Exploration of Metal-Molecule interaction of subnanometric heterogeneous catalysts via simulated Raman spectrum

Abstract

To date, using either state-of-the-art direct image or indirect spectroscopic techniques to simultaneously identify the surface fine structure of heterogeneous catalyst and predict the chemical state of surface species under operando conditions, particularly down to subnanometry and even atomic scale, remains a substantial challenge. Nevertheless, reducing the size of the heterogeneous catalyst from bulk down to atomic level, the spectroscopic characteristics responsible for the unique interaction between metal and adsorbed molecules will thereby be tuned, giving rise to non-coherent spectroscopic characteristics for even the same metal/molecule combination, as repeatedly witnessed in literatures. This work details a new chemical strategy to identify the tangling characteristics of Raman spectra derived from the subnanometric cluster and even single atom catalysts under reactive atmosphere, a long-standing issue that impeded the further implementation of Raman techniques in miniaturized heterogeneous catalysis. We illustrate this concept through the use of a density functional theory (DFT) approach to simulate the Raman spectra of three typical Ptx/CeO2 (x = 1, 2, 9) systems of increasing sizes which represent isolated atom, layered clusters, and multiple layer clusters, respectively, under CO atmosphere to acquire the spectroscopic characteristics, usually masked by multiple interferences from the inevitable CO/Pt interaction circulated in relevant experimental studies. The novel approach explored in this manuscript should open up a new avenue for the use of theoretical chemistry method as a general tool to complement the current experimental method in identifying the intrinsic spectroscopic features masked by multiple interferences originated from complex chemical environment.