Abstract:

Recent studies have revealed the extraordinary performance of zirconium oxide in propane dehydrogenation, which is attributed to the excellent reactivity of the coordinatively unsaturated zirconium sites (Zr_cus) around the oxygen vacancies. The origin of the enhanced catalytic activity of ZrO₂ with defective tetrahedral Zr sites was examined by direct comparison with its pristine counterpart in the current study. Electronic-structure analysis revealed that electrons from oxygen removal were localized within vacancies on the defective surface, which directly attacked the C-H bond in propane. The involvement of localized electrons activates the C-H bond via back-donation to the antibonding orbital on the defective surface; conversely, charge is transferred from propane to the pristine surfaces. The barrier for the first C-H bond activation is clearly significantly reduced on the defective surfaces compared to that on the pristine surfaces, which verifies the superior activity of Zr_cus. Notably, however, the desorption of both propene and hydrogen molecules from Zr_cus is more difficult due to strong binding. The calculated turnover frequency (TOF) for propene formation demonstrates that the pristine surfaces exhibit better catalytic performance at lower temperatures, whereas the defective surfaces have a larger TOF at high temperatures. However, the rate-determining step and reaction order on the defective surface differ from those on the pristine surface, which corroborates that the catalysts follow different mechanisms. A further optimization strategy was proposed to address the remaining bottlenecks in propane dehydrogenation on zirconium oxide.

Key words: Propane dehydrogenation, Zirconium oxide, Oxygen vacancy, Density functional theory, Microkinetic