Decomposition of methanol-d₄ on a thin film of Al₂O₃/NiAl(100) under near-ambient-pressure conditions

We have studied the decomposition of methanol-d₄ on thin film Al₂O₃/NiAl(100) under near-ambient-pressure conditions, with varied surface-probe techniques and calculations based on density-functional theory. Methanol-d₄ neither adsorbed nor reacted on Al₂O₃/NiAl(100) at 400 K under ultrahigh vacuum conditions, whereas they dehydrogenated, largely to methoxy-d₃ (CD₃O*, * denoting adsorbates) and formaldehyde-d₂ (CD₂O*), on the surface when the methanol-d₄ partial pressure was increased to 10⁻³ mbar and above. The dehydrogenation was facilitated by hydroxyl (OH* or OD*) from the dissociation of little co-adsorbed water; a small fraction of CD₂O* interacted further with OH* (OD*) to form, via intermediate CD₂OOH* (CD₂OOD*), formic acid (DCOOH* or DCOOD*). A few surface carbonates were also yielded, likely on the defect sites of Al₂O₃/NiAl(100). The results suggest that alumina not only supports metal clusters but also participates in reactions under realistic catalytic conditions. One may consider accordingly the multiple functions of alumina while designing ideal catalysts.