Abstract
The formation characteristics of N2O were investigated with respect to copper-functionalized zeolites, i.e., Cu/SSZ-13 (CHA), Cu/ZSM-5 (MFI), and Cu/BEA (BEA) and compared with the corresponding zeolites in the H form as references to elucidate the effect of the framework structure, copper addition, and water. Temperature-programmed reduction with hydrogen showed that the CHA framework has a higher concentration of Cu2+ (Z2Cu) compared to MFI and BEA. The characterizations and catalyst activity results highlight that CHA has a framework structure that favors high formation of ammonium nitrate (AN) in comparison with MFI and BEA. Moreover, AN formation and decomposition were found to be promoted in the presence of Cu species. On the contrary, lower N2O formation was observed from Cu/CHA during standard and fast SCR reactions, which is proposed to be due to highly stabilized AN inside the zeolite cages. On the other hand, significant amounts of N2O were released during heating due to decomposition of AN, implying pros and cons of AN stability for Cu/CHA with possible uncontrolled N2O formation during transient conditions. Additionally, important effects of water were found, where water hinders AN formation and increases the selectivity for decomposition to NO2 instead of N2O. Thus, less available AN forming N2O was observed in the presence of water. This was also observed in fast SCR conditions where all Cu/zeolites exhibited lower continuous N2O formation in the presence of water.
Highlights
Nitrous oxide (N2O) is a strong greenhouse gas (GHG), which is 297 times more potent than CO2.1 It is critical to minimize N2O formation in after-treatment systems during reduction of nitrogen oxides (NOx)
SSZ-13 was studied because it is a commercial zeolite for selective catalytic reduction (SCR), while BEA and ZSM-5 were chosen due to their different structures to find an understanding about the structure−activity relation
The Cu/SSZ-13 sample deactivates slower during SO2 exposure than the other two catalysts but reaches a lower conversion during time on stream. These results are in line with the recent study by Auvray et al.[32] where it was reported that Cu/BEA was significantly less affected than Cu/SSZ-13 from SO2 or SO3, and the reason for this was suggested to be less steric hindrance of Cu/BEA by sulfur species
Summary
Nitrous oxide (N2O) is a strong greenhouse gas (GHG), which is 297 times more potent than CO2.1 It is critical to minimize N2O formation in after-treatment systems during reduction of nitrogen oxides (NOx). Urea-SCR systems selectively convert engine-out NOx emissions to nitrogen (N2) and water by using NH3 resulting from thermal decomposition and hydrolysis of a urea solution. N2O is produced reactions of NOx as one of the by-products during over a wide temperature range.[2,5−8] the SCR Thermal decomposition of ammonium nitrate (AN) has been reported to be the ature.[7−10] main In the source of N2O formation high-temperature region, at low temperboth unselective ammonia oxidation and SCR reactions can result in N2O formation.[7,8,11] The development of robust novel catalyst materials having excellent DeNOx performance and lower N2O formation is necessary
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
