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Preparation of mixed metal oxide catalysts for VOC total oxidation

Shah, Parag 2019. Preparation of mixed metal oxide catalysts for VOC total oxidation. PhD Thesis, Cardiff University.
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Abstract

The preparation, characterisation and total oxidation of VOCs, propane and naphthalene, over ceria-zirconia, ceria-manganese and iron-manganese mixed metal oxide catalysts were investigated. Ceria-zirconia mixed metal oxides were prepared using a mechanochemical method from nitrate and carbonate precursors. Addition of low concentrations of zirconia into ceria produced the most active ceria-zirconia mixed metal oxide catalysts. Ceria-zirconia mixed metal oxides produced from nitrates were more active for naphthalene total oxidation, and the catalysts prepared from carbonates were more active for propane. The higher activity of the ceria-zirconia mixed metal oxides was ascribed to higher surface area, lower reduction temperatures and higher relative concentration of surface oxygen defects, when compared to the parent oxides. Ceria-manganese mixed metal oxides with higher concentrations of manganese produced the most active VOC total oxidation catalysts. The optimal way to produce ceria-manganese mixed metal oxide catalysts were co-precipitation which were washed with 2 l of water. The presence of large crystallites of Mn2O3, higher surface area and lower reduction temperatures led to the high VOC total oxidation activity over these catalysts. Along with this, phase separation between ceria and manganese oxide crystallites led to an increase in activity. The preparation of iron-manganese mixed metal oxides was optimised using co-precipitation. Fe0.50Mn0.50Ox prepared using ammonium hydroxide and calcined at 500 °C produced the most active propane total oxidation catalyst of the study. However, no synergy between iron oxide and manganese oxide for naphthalene total oxidation was observed over these catalysts. The high activity of the Fe0.50Mn0.50Ox sample was attributed to the presence of bulk and surface Mn3O4, which was noted to be more active than Mn2O3 in the iron-manganese mixed metal oxide catalysts. These catalysts also had large manganese oxide crystallites and no bulk or surface contaminants from sodium or potassium which also led to the high activity.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Chemistry
Subjects: Q Science > QD Chemistry
Date of First Compliant Deposit: 2 August 2019
Last Modified: 06 Aug 2019 09:24
URI: http://orca-mwe.cf.ac.uk/id/eprint/124657

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