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Cobalt Substituted for Rhodium in an Experimental NO Reduction Catalyst

The effectiveness of supported bimetallic catalysts depends on the surface structure and composition of the active phase, which is typically present as nanoparticles. Bimetallic nanoparticles that perform better than either metal component alone are termed synergistic. The ideal nanoparticle surface microstructure for achieving synergy in a Pt-Rh catalyst for NO reduction with H 2 as been proposed: single atoms of Rh surrounded by Pt [1]. By applying our understanding of how to form and tailor bimetallic nanoparticles, we designed and synthesized a synergistic Pt-Co catalyst by mimicking the microstructure of the synergistic Pt-Rh catalyst and replacing Rh with Co [2]. The Pt-Co particles were formed and tailored by applying time-temperature-atmosphere treatments to sequentially impregnated metal salt precursors. The Pt-Co alloy nanoparticles thus formed were synergistic in activity and selectivity, both with and without calcining after the addition of the Pt component (Figure 1). While both preparation routes produced catalysts with similar activity, the uncalcined catalyst produced 4x more N 2 compared to N 2 O + NH 3 than Pt/ γ -Al 2 O 3 and the calcined catalyst produced 2.5x more N 2 compared to N 2 O + NH 3 than Pt/ γ -Al 2 O 3 . Synergistic performance was not observed until the bimetallic catalysts were conditioned exposure to reaction conditions at 250 o C. Since the catalysts were prepared by the decomposition of metal-salt precursors, a distribution of nanoparticles in both size and composition may be present on the catalyst support. Since most of the observed nanoparticles are less than 5 nm, aberration-corrected scanning transmission electron microscopy was used to identify differences in nanoparticle size and structure. Figure 2 shows a HAADF image of a synergistic Pt(98wt%)C-Co(2wt%)/