(617r) Understanding Direct NOx Decomposition over Pdo/SiO2: Influence of Reaction Temperature and Pretreatment

More stringent emission requirements highly demand advanced NOx abatement methods to purify NOx from emission exhaust. While the automotive industry continues to improve existing 3-way catalyst systems as well as developing new technologies for emission control under lean conditions, direct NO_x decomposition (dNOd) provides an ultimate solution as NO_x is converted into environmental friendly N₂ and O₂ withoutthe need of a secondary reducing agent. However, the discovery of an effective catalyst to drive the kinetically sluggish dNOd reaction remains the biggest hurdle for scientific research. Several types of catalysts such as perovskites,¹ rare earth oxides,² ceria based oxides³ were reported for direct NOx decomposition. However, these catalysts are typically only active at temperatures higher than the emission exhaust. For instance, although platinum group catalysts (PGMs) exhibit decent activity at temperatures higher than 500 °C, at lower temperatures they suffer from severe deactivation issue.^4,5 A mechanistic study about dNOd on PGM is clearly beneficial to provide fundamental insights for the design of novel catalysts. For this purpose we used PdO supported on silica as a model system to investigate dNOd in a broad temperature region from 100 to 800 ^oC, focusing on the effect of structural and surface properties of PdO/SiO₂ on the catalytic performance. Using a series of characterization techniques such as XRD and XPS, the dNOd mechanism was revealed to be highly dependent on reaction temperatures, suggesting different strategies should be applied to improve the performance at different temperature regions. In addition, the activity was critically affected by the pretreatment of the catalyst before the reaction. Our results provide the first-hand evidence about a reaction with both scientific significance and technical importance. The insights from our work towards the design of novel dNOd catalysts will also be discussed.

References

1. J. Zhu, A. Thomas, Appl. Catal. B, 92, 2009, 225

2. H. Masaki, et al, J. Alloys and Comp. 451, 2008, 406

3. N. Drenchev, et al. Appl. Catal. B,138â?? 139, 2013, 362

4. S. Naito, et al. Catal. Today ,73, 2002, 355

5. J.D. Consul, et al. J. Mol. Catal. A, 246, 2006, 33