Carbon dioxide reforming with Rh and Pt-Re catalysts dispersed on ceramic foam supports

Considerable research over the past decade has indicated that supported rhodium is the best overall catalyst, in terms of activity and stability, for dry reforming of methane with carbon dioxide. An alternative catalyst is Pt-Re with a mass Pt/Re ratio of 0.25 supported on gamma-Al2O3 that gives equivalent stability although with less activity. This paper describes the loading of this catalysts onto washcoated alpha-Al2O3 and the advantages arising from the unique properties of the foams as catalyst supports. Procedures are given for adding high surface area washcoats of gamma-Al2O3 to 20- and 30-pores per inch (PPI) alpha-Al2O3 foams and for impregnating them with precursor solutions to obtain uniform deposits of Rh or Pt-Re complexes. Comparison with similar commercial catalysts indicate equivalent rates using foams and crushed catalysts, thereby showing that intrinsic activities displayed by the crushed catalysts were successfully reproduced with the foams. In the case of Rh, comparison with 3.2-mm pellets show a large enhancement in rate, since the pellets and foam exhibited low and high effectiveness factors, respectively. Measured power law rate equations for foams demonstrated a positive CO2 order with Rh and but a negative order for Pt-Re, consistent with a mechanism which ascribed the activity enhancement of Pt-Re to strong chemisorption Of CO2 on the Re sites. Long-term stability is observed for both systems, except that deactivation below 700 degreesC occurs for Pt-Re due to CO2 poisoning of the sites. The results a 1-D mathematical model confirm that improved heat transfer gives more uniform temperature distribution during reaction in the foam. This research confirms that, while Rh is the best overall catalyst, Pt-Re is an attractive alternative for purely dry reforming. (C) 2003 Elsevier B.V. All rights reserved.