Clark, Adam Hugh;
(2018)
Combined scattering and spectroscopic structure determination of nano-catalysts.
Doctoral thesis (Eng.D), UCL (University College London).
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Abstract
Several types of nano-catalysts, which includes oxides, supported mono and bimetallic catalysts have been used extensively for a range of catalytic reactions. Understanding the structure and reactivity has been a main theme to elucidate structure-function relationships. Herein, the behaviour of nano-catalysts has been studied using a range of experimental tools, with Synchrotron Radiation techniques as the major component. In addition, a range of analysis methods have been explored to determine structure using in situ and ex situ methods. Investigations into the structure of bimetallic silica supported PtZn nano-particles were conducted in situ during exposure to formic acid using X-ray absorption spectroscopy (XAS). Here it has been demonstrated that Zn is highly dispersed and bonded to the channel walls within the SBA-15 porous silica, whilst Pt forms oxide particles within the channels, in the as-synthesised form. On exposure to formic acid conversion of ZnO like species to Zn formate is observed to occur concurrent to the reduction of Pt oxide to Pt metal nano-particles. The redox characteristics of ceria supported platinum group metal (PGM) samples and ceria coated PGM metals supported on alumina have been studied in detail. XAS has been employed following the oxidation state of both the cerium and supported PGM, in addition to X-ray total scattering following the lattice structural changes, under in situ reduction-oxidation conditions. Detailed analysis has elucidated a promoted reduction of ceria upon reduction of the initial PGM oxide is observed. In the case of the inverse ceria alumina catalysts partial re-oxidation is observed upon cooling under a reducing atmosphere. Upon exposure to air, a full re-oxidation of the ceria support takes place, however only a partial oxidation (passivation), of the PGM to occur. Further reduction cycles result in ca room temperature reduction of the PGM and ceria.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Eng.D |
| Title: | Combined scattering and spectroscopic structure determination of nano-catalysts |
| Event: | UCL (University College London) |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Third party copyright material has been removed from ethesis. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10059089 |
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