Surface chemistry of selected supported metallocene catalysts studied by DR-FTIR, CPMAS NMR, and XPS techniques

Two supported metallocene catalysts (CS1: PQ 3030/MAO/Cp ₂ZrCl ₂ and CS 2: PQ 3030-BuGeCl ₃/MAO/Cp ₂ ZrCl ₂) were prepared by sequentially loading MAO and Cp ₂ZrCl ₂ on partially dehydroxylated silica PQ 3030. In catalyst CS 2, ⁿBuGeCl ₃ was used to functionalize the silica. These catalysts were characterized by DR-FTIR spectroscopy, CPMAS NMR spectroscopy, and XPS. Their catalytic performance was evaluated by polymerizing ethylene using the MAO cocatalyst and characterizing the resulting polymers by GPC. Both catalysts produced two metallocenium cations (Cation 1: [Cp ₂ZrCl] ⁺ and Cation 2: [Cp ₂ZrMe] ⁺) with comparable equilibrium concentrations and showed varying solid-state electronic environments. The modified supports (PQ 3030/MAO and PQ 3030-BuGeCl ₃/MAO) acted as weakly coordinating polyanions and stabilized the above cations. BuGeCl ₃ did not affect the solid-state electronic environment. However, it increased the surface cocatalyst to catalyst molar ratio (Al:Zr), acted as a spacer, increased catalyst activity, and enhanced chain-transfer reactions. The separately fed MAO cocatalyst shifted the equilibrium between Cation 1 and Cation 2 toward the right. Consequently, more Cation 2 was generated, which acted as the effective and active single-site catalytic species producing monomodal PDI.