Extended-Hückel calculations on chemisorption. Comparison of the results for acetylene on Ni(111), Rh(111) and Pt(111) surfaces

The application of extended-Hückel calculations to comparative predictions of the chemisorption of acetylene and a number of organic fragments on various metals is tested. The reactivity of the adsorbates to chemisorption on different metals is found to be similar. Ni, Rh and Pt catalyse the rearrangement of adsorbed acetylene to vinylidene, but Ni is found to catalyse the reverse reaction also. However, Ni is the best catalyst for carbon–carbon bond-breaking in acetylene. Adsorbate–adsrobate interactions (of the van der Waals type) force the acetylene molecule to tilt out of the plane parallel to the surface on Ni(100). These interactions are scarcely significant on the (111) face of these three metals. Some results for chemisorption on Co(111) and Ir(111) are presented.