Design of nanosized ceria-based catalysts for mercury removal in simulated flue gas.

Deshetti, J 2015, Design of nanosized ceria-based catalysts for mercury removal in simulated flue gas., Doctor of Philosophy (PhD), Applied Science, RMIT University.


Document type: Thesis
Collection: Theses

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Title Design of nanosized ceria-based catalysts for mercury removal in simulated flue gas.
Author(s) Deshetti, J
Year 2015
Abstract The anthropogenic mercury emissions from various sources have been a global concern because of their potential risks to the human health and environment. Coal-fired power plants are the major source of worldwide mercury emissions. When mercury emits from coal-fired power plants, it is vaporized into elemental form (Hg0) in coal combusted flue gas. It undergoes several reactions with other gaseous components (homogeneous) and solid materials (heterogeneous) in coal-fired flue gases. The existing conventional technologies such as wet scrubbers, electrostatic precipitators, and fabric filters could easily control oxidized mercury from coal-fired flue gas. However, the elemental form of mercury is very difficult to control due to its high volatility and insoluble in water. Therefore, the catalytic conversion of elemental form (Hg0) to its oxidized from (Hg2+) is significant, because the oxidized mercury can be easily removed by wet scrubbers due to its high solubility.

In this work, various efficient and cost-effective CeO2-based materials were developed and evaluated towards elemental mercury oxidation and adsorption under different flue gas conditions at low operating temperatures. During the last decade, ceria-based materials have been intensively studied for several applications such as three way catalysis (TWCs), water gas shift reaction (WGS), sensors, etc., due to the multiple positive effects on the enhancement of catalytic performance. It has proved to be a material of exceptional technological importance due to its unique properties, including high mechanical strength, oxygen ion conductivity and oxygen storage capacity (OSC) via the redox shift between Ce4+ and Ce3+ under oxidizing and reducing conditions, respectively. Additionally ceria is also interesting for catalytic conversion economically because it has been shown that adding comparatively inexpensive ceria can allow for substantial reductions in the amount of noble metals needed in various commercial applications. Because of their tremendous properties, it has been also investigating for mercury removal technologies. Therefore, there is still big interest in identification of the catalyst physicochemical properties and plausible mechanisms that lead to improve mercury oxidation performance is obviously important for the development of catalysts for mercury removal in coal-fired power plants.

The plausible mechanisms involved in elemental mercury oxidation onto various CeO2-based materials have been investigated through packed-bed experiments in a stream of simulated flue gas conditions, including hydrogen chloride (HCl), oxygen (O2), and ammonia (NH3). The flue gas components such as HCl and O2 enhance the Hg0 oxidation, while NH3 is found to decrease the Hg0 oxidation significantly by occupying the active sites on the catalyst surface. In recent years, the CeO2-based materials epitomize the most important catalysts for mercury removal and therefore have been investigated for mercury oxidation in this work. Future work will include optimization of catalysts compositions and using other flue gas components such as SO2, NOx, and humidity (H2O) to test the different CeO2-based materials for the mercury oxidation performance.
Degree Doctor of Philosophy (PhD)
Institution RMIT University
School, Department or Centre Applied Science
Keyword(s) Doped Ceria
Coal-fired flue gas
Elemental Mercury Oxidation
Oxygen Vacancy
Codoped
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