At the Cutting Edge – NMR Studies Reveal Distinct Reactivities of Specific Edge Sites on Needle-Shaped γ-Al2O3 Nanocrystals Toward Pt(II) Precursors
Despite being a crucial component of many relevant catalytic systems such as Pt/Al2O3, the surface features of γ-Al2O3 remain poorly understood to date. Only very recently, the potential role of highly reactive edge sites was introduced to the research community. Those edge sites are proposed to be contained within the high-field signal (approx. 0 ppm) of the 1H NMR spectrum of γ-Al2O3. [1] By combining the development of well-defined, needle-shaped γ-Al2O3 nano-crystals having a high relative fraction of edge sites with state-of the art 2D and pseudo-3D solid-state NMR spectroscopy, we have been capable to go beyond what has been previously reported and resolved two distinct hydroxyl sites in the high-field 1H-NMR signal of our γ-Al2O3 material. [2]
Here, we capitalize on these findings and compare the NMR signatures of our γ-Al2O3material before and after grafting of [Pt(COD)Me2]. Surprisingly, the resolved hydroxyl sites possess different reactivities toward this molecular platinum-precursor as revealed by single-quantum-double-quantum 1H-1H and recoupling-time encoded {27Al}-1H D-HMQC NMR spectroscopy. The herein presented analysis does not only provide a complementary tool to 195Pt-NMR spectroscopy for the analysis of the surface-organometallic chemistry of platinum on alumina materials, it might also enable the tailored design of γ-Al2O3 nanocrystals which are ideal supports for the synthesis of mono-dispersed Pt nanoparticles.