Elucidating Structural Characteristics of Catalysts at the Nanometer or Atomic Level

2 Elucidating Structural Characteristics of Catalysts at the Nanometer or Atomic Level 

Early transition metal carbides are catalyticaUy active for a variety of reactions. Since they are refractory and of high surface area, they could also be promising alternatives to oxides as supports for heterogeneous catalysts. Only a few investigations have used them for this purpose. And in these limited investigations, the metals were loaded onto intentionally passivated Mo C powders due to their high pyrophoricity. 

FIGURE 4.3 Mossbauer spectra of (a) the as-prepared Fe O C spheres, recorded at 298 K (b) Fe O C spheres reduced by 5% FI /Ar at 673 K for 16 h, recorded at 298 K and (c) sample (b), recorded at 15 K. The computer fits are shown as solid Unes. Reprinted with permission from Ref. [64]. American Chemical Society. (See insert for color representation of the figure.) 

Therefore, the loaded metals virtually interacted with an oxidized surface rather than the native carbide surface. Schweitzer et al. developed a synthesis method that could allow a direct contact of Pt with the genuine Mo C surface [65]. In the WGS reaction, the resulting Pt/MOjC catalysts exhibited a higher activity than the most active oxide-supported Pt catalysts and a commercial Cu-Zn-Al catalyst. Moreover, the experimental rates were more consistent with those predicted by the perimeter model than by the particle surface model, suggesting that the rate-determining step for WGS on Pt/Mo C catalysts occurred at the perimeters of the Pt particles. 

FIGURE 4.4 High-resolution H AADF-STEM electron micrographs of (a) a Pt particle supported on MOjC and (b) a Pt particle supported on carbon, (c) Intensity line scans for the Pt particle supported on Mo C in (a) and the Pt particle supported on carbon in (b). Reprinted with permission from Ref. [65]. American Chemical Society. 

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