Original Paper

Topics in Catalysis

, Volume 55, Issue 5, pp 300-312

First online:

Aqueous N2O Reduction with H2 Over Pd-Based Catalyst: Mechanistic Insights From Experiment and Simulation

  • Dorrell C. McCalmanAffiliated withDepartment of Chemical and Biomolecular Engineering and Department of Chemistry and Biochemistry, University of Notre DameCenter of Advanced Materials for the Purification of Water with Systems, University of Illinois at Urbana-Champaign
  • , Kathleen H. KelleyAffiliated withDepartment of Chemistry and Center of Advanced Materials for the Purification of Water with Systems, University of Illinois at Urbana-Champaign
  • , Charles J. WerthAffiliated withDepartment of Civil and Environmental Engineering, and Center of Advanced Materials for the Purification of Water with Systems, University of Illinois at Urbana-Champaign
  • , John R. ShapleyAffiliated withDepartment of Chemistry and Center of Advanced Materials for the Purification of Water with Systems, University of Illinois at Urbana-Champaign Email author 
  • , William F. SchneiderAffiliated withDepartment of Chemical and Biomolecular Engineering and Department of Chemistry and Biochemistry, University of Notre DameCenter of Advanced Materials for the Purification of Water with Systems, University of Illinois at Urbana-Champaign Email author 

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Abstract

Nitrous Oxide (N2O), an ozone depleting greenhouse gas, is an observed intermediate in aqueous nitrate/nitrite reduction mediated by both natural microbial and synthetic laboratory catalysts. Because of our interest in catalytic nitrate/nitrite remediation, we have endeavored to develop a detailed concordant experimental/theoretical picture of N2O reduction with H2 over a Pd catalyst in an aqueous environment. We use batch experiments in H2 excess and limiting conditions to examine the reduction kinetics. We use density functional theory (DFT) to model the elementary steps in N2O reduction on model Pd(100), Pd(110), Pd(111) and Pd(211) facets and including the influence of adsorbed O, H, and of H2O. Both experiments and theory agree that hydrogen is necessary for removal of adsorbed oxygen from the catalyst surface. The dissociation of N2O to N2(g) and O(ads) is facile and in the absence of H proceeds until the catalyst is O-covered. Water itself is proposed to facilitate the hydrogenation of surface O by transferring absorbed hydrogen to Pd-absorbed O and OH. We measure an apparent activation energy of 41.4 kJ/mol (0.43 eV) for N2O reduction in the presence of excess H2, a value that is within 0.1 eV of the barriers determined theoretically.

Keywords

Nitrous oxide reduction Hydrogen Palladium Aqueous Density functional theory