Toward Fully Selective Ethylene Oxychlorination through Engineering the Cu Oxidation State Spatial Profile

Abstract

The understanding of selectivity in heterogeneous catalysis is of paramount importance to society today. Ethylene oxychlorination is a well-developed industrial process, but the selectivity needs to be further improved under very high conversion. In this work, we demonstrate the different behavior of CuCl2/Al2O3-based catalysts at a wide conversion range and reveal the importance of spatially distributed CuCl2 concentration for the catalytic performance through the spatial-time-resolved UV–vis–NIR approach. The higher CuCl2 concentration leads to higher activity, ethylene dichloride (EDC) selectivity, and stability. Moreover, the steady-state oxidation of Cu was precisely controlled by adjusting the reduction and oxidation potentials within the redox cycle. This was achieved by synergistically coupling CuCl2 to specific promoters. Through the engineering of CuCl2 to maintain a spatially distributed high-level oxidation state, the tripromoter-doped KMgLa–CuCl2/Al2O3 catalyst exhibits outstanding performance, achieving full conversion with nearly 100% selectivity toward EDC. This study connects catalytic performance to dynamic copper active sites on a spatial scale in real reactions. Understanding this dynamic nature offers fundamental and practical insights, enabling the potential for achieving a maximum catalytic performance.

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

“…However, at high conversion levels (X Ethylene > 60%), there is a distribution of CuCl 2 and CuCl along the catalyst bed height, with CuCl 2 still serving as the active phase to produce EDC. However, CuCl contributes to the generation of undesired byproduct carbon dioxide, particularly at high ethylene conversions, and CO x serves as the primary product of the direct combustion of ethylene . This analysis consolidates previous findings to elucidate these distinct contributions and provides insights into the complex dynamics of the ethylene oxychlorination process.…”

“…The distribution of these products is heavily influenced by the catalyst’s nature and the reaction conditions. ,, The highly dispersed CuCl 2 is identified as the active phase in the oxychlorination of ethylene to yield EDC, achieved through the pulse and direct reduction of CuCl 2 by ethylene. Concurrently, CuCl 2 undergoes reduction by ethylene to produce CuCl, a highly volatile compound that diminishes the lifespan of the CuCl 2 catalyst. − However, CuCl species prefer to form the most unwelcome byproduct, carbon dioxide. , Besides, ethyl chloride (EC) formation, this is also a crucial reaction step for the byproduct formation, which is typically catalyzed by exposing acid sites (Bro̷nsted and Lewis type) on the Al 2 O 3 support through reversible dehydrochlorination reactions. , By introduction of appropriate promoters, the exposure of acid sites can be adjusted, thereby further inhibiting side reactions. Incorporating alkali metals such as KCl through doping can substantially reduce the presence of Lewis acid sites on alumina, consequently impeding the formation of EC, which is believed to contribute to the improved EDC selectivity.…”