(600ac) Investigation of Arsenic Poisoning on Novel SCR Catalysts
The reduction of nitrogen oxides (NOX) using selective catalytic reduction (SCR) through the injection of ammonia is a common practice in coal-fired power plants today. However to meet increasing emission standards, numerous novel SCR catalysts have been developed to make the catalysts more reactive over a wider range of operating conditions, such as temperature. Modern mixed-oxide catalysts used to carry out this reaction are susceptible to poisoning and deactivation over time due to the numerous species present in the flue gas such as arsenic. To increase the catalysts operating lifetime under exposure to such species, sorbents, such as CaO, can be added into the flue gas. Due to these limitations of current SCR catalysts, novel SCR catalysts are currently being investigated. While the deactivation mechanism has been studied on traditional V-Mo-Ti oxide catalysts to an extent, it is unknown what effect the arsenic species might have on novel SCR catalysts.
In this study, small pore zeolites, SSZ-13 and SAPO-34, both with and without metal ion exchange, are evaluated for their resistance to arsenic as they have shown promise as SCR catalysts in other deNOX applications. They are compared to a commercially available (V-W-Ti oxide) catalyst, as well several large pore zeolites such as ZSM-5 and zeolite-Y. The catalysts are exposed to a simulated flue gas stream that is created by combusting methane, creating an environment representative of the one present in a coal-fired boiler. Prior to combustion, the stream is premixed with arsine (AsH3), which is converted to arsenic oxide (As2O3) as it passes through the oxygen-rich flame. The catalysts are characterized before and after exposure to arsenic using XPS, XRD, SEM/EDX and NH3-TPD, to determine the specific mechanism of arsenic adsorption on the surface of the catalysts. Finally, the gas stream composition is varied to include SO2, NO, NO2, and HCl to study the effect that other flue gas components play in arsenic adsorption.