(661x) Understanding Reactivity Trends in CO2 Assisted Ethane Dehydrogenation – Towards the Rational Design of Bimetallic Alloys

A comprehensive ab initio microkinetic modeling (MKM) investigation is undertaken to gain mechanistic insights into CO₂ assisted ethane dehydrogenation over terrace and step sites of transition metal catalysts. Obtained results on both the facets show similarity in plots for ethane conversion and formation of ethylene and hydrogen; as well as CO formation plots and CO₂ consumption. Over the terrace sites, the activity order for ethylene and CO formation being Rh > Pt > Pd ~ Ni ~ Co > Ru > Cu and Co > Rh ~ Ni > Ru, respectively (Figure 1a and 1b). CO₂ predominantly reduced through the reverse water gas shift reaction, since the production rates of H₂O (Figure 1c) and CO are comparable to the consumption rates of CO₂. For the stepped (211) sites, consumption rate of ethane and production of ethylene and H₂ (Figure 1d) is following the order: Rh ~ Ni > Ru > Co > Pd > Pt > Re ~ Cu whereas CO₂ consumption and CO formation (Figure 1e) follows: Co > Ru > Ni > Rh > Pt > Pd > Re > Cu. For the active metals (Rh, Ru, Ni and Co), direct CO₂dissociation rates (Figure 1f) correspond to CO₂ consumption suggesting that most of CO₂ is converted by direct dissociation on these metals. Coke formation plots (Figure 1g) over stepped sites show that Rh, Ru, Ni and Pd exhibit highest coking propensity followed to Co. To reduce the coke deposition on (211) sites, bimetallic alloy candidates of Ni and Pt are explored based on four metrics: same or higher ethane turnovers, higher CO₂ turnovers, same or higher ethylene turnovers and lesser coke production. Amongst the alloys of Ni (Figure 1h), Ni₃Fe and Ni₃Co meet the criterion mentioned while of the alloys of Pt, it is Pt₃Co (Figure 1i).