Novel catalyst screening for low temperature NOx abatement
Date
2010-05
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Publisher
University of Delaware
Abstract
NOx compounds are pollutants formed in fossil fuel combustion which lead to global warming, acid rain, toxic particulates and other health concerns. Due to the high activation energy of the direct decomposition reaction 2NOx ? N2 + xO2 a catalyst is needed to reduce NOx pollution in fossil fuel burning applications which provide 85% of the worlds increasing energy demand. One of the ways to catalytically remove NOx is through Selective Catalytic Reduction (SCR) which requires a reductant, such as ammonia, to be introduced to the effluent stream of the fossil fuel combustion. Due to the requirement of additional feed stock SCR has been heavily used in high temperature stationary applications but the desire and technology for the utilization of SCR in lower temperature automotive applications is currently emerging in the market. Therefore, a catalyst needs to be optimized that can penetrate the market to replace less fuel efficient three way catalysts (TWC). Using a high-throughput experimentation set-up with a Fourier transform infrared (FTIR) spectrometer this work has compared 1% platinum and ruthenium catalysts synthesized via reverse micelle synthesis, which creates a narrow nanoparticle size distribution, to compare SCR activity and selectivity for the two metals. The Pt catalysts were able to maintain the conversion of NO close to or at 100% over a longer, lower (from 150 to 250oC) temperature span than the Ru catalysts. The Ru catalysts were not able to reach 100% conversion until temperatures around 300oC, but they were able to able to achieve a higher selectivity towards N2 than the Pt catalysts over the entire temperature span studied. The utilization of two different surfactant chemistries was also explored. Catalysts synthesized with a Brij-30 were able to sustain 100% or close to 100% NO conversion over a longer temperature range then catalysts synthesized with a Triton-X 100 chemistry. A designed set of incipient wetness catalysts were screened for SCR in an attempt to find a relationship between the weight loadings of Ru and Co and the selectivity and activity in the chemistry. It was found that the 4Ru5Co15Ba, the 4Ru15Ba, and the 2.5Ru2.5Co15Ba preformed the best, in terms of activity and selectivity at 150 and 300 oC. But the relationship between the metal weight loadings and the SCR activity and selectivity was weak and unsubstantial. It was observed that a 5Co15Ba catalyst out performed other Ru catalysts with comparable activities in terms of selectivity and was deemed the cheapest most viable option out of the catalysts screened.