First-principles investigation on the segregation of Pd at LaFe 1-x Pd x O 3-y surfaces
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NANO EXPRESS
Open Access
First-principles investigation on the segregation of Pd at LaFe1-xPdxO3-y surfaces Zhi-xue Tian1, Akifumi Uozumi2, Ikutaro Hamada3, Susumu Yanagisawa4, Hidetoshi Kizaki1, Kouji Inagaki1 and Yoshitada Morikawa1,5*
Abstract First-principles calculations were performed to investigate the effect of Pd concentration and oxygen vacancies on the stability of Pd at LaFeO3 surfaces. We found a much stronger tendency of Pd to segregate by taking the aggregation of Pd at LaFe1-xPdxO3-y surfaces into consideration, resulting in a pair of Pd-Pd around a vacancy. Moreover, we predicted that one oxygen-vacancy-containing FeO2-terminated surfaces would be stable at high temperatures by comparing the stability of LaFe1-xPdxO3-y surfaces, which further supports our previous conclusion that a Pd-containing perovskite catalyst should be calcined at 1,073 K or higher temperatures in air to enhance the segregation of Pd in the vicinity of surfaces to rapidly transform the Pd catalyst from oxidized to reduced states on the perovskite support. Keywords: Perovskite, LaFeO3, Palladium, Density functional theory, Surface segregation
Background A three-way catalyst simultaneously transforms toxic exhaust emissions from motor vehicles into harmless gases. However, the sintering problem, i.e., the growth and agglomeration of precious metal particles on conventional catalysts during vehicle use dramatically degrades catalytic activity, and large amounts of precious metals are required to retain the activity of catalysts after long periods of use. Thus, intelligent catalysts have attracted worldwide attention due to their greatly improved durability as a result of the self-regenerative function of precious metal nanoparticles [1-3]. It has been confirmed that the activity of catalysts can be preserved, and the amount of precious metals that are required can be reduced by 70% to 90% [4,5]. The self-regenerative function, which can be explained as resulting from the transformation of the state of precious metals (Pd, Pt, and Rh) that reversibly move into and out of the LaFe1-xMxO3 perovskite lattice,
* Correspondence: [email protected] 1 Division of Precision Science & Technology and Applied Physics, Graduate School of Engineering, Osaka University, 2-1, Yamada-okaSuita, Osaka 565-0871, Japan 5 Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University, Katsura, Kyoto 615-8520, Japan Full list of author information is available at the end of the article
significantly suppresses the growth of precious metals during the use of catalysts. Thus far, many experiments have been devoted to research on the state of Pd in perovskite in redox processes. Uenishi et al. [6] investigated the superior startup activity of LaFePdOx at low temperatures (from 100°C to 400°C) using X-ray spectroscopic techniques under the practical conditions where they controlled automotive emissions. They found the Pd0 phase partially segregated outside the surface even at low temperatures; thus, the segregation o
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