Synergetic effect between Pd2+ and Ir4+ species promoting direct ethane dehydrogenation into ethylene over bimetallic PdIr/AC catalysts

Abstract

This work reported an efficient PdIr/activated carbon (PdIr/AC) catalyst and its application during direct ethane dehydrogenation (EDH) into ethane. The XRD and HADDF-STEM results revealed Pd/Ir nano-particles and atomically dispersed Pd²⁺ and Ir⁴⁺ species simultaneously. The activity tests demonstrated that Ir species showed higher C₂H₄ selectivity than Pd species and the co-presence of Pd/Ir could further improve the catalytic stability and inhibit carbon deposition over the bimetallic Pd/Ir catalyst. Nevertheless, raising the reaction temperature from 500 °C to 600 °C boosted coking including carbon nanotubes (CNTs) and carbon particles. XPS results of Pd7Ir2/AC-B after Ar or H₂ pretreatment proved that the active sites are Pd²⁺/Ir⁴⁺ species. The simulation results exposed the reaction pathway over Ir⁴⁺/Pd²⁺ species, and ethane dehydrogenation was the rate-determining step over the PdIr/AC sample; meanwhile, the synergetic effect between Pd²⁺ and Ir⁴⁺ increased their TOF (C₂H₄). Finally, a deactivation mechanism was also proposed to examine the coking over various metal species.