Supported bimetallic clusters, effect interactions

The Effect of Support-Metal Precursor Interactions on the Surface Composition of Supported Bimetallic Clusters... 

The effect of precursor-support interactions on the surface composition of supported bimetallic clusters has been studied. In contrast to Pt-Ru bimetallic clusters, silica-supported Ru-Rh and Ru-Ir bimetallic clusters showed no surface enrichment in either metal. Metal particle nucleation in the case of the Pt-Ru bimetallic clusters is suggested to occtir by a mechanism in which the relatively mobile Pt phase is deposited atop a Ru core during reduction. On the other hand, Ru and Rh, which exhibit rather similar precursor support interactions, have similar surface mobilities and do not, therefore, nucleate preferentially in a cherry model configuration. The existence of true bimetallic clusters having mixed metal surface sites is verified using the formation of methane as a catalytic probe. An ensemble requirement of four adjacent Ru surface sites is suggested. 

However, iron complexes may also display a beneficial effect. Thus, a promoting effect on hydroformylation was observed with Si02-supported Rh-Fe " bimetallic carbonyl clusters (Scheme 1.61) [12]. Based on Mossbauer spectroscopy, it was proposed that iron assists during the insertion reaction of CO into the Rh-C bond. Likewise, the hydrogenation of the intermediary alkoxy rhodium species to produce the alcohols may benefit from this bi-site interaction. 

---