Abstract
Selective catalytic reduction (SCR) with NH3 is the most efficient and economic flue gas denitrification technology developed to date. Due to its high low-temperature catalytic activity, Mn-based catalysts present a great prospect for application in SCR de-NOx at low temperatures. However, overcoming the poor resistance of Mn-based catalysts to H2O and SO2 poison is still a challenge. This paper reviews the recent progress on the H2O and SO2 resistance of Mn-based catalysts for the low-temperature SCR of NOx. Firstly, the poison mechanisms of H2O and SO2 are introduced in detail, respectively. Secondly, Mn-based catalysts are divided into three categories—single MnOx catalysts, Mn-based multi-metal oxide catalysts, and Mn-based supported catalysts—to review the research progress of Mn-based catalysts for H2O and SO2 resistance. Thirdly, several strategies to reduce the poisonous effects of H2O and SO2, such as metal modification, proper support, the combination of metal modification and support, the rational design of structure and morphology, are summarized. Finally, perspectives and future directions of Mn-based catalysts for the low-temperature SCR of NOx are proposed.
Highlights
Nitrogen oxides (NOx, x = 1,2) emitted from power plants and diesel engines are major air pollutants that can cause acid rain, photochemical smog, ozone depletion, and other severe environmental problems [1,2,3,4,5]
Kang et al prepared two manganese oxide (MnOx) catalysts using sodium carbonate (SC) and ammonia (AH) as precipitants [23]. They found that an MnOx -SC catalyst showed better Selective catalytic reduction (SCR) activity and great sulfur and water tolerance, and they ascribed this to the larger surface area
It should be noted that the shift between Ce4+ and Ce3+ can result in the formation of oxygen vacancies and anincrease in the chemisorbed oxygen on the surface of Mn–Ce binary metal oxide catalysts, which are helpful for the enhancement of water and sulfur resistance [25,82]
Summary
V2 O5 -based catalysts have drawbacks, such as the toxicity of vanadium, SO2 oxidation to SO3 , over-oxidation of NH3 to N2 O, and a high working temperature [8]. Our research group has made a series of progress in the low-temperature SCR of NO with NH3 over Mn-based catalysts [15,16,17,18,19,20,21]. Several problems, including thermal instability, narrow operation window, and poor resistance to H2 O and SO2 poison, remain Among these drawbacks, the poor tolerance to H2 O and Catalysts 2018, 8, 11; doi:10.3390/catal8010011 www.mdpi.com/journal/catalysts. We focused on the recent progress on the water and sulfur resistance of Mn-based catalysts.
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