Ethylene is one of the most important products of the chemical manufacturing industry. Its synthesis is gradually shifting from traditional steam cracking of petroleum feedstocks to catalytic dehydrogenation of ethane from natural gas. This is motivated by the increasing availability of ethane from shale gas and the pursuit of ethylene with polymer-quality purity. Cr/SiO₂ catalysts are widely used in industry for ethane dehydrogenation to ethylene, but their application is limited by low yields and short catalyst lifetimes. The use of CO₂ as co-reactant was reported to improve dehydrogenation activity and catalyst stability. However, the mechanistic role of CO₂ and the effect of the siliceous catalyst support in facilitating the ethane dehydrogenation have not been fully elucidated.
This work studies the ethane dehydrogenation in tandem with CO₂ reduction over dispersed Cr cations supported on the crystalline silicate Si-MFI. Catalytic packed-bed reactor measurements combing in-situ spectroscopic characterization reveal that CO₂ impacts the reaction outcomes for ethane conversion to ethylene, and that small amounts of CO₂ (CO₂ / C₂H₆ < 0.5) can significantly change ethane dehydrogenation kinetics (Fig 1a). The improved dehydrogenation rates can be attributed to a modification of Cr average oxidation states by CO₂, as reflected by the overall blue shift of XANES spectra when the amount of co-fed CO₂ increases (Fig 1b). These results together generate insights into reaction kinetics and mechanisms, informing catalyst design toward achieving higher ethylene yields.

Wenqi Zhou

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