Identification of catalytically active sites on reduced molybdena-alumina catalysts

Abstract

Nitric oxide selectively poisoned propylene metathesis over alumina- or silica-supported molybdenum carbonyl (Catalyst A). Nitric oxide selectively poisoned olefin hydrogenation, but not metathesis or isomerization, over reduced molybdena-alumina catalysts (catalyst B). IR spectroscopy revealed dinitrosyl surface complex on the poisoned catalysts. The over-all reaction rate of a 5:1 mixture of hydrogen-propylene at 200/sup 0/C was over 15 times higher on A than on B, but both catalysts yielded similar product distributions. The dimeric nature of the NO species on catalyst B was confirmed with nitrogen-15 labeled nitric oxide. The oxidation state of molybdenum in catalyst A was +2 and in catalyst B, near +4. The data suggested that the active site for hydrogen activation is multiply coordinatively unsaturated and probably involves molybdenum(III) centers. The study was partly based on available data.