Elucidating Selective and Total Oxidation Elementary Reactions over a Ni-Based Catalyst for Sustainable Ethylene Production via Oxidative Dehydrogenation of Ethane: Microkinetic Analysis

Abstract

This work develops a microkinetic model to investigate the selective and total oxidation elementary reactions involved in the Oxidative Dehydrogenation of Ethane (ODH-C2) over a SnO2-NiO based catalyst. The kinetic parameters were determined accounting for statistical significance and thermodynamic consistency. The pre-exponential factors were calculated using the Transition State Theory (TST) and statistical thermodynamics, while the activation energies were, first, approximated by using the UBI-QEP method and, then, tuned through regression analysis using experimental data at a temperature range of 603 to 753 K, inlet oxygen partial pressures between 3 and 12 kPa, inlet ethane partial pressures between 6 and 27 kPa, space-times (W/FC2H6,0) between 5 and 53 kg s/mol, and total pressures from 100 to 300 kPa. The microkinetic model adequately described experimental data. The model was able to predict the conversion of ethane and the selectivity to ethylene in the range of 4 % to 69% and 50% to 90%, respectively. Microkinetic analysis delivered a solid mechanistic hypothesis that elucidates the following: (i) the formation of nucleophilic and electrophilic oxygen species on the active metallic surface promote selective and total oxidation reactions, respectively; (ii) the hydrogen abstraction from ethane, double bond cleavage on ethylene, and water desorption are the energetically relevant elemental reaction steps during the ODH-C2; and (iii) O2/C2H6 ratios less than unity favor the formation of nucleophilic oxygen species, leading to increased ethylene selectivity. Overall, microkinetic analysis establishes the groundwork for future research aimed at both redesigning the catalyst and scaling up the ODH-C2.