Role of zirconium in direct CO2 hydrogenation to lower olefins on oxide/zeolite bifunctional catalysts
2018
Dang, Shanshan | Gao, Peng | Liu, Ziyu | Chen, Xinqing | Yang, Chengguang | Wang, Hui | Zhong, Liangshu | Li, Shenggang | Sun, Yuhan
Direct production of lower olefins (C₂⁼−C₄⁼: ethylene, propylene and butylene), basic carbon-based building blocks, from carbon dioxide (CO₂) hydrogenation is highly attractive, although the selectivity towards olefins has been too low. Here we present a series of bifunctional catalysts contained indium-zirconium composite oxides with different In:Zr atomic ratios and SAPO-34 zeolite, which can achieve a selectivity for C₂⁼–C₄⁼ as high as 65–80% and that for C₂–C₄ of 96% with only about 2.5% methane among the hydrocarbon products at CO₂ conversion of 15–27%. The selectivity of CO via the reverse water gas shift reaction is lower than 70%. The product distribution is completely different from that obtained via CO₂-based Fischer-Tropsch synthesis and deviates greatly from the classical Anderson-Schulz-Flory distribution. The zirconium component plays a critical role in determining the physicochemical properties and catalytic performance of bifunctional catalysts. Catalyst characterization and density functional theory calculations demonstrate that the incorporation of a certain amount of zirconium can create more oxygen vacancy sites, stabilize the intermediates in CO₂ hydrogenation and prevent the sintering of the active nanoparticles, thus leading to significantly enhanced catalytic activity, selectivity of hydrocarbons and stability for direct CO₂ hydrogenation to lower olefins at the relatively high reaction temperature of 380 °C.
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