Density functional theory and microkinetics of ethylene chain growth and termination on silica grafted group 4 metal hydrides

Abstract

The creation and ethylene oligomerization function of silica-anchored group 4 metal (M = Ti, Zr, Hf) hydrides as a function of anchor site structure are explored using density functional theory models. Oligomerization potential energy surfaces are sensitive both to metal ion and to the structure of the anchoring site. Microkinetic models predict oligomerization rate and degree of polymerization as a function of site, temperature, and reactant pressures. Intrinsic catalytic activity is predicted to vary as Ti < Zr > Hf down the group, irrespective of site model, while absolute rates and product distributions are strongly sensitive to site model, temperature, and hydrogen pressure. Catalysts based on these sites are plausible candidates for high-temperature ethylene oligomerization of interest for generating fuels from ethylene, but selectivity is expected to require careful control over site structure and reaction conditions.