EVIDENCE FOR OLEFIN METATHESIS CATALYZED BY METALLIC MOLYBDENUM PROCEEDING VIA AN ASSOCIATIVE MECHANISM AT HIGH-TEMPERATURE

The reaction of ethylene catalyzed by metallic molybdenum at 875 K yie lds higher hydrocarbons (>C-2) with a distribution that is well descri bed by a Schulz-Flory plot suggesting that their formation arises from the polymerization of surface C-1 species. This observation is in acc ord with results from surface science experiments that show facile C=C cleavage in alkenes. A similar molybdenum-catalyzed reaction of propy lene yields metathesis and hydrogenolysis products. In view of the pro duct distribution found with ethylene, these products are proposed to arise from the recombination of surface species formed by propylene di ssociation. This result is confirmed by modifying the Schulz-Flory fun ction assuming equal surface coverages of carbenes and methyl carbenes which adequately predicts the measured product distribution.