Atomic Layer Deposition-Assisted Surface-Selective Isotopic Labeling for the ¹⁷O Solid-State NMR Studies of Metal Oxide Surfaces

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17 O solid-state NMR spectroscopy is widely used to investigate metal oxide surfaces and is increasingly recognized for the unique insights into surface structures. Given the low natural abundance of the 17 O nucleus (0.037%), 17 O surface-selective isotopic labeling is commonly employed in relevant studies. Conventional thermal treatment (CTT)-labeling methods rely on rapid 17 O/ 16 O exchange may yield insufficient labeling on less reactive surfaces. Our approach uses atomic layer deposition (ALD) epitaxial growth to directly deposit 17 O onto metal oxide surfaces regardless of surface reactivity. This method minimizes the formation of excessive surface hydroxyl groups, reducing overlapping NMR signals and enabling better 17 O NMR identification of hydroxyl groups, as observed in Al 2 O 3 . Moreover, heteronuclear 27 Al{ 17 O} J -HMQC NMR analysis reveals that the CTT method creates more correlations between penta-coordinated Al sites and hydroxyl groups in Al 2 O 3 compared to ALD, indicating that the labeling techniques vary in their effectiveness at different surface sites.