“Surface Organometallic Chemistry: Newselective Bimetallic Ru-Sn/SiO₂ Catalysts Prepared by Reaction of Tetra-N-Butyl Tin with RuO₂ Supported on Silica”

The reaction of tetra-n-butyl tin with superficially oxidized supported ruthenium particles occurs at moderate temperature, from 323 to 673 K, via a two steps process. Only butane and butenes are evolved in a total amount close to 4 C4 radicals per anchored tin atom. The Sn/Ru ratio can reach a value as high as 3 via this procedure. Electron microscopy studies indicate that the size of the particles increases slightly as the reaction between SnBu⁴ and superficial RuO2 goes on. These particles have an homogeneous bimetallic composition as demonstrated by STEM and no tin signal is detected in significant amount on the support. Chemisorption of both H2 and CO is strongly inhibited by the addition of tin. Depending on the Sn/Ru ratio, the selectivity for the hydrogenolysis of ethyl-acetate can be quite different. With Ru/SiO2, the reaction is not selective: CH4, C2H6, CO, CO2 as well as ethanol and acetic acid are produced. Low tin content catalysts are fairly selective for the formation of acetic acid; while at higher Sn/Ru ratios, ethanol is the only detected product. A mechanism based on the concept of “site isolation” is proposed.