Versatile halloysite-supported core@shell nanoparticle for the elimination of automotive exhaust pollutants
Wei Jing Li, University of Michigan
Support collapse and metal sintering are two of the dominant deactivation mechanisms for three-way catalysts. In this study, we investigate how changing the support and active site structure can address these deactivation challenges. We study halloysite nanotubes (Al2Si2O5×2H2O), which exhibit versatile physical and chemical properties and high thermal resistance, as an alternative supporting material 1. Using core@shell architectures, where active Pd is encapsulated with porous CeO2, we compare the catalytic performance and stability when Al2O3 and halloysite are used as the supporting materials. We find that halloysite support imparted thermal stability for enhanced catalytic stability under long-term and high-temperature reaction conditions compared with Pd@6CeO2/Al2O3 catalysts.
To identify the best performing active site structure for halloysite-supported catalysts, we examine the role of active site placement by comparing Pd@CeO2 and CeO2@Pd core@shell architectures 2. By studying the activity and stability of these two catalysts at calcination temperatures up to 1100 °C, we find that CeO2@Pd/halloysite undergoes significant aggregation and structural collapse. CeO2@Pd/halloysite shows temperature sensitivity during the elevated thermal treatment, accompanied by the deterioration of catalytic activity. Pd@CeO2/halloysite exhibits lower light-off temperatures for NOX, CO and C3H8 conversion after 1100 °C aging in comparison, which is indicative of superior stability. Possible explanations for this improved catalyst structure and performance will be discussed.
References:
(1) Li, W. J.; Wey, M. Y. Sintering-Resistant, Highly Thermally Stable and Well-Dispersed Pd@CeO2/Halloysite as an Advanced Three-Way Catalyst. Sci. Total Environ. 2020, 707, 136137. https://doi.org/10.1016/j.scitotenv.2019.136137.
(2) Li, W. J.; Wey, M. Y. Design of a Thermally Resistant Core@shell/Halloysite Catalyst with Optimized Structure and Surface Properties for a Pd-Only Three-Way Catalyst. Appl. Catal. A Gen. 2020, 602, 117732. https://doi.org/10.1016/j.apcata.2020.117732.
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