Construction of a Thermally Stable Low-HgCl<sub>2</sub> Catalyst via Chalcogen Bonding and Its Enhanced Activity in Acetylene Hydrochlorination
Songyuan Sun, Haomiao Xu, Yurui Fan, Zhisong Liu, Qinyuan Hong, Wenjun Huang, Zan Qu, Naiqiang Yan
Abstract
The polyvinylchloride industry is an important mercury emission source derived from the decomposition of commercial activated carbon-supported mercuric chloride (HgCl2/AC, with 12–15 wt % HgCl2) in acetylene hydrochlorination. Our results indicated that the loss of mercury was ascribed to the Hg–Cl bond breaking from the HgCl2 molecule at elevated temperatures that resulted in slip Hg0 in the exhausted gas. Herein, we employed a novel strategy that uses chalcogen bonding (ChB, e.g., S-, Se-, and Te-) interactions to anchor HgCl2 molecules, to improve the thermal stability and catalytic performances. The mercury desorption temperature reached approximately 300 °C, which is much higher than the optimum hydrochlorination reaction temperature. Notably, low-mercury catalysts (5 wt % HgCl2) guaranteed high catalytic performances, and Se–HgCl2/AC exhibited 83% acetylene conversion efficiency and near-perfect 100% selectivity. Moreover, the online mercury monitoring results showed that Se–ChB significantly inhibited the escape of mercury during the reaction. Density functional theory results confirmed that the reaction followed an Eley–Rideal (E–R) mechanism, which showed that the strong adsorption of HCl endowed the catalyst with superior durability and facilitated the reaction by reducing the energy barrier from 0.94 to 0.54 eV. Thus, the new strategy for highly stable low-mercury catalyst preparation can solve the problem of mercury contamination and enhance the productivity of PVC production.