Search Results

The performance of a commercial Cu-zeolite SCR catalyst after differing degrees of hydrothermal aging (aged for 72 hours at 500, 700 and 800°C with 10% moisture balanced with air) was studied by spatially resolving different key reactions using gas-phase FTIR measurements. Gases were sampled along a channel at different positions and analyzed using FTIR, which overcomes the interference of water and nitrogen on ammonia concentration detection encountered in standard mass spectrometer-based spatial resolution measurements. The NO:NO₂ concentration ratio was changed so that the standard (NO:NO₂ = 1:0), fast (NO:NO₂ = 1:1) and NO₂ (NO:NO₂ = 0:1) SCR reactions could be investigated as a function of the catalyst's hydrothermal aging extent. In addition, the effects of hydrothermal aging on the activity of NH₃ and NO oxidation were also investigated. Hydrothermal aging had little effect on NO oxidation activity.

The performance characteristics of a commercial lean-NOX trap catalyst were evaluated between 200 and 500°C, using H2, CO, and a mixture of both H2 and CO as reductants before and after different high-temperature aging steps, from 600 to 750°C. Tests included NOX reduction efficiency during cycling, NOX storage capacity (NSC), oxygen storage capacity (OSC), and water-gas-shift (WGS) and NO oxidation reaction extents. The WGS reaction extent at 200 and 300°C was negatively affected by thermal degradation, but at 400 and 500°C no significant change was observed. Changes in the extent of NO oxidation did not show a consistent trend as a function of thermal degradation. The total NSC was tested at 200, 350 and 500°C. Little change was observed at 500°C with thermal degradation but a steady decrease was observed at 350°C as the thermal degradation temperature was increased.

The effects of propylene (C₃H₆) and dodecane (n-C₁₂H₂₆) exposure on the NH₃-based selective catalytic reduction (SCR) performance of two Cu-exchanged zeolite catalysts were investigated. The first sample was a model Cu/beta zeolite sample and the second a state-of-the-art Cu/zeolite sample, with the zeolite material characterized by relatively small pores. Overall, the state-of-the-art sample performed better than the model sample, in terms of hydrocarbon inhibition (which was reduced) and N₂O formation (less formed). The state-of-the-art sample was completely unaffected by dodecane at temperatures lower than 300°C, and only slightly inhibited (less than 5% conversion loss), for standard SCR, by C₃H₆. There was no evidence of coke formation on this catalyst with C₃H₆ exposure. The model sample was more significantly affected by hydrocarbon exposure. With C₃H₆, inhibition is associated with its partial oxidation intermediates adsorbed on the catalyst surface.