Prediction and Tuning of the Defects in the Redox Catalysts: Ethylene Oxychlorination

Abstract

The defect plays a significant role in tuning the electronic structure of metal compounds such as oxides, chlorides, sulfides and nitrides, which is frequently used to explain the enhanced catalytic activity. However, the dynamic change of defect relating to the oxidation state change during the reaction is rarely addressed, and it is still not able to be appropriately predicted since the kinetic modeling of the redox reaction involving the in‐situ formation of defects is challenged by the dynamic evolution of the active sites and the complex kinetic phenomena. Here, for the first time, we present a general method to build a new kinetic model of the redox reaction cycle by combined kinetics of reduction‐ and oxidation steps to predict the time and spatially resolved formation of defects of solid catalysts and the reaction products in ethylene oxychlorination on CuCl2/Al2O3 catalyst. The defect concentration can be tuned by manipulating the relative rates of the reduction‐ and oxidation steps.

Insights of the Dynamic Copper Active Sites in Ethylene Oxychlorination Studied by the Multivariate UV–vis–NIR Resolution Kinetic Approach

“…CuCl 2 reacts with C 2 H 4 in the reduction step (eq ) to form EDC and CuCl in principle. It is consistent with the observation of density functional theory (DFT) , and kinetic studies, , where ethylene first attracted two Cl atoms from CuCl 2 with a very low energy barrier. However, CuCl 2 is rapidly converted to an intermediate instead of CuCl, as shown in Figure b.…”

“…It reflects the activity of the CuCl 2 with different coordination numbers, where the activity of Cu with 4 coordination Cl is much higher than the one of Cu with 3 coordination. It agrees with the results of DFT calculations and kinetic studies that the Cl vacancy in the CuCl 2 layer plays a significant role in its activity. ,− …”

“…The intermediate should be Cu species with an oxidation state between CuCl 2 and CuCl. The coordination numbers of Cu with the Cl were found to be 4 and 2 for CuCl 2 and CuCl, respectively. ,− The reaction of CuCl 2 with C 2 H 4 removed the lattice Cl to form Cl vacancy on CuCl 2 catalysts. DFT study suggested that CuCl 2 with vacancy could have coordination numbers of 3 and 2 for low and high concentrations of Cl vacancy, respectively. , Lattice Cl is rather mobile in CuCl 2 and can rapidly redistribute on the surface .…”

Reaction Network and Byproduct Formation in Ethylene Oxychlorination on K-Doped CuCl2/γ-Al2O3 Catalyst

“…In our previous works, we developed kinetic models for the dynamic evolution of active sites on both neat CuCl 2 /Al 2 O 3 and K-doped CuCl 2 /Al 2 O 3 catalysts for ethylene oxychlorination, based on the three-step redox mechanism. ,, These models accounted for the dynamic nature of Cu species to forecast changes in reactant and product as well as CuCl 2 concentration in the solid catalyst. These kinetic models aptly describe the transient response of reduction and oxidation steps, along with reactions at steady-state under diverse reaction conditions.…”