First-principles investigation on the segregation of Pd at LaFe1-xPd x O3-y surfaces

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.

A Brief Review on Key Role of Perovskite Oxides as Catalyst

“…[13] In his study it has shown that when catalyst is acting either in oxidizing or in reducing atmosphere then Pd(present at B-site) enter and out of the perovskite lattice in a reversible manner. Such excellent performances of perovskite-structured based catalysts has been reported by several authors wherein perovskite as catalyst was found to be helpful in holding and soothing highly precious metals (such as Pd) during NO reduction under high temperature conditions [127][128][129][130][131][132] (iv) Reduction of NO using NH 3…”

Emergence and Future of Exsolved Materials

“…Most studies agree that they have a determining role in this process either because they seem to stabilize the segregated/exsolved phases [ 7,46 ] or because they enable those phases to form. [ 47,48 ] In particular, density functional theory (DFT) calculations supports the premise that the crystal reconstruction induces the loss of coordinated oxygen surrounding B‐site cations, serving as the driving force for steering fast nanoparticle growth. [ 45 ]…”

Progress of Exsolved Metal Nanoparticles on Oxides as High Performance (Electro)Catalysts for the Conversion of Small Molecules

“…Several factors, such as surface configuration, oxygen vacancy , and A‐site vacancy formation, can strongly modify segregation energies, leading to changes in exsolution behaviors. [ 53,57,168,170,209 ]…”

“…Such particle sizes range between 40 and 50 nm, while the total surface number density of exsolved Ni nanoparticles is 80 particles µm −2 . Noble metals (Rh, Pt, Pd, Ru, and Ir) [ 66,87–89,94,168–170 ] are also reported to easily exsolve toward surfaces. Zhang et al.…”

“…Tian et al. [ 170 ] reported that Pd atoms in LaFe 1− x Pd x O 3− y tended to repulse each other without oxygen vacancies. If oxygen vacancies were present at the subsurface layer, Pd atoms became attractive, forming a pair of Pd atoms through sharing one oxygen vacancy.…”