Molecular structure of titania-supported molybdena: in situ Raman and FTIR spectroscopy of distinct MoVIOx configurations dispersed on titania

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RSC Adv., 2026, 16,23019-23036DOI: 10.1039/D6RA00034G, Paper Open Access &nbsp This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.Theocharis Kentri, Paraskevas Dimitropoulos, Konstantina Niavi, Eleana Kordouli, Soghomon Boghosi…

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Molecular structure of titania-supported molybdena: in situ Raman and FTIR spectroscopy of distinct MoVIOx configurations dispersed on titania

* Corresponding authors

a Department of Chemical Engineering, University of Patras, Patras, Greece
E-mail: [email protected]

b Institute of Chemical Engineering Sciences, FORTH/ICE-HT, Patras, Greece

c Department of Chemistry, University of Patras, Patras, Greece

d School of Science and Technology, Hellenic Open University, GR-26335 Patras, Greece

Abstract

In situ Raman and FTIR spectroscopy, the former complemented by 18O/16O exchange, are used to unravel the structural and configurational properties of the (MoOx)n phase dispersed on two TiO2 polymorphs (anatase and Degussa P25) at the temperature range of 430–120 °C and Mo surface density in the range of 0.5–5 Mo per nm2 under oxidative dehydrated conditions. The dispersed (MoOx)n phase supported on titania is heterogeneous; at coverages below ca. 1 Mo per nm2, isolated species prevail. Under dehydrated conditions, three MoOx species occur on titania in either mononuclear or polynuclear form depending on the temperature and coverage: (i) Species-I with a tetrahedral-like mono-oxo configuration, OMo(–O–Ti)3 with νMoO = 996–999 cm−1; (ii) Species-II with a pyramidal-like mono-oxo configuration, OMo(–O–Ti)4 with νMoO = 989–993 cm−1; and (iii) Species-III with a di-oxo termination configuration with νs/νas = 980–983/965–971 cm−1. Species-I is formed with the first order of priority and prevails at low coverages (<1 Mo per nm2), while its formation ceases at higher coverages. Species-II prevails at coverages of and above 1 Mo per nm2, while it constitutes the building unit of the associated polynuclear (MoO5)n domains at coverages higher than 2 Mo per nm2. Temperature cycling in the 430 °C → 250 °C → 175 °C → 120 °C → 430 °C sequence results in a reversible temperature-dependent Species-II ↔ Species-III transformation, mediated by the surface-retained water molecules. Species-II exhibits higher reactivity than Species-I, both with respect to surface-retained water molecules and hydrogen; the latter is judged from its subjection to facile 18O/16O exchange. These results are important for tuning the configuration of dispersed MoOx sites on titania and designing MoOx/TiO2 catalysts at the molecular level.