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

Monitoring and simulating the events occurring on the catalysts under the real reaction conditions has significant meaning for elucidating the dynamic changes of the active sites during the reactions and for a better understanding of the reaction mechanisms. Herein, we use the operando ultraviolet-visible and near-infrared (UV-vis-NIR) spectroscopy to study the CuCl2/gamma-Al2O3-based catalyst in ethylene oxychlorination, one of the most important processes for producing vinyl chloride in the industry, to elucidate the dynamic changes of the copper active sites. The full spectra of Cu species such as CuCl2, CuCl2 with vacancies, CuCl, and Cu2OCl2 were detected and identified for the first time, and their transient changes and contribution in the reduction, oxidation, and hydrochlorination steps as well as at the steady-state operation in the catalytic cycle can be accurately imaged by resolving the UV-vis-NIR spectra dataset using the multivariate curve resolution (MCR) analysis. The distribution and changes of the Cu species are correlated to the catalytic activity, selectivity, and stability. The time-resolved spectra and their correlation with the catalytic performance provide better insights into the dynamic nature of the active sites and their role in the Mars-van Krevelen-type reaction. This method is expected to be exploited to analyze the dynamics of the active sites and kinetic studies in other catalytic redox systems.

Automated summary

The study used UV-vis-NIR spectroscopy to investigate the dynamic changes of copper active sites in CuCl2/gamma-Al2O3-based catalyst during ethylene oxychlorination. Various Cu species such as CuCl2, CuCl, and Cu2OCl2 were identified for the first time, and their transient changes and contribution in the catalytic cycle were accurately imaged using MCR analysis, correlating with catalytic activity, selectivity, and stability. The time-resolved spectra and their correlation with catalytic performance provide better insights into the dynamic nature of active sites and their role in the reaction.