Deviations from Ideal Langmuir Adsorption Govern the Reaction Rate and Mechanism in Ethane Dehydrogenation on Pt–Sn/ZnAl ₂ O ₄

Nonoxidative dehydrogenation (NODH) of light alkanes over Pt-based catalysts has been primarily studied at low alkane, H2, and olefin partial pressures, resulting in Langmuir–Hinshelwood-based reaction mechanisms involving coverage independent adsorption thermodynamics. Here, we have combined detailed reaction kinetics and transition state treatments to demonstrate that ethane NODH on a Pt–Sn/ZnAl2O4 catalyst is strongly affected by the hydrogen and ethylene surface coverages. We found that high hydrogen and ethylene surface coverages lead to important deviations from ideal Langmuir adsorption. For hydrogen adsorption, this was attributed to a combination of lateral interactions and reduced hydrogen surface mobility at high surface coverages. By contrast, for ethylene, the deviation from Langmuir adsorption can be ascribed to stronger ethylene adsorption configurations, more undercoordinated Pt sites covered, and/or less lateral interactions existing for lower surface coverages. Exploring the impact of large changes in hydrogen and ethylene partial pressures on this reaction is highly relevant when integrating this reaction in a membrane reactor where large concentration gradients and, thus, gradients in the surface coverage distribution are expected along the reactor bed.