The University of Southampton
University of Southampton Institutional Repository

Preparation and characterisation of some nano-structured catalytic materials for low-temperature oxidation of carbon monoxide

Preparation and characterisation of some nano-structured catalytic materials for low-temperature oxidation of carbon monoxide
Preparation and characterisation of some nano-structured catalytic materials for low-temperature oxidation of carbon monoxide
This project is focused on the synthesis, modification and characterization of rhodium based catalysts supported on MCM-41 mesoporous silica to produce well-defined active sites for catalysis of CO oxidation at low-temperature. The Rh catalysts were prepared by incipient wetness impregnation (IWI) then modified by the inclusion of different transition metal oxides (ca. CeOx, ZrOx, CrOx, Ce0.5Zr0.5Ox and Ce0.5Cr0.5Ox) via two different routes. The first was achieved by pre-modification of MCM-41 support during its synthesis using the inorganic precursors of the promoter oxides followed by the addition of the specified Rh precursor (0.5 - 2.5 wt%), i.e. post-synthesis of Rh catalysts. The second route was performed by the post addition of the promoters using their non-inorganic sources [ca. Ce(acac)3, Zr(acac)4 and bis(benzene)chromium] by the controlled surface modification (CSM) method. The catalysts were characterized by using TGA, FT-IR, N2 physisorption analysis, PXD, SEM-EDX, TEM, DR UV/Vis spectroscopy and XPS. Furthermore, the structure-performance relationship and the dependence of the preparation method towards CO oxidation were also investigated by in situ QEXAFS-MS spectroscopy in the temperature range of 300 - 573 K. The combination of soft and hard X-ray absorption edges was applied to in situ structural studies. In addition to the Rh K-edge, the Ce L3, Zr K or Cr K-edges were used as probes of the catalysts as a function of temperature (300 - 573 K) under of different ambient gases (He, 10% H2/He, 10% O2/He and 10% CO/O2/He) during activation and reaction conditions. As a result, the fractions of Rh active species, coordination numbers and atom-to-atom distances were extracted from analysis of XANES and EXAFS results. In addition, the turnover frequency (TOF) values and CO conversion% over these catalysts were also calculated. The results revealed that Rh species and/or the promoter oxides prepared by both two methods were well confined into the mesoporous framework of silica support in amorphous nano-sized scale. However, the distribution of the Rh atoms and/or the promoter oxides depends mainly on the preparation method with much more homogeneity and local vicinity in those prepared by the CSM method. Furthermore, the preparation method played a crucial rule not only in the local structure, but also in the catalysts performance towards CO oxidation with high activity for catalysts prepared by CSM.
Mohammed, Khaled
f50a275b-4588-43b0-ba9c-5f108f23d3fc
Mohammed, Khaled
f50a275b-4588-43b0-ba9c-5f108f23d3fc
Evans, John
05890433-0155-49fe-a65d-38c90ea25c69

Mohammed, Khaled (2014) Preparation and characterisation of some nano-structured catalytic materials for low-temperature oxidation of carbon monoxide. University of Southampton, Chemistry, Doctoral Thesis, 350pp.

Record type: Thesis (Doctoral)

Abstract

This project is focused on the synthesis, modification and characterization of rhodium based catalysts supported on MCM-41 mesoporous silica to produce well-defined active sites for catalysis of CO oxidation at low-temperature. The Rh catalysts were prepared by incipient wetness impregnation (IWI) then modified by the inclusion of different transition metal oxides (ca. CeOx, ZrOx, CrOx, Ce0.5Zr0.5Ox and Ce0.5Cr0.5Ox) via two different routes. The first was achieved by pre-modification of MCM-41 support during its synthesis using the inorganic precursors of the promoter oxides followed by the addition of the specified Rh precursor (0.5 - 2.5 wt%), i.e. post-synthesis of Rh catalysts. The second route was performed by the post addition of the promoters using their non-inorganic sources [ca. Ce(acac)3, Zr(acac)4 and bis(benzene)chromium] by the controlled surface modification (CSM) method. The catalysts were characterized by using TGA, FT-IR, N2 physisorption analysis, PXD, SEM-EDX, TEM, DR UV/Vis spectroscopy and XPS. Furthermore, the structure-performance relationship and the dependence of the preparation method towards CO oxidation were also investigated by in situ QEXAFS-MS spectroscopy in the temperature range of 300 - 573 K. The combination of soft and hard X-ray absorption edges was applied to in situ structural studies. In addition to the Rh K-edge, the Ce L3, Zr K or Cr K-edges were used as probes of the catalysts as a function of temperature (300 - 573 K) under of different ambient gases (He, 10% H2/He, 10% O2/He and 10% CO/O2/He) during activation and reaction conditions. As a result, the fractions of Rh active species, coordination numbers and atom-to-atom distances were extracted from analysis of XANES and EXAFS results. In addition, the turnover frequency (TOF) values and CO conversion% over these catalysts were also calculated. The results revealed that Rh species and/or the promoter oxides prepared by both two methods were well confined into the mesoporous framework of silica support in amorphous nano-sized scale. However, the distribution of the Rh atoms and/or the promoter oxides depends mainly on the preparation method with much more homogeneity and local vicinity in those prepared by the CSM method. Furthermore, the preparation method played a crucial rule not only in the local structure, but also in the catalysts performance towards CO oxidation with high activity for catalysts prepared by CSM.

PDF
__soton.ac.uk_ude_PersonalFiles_Users_lp5_mydocuments_Theses PDF files_KhaledMohammedThesis_final.pdf - Other
Download (35MB)

More information

Published date: 30 June 2014
Organisations: University of Southampton, Chemistry

Identifiers

Local EPrints ID: 367130
URI: http://eprints.soton.ac.uk/id/eprint/367130
PURE UUID: 5d6d6e2f-72d6-4e9d-8d91-333cfbbacac6

Catalogue record

Date deposited: 23 Oct 2014 10:15
Last modified: 18 Jul 2017 04:31

Export record

Contributors

Author: Khaled Mohammed
Thesis advisor: John Evans

University divisions

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of http://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×