(509aw) Site Requirements and Kinetics of Ethane Oxidative Dehydrogenation over Bulk NiO Based Catalysts

Oxidative dehydrogenation of ethane (ODHE) over NiO based materials has been studied as an alternative pathway for ethylene production. The lack of characterization techniques for quantifying different surface oxygen entities has led to open questions regarding the role of (non)-stoichiometric oxygen in mediating ODHE activity and selectivity,which has prevented in-depth understandings of reaction sequences over NiO catalyst surfaces or the effect of aliovalent dopants on promoting the catalyst performance.¹ In this presentation, we will provide evidence for non-stoichiometric oxygen (NSO) assisting ODHE over NiO for the first time by leveraging CO₂ co-feeds as an exclusive and reversible titrant for NSO. The ODHE rate subjected to change by CO₂ co-feeds corresponds with the NSO density on catalyst surfaces during steady state and transient ODHE conditions, while the remained ODHE activity can be attributed to surface stoichiometric oxygen that is less active and does not bind CO₂, consistent with density functional theory (DFT) predictions. Dopant (i.e. niobium) impregnation gradually decreases surface NSO to stoichiometric oxygen ratio, leading to lower CO₂ inhibition on ODHE rate. We further show kinetic and isotopic evidence for the reversibility and kinetic relevance of elementary steps involved in ethane conversion to ethylene and CO₂. Ethane oxidation proceeds via kinetically relevant C-H bond activation on surface NSO. By-product H₂O and side product CO₂ reversibly adsorb on the active oxygen site and therefore cause inhibition on ODHE and total oxidation rates. Collectively, these findings shed light on the structural-catalytic relation and mechanism of (non-)stoichiometric oxygen for partial oxidation chemistry catalyzed by mixed metal oxides.

Reference:

1. Skoufa et al.; J. Catal. 2015, 322, 118–129