DFT insight into RH-stabilized oxygen-vacancy ensembles on In₂O₃ for selective propanal hydrogenation to 1-propanol

Title : DFT insight into RH-stabilized oxygen-vacancy ensembles on In₂O₃ for selective propanal hydrogenation to 1-propanol

Abstract:

Rhodium-modified In₂O₃ has shown promising performance for selective alcohol formation in reductive hydroformylation, where experimental characterization suggests a strong connection between dispersed oxidized Rh species, oxygen-defective In₂O₃, and enhanced 1-propanol selectivity. In this work, density functional theory calculations were used to clarify the atomistic role of Rh and oxygen vacancies on In₂O₃(111), with reference to experimental XPS, Raman, and H₂-TPR results.
The calculations first examined Rh anchoring and oxygen-vacancy formation on stoichiometric and defective In₂O₃ surfaces. Rh was found to interact cooperatively with surface oxygen vacancies. Oxygen-deficient sites strengthen Rh binding compared with the vacancy-free surface, supporting the stabilization of isolated Rh species on defective In₂O₃. In turn, Rh promotes local surface reduction: formation of an additional oxygen vacancy, which is unfavorable on bare In₂O₃, becomes thermodynamically favorable adjacent to Rh. This leads to a stable Rh-divacancy motif and provides a molecular-level explanation for the experimentally observed Rh-assisted reducibility and oxygen-defective nature of Rh-In₂O₃.
This Rh-stabilized oxygen-deficient ensemble was then used to model propanal hydrogenation to 1-propanol, a key step governing alcohol selectivity. Reaction profiles were compared for vacancy-free, single-vacancy, and double-vacancy Rh-In₂O₃ models prior to propanal adsorption. The DFT results show that increasing local oxygen deficiency around Rh facilitates hydrogen transfer to the aldehyde intermediate and lowers the barrier for C-O hydrogenation. The double-vacancy Rh site provides the most favorable pathway, consistent with the higher alcohol selectivity observed experimentally for the most oxygen-defective Rh-In₂O₃ catalyst.Overall, the calculations identify an oxidized Rh-oxygen-vacancy ensemble as the catalytically relevant interfacial motif. Rh acts not only as a hydrogenation center, but also as a promoter of local oxygen-vacancy formation, while the defective In₂O₃ surface tunes the Rh site for selective propanal hydrogenation. These findings highlight the importance of cooperative metal-defect interactions in designing oxide-supported single-site catalysts for selective C-O hydrogenation reactions.

Biography:

Dr. Rafia Ahmad is a Research Scientist at the KAUST Catalysis Center, specializing in computational chemistry, heterogeneous catalysis, and materials modeling. Her research uses density functional theory and machine-learning-based approaches to understand catalytic surfaces, oxygen vacancies, reaction mechanisms, and energy-relevant transformations. She earned her Ph.D. in Materials Science from the Indian Institute of Science, Bangalore, and has extensive experience in oxide catalysts, metal-support interactions, carbon capture and utilization, and sustainable energy innovation.