Contents lists available at ScienceDirect Catalysis Today journal homepage: www.elsevier.com/locate/cattod XANES study of the dynamic states of V-based oxide catalysts under partial oxidation reaction conditions M.O. Guerrero-Pérez a, ⁎ , R. López-Medina b,c , E. Rojas-Garcia b,d , M.A. Bañares b, ⁎ a Departamento de Ingeniería Química, Universidad de Málaga, E-29071, Málaga, Spain b SpeICat – Catalytic Spectroscopy Laboratory, Instituto de Catálisis y Petroleoquímica, ICP-CSIC, Marie Curie 2, E-28049, Madrid, Spain c Departamento de Energía, Área de Procesos de la Industria Química, Universidad Autónoma Metropolitana-Azcapotzalco, Av. San Pablo 180, Col. Reynosa, Tamaulipas, 02200, Mexico d Departamento de Ingeniería de Procesos e Hidráulica, Universidad Autónoma Metropolitana-Iztapalapa, Av. San Rafael Atlixco 186, Col. Vicentina, Iztapalapa, 09340, Mexico ARTICLE INFO Keywords: VSbO 4 M1 Supported nanoscaled bulk catalyst Multioxide catalysts XANES Operando ABSTRACT A XANES study under reaction conditions has been performed with two different V-based catalytic systems, Mo- V-Nb-Te-O and V-Sb-O. For this study, an alumina-supported nanoscaled bulk catalyst has been used. In all cases XANES determined the average vanadium oxidation state during reaction. XANES also demonstrated that the nanosized phases are more dynamic, and able to participate in the redox catalytic cycle without significant changes either in their structure or in the overall vanadium oxidation state. Such a stability is also apparent under oxidizing conditions. 1. Introduction Vanadium is a particularly interesting element for catalytic appli- cations; its extremely rich chemistry endows it with a broad range of functional and interesting properties [1–5]. Among those, vanadium oxides are fascinating materials that find several industrial applications such as gas sensors, electrochromic devices, optical switching devices, reversible cathode materials for Li batteries and in catalysts. Thanks to vanadium’s five valence electrons, there are several vanadium oxides that can be formed: vanadium (II), V 2 O 5 , VO, vanadium (III), V 2 O 3 , vanadium (IV), VO 2 and vanadium (V) oxides, in addition, there are some mixed valence oxides, such as V 3 O 7 ,V 6 O 13 , and V 8 O 15 . These mixed valence oxides are formed by introducing oxygen vacancy de- fects, resulting in a series of oxides with related stoichiometries [6]. Vanadium is subsequently a key element for several industrial mixed oxide catalysts. There are several vanadium-based gas-phase industrial oxidation process in which vanadium atoms appear involved as the critical site for the reaction mechanism. The partially filled d-orbitals provide a wide variety of electronic, magnetic and catalytic properties that vanadium atoms can adopt. The conversion among those oxides and stoichiometries with the subsequent formation of oxygen vacancies is relatively easy; enabling selective oxidation reactions. Thus, the va- nadium oxidation states are related with their catalytic performance and is, thus, a crucial factor to monitor during reaction, in order to uncover the reaction mechanism and the active sites, to understand the catalytic mechanism and for designing more active and selective cata- lysts. Mixed V-containing oxide catalysts present many advantages, whose performance can be further modulated by its interaction with other elements. There are several well-known mixed oxide vanadium containing catalytic systems that have demonstrated to be active and selective for partial oxidation reactions, such as VSbO [7–11] –used mainly for ammoxidation reactions-, or Mo-V multioxide systems [12–15] -selective for the propane transformation into acrylic acid. Mixed Mo-V oxide based catalytic materials present several active phases, named as M1, M2 and rutile [16]. The M1 phase (TeM 20 O 31 orthorhombic) crystallizes in the orthorhombic system and undergoes oxidation and reduction to a certain degree without significant struc- tural changes [17–22]. The M2 phase (Te 0.33 MO 3.33 ) is pseudo-hex- agonal [23]. It seems that there is a synergistic effect between these two phases; M1 is reported to be the phase that activates propane molecule, whereas M2 improves the selectivity of the catalysts towards acrylic acid [10,24,25]. In the case of Sb-V-O catalysts, the trirutile VSbO 4 phase is one of the active phases 11, since exhibits a unique behavior that accepts large changes of composition and oxidation state of the vanadium atoms, with the subsequent introduction of cationic va- cancies [26,11,65,66,27]; this is an extremely flexible system, which appears related to the performance for propane activation to propylene https://doi.org/10.1016/j.cattod.2017.12.016 Received 6 September 2017; Received in revised form 4 December 2017; Accepted 11 December 2017 ⁎ Corresponding authors. E-mail addresses: oguerrero@uma.es (M.O. Guerrero-Pérez), banares@icp.csic.es (M.A. Bañares). Catalysis Today xxx (xxxx) xxx–xxx 0920-5861/ © 2017 Elsevier B.V. All rights reserved. Please cite this article as: Guerrero-Pérez, M.O., Catalysis Today (2017), https://doi.org/10.1016/j.cattod.2017.12.016