Work

Cr(II)/SiO2 Phillips catalysts for olefin polymerization: How calcination and support morphology control site accessibility and polymer microstructure

Year: 2025

Type: article

Abstract: This work presents a comparative spectroscopic and catalytic study of two Cr/SiO2 Phillips-type catalysts supported on industrial-grade Grace-Davison-955 and high-surface-area AGC-DML-302 silicas. By combining DR UV-Vis-NIR and FT-IR spectroscopy of adsorbed CO with in-situ olefin polymerization experiments, we investigated how calcination temperature and support morphology influence the formation, accessibility, and reactivity of Cr(II) active sites. Spectroscopic data reveal that increasing calcination temperature enhances the number of coordinatively unsaturated Cr(II) sites without significantly altering their speciation. While both supports exhibit similar Cr(II)A/Cr(II)B distributions, the Grace-based catalyst shows a lower density of accessible sites. Nevertheless, Cr/Grace outperforms Cr/AGC in ethylene polymerization under standard slurry-phase conditions. This is attributed to its larger pores and greater fragmentation propensity, which enhance monomer diffusion and polymer chain escape. Cr/AGC, on the other hand, produces polyethylene with higher molecular weight and crystallinity, consistent with the confinement effect suppressing chain termination. Under mild conditions, analogous to industrial pre-polymerization steps, the same confinement effect in Cr/AGC leads to amorphous polymer due to limited chain mobility and hindered crystallization. These findings underscore the regime-dependent nature of polymer growth and highlight the value of integrating spectroscopic characterization with catalytic testing to fully understand how support morphology and thermal history shape catalyst performance and polymer architecture.

Source: Journal of Catalysis

DOI: 10.1016/j.jcat.2025.116493

Authors: Shiyang Wang, Anna Maria Fovanna, Chunlin Yang, Boping Liu, Yulong Jin, Elena Groppo

Institutions: South China Agricultural University, National Interuniversity Consortium of Materials Science and Technology, University of Turin

Language: English

Topic: Organometallic Complex Synthesis and Catalysis

Subfield: Organic Chemistry

Field: Chemistry

Domain: Physical Sciences

Open Access status: hybrid

Estimated APC paid: $4,250

Funder: China Scholarship Council