LOW REACTIVITY OF RHX CLUSTERS PRODUCED IN THE PRESENCE OF CO

Rhodium dicarbonyl, Rh(I)(CO)2, produced by the CO-induced disruption of Rh(x) crystallites at and below 300 K, undergoes reductive agglomeration in the presence of CO above 448 K or during the high-temperature reaction involving CO. The Rh(x) clusters formed at 523-573 K exhibit a much lower reactivity toward CO than that of the sample produced by reduction with H2 at 1173 K: no or only a limited re-formation of Rh(I)(CO)2 was observed. The effects of several factors are examined. It appears that the surface C produced in the CO dissociation plays a dominant role in preventing the occurrence of the CO-induced disruption at low temperature. The regeneration of reactive Rh(x) clusters can be achieved only by oxidative and reductive treatment at 673 K.