(268a) NO Reduction by H2 On Platinum Catalysts

Environmental concerns and the resulting increasingly stringent regulations motivate the development of highly efficient processes for the selective reduction of NO to N₂. Typical three-way catalysts, which reduce NO to N₂ in automotive exhaust, contain Pd or Pt and Rh, with Rh as the metal that accounts for the high selectivity to N₂.^1-2 Despite the efficacy of these catalysts, the high cost and low availability of Rh motivate the development of Rh-free catalysts for NO reduction. When utilized independently for the low temperature reduction of NO by H₂, Pt catalysts demonstrate high conversion of NO but low selectivity toward N₂ and unfavorable production of side-products, namely N₂O and NH₃.^3-4 We will discuss a Density Functional Theory approach combined with experimental kinetic and isotopic studies of NO reduction by H₂ on Pt to probe key elementary steps with specific emphasis on the relative importance of direct versus H-assisted pathways in NO dissociation. The experimental evidence for weak cluster size effects on turnover rates and selectivity led us to consider these elementary steps using periodic DFT methods on low-index Pt(111) facets. The experimental and theoretical evidence is consistent with the presence of chemisorbed NO and H-atoms as the most abundant surface species and with the involvement of H-atoms in the activation of NO molecules and the formation of N₂O, N₂ and NH₃ products.

1. Heck, R. M.; Farrauto, S. T.; Gulati, S. T., Catalytic Air Pollution Control: Commercial Technology Wiley, New Jersey 2009.

2. Taylor, K. C., Automotive Catalytic Converters Springer, Berlin 1984.

3. Kobylins, T. P.; Taylor, B. W., Catalytic chemistry of nitric-oxide 2. Reduction of nitric-oxide over noble-metal catalysts. Journal of Catalysis 1974, 33 (3), 376-384.

4. Taylor, K. C.; Klimisch, R. L., The catalytic reduction of nitric oxide over supported ruthenium catalysts. Journal of Catalysis 1973, 30 (3), 478-484.