INFLUENCE OF THE PT RH MOLAR RATIO ON THE FINAL STRUCTURE OF BIMETALLIC RHPT CLUSTERS SUPPORTED ON NAY ZEOLITE/

The EXAFS analysis of two complete series (differing in the total amou nt of metal) of RhPt bimetallic clusters supported on NaY, having vari ous Ph/Pt molar ratios (1/0, 7/1, 4/1, 2/1, 1/1, 1/2, 1/4, 1/7, 0/1), enabled us to evaluate the influence of the molar ratio on the final s tructure of the clusters. In particular, we attempted to determine the degree of randomness of the metallic bonds. The coordination numbers Ph-Ph and Rh-Pt at the Ph-edge and Pt-Pt and Pt-Rb at the Pt edge vari ed according to the molar ratio, but this variation was not directly p roportional to the ratio. When Ph predominated (Rb/Pt=2/1, 4/1, 7/1) t he metal-metal bonds were not statistically distributed. The coordinat ion numbers at both absorption edges indicated a prevailing presence o f monometallic bonds, thus suggesting the presence of monometallic clu sters in addition to bimetallic clusters. On the other hand, when Pt a toms were predominant (Rh/Pt=1/2, 1/4), the distribution of the metal- metal bonds was much more random, and, in the case of Rh/Pt=1/7, the c oordination numbers indicated an almost completely random structure. T hese results can be related to the initial formation of the metal atom s.