H-1-NMR OF HYDROGEN CHEMISORBED ON PT-AU/AL2O3 CATALYSTS - EVIDENCE FOR THE FORMATION OF MIXED PARTICLES

The evolution of the Pt-Au/Al2O3 system with the reduction time can be followed by (1)HNMR of chemisorbed hydrogen. When the reduction time increases, the signal with the positive shift, due to hydrogen chemisorbed on pure gold, decreases and disappears completely. At the same time there is a large variation in the negative chemical shift of the hydrogen chemisorbed on the particles containing platinum. This evolution of the NMR spectra demonstrates that mixed Pt-Au particles are formed. Although it appears that after a very long reduction time the platinum covers the gold, the distribution of these two metals in the particles at the atomic scale cannot be determined by this technique.