(560gx) Defect Engineering of in-Situ Exsolved Nanoparticle Catalysts on Perovskite Supports

2019
AIChE Annual Meeting

Abstract for
Poster Presentation

Defect Engineering
of In-Situ Exsolved Nanoparticle Catalysts on Perovskite Supports

Soham Shah*¹, Samuel Sayono² and Kandis Leslie
Abdul-Aziz^1,2

1.     
Department
of Chemical and Environmental Engineering, University of California, Riverside.

2.     
Materials
Science and Engineering Program, University of California, Riverside

sshah034@ucr.edu

Perovskites are a
class of mixed metal oxides with general stoichiometry of ABO₃ and have
drawn the interest of researchers for their versatility in applications from
solar cells to fuel cells and catalysts. An interesting phenomenon occurs in
some defective perovskites – dopant metals leave their positions in the
lattice, when subjected to high temperatures in a reductive atmosphere. These
atoms diffuse or “exsolve” through the perovskite matrix and form nanoparticles
on the surface of the parent perovskite. Exsolved nanoparticles display strong
adherence to the perovskite support from which it emerged. Consequently, their
enhanced resilience and activity makes them stand out as candidates for
catalysis, fuel cells and other emerging energy conversion technologies.

With the objective
to gain insight about the driving forces behind exsolution, a series of
lanthanum ferrite perovskites were synthesized, with nickel and cobalt as
dopant metals. These perovskites either had deficiencies in La (A site), Fe (B
site) or neither site (Over-Stoichiometric). The perovskites were reduced and
characterized with XRD, SEM, TPR, XPS, STEM, EDS and these methods confirmed
the exsolution of Ni and Co oxide nanoparticles in samples reduced at 600^oC.
However, samples reduced at 700^oC had nanoparticles that also
contained iron while what remained of the parent support material was largely
lanthanum oxide. We conclude that at higher temperatures as the diffusion of B
site atoms is accelerated, the Fe iron atoms could also exsolve along with the
dopant atoms and form alloyed nanoparticles. This could open new avenues in the
study of in-situ exsolution and their application in devising multi-metallic
particles for catalysts.

The objective is
to understand the role of defects in perovskites in driving exsolution of
nanoparticles. “Defect Engineering” can then be exploited to direct perovskite
materials to have optimized properties relevant to specific applications.