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Exploring the Synergistic Performance of a Pt-Rh/γ-Al2O3 Catalyst for the Reduction of NO with H2

Paul S. Dimick, Chemical Engineering, Lehigh University, Whitaker Laboratory, 5 E. Packer Ave, Bethlehem, PA 18015, Richard G. Herman, Chemistry, Lehigh University, Seeley Mudd Building, 6 E. Packer Ave, Bethlehem, PA 18015, and Charles E. Lyman, Materials Science and Engineering, Lehigh University, Whitaker Laboratory, 5 E. Packer Ave, Bethlehem, PA 18015.

The performance of two bimetallic Pt-Rh catalysts Pt(95%)-Rh(5%)/γ-Al2O3 (95/5) and Pt(90%)-Rh(10%)/γ-Al2O3 (90/10) was compared to Pt/γ-Al2O3 and Rh/γ-Al2O3 for the reduction of NO with H2 resulting in the following order of relative activity: 95/5 > Pt/γ-Al2O3 ≈ 90/10 > Rh/γ-Al2O3. A conditioning step, equilibrating the catalyst to reaction conditions at 250C for 10 h, was necessary to observe the maximum synergistic performance of 95/5, a five-fold increase over the activity of Pt/γ-Al2O3. Prior to conditioning, 95/5 had similar activity to Pt/γ-Al2O3. The prepared catalysts were characterized with in-situ FTIR spectroscopy and electron microscopy to gain insight into the difference in performance between 95/5 and 90/10. In-situ FTIR studies were conducted using NO and NO + H2 as probes to qualitatively examine the surfaces of the supported Pt-Rh alloy nanoparticles. Results indicate that metallic Pt and Rh are both present on the surface of 95/5, while the surface of 90/10 contains oxidized Rh in addition to metallic Pt. The non-synergistic performance of 90/10 is attributed to the presence of oxidized Rh and/or an increased surface fraction of Rh.