This contribution reports a detailed, quantitative investigation of surface chemistry and catalysis involving selected organoactinides and partially dehydroxylated (PDA) or dehydroxylated (DA) alumina supports. For the complexes Cp'2M(CH3)2and Cp'2M(CD3)2(Cp' = η5-(CH3)5C5; M = Th, U), methane-evolving surface reaction pathways are identified as M-CH3protonolysis via surface OH (especially on PDA), Cp' H atom abstraction, and intramolecular elimination of methane within M(CH3)2units. This latter process is proposed on the basis of methylene transfer to acetone and some olefin metathesis activity to result in Al3+-stabilized alkylidenes. Hydrogenolysis studies indicate that ca. 25% of the Cp'2M(CH3)2/DA surface M-CH3groups are removable as methane; reduction of methyl chloride to methane confirms the presence of surface M-H groups produced by hydrogenolysis. The Cp'2M(CH3)2/DA complexes are active catalysts for propylene hydrogenation following a variety of pretreatment conditions, with Nx≈ 0.5 s-1in a flow reactor at -63 °C (about 10 times more active than typical Pt/Si02catalysts under the same conditions). M = Th and U are comparable in hydrogenation activity, and CO poisoning experiments indicate that ca. 3% of the adsorbed molecules is catalytically active. Cp'2M(CH3)2complexes on PDA and silica gel are considerably less active catalysts. The Cp'2M(CH3)2/DA systems are also active catalysts for ethylene polymerization and weakly active for butene isomerization. Experiments with Cp'2Th[CH2C(CH3)3]2and [Cp'2Th(μ-H)H]2on DA reveal activity for propylene hydrogenation comparable to the Cp'2M(CH3)2systems. In contrast, more coordinatively saturated Cp3UCH3and Cp3Th(n-C4H9) (Cp = η5-C5H5) are far less active, while Cp'Th(CH2C6H5)3is far more active (Nt≈ 10 s-1). Much of the stoichiometric and catalytic surface chemistry can be understood in terms of solution organoactinide reactivity patterns.
ASJC Scopus subject areas
- Colloid and Surface Chemistry