Catalytic decomposition of N2O on supported Rh catalysts

Abstract Numerous Rh catalysts were evaluated for N 2 O decomposition for automotive applications. Some Rh-containing spinel materials exhibit excellent fresh activities in the absence of H 2 O but become inactive after hydrothermal aging or when tested in a wet feed. Rh catalysts supported on zeolites can be very active in a dry feed even after aging but are extremely sensitive to H 2 O. Rh/CeO 2 is an exceptional catalyst for this reaction in the presence of both H 2 O and O 2 . Hydrothermal aging (750 °C/20 h) significantly increases its activity. A similar activity enhancement was found by calcining the support before Rh impregnation. XPS results show a surface enrichment of Rh species on the aged Rh/CeO 2 catalyst relative to the fresh catalyst. Aberration corrected STEM images reveal that Rh is buried in the bulk on the fresh catalyst and pulled out onto the surface of the support after thermal treatments. All catalysts are inhibited by H 2 O with the zeolite-based Rh catalysts being the worst. The aged Rh/CeO 2 catalyst is less sensitive to H 2 O relative to others. DRIFTS data show that H 2 O sensitivity is related to catalyst hydrophilicity; a high coverage of OH groups on a catalyst reduces its N 2 O decomposition activity. H 2 -TPR results show that a Rh/CeO 2 catalyst can be readily reduced at 2 catalyst, near complete N 2 O conversion can be obtained with a lean feed at 250 °C for a duration equivalent to its oxygen storage capacity. The N 2 O-DRIFTS experiments over a pre-reduced Rh/CeO 2 catalyst show that Ce 3+ sites are quickly oxidized to Ce 4+ upon contacting N 2 O at room temperature, resulting N 2 and adsorbed O, with the latter being an efficient oxidizer. Based on these results, a N 2 O decomposition mechanism is proposed for the Rh/CeO 2 catalyst.