Effect of oxygen storage materials on the performance of Pt-based three-way catalysts

Abstract

The cost of Pt is currently lower than that of Pd and Rh, however, Pt-based three-way catalysts (TWCs) have attracted less attention than Pd- and Rh-based TWCs. Consequently, the fundamental understanding of the properties of Pt-based TWCs remains insufficient. Herein, we demonstrate the effect of oxygen storage materials (OSMs), including CeO₂ and CeO₂–ZrO₂ solid-solutions having different ceria contents (20%, 45%, and 66%), on the three-way catalysis performance of Pt/OSMs using various spectroscopic observations in combination with kinetic studies. In comparative assessments of powdered and monolithic (honeycomb) catalysts, fresh Pt/OSM(100%CeO₂) and aged Pt/OSM(66%CeO₂) exhibited the highest NO conversion among their corresponding series, showing that Pt/OSM(66%CeO₂) is the most promising and stable among the TWCs. In situ CO adsorption infrared (IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) revealed that the Pt⁰ species loaded on OSMs having a higher ceria content were more electron-deficient. Operando IR and kinetic investigations suggested that increasing the ceria content in fresh Pt/OSMs enhanced not only the formation of nitrite species and their reactivity toward CO but also the resistance to CO poisoning during NO–CO reactions. In situ X-ray absorption spectroscopy (XAS) indicated that both Ce and Pt species in Pt/OSM catalysts are involved in NO–CO reactions through their redox cycles. In situ XAS in combination with X-ray diffraction (XRD) measurements revealed that the hydrothermal ageing treatment resulted in the aggregation of Pt particles and lattice contraction of CeO₂ in Pt/OSMs, causing severe degradation of the redox ability of Pt and Ce species and reducing the promoting effect of ceria on the formation of nitrites and their reactivity toward CO.