Figure 7.

Operando IR spectroscopy allows the detection of the formation of oxygenated byproducts during the reduction of Cr(VI)/SiO₂ by ethylene. These byproducts are responsible for a structural rearrangement of the reduced chromium sites, which precedes ethylene polymerization. (a) Operando IR spectra collected during reaction of ethylene with Cr(VI)/SiO₂ at 150 °C. Color code: black, spectrum collected prior ethylene dosage; gray, spectra collected in the presence of ethylene as a function of time; and green, spectra collected after 30 min. (b–d) Final spectra after subtraction of those collected prior to ethylene dosing, magnified in (b and d) two spectral regions characteristic of the oxygenated byproducts and (c) in the region containing the first overtone of the ν(Cr=O) vibrational mode. Spectra reproduced with permission from ref (130). Copyright 2017 American Chemical Society.