Understanding the Mechanochemical Synthesis of Mixed Oxi j1es using Synchrotron and Neutron Techniques

Lead Research Organisation: University of Southampton
Department Name: School of Chemistry

Abstract

The mechanochemical synthesis of mixed oxides is of interest within JM as a potential new route to the manufacture of catalysts and absorbents. There are advantages from using this route such as reduced energy and simplified process flow sheets. However, the mechanism of the transformation of reagents to active phases under mechanical action is not well understood and knowledge of how key parameters such as milling technique, time, initial reagent ratios and the presence of additives is needed. Knowledge is required of which phases (amorphous and crystalline) form during milling time and how the process can be optimised.

The project will use tomography, PDF, XAS, XRD, Raman neutron techniques to understand the mechanism of mechanochemical transformation with milling time and key parameters for oxides such as perovskites or molybdates. In situ techniques will also be developed.

Publications

10 25 50

Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/P510646/1 01/10/2016 30/09/2021
1795413 Studentship EP/P510646/1 01/10/2016 30/09/2020 Rachel Blackmore
 
Description My research focuses on the development and understanding of mechanochemistry for the synthesis of perovskites / mixed metal-oxides. This technique is known to offer a solventless, waste-free route to preparing metal oxide catalysts, however, there is limited information on the chemical steps involved. Due to the continuing tightening of emission regulations and increasing prices of precious metals for existing commercial catalysts is driving the need to develop cheaper, more sustainable catalysts.

In this work the perovskite LaMnO3 has been successful synthesised via mechanochemistry from metal oxide powders La2O3 and Mn2O3, using a planetary ball mill, with ex situ time slices taken of the catalyst during the milling procedure to provide insights into the underlying chemistry. I have been able to extensively use advanced characterisation, such as X-ray Absorption Spectroscopy (XAS) and near ambient X-ray Photoelectron Spectroscopy (XPS), which as been vital to my research. Due to the milled materials containing a high proportion of amorphous material it is not possible to analyse using solely lab-based techniques such as XRD. XAS allows for probing both the Mn K-edge and La L3-edge, as it is not reliant on periodic ordering, with each edge providing a very different picture. The XAS data shows that there are significant structural alterations at the early stages of milling, with the La precursor dispersed over Mn2O3. Increasing milling time then allows for mechanical activation of both precursors and the formation of powdered LaMnO3, with no calcination step required. Testing for the decomposition of the environmental pollutant N2O showed the milling time of 3 h for the LaMnO3 catalyst to have a much early onset production of N2 compared to a traditional sol-gel synthesized LaMnO3. This is an encouraging sign that mechanochemical routes can be harnessed to provide a sustainable route to preparing perovskite catalysts with enhanced catalytic performance. Currently investigations into further XAS experiments with HERFD and K-beta emission to further understand the structures of the ball milled materials along with in situ studies of deN2O.

Further work has now been started on understanding of the role of La and different A-site oxide precursors in the mechanochemical synthesis of perovskites, ABO3.
Also I am investigating the effect of milling Au supported nanoparticles has on their catalytic activity.
Exploitation Route By understanding a simplified perovskite compound and how improved characteristics effect the catalytic activity the knowledge can therefore be applied to more complicated analogous materials for commercial use within the automotive industry.
Sectors Chemicals,Energy,Environment