CuO–CeO2/TiO2 catalyst for simultaneous NO reduction and Hg0 oxidation at low temperatures

Abstract

CuO–CeO₂/TiO₂ (CuCeTi) catalyst prepared by a sol–gel method was employed for the first time to simultaneously reduce nitrogen monoxide (NO) and oxidize elemental mercury (Hg⁰) in the presence of ammonia (NH₃) at low flue gas temperatures. The combination of copper oxides and cerium oxides yielded apparent synergy for NO reduction and Hg⁰ oxidation. Over 90% of NO reduction and over 80% of Hg⁰ oxidation were simultaneously obtained on the CuCeTi catalyst at 200 °C to 250 °C under simulated coal combustion flue gas with a gas hourly space velocity (GHSV) of 54 000 h⁻¹ which is more than 10 times higher than the actual GHSV in selective catalytic reduction (SCR) reactors. The well-dispersed active species and abundant chemisorbed surface oxygen on the CuCeTi catalyst were responsible for its excellent catalytic performance. Neither Hg⁰ vapor in flue gas nor HgO loaded on the catalyst surface inhibited NO reduction by NH₃ at 200 °C. In the absence of gas phase oxygen (O₂), NH₃ consumed surface oxygen and hence resulted in the deactivation of Hg⁰ oxidation. In the presence of O₂, neither NO nor NH₃ individually exhibited an inhibition on Hg⁰ oxidation. However, Hg⁰ oxidation over the CuCeTi catalyst was inhibited by the co-presence of NO and HH₃. Fortunately, this inhibitive effect was entirely scavenged when a lower GHSV was adopted. This study reveals the feasibility of simultaneously reducing NO and oxidizing Hg⁰ at low flue gas temperatures. Such knowledge is of fundamental importance in developing efficient, practical and economical NO and Hg⁰ control technologies for coal-fired power plants.