Understanding the conversion of ethanol to propene on In₂O₃ from first principles

It is highly desirable to convert bioethanol to value-added chemicals. As such, conversion of ethanol to propene (ETP) is attractive because propene is an important raw material for the production of plastics. In₂O₃ has shown promising catalytic performance for ETP conversion. However, the underlying mechanisms remain elusive. In this work, we use density functional theory (DFT) to investigate ETP reaction pathways on the In₂O₃ (110) surface. We find that the ETP reactions proceed through three major stages: ethanol to acetaldehyde, acetaldehyde to acetone, and acetone to propene. The ethanol-to-acetaldehyde step is kinetically facile. Comparing the two pathways from acetaldehyde to acetone, we show that the aldol reaction pathway via direct coupling of two acetaldehyde is more favorable than the acetate-ketonization pathway. The acetone-to-propene process is found to be the rate-limiting step of the overall reaction. This work provides a detailed mechanistic view of the ETP chemistry on In₂O₃(110) that paves the way for further exploration of effects such as surface termination, surface doping, and co-feeding of H₂ and H₂O on selectivity and catalyst stability.