Tracer studies of cyclopropane reactions on molybdena-alumina catalysts

The oxidation state of a molybdena-γ-Al2O3 (8%) catalyst was varied by reduction with either H2 or CO under carefully controlled conditions. The decomposition of cyclopropane was studied and correlations were sought between surface chemistry and catalytic function. Temperatures between 50 and 1300C and a pulse reactor were employed. In every case propylene, ethylene, and n-butenes were produced in proportions depending upon the extent of reduction. When cyclopropane was reacted over a catalyst reduced with D2, deuterated propylenes were formed in increasing percentages with higher extents of reduction. Similar results were obtained when the catalyst was first thoroughly reduced with D2, then reoxidized and finally reduced to different extents with CO. When mixtures of cyclopropane-d0 and -d6 were co-isomerized, the products were readily equilibrated. Methylcylopropane reacted much faster than cyclopropane, yielding both isomerization and metathesis products. No trace of isobutane was detected. A small portion of the first cyclopropane to contact the catalyst reacted to form ethylene and the methylene carbene. Otherwise the data were consistent with a proton-catalyzed ring opening followed by metathesis on coordinatively unsaturated Mo (IV) ions occurring through a carbene mechanism. The results are discussed in terms of current literature