Enhanced performance of Pd-[DBU][Cl]/AC mercury-free catalysts in acetylene hydrochlorination

Abstract

Compared with the rapid deactivation of the Pd/AC catalyst, an eco-friendly Pd-[DBU][Cl]/AC ([DBU][Cl], 1,8-diazabicyclo[5.4.0]undec-7-ene hydrochloride) catalyst with enhanced stability was synthesized and applied in the hydrochlorination of acetylene. The Pd-20[DBU][Cl]/AC catalyst exhibits 96.7% acetylene conversion and 98.9% selectivity of vinyl chloride within the 24 h evaluation under the conditions of T = 180 °C, GHSV(C2H2) = 360 h–1 and V(HCl)/V(C2H2) = 1.2. The enhanced stability of the Pd-[DBU][Cl]/AC catalyst is attributed to the prevention of the reduction of Pd(II) to Pd(0), the inhibition of the formation of coke deposition on the catalyst surface, and the reduction of the loss of Pd species during the reaction. TPD characterization and DFT theoretical simulations confirmed that the PdCl2-[DBU][Cl] complex has stronger adsorption of HCl and weaker adsorption of C2H2 and C2H3Cl compared to PdCl2. Furthermore, the catalytic mechanism of acetylene hydrochlorination over the PdCl2 and PdCl2-[DBU][Cl] site was put forward based on theoretical simulations. The good activity and stability of Pd-20[DBU][Cl]/AC in the 60 h lifetime test indicates that it is likely to be a promising alternative to HgCl2 catalysts.