- Title
- Study of catalytic oxidation of NO in flue gas over Mn-doped Co-Ti-Ox catalysts
- Creator
- Rahman, S. M. Ashiqur
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2022
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The nitrogen oxides (mainly nitric oxide (NO)) are major air pollutants that lead to a number of environmental problems, including photochemical smog, acid rain and haze. The catalytic oxidation of NO to NO2 is regarded as a key step in the treatment of NOx. In recent decades, a variety of oxidation catalysts for NO have been developed to increase the efficiency of the oxidation process. In this research study, a series of manganese cobalt titanium oxide (Mn Co Ti Ox) catalysts were prepared using a co-precipitation method and were tested for the low temperature catalytic oxidation of NO in the presence of O2 in a fixed-bed reactor. The experimental results showed that the highest oxidation rate was achieved at a temperature of 200 °C at a space velocity (SV) of 20,000 h-1. As the Co content was increased to 0.3 molar mass, the oxidation rate increased significantly, while further increases of the Co content, to 0.4 and 0.5 molar masses, led to decreases in the oxidation rate. The effects of the calcination temperature of the catalyst on the reaction rate was also investigated, and it was found that the catalyst which was calcined at a temperature of 300 °C showed the highest reaction rate. It was also found that the oxidation rates were varied due to the concentrations of the reactants (NO and O2). The effects of sulphur poisoning were also investigated in the oxidation reactions. When SO2 was introduced into the NO gas stream, the catalytic activity of all of the catalysts decreased because the active sites on the catalysts were covered by a thermally stable sulphate formed by the oxidation of the SO2. However, it was also found that there was no significant changes in the oxidation rate due to the SO2 poisoning for the Mn (0.2)-Co (0.3)-TiO2 (0.5) catalyst, and that the rate was stable until 6 hours of catalytic oxidation were completed. It is also shown that the attraction of the SO2 onto the active sites of the Mn (0.2)-TiO2 (0.3) catalyst were reduced because of the intense interaction of the Co with the sulphur. The research showed that the interactions of the Mn and SO2 could be diminished when Co was present in the catalyst heterojunction. The modified catalysts were characterized using X-ray photoelectron spectroscopy (XPS), X-ray diffraction analysis (XRD), Brunauer-Emmett-Teller (BET) measurements, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). It was found that the coexistence of Mn, Co and TiO2 reduced the crystallization of the catalysts and enhanced the dispersion of the active metals, thereby improving the reactivity of the catalysts. The BET results showed that the catalysts which calcined at a temperature of 300 °C had the highest surface areas and pore volumes, which was believed to play a vital role in their oxidation rates. The TEM micrographs implied that the calcination temperature and the loading of the Co onto the catalysts affected their particle sizes. The XPS results showed no massive changes in the peaks before and after the thermal regeneration of the used catalysts. It is postulated that the SO2 only occupied a few of the active sites on the catalysts and that most of their active sites were accessible for NO oxidation reactions. The analysis of the catalysts suggested that their high catalytic oxidation performances could be attributed to the dual redox cycles: (Mn3++ Co3+ Mn4++ Co2+; Mn3++ Ti4+ Mn4++ Ti3+). This work was aimed to reduce the emission of NO, NO2 and SO2 in coal fired flue gas in the coal fired powerplants. To reduce the NO emission catalytic oxidation process was used and TiO2 based catalyst was modified using Mn and Co to ensure the stability and high oxidation rate.
- Subject
- nitric oxide; catalytic oxidation; air pollutants; manganese cobalt titanium oxide
- Identifier
- http://hdl.handle.net/1959.13/1508298
- Identifier
- uon:56116
- Rights
- Copyright 2022 S. M. Ashiqur Rahman
- Language
- eng
- Full Text
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