappa-phase CZ (κ-Ce2Zr2O8) has been examined as a promising alternative to the traditional CZ used in the three-way catalysts (TWCs). However, forming pure κ-Ce2Zr2O8 requires huge energy, and it remains obscure whether more κ-Ce2Zr2O8 is better. Herein we synthesized a series of CZ with increasing κ-Ce2Zr2O8 content by increasing reduction time, as well as the supported Pd-only catalysts, for investigating the influence of κ-Ce2Zr2O8 content on TWC performance. The results evidenced that κ-Ce2Zr2O8 started to form at surface and gradually covered the whole surface. The crystal interface between κ-Ce2Zr2O8 and the cubic-phase matrix, was thus first increased but then decreased as the κ-Ce2Zr2O8 content increased from 0 % to 34.3 %. Interestingly, the presence of 19.8 % κ-Ce2Zr2O8 could dramatically improve the reducibility of CZ, making reduction temperature decrease from 598 ℃ to 446 ℃, however, further improvement was not achieved by increasing κ-Ce2Zr2O8. More importantly, the Pd-CZ interaction strength was found to be positively corelated with the amount of the mentioned crystal interface. The catalytic activity followed the similar variation tendency with the Pd-CZ interaction. Among them, Pd/CZ1 with 19.8 % κ-Ce2Zr2O8 showed the optimal catalytic performance. Based on the analyses, the improved TWC performance by κ-Ce2Zr2O8 was ascribed to the strengthened Pd-CZ interaction. Therefore, instead of increasing the κ-Ce2Zr2O8 content by consuming huge energy, constructing larger content of the mentioned crystal interface is more efficient for improving TWC performance.