Dynamic Active Site Evolution in Lanthanum‐Based Catalysts Dictates Ethane Chlorination Pathways

Abstract Radical‐mediated chlorination of ethane presents a low‐carbon alternative for polyvinyl chloride (PVC) synthesis, yet selectivity toward 1,2‐dichloroethane remains challenged by uncontrolled over‐chlorination. Lanthanum oxychloride (LaOCl) has emerged as a promising catalyst, but its structural dynamics under Cl 2 ‐rich conditions and the origin of selectivity loss remain elusive. Here, we integrate advanced spectroscopic techniques with theoretical calculations to address this knowledge gap. Our findings unveil a sequential LaOCl → LaCl 3 transformation that dictates product distribution shifting from 1,2‐dichloroethane to trichloroethane. Mechanistic insights reveal that surface hydroxyl groups, generated during catalyst chlorination, promote bidentate adsorption of 1,2‐dichloroethane via hydrogen‐bond networks, thereby activating C─Cl over‐chlorination. Additionally, by employing Al 2 O 3 ‐supported LaCl 3 model catalysts, the size‐dependent chlorophilicity of the LaCl 3 species is demonstrated. The bonding of interfacial oxygen with monolayer‐dispersed LaCl 3 species generates empty 4f‐states above the Fermi level, creating strong Lewis acid sites that stabilize Cl radicals and selectively convert chloroethane to 1,2‐dichloroethane. In contrast, aggregated nanoparticles are inactive due to their inability to stabilize chlorine radical. Our findings establish important structure sensitivity in lanthanum‐catalyzed chlorination and provide guiding principles for catalyst design, highlighting the importance of stabilizing metastable LaOCl x species and modulating surface hydroxyl chemistry to overcome selectivity limitations.