(320h) Revealing the Structural Dynamics of MoOx Catalysts through Static and Transient Raman Spectroscopy

Supported molybdenum-based catalysts have gained interest for their efficiency in diverse chemical applications. Modifying the physicochemical characteristics of active molybdenum has proven to enhance its catalytic activity. However, the coexistence of multiple MoO_x species introduces challenges in understanding the correlation between catalyst preparation and performance. Investigation on these materials have shown to have di-oxo structure and more complex structures in supports like SiO₂, Al₂O₃ and TiO₂ . This study presents a methodological approach for depositing (MoO_x)n species on mixed CeO₂-TiO₂ and anatase TiO₂ using the equilibrium deposition filtration (EDF) method. Surface species are analyzed through in-situ Raman spectroscopy with selective isotopic labeling under transient conditions. The work further examines the sequence and mechanism of oxygen site removal and substitution. The study employs EDF method to carefully impregnate the type of molybdenum species anchoring on the support and below the monolayer coverage. We then use advanced characterization like in-situ Raman coupled with isotopic labelling with ¹⁸O provides insights into the MoO_x configurations. The results show that the distribution of the Molybdenum oxide depend mainly on the pH of the precursor solution in both the supports used. Analysis of the spectra shows that the structure of oxide to be mono-oxo. The framework is further extended by integrating pulse experiments with operando Raman spectroscopy to differentiate oxygen site reactivity. Combined results reveal that H₂ exposure initially removes oxygen from terminal (Mo=O) sites, followed by disruption of some Mo–O–Support bonds. This enables oxygen exchange among various Mo–O bonds during reoxidation.