Active Sites in Cr(III)-based Ethylene Polymerization Catalysts from Machine Learning-Supported XAS and EPR Spectroscopy

08 September 2023, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


The ethylene polymerization Phillips catalyst has been employed for decades and is central to the polymer industry. While Cr(III) alkyl species are proposed to be the propagating sites, there is so far no direct experimental evidence for such proposal. In this work, by coupling Surface organometallic chemistry (SOMC), EPR spectroscopy, and machine learning-supported XAS studies, we have studied the electronic structure of well-defined silica-supported Cr(III) alkyls, and identified the presence of several surface species from high to low spin Cr(III), associated with different coordination environments. Notably, low-spin Cr(III) sites are shown to participate in ethylene polymerization, indicating that similar Cr(III) alkyl species could be involved in the related Phillips catalyst.


EPR spectroscopy
X-ray absorption spectroscopy
Machine learning
Phillips catalyst
Surface chemistry
Ethylene polymerization
Cr(III) alkyl

Supplementary materials

Supporting Information
Experimental procedure and additional data


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