Comparative study of Rh/MgO modified with Fe, Co or Ni for the catalytic partial oxidation of methane at short contact time. Part I: Characterization of catalysts

Rh/MgO catalysts modified with Fe, Co and Ni for the catalytic partial oxidation of methane were investigated by means of temperature-programmed reduction (TPR), H2 adsorption measurement, transmission electron microscopy (TEM) and extended X-ray absorption fine structure studies (EXAFS). The reduction of the additives (Fe, Co, Ni) on MgO was promoted by the presence of Rh, and the reducibility was Fe > Co > Ni. The Rh-Ni/MgO tends to give the metal particles with higher dispersion than Rh/MgO. In contrast, the addition of Fe to Rh/MgO aggregated the metal particles. The Co addition did not affect the size of metal particles so significantly. The Rh–M alloy formation (M = Fe, Co, Ni) was detected by the Rh K-edge and M K-edge EXAFS analyses. The miscibility of the additives with Rh is also discussed on the basis of the EXAFS analysis, and this property can be related to the surface concentration of the additives on the alloy particles.

On Rh-Fe/MgO, added Fe is almost fully reduced to form large Rh–Fe alloy particles. On Rh-Ni/MgO, a part of the added Ni is reduced to form small Rh–Ni alloy particles. Added Co was reduced to some extent to form Rh–Co alloy particles, where the miscibility of Co with Rh can be lower than that of Fe and Ni.Figure optionsDownload high-quality image (104 K)Download as PowerPoint slide