Techniques that can characterize the molecular structures of dilute surface species are required to facilitate the rational synthesis and improvement of Pt-based heterogeneous catalysts. 195 Pt solid-state NMR spectroscopy could be an ideal tool for this task because 195 Pt isotropic chemical shifts and chemical shift anisotropy (CSA) are highly sensitive probes of the local chemical environment and electronic structure. However, the characterization of Pt surface-sites is complicated by the typical low Pt loadings that are between 0.2 and 5 wt% and broadening of 195 Pt solid-state NMR spectra by CSA. Here, we introduce a set of solid-state NMR methods that exploit fast MAS and indirect detection using a sensitive spy nucleus ( 1 H or 31 P) to enable the rapid acquisition of 195 Pt MAS NMR spectra. We demonstrate that high-resolution wideline 195 Pt MAS NMR spectra can be acquired in minutes to a few hours for a series of molecular and single-site Pt species grafted on silica with Pt loading of only 3-5 wt%. Low-power, long-duration, sidebandselective excitation, and saturation pulses are incorporated into t 1 -noise eliminated dipolar heteronuclear multiple quantum coherence, perfect echo resonance echo saturation pulse double resonance, or J-resolved pulse sequences. The complete 195 Pt MAS NMR spectrum is then reconstructed by recording a series of 1D NMR spectra where the offset of the 195 Pt pulses is varied in increments of the MAS frequency. Analysis of the 195 Pt MAS NMR spectra yields the 195 Pt chemical shift tensor parameters. Zeroth order approximation density functional theory calculations accurately predict 195 Pt CS tensor parameters. Simple and predictive orbital models relate the CS tensor parameters to the Pt electronic structure and coordination environment. The methodology developed here paves the way for the detailed structural and electronic analysis of dilute platinum surface-sites.

Surface organometallic chemistry (SOMC) represents a unique synthetic platform for the preparation of model heterogeneous catalysts resembling those broadly applied in industry. SOMC techniques usually rely on the grafting of tailored molecular precursors onto the surface OH groups of oxide supports. The development of such precursors and the understanding of their reactivity with the supports are therefore crucial for the development of well-defined surface species. While a large number of organometallic precursors of early transition metals are known, only few examples of group-10 metal complexes are reported, in spite of the great interest for heterogeneous catalysts based on the Pt-group elements. Herein, we report the reactivity of a family of group-10 (Ni, Pd and Pt) alkyl complexes, towards partially dehydroxylated SiO 2 yielding well-defined supported species. We studied the effect of the metal, ligand, and support on the grafting mechanism of such precursors through a combined experimental and computational approach. Ultimately, we showed that at least two grafting pathways are possible for these compounds, namely the protonolysis of the M-alkyl bond by surface OH groups and the opening of strained siloxane bridges: the proportion of the two depending on the nature of the metal and its ancillary ligand.

Advances in solid-state nuclear magnetic resonance (NMR) methods and hardware offer expanding opportunities for analysis of materials, interfaces, and surfaces. Here, we demonstrate the application of a very high magnetic field strength of 28.2 T and fast magic-angle-spinning rates (MAS, >40 kHz) to surface species relevant to catalysis. Specifically, we present as case studies the 1D and 2D solid-state NMR spectra of important catalyst and support materials, ranging from a well-defined silica-supported organometallic catalyst to dehydroxylated γ-alumina and zeolite solid acids. The high field and fast-MAS measurement conditions substantially improve spectral resolution and narrow NMR signals, which is particularly beneficial for solid-state 1D and 2D NMR analysis of 1H and quadrupolar nuclei such as 27Al at surfaces.

Techniques that can characterize the molecular structures of dilute surface species are required to facilitate the rational synthesis and improvement of single-site and single-atom, such as the important class of Pt-based systems. In this context, 195Pt solid-state NMR spectroscopy could be an ideal tool for this task because 195Pt NMR spectra and sizeable chemical shift anisotropy (CSA) are highly sensitive probes of the local chemical environment and electronic structure. However, the broadening of 195Pt solid-state NMR spectra by CSA often results in low NMR sensitivity. Furthermore, characterization of Pt sites on surfaces is complicated by the typical low Pt loadings that are between 0.2 to 5 wt.%. Here, we introduce a set of solid-state NMR methods that exploit fast MAS and indirect detection of a sensitive spy nucleus (1H or 31P) to enable rapid acquisition of 195Pt MAS NMR spectra. We demonstrate that high-resolution wideline 195Pt MAS NMR spectra can be in minutes to a few hours for a series of molecular and single-site Pt species grafted on silica with Pt loading of only 3-5 wt.%. Low-power, long-duration, sideband-selective excitation and saturation pulses are incorporated into t1-noise eliminated (TONE) dipolar heteronuclear multiple quantum coherence (D-HMQC), perfect echo resonance echo saturation pulse double resonance (PE RESPDOR) or J-resolved pulse sequences. The complete 195Pt MAS NMR spectrum is then reconstructed by recording a series of 1D NMR spectra where the offset of the 195Pt pulses is varied. Analysis of the 195Pt MAS NMR spectra yields the 195Pt chemical shift tensor parameters. Analysis of the NMR signatures based on relativistic zeroth order approximation (ZORA) DFT calculations enables the rationalization of changes in the observed 195Pt CSA across the series of Pt compounds. Simple and predictive orbital models relate the measured spectral signatures to specific electronic environments and allows the identification of coordination environment by inspection of the CSA (isotropic chemical shift and measured spans). The methodology developed here paves the way for the detailed structural and electronic analysis of dilute platinum sites in single-atom and single-site heterogeneous catalysts.