A critical evaluation of the catalytic role of CO2 in propane dehydrogenation catalyzed by chromium oxide from a DFT-based microkinetic simulation

Abstract

Propane dehydrogenation under CO₂ is an important catalytic route to obtain propene with a good balance between selectivity and stability. However, a precise description of the catalytic role of CO₂ in propane dehydrogenation is still absent. In this work, we focus on the elucidation of the role of CO₂ by using DFT-based microkinetic simulation. The influence of CO₂ is categorized as direct and indirect effects. It was found that the chemisorbed CO₂ can directly abstract hydrogen from propane and propyl with a comparable barrier to the counterpart at the surface oxygen site. On the other hand, the dissociation of CO₂ yields active surface species of CO* and O* which are actively involved in the removal of surface hydroxyls. It is found that the TOFs of both propane conversion and propene formation are significantly increased with the presence of CO₂, which is explained by the reduced apparent activation energy. The primary hydrogen abstraction is identified to be the most influential step from the DRC analysis. The main effects of CO₂ are concluded to be removing hydrogen and restoring oxygen vacancies from reaction pathway analysis.