The role of the carbonaceous overlayer in the competitive hydrogenation of cyclopropanes and olefins

In the competitive hydrogenation of olefin-cyclopropane mixtures (2-Me-2-butene + 1,1-diMe-cyclopropane and 2,4-diMe-2-pentene + 1,1,2,2-tetraMe-cyclopropane) over silica supported Pt, Pd and Rh catalysts at 318 K and 373 K, only the olefin is hydrogenated. The other component does not react even after the complete hydrogenation of the olefin. The olefin creates a hydrogen-rich carbonaceous overlayer which is the active phase for its hydrogenation but it is a permanent poison for the hydrogenative ring opening of the cyclopropane ring. On Ni/SiO₂ at 473 K, however, such an overlayer does not form and both reactants transform in parallel in a complex way.