Abstract:

To obtain a Co-based catalyst with high-activity for CO₂-assisted ethane dehydrogenation to ethylene, a series of Co/SSZ-13 catalysts were prepared by ion-exchange and impregnation methods. Raman and XPS were employed to investigate the coordination environment and valence state of Co species, while reaction pathway analysis revealed the synergistic mechanism of highly dispersed dual-site Co ^{species in catalyzing the reaction. The additional impregnation step following ion-exchange significantly enhanced catalytic activity, increasing ethylene yield from 23.46% to 38.20% at 675℃. Ion-exchange method primarily anchored highly dispersed Co(Ⅱ) species on SSZ-13, which exhibited excellent ethane direct dehydrogenation (EDH) activity. Subsequent impregnation increased the content of Co₃O₄, which promoted the reverse water-gas shift (RWGS) reaction because of the in situ reduction to Co0 during reaction evaluation and synergistically improved the apparent oxidative dehydrogenation (ODHE) performance with Co(Ⅱ). However, excessive Co₃O₄ content induced excessive Co0 species during catalytic evaluation process, leading to severe side reactions and reduced selectivity to ethylene. This work elucidates the cooperative mechanism of dual-site Co species and demonstrates the necessity of precisely tuning the ratio of dual-sites of the fresh catalysts to balance activity and stability.}

Key words: CO₂, ethane, oxidative dehydrogenation, chemical reaction, catalyst, molecular sieves

摘要：

为了获得具有高CO₂氧化乙烷脱氢制乙烯活性的Co基催化剂，依次通过离子交换法及浸渍法制备了一系列Co/SSZ-13催化剂。通过Raman、XPS等表征手段探究了Co物种的落位和价态，并基于本课题组提出的反应路径分析方法揭示了高分散双位点Co物种协同催化CO₂氧化乙烷脱氢制乙烯的机理。结果表明，在离子交换法基础上通过浸渍在催化剂上二次负载Co物种能够有效提升催化剂活性，675℃时乙烯收率由23.46%升至38.20%；离子交换法主要在分子筛上锚定高度分散的Co（Ⅱ）物种，其表现出良好的直接脱氢活性；在此基础上进行浸渍能够在表面负载Co₃O₄物种，其在反应过程中还原为Co⁰物种从而促进逆水煤气反应，进而提升催化剂的表观氧化脱氢性能。然而，当浸渍负载量过高时，Co₃O₄物种在反应过程中原位还原为低分散度的Co⁰物种，降低了催化剂乙烯选择性。本文揭示了双位点Co物种的协同机制，指出需精准调控催化剂原始双位点比例以兼顾活性和稳定性。

关键词: CO₂, 乙烷, 氧化脱氢, 化学反应, 催化剂, 分子筛