Area of research
Catalysis · Organic Chemistry
Research interest
Research topics from publications: Mechanism of Initiation in the Phillips Ethylene Polymerization Catalyst: Redox Processes Leading to the Active Site; Mechanism of Initiation in the Phillips Ethylene Polymerization Catalyst: Ethylene Activation by Cr(II) and the Structure of the Resulting Active Site. Representative work: The detailed mechanism by which ethylene polymerization is initiated by the inorganic Phillips catalyst (Cr/SiO2) without recourse to an alkylating cocatalyst remains one of the great unsolved mysteries of heterogeneous catalysis. Generation of the active catalyst starts with reduction of CrVI ions dispersed on silica. A lower oxidation state, generally accepted to be CrII, is required to activate ethylene to form an organoCr active site. In this work, a mesoporous, optically transparent monolith of CrVI/SiO2 was prepared using sol–gel chemistry in order to monitor the reduction process spectroscopically. Using in situ UV–vis spectroscopy, we observed a very clean, stepwise reduction by CO o The structure and mechanism of the formation of sites which initiate ethylene polymerization in the atomically dispersed Phillips catalyst (Cr/SiO2) are two of the great unsolved mysteries of heterogeneous catalysis. After CO or C2H4 reduction of silica-supported CrVI ions to CrII ions in the precatalyst, exposure to ethylene results in the formation of organoCrIII sites that are capable of initiating polymerization without recourse to an external alkylating cocatalyst. In this work, a Phillips catalyst prepared, via sol–gel chemistry, as a mesoporous, optically transparent monolith was reduced with CO to the spectroscopically determined CrII end point. Ethylene causes rapid reoxidation of t