| Project Detail |
Heterogeneous catalysis is a central science in modern society enabling a more sustainable synthesis and transformation of chemicals. Heterogeneous catalysts often consist of metallic species, ranging from isolated atoms to nanoparticles, often dispersed on a variety of supports. Among the various metals employed, platinum is ubiquitous in catalysis, where platinum and platinum-alloyed nanoparticles (NPs) and clusters supported on large-area metal oxides (such as SiO2, Al2O3, CeO2 and Fe2O3) are broadly applied in the petrochemical, pharmaceutical, agrochemical sectors.Due to the low loading of the active metal and the ill-defined nature of industrial catalysts, the determination of the geometry, electronics and reactivity of the active sites down to a molecular level represents a challenge and cannot be addresses unambiguously, even if complementary techniques such as spectroscopy, microscopy and computations are used jointly. The development of novel synthetic approaches and characterization methodologies is therefore needed to shade light on these catalytic systems, with the goal of rationalising the catalyst design.Solid-state 195Pt NMR spectroscopy has recently emerged as a promising tool to directly probe the environment of molecular Pt species and of grafted isolated Pt sites, but important roadblocks still prevent its application to a broad range of systems of chemical relevance, such as metal clusters and nanoparticles. In this proposal, we aim to bypass these roadblocks with the development and implementation of advanced and high-sensitivity solid-state NMR methods, augmented with computational analyses, to study the coordination environment, electronic structure and, ultimately, reactivity of supported Pt-based catalysts.We will first generate and characterize model catalysts with different and controlled nuclearity, based on dispersion of atom-precise Pt-based clusters of various sizes, shapes, metal composition and surface ligands on metal-oxides and carbonaceous supports. This unique synthetic platform will allow for a thorough characterisation of both the supported materials and the molecular precursors with state-of-the-art spectroscopical tools (FTIR, XAS, PDF, XPS, as well as NMR) and advanced imaging techniques (HT-TEM, STEM, EDX). We will then develop multi-dimensional heteronuclear correlation experiments which will allow to access 195Pt NMR signals of surface platinum sites via indirect detection on the ligand probe nuclei such as 1H, 31P, 15N or 13C under fast magic-angle spinning and dynamic nuclear polarization. In parallel, a computational methodology will be developed so to understand the NPs/support interaction and the changes in spectroscopical signatures upon deposition. These techniques will finally be used to acquire the NMR signatures of the grafted Pt sites and compare them with those derived from supported Pt nanoparticles prepared by more classical approaches, with the ultimate goal to draw structure-activity relationships |
