Synergistic sites over the ZnxZrO catalyst for targeted cleavage of the C–H bonds of ethane in tandem with CO2 activation

Abstract

The CO₂-assisted oxidative dehydrogenation of ethane (CO₂-ODHE) provides a promising way to produce ethylene and utilize CO₂. Simultaneous upgrading of ethane into the high value–added chemical products and the reduction of greenhouse gas CO₂ emissions could be achieved. However, the targeted breaking of the C–C/C–H bonds of ethane is still a challenge for the designed catalysts. In this paper, ZnO-doped ZrO₂ bifunctional catalysts (Zn_xZrO) with different Zn/Zr molar ratios were prepared by the deposition-precipitation method, and the functions of various sites for CO₂-ODHE reaction were revealed by in situ characterizations and ethane pulse experiment: the medium-strength acidic Zn-O-Zr sites are responsible for the purposefully cracking of ethane C–H bonds to ethylene, while the more oxygen vacancies (O_V) created by the introduction of Zn²⁺ are responsible for the efficient activation C=O bonds of CO₂, thus promoting the RWGS reaction. In addition, the Zn_0.2ZrO catalyst demonstrated excellent catalytic performances, with C₂H₆ conversion, C₂H₄ yield, and CO₂ conversion about 19.1%, 10.5%, and 10.6% within 5 h, respectively (600 °C, GHSV = 3000 mL/(g·h)). Especially, the initial ethylene space-time yield of 355.5 μmol/(min·g) was obtained under 6000 mL/(g·h); Finally, the tandem reaction mechanism of ethane dehydrogenation and RWGS was revealed.