CU-RU/MGO SYSTEMS - SPECTROSCOPIC EVIDENCE OF THE FORMATION OF BIMETALLIC PARTICLES - CO ADSORPTION AND CO-O2 INTERACTION

Ru/MgO, Cu/MgO, and Ru-Cu/MgO systems were characterized by FT-IR spectroscopy of adsorbed CO. The systems studied contained a total amount of metal of about 2 wt%: RCM100, RCM083, RCM070, RCM046, RCM034, and RCM000, with Ru/(Cu + Ru) atomic ratios 1, 0.83, 0.70, 0.46, 0.34, and 0.00, respectively. A comparison was made between the spectroscopic results and the catalytic properties in propane hydrogenolysis. On the Ru/MgO (RCM100) system CO originated an asymmetric band centered at 2038cm-1, shifting to lower frequency upon evacuation, in the spectral range of CO linearly adsorbed on (0001) faces. On Cu/MgO (RCM000) CO revealed the presence of two sites on which CO is adsorbed linearly giving bands at 2078 and 2060 cm−1. On RCM083 catalyst large islands of uncovered Ru coexisted with areas of Ru heavily decorated by Cu, as revealed by the presence, upon CO adsorption, of a band at ≈2040 cm-1 and of a very broad band at ν < 2000 cm-1. On RCM070 catalyst only areas of Ru heavily decorated by Cu were present, while on RCM046 and RCM034 samples large islands of uncovered Ru coexisted with areas of Ru heavily decorated by Cu, despite the increase in the Cu content. On the four bimetallic catalysts a variety of Cu(0) sites were revealed, bonding CO linearly (sharp CO stretching bands in the 2140-2098 cm-1 region), belonging to different Cu aggregates adsorbed on Ru microcrystals. These results are consistent with those obtained by catalytic measurements: the minimum catalytic activity and the maximum selectivity in ethane formation are found for the RCM070 sample, which shows only surface Ru(0) heavily decorated by Cu, as expected. © 1993 Academic Press, Inc.