On the Activity and Selectivity of Ag/Al2O3 Catalyst During the Lean Reduction of NO by C3H8 Studied At High Space Velocities

Monday, October 17, 2011: 4:35 PM
200 C (Minneapolis Convention Center)
M. Eugenia Hernández-Terán1, Isidro Mejia-Centeno2, Sergio A. Gómez1 and Gustavo A. Fuentes1, (1)Department of Process Engineering, UAM-Iztapalapa, Mexico DF, Mexico, (2)División de Química Molecular, Instituto Mexicano del Petróleo, Mexico, DF, Mexico

Ag/Al2O3 is considered a promising catalyst for the direct selective lean reduction of NOx by hydrocarbons and oxygenates. It has been reported to have high activity, good selectivity to N2, stability, durable activity in presence of water and SO2, moderate operating temperature window and relatively low cost (1-4). Most of the studies have been made at low space velocities, however, and that difficults the analysis of intermediates and the effect of catalyst composition.

In this study we present results obtained at high space velocities (F/W =666-32,000 cm3.g-1.min-1) using a ~2 wt% Ag/Al2O3 catalyst prepared by impregnation. The feed gas mixture contains 200 ppm NO, 1750 ppm C3H8, 3% O2 and 6% H2O diluted in nitrogen as a balance gas. The reactions were carried out in a tubular quartz microreactor equipped with a mass flow controllers and PID temperature control. The gas analyses were done by GC (HP 6890 and Shimadzu GC-12A), on line with an FTIR (Bruker Tensor 27) equipped with 0.75 m path-length infrared gas cell heated at 120ºC to prevent condensation, and a chemiluminescence NO-NOx analyzer (Rosemount 951A).

We observed that the reduction of NO with C3H8 occurs in the 375-500°C temperature range in the absence of H2. By adding a small amount of H2 to the feed the light-off temperature decreases nearly 200ºC. These results are in line with those reported in the literature (2), but operation at high F/W shows that our catalyst is significantly more active in the reduction of NOx. The conversion - W/F behavior, particularly at low temperature, suggests that the mechanism involves consecutive reactions. This issue is being studied and will be discussed further. Characterization of the catalysts using UVVis in situ allows us to understand the role of Ag nanoparticles and AgOx species present under reaction conditions and to dwelve into the reason for the high activity of this class of catalysts.

References

  1. Midyadera, T., Appl. Catal. B 2 (1993) 199.
  2. Zhu, T., Hao, J., Fu, L., Li, J., Liu, Z., React. Kinet. Catal. Lett. 84,1(2005) 61.
  3. She, X., Flytzani-Stephanopoulos, M., Catalysis Today 127 (2007) 207.
  4. DiMaggio, C., Fisher, G., Rahmoeller, K., Sellnau, M., SAE Paper 2009-01-0277

Extended Abstract: File Not Uploaded
See more of this Session: Applied Environmental Catalysis II
See more of this Group/Topical: Catalysis and Reaction Engineering Division