Catalytic Methane Abatement for Natural Gas Engines
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To reduce the greenhouse emissions it is proposed to use natural gas vehicles in the marine sector, instead of conventional vehicles using heavy fuel oil. Use of natural gas will reduce NOx, SOx and CO2 emissions, and will give a low content of particulates in the exhaust gas. The resources of natural gas are available worldwide and are today much larger than crude oil. Natural gas engines are more economic and operate under lean conditions, which increases the fuel efficiency. However, a huge disadvantage is the unburned methane in the exhaust gas, a potent greenhouse gas. The emissions of methane need to be reduced before application, and after treatment of the exhaust gas by catalytic oxidation of methane is one method to achieve this. The transition metal oxides nickel and cobalt have shown a promising low temperature activity. In this master thesis, complete catalytic oxidation of methane has been studied using a nickel cobalt catalyst. Three main aspects were investigated; the addition of hydrogen to the reaction feed, utilizing a new synthesis method called fast coprecipitation method and the use of monolithic samples coated with the ready made catalyst. The catalytic activity was tested for both the powder catalysts and the monolithic catalysts, and different reaction conditions were altered, such as the methane concentration, total flow rate and introduction of water to achieve realistic conditions of the exhaust gas. The powder catalysts were investigated with the characterization techniques X-ray diffraction, N2 physisorption and X-ray fluorescence. It was found that the addition of hydrogen displayed a lower catalytic activity over the catalyst, as the catalyst seemed to easier activate H2 than CH4. The fast coprecipitation method showed a small increase in the catalytic activity compared to the standard coprecipitation and could be of high commercial value since it would be cheaper and take less time. The monolithic catalysts showed high catalytic activity compared to the low amount of catalyst coated, and all of the catalyst coated seemed to be utilized during the reactions. However, the monolithic samples seemed to deactivate over time, most likely due to loss of catalytic material.