Investigation of metal nanoparticles exsolved from perovskite titanate

Abstract

Nowadays, the energy and environment have become the restrictions to the development of human society. To solve the crisis coming from energy and environment, nanoparticles play a dominant role as the catalysts. However, traditional catalysts are easy to agglomerate to decrease their properties under high working temperatures. As a promising method to prepare nanoparticles, a new strategy, called exsolution, was proposed and has obtained much attention in many fields in catalysis and energy conversion and storage field due to the nanoparticles with the well-anchored and strained socketed structure.

This thesis illustrates the fundamental properties by doping different transition metals into the B-site of the perovskite. The parameters of the unit cells matched very well with the ionic radii of dopants. The corresponding nanoparticles exsolved successfully after the reduction post-treatments.

In particular, the thesis demonstrates the effects of reducing temperature and holding time on exsolution. In the exploration of the behaviours of exsolved nanoparticles after the redox experiments, it was found that the population and size of nanoparticles exsolved at lower temperatures were more sensitive than those exsolved at high temperatures.

The evolution of nanoparticles with different ratio of Ni and Co after CO oxidation experiments with different CO partial pressure was explored. As the loading of Co increases, the shape of the nanoparticles oxidized in CO oxidation experiments transformed from spherical to cubic, while the elemental distribution was still homogenous.

The thesis also explores the exsolution of small-sized metallic Cu nanoparticles from single-phase perovskite. We show that this is possible by selecting the suitable Cu precursor and control the parameters of the preparation to achieve Cu exsolution and its practical utility by preparing a nanostructured Cu metal catalyst which rival conventionally prepared Cu-based samples applied for CO oxidation. The catalytic properties of perovskite with exsolved nanoparticles can be tailored by doping Fe and Zn due to the synergistic effect.