Catalyst continued rhenium

Catalyst deactivation. The molybdenum-based catalysts deactivate faster than the rhenium-based ones. Studies concerning the stability of the catalyst during continuous metathesis of propene showed a loss of activity due to an intrinsic deactivation mechanism. Because of the high stability of both [Mo]=CH2 and [Mo]=CHCH3, the deactivation of the catalyst is assigned to isomerization of the intermediate metallacyclobutane complexes, leading to inactive 7i-complexes, in a way analogous to that depicted in Scheme 2. This hypothesis is supported by in situ UV/vis spectroscopic studies [67]. 

A special volume is dedicated to the papers from the 9th International Symposium on Olefin Metathesis.274 xhe development of well-defined metathesis catalysts is the subject of a review s and some theoretical calculations. 276 However, the development of mixed component systems continues with molybdenum and rhenium carbonyls and nitrosyl precursors enjoying topical popularity. 

Molybdenum and rhenium oxide eatalysts based on siliceous mesoporous sieves and OMA, respectively, proved enhanced catalytic activity in comparison witii corresponding catal) using conventional supports. The origin of tiiis enhanced activity is not completely clear and is still a subject of discussions and continuous research. The better accessibility of catalysts site located in mesopores undoubtedly represents tire essential contribution to the increased catalytic activity. Rhenium (VII) oxide on organized mesoporous alumina preserves known tolerance of Re catalysts to the polar-substituted olefins. The presence of cocatalysts like Mc4Sn is essential similarly as for conventional systems. However, tire catalysts with higher pore size were found to deliver better results. 

The success of the platinum/rhenium catalyst was evident, as more than 80% of all catalyst replacement charges were bimetallic by 1972. By then 30% of all reformers were using the rhenium catalyst." Acceptance continued in all reforming processes so that more than two-thirds of installed catalyst capacity was bimetallic by 1979." " Catalyst improvements also continued during this period, and the original Chevron catalyst. Grade A, was replaced several times up to Grade F. ... 

---