Mercury oxidation over Cu-SSZ-13 catalysts under flue gas conditions

Abstract

Increasing concerns over mercury (Hg) emissions from coal-fired power plants have led to the implementation of various novel technologies. Selective catalytic reduction (SCR) catalysts have shown promise as bifunctional catalysts for limiting both nitrogen oxide and Hg emissions. Cu-SSZ-13 has shown promise as a SCR catalyst for diesel exhaust, but has not yet been investigated for coal-fired plant application where Hg oxidation would be of great importance. To develop the next generation of SCR catalysts, Cu-SSZ-13, a small pore zeolite, was investigated for its ability to oxidize Hg under a variety of flue gas conditions. The Cu-SSZ-13 catalyst was compared to SSZ-13 to understand the effect of copper (Cu) in the Hg oxidation mechanism. The Hg oxidation performances of both zeolites were compared to that of a commercial SCR catalyst as a benchmark. All catalysts required hydrogen chloride (HCl) to exhibit any Hg oxidation with the zeolites outperforming the commercial catalyst. However, the activity of all catalysts significantly decreased in the presence of either sulfur oxides (SOx) or SCR reactants (nitrogen oxide (NO) + ammonia (NH3)) in the flue gas, with SOx having a greater effect on Cu-SSZ-13 and SCR reactants having a greater one on the commercial catalyst. Additionally, it was determined that while Cu was the active site for the SCR reaction, it did not enhance Hg oxidation. In fact, in the presence of SO2, Cu actually contributed to the deactivation of the catalyst for Hg oxidation.