Structure–Property Relationship of Supported Organochromium Catalysts Using Combined Computational XANES Analysis and Mechanistic Simulation
Yu Lim Kim, Jacklyn N. Hall, Jiayi Xu, David M. Kaphan, Massimiliano Delferro, Arthur Jeremy Kropf, Cong LiuABSTRACT
Understanding the structure–activity relationships of single‐site chromium catalysts is important for advancing selective ethylene oligomerization. A series of organochromium catalysts supported on SiO 2 , Li‐modified SiO 2 (Li/SiO 2 ), TiO 2 , and Li‐modified TiO 2 (LiTiO 2 ) have been synthesized and fully characterized, revealing that Cr/LiTiO 2 exhibits superior selectivity toward C 6 olefin products. However, the active site structures and the underlying reaction mechanisms as a function of the support remain elusive due to the large number of possible binding motifs on oxide surfaces. Herein, systematic x‐ray absorption near‐edge structure (XANES) simulations were carried out to build a library of spectra associated with candidate structures of catalytically active species. The most representative catalytic sites and their ratios were identified via integrated qualitative XANES analysis, quantitative XANES scoring, linear combination fitting (LCF), and fitting of extended x‐ray absorption fine structure (EXAFS). Complementary reaction mechanism studies validated the proposed active site models and highlighted the critical role of lithiation in modulating catalyst selectivity. These findings provide valuable molecular insights into the supported organochromium catalysts and demonstrate a generalizable approach for determining active site structures and catalytic properties of supported organometallic catalysts.