Understanding the Mechanochemical Synthesis of Mixed Oxi j1es using Synchrotron and Neutron Techniques
Lead Research Organisation:
University of Southampton
Department Name: Sch 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.
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.
People |
ORCID iD |
| Peter Wells (Primary Supervisor) | |
| Rachel Blackmore (Student) |
Publications
Blackmore RH
(2020)
Understanding the mechanochemical synthesis of the perovskite LaMnO3 and its catalytic behaviour.
in Dalton transactions (Cambridge, England : 2003)
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. Recent investigations into further XAS experiments with HERFD and K-beta emission performed on I20-Scanning beamline, DLS, UK, show significant alterations observed within the ball milled perovskites. These changes indicate disruption to the Mn-La coordination, specifically to the lack of Mn4p La5d hybridisation, in comparison to the sol-gel prepared LaMnO3. XES performed at the MnKß1,3 emission line suggest a 'bulk' Mn(III) oxidation state throughout the mechanochemical synthesis. By performing in situ NAP-XPS deN2O we were able to further this understanding of this improved catalytic activity whilst studying the different LaMnO3 catalysts under working conditions. Within the O1s region the argon milled catalyst showed a higher proportion of adsorbed species on exposure to N2O at RT, indicating an increase interaction with this species. It also highlighted that all catalysts remained with a mixed Mn(III)/Mn(IV) valency, even at elevated temperatures of 600°C whilst working under catalytic conditions. This recent work has demonstrated how the use of further advanced characterisation, such as HERFD, XES and NAP-XPS, can provide an in-depth understanding of the electronic, structural and surface properties of LaMnO3 induced by the mechanochemical synthesis, not previously possible by simple lab-based techniques. Further work is still being continued on the 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, clean air and battery industries. Furthermore compiling the knowledge of the mechanochemical synthesis of different A-site manganite perovskites we can start to form generalised rules for perovskite sysnthesis by linking precursor properties to reaction conditions. |
| Sectors | Chemicals,Energy,Environment |
| URL | https://pubs.rsc.org/en/content/articlelanding/2020/dt/c9dt03590g |
| Description | Understanding the mechanochemical synthesis of perovskites using synchrotron and neutron techniques |
| Organisation | Johnson Matthey |
| Department | Johnson Matthey Technology Centre |
| Country | United Kingdom |
| Sector | Private |
| PI Contribution | Project directly contributes to the understanding of their materials and synthetic routes used within their business. |
| Collaborator Contribution | Initial use of materials: Mn2O3 and La2O3 Provided 50 g batch of 0.5wt%Au/Al2O3 Occasional use of equipment such as: planetary ball mill, milling jars, milling media, attritor mill, argon glove box, lab space Use of characterisation equipment: X-ray diffractometer, transmission electron microscope, aboration correction microscope, quadrasorb for BET analysis, Inductively Coupled Plasma Spectroscopy Software: DIFFRAC.SUITE EVA 4.2 and DIFFRAC.SUITE TOPAS 4.2 to analyse X-ray diffraction data |
| Impact | https://doi.org/10.1039/C9DT03590G |
| Start Year | 2016 |
| Description | National conference talk at the UK Catalysis Conference titled: Understanding the Mechanochemical Synthesis of Perovskite LaMnO3 and its Catalytic Behavior |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | National |
| Primary Audience | Postgraduate students |
| Results and Impact | 40 people attended my talk during the UK catalysis conference, which resulted in a question answer session afterwards. I was able to also publicise my paper, for which the talk was based on and increase the understanding and awareness of my topic. |
| Year(s) Of Engagement Activity | 2020 |
| URL | https://www.linkedin.com/feed/update/urn:li:activity:6623519273795104768/ |