On the Nature of the Unusual Redox Cycle at the Vanadia Ceria Interface

Abstract

This work investigates the effect of changing the vanadia/support interface on the redox properties of the material for the oxidative dehydrogenation reaction of small alkanes. In particular, ternary V2O5/CeO2/SiO2 catalysts are compared to vanadia on ceria and CeVO4 catalysts. Modifications in the CeO2 phase by the effect of the silica support and the creation of new V–Ce–Si interfaces induce substantial changes in the phases and behavior of vanadium species as well as CeO2, thus modifying the reaction mechanism. Powerful characterization techniques, XRD, in situ XANES, and Raman, as well as studies of ethane oxidative dehydrogenation catalytic activity provide a solid description of the phenomena associated with the different interfaces on a molecular level. Bulk CeO2 entities react with the vanadium species, leading to the formation of vanadate inhibiting the redox pair of V. These centers are very active but selective to ethane total oxidation. However, smaller ceria domains achieved by dispersion on a silica support do not undergo this solid-state reaction, resulting in new contacts with different behavior where both V and Ce participate. The extent of the participation and the reactivity depends also on the dispersion of both the ceria and the vanadium species. Vanadium polymeric species are more selective to ethene when dispersed on ceria entities with an epitaxial relationship between ceria and the underlying silica, which largely influences the properties of relatively small 3D-Ce particles and modifies the oxygen lattice lability. Therefore, how the electronic and structural properties of the support materials are modified affects vanadia reactivity, determining, in turn, the type and distribution of the V–O–Ce species, which might be the reason for the variation in reactivity and selectivity.

Raman spectroscopy as a powerful tool to characterize ceria-based catalysts

“…In the case of ceria-zirconia supports, polyvanadates were shown to interact preferentially with the CeO 2 portion of the mixed oxides and to form CeVO 4 at high temperature [122]. Operando studies during oxidative dehydrogenation of ethane suggested that the V-O-Ce bonds must be the sites involved in the rate-determining step [123,124]. Finally, the vanadia structures on different nanoshaped ceria were identified by in situ visible (633 nm) and UV (325 nm)…”

Insights into Redox Dynamics of Vanadium Species Impregnated in Layered Siliceous Zeolitic Structures during Methanol Oxidation Reactions

“…Another important factor to be considered in combination with speciation‐driven reactivity is the dynamic behavior of the active sites under reducing and oxidizing environments. Operando XANES/EXAFS studies allowed the identification of differences in vanadium site dynamics during redox cycles in V‐based mixed oxides and binary V 2 O 5 /CeO 2 and ternary V 2 O 5 /CeO 2 /SiO 2 systems . Recently, Ek et al .…”

“…Operando XANES/EXAFS studies allowed the identification of differences in vanadium site dynamics during redox cycles in Vbased mixed oxides [27] and binary V 2 O 5 /CeO 2 and ternary V 2 O 5 / CeO 2 /SiO 2 systems. [28] Recently, Ek et al [29] explored the facetdependent reactivity of VO x species on TiO 2 previously observed in the selective reduction of NO to NH 3 [30] by visualizing redox dynamic processes over (001) and (101) facets of the oxide applying combined atomic-resolution TEM and electron energy loss spectroscopy (EELS) under alternated oxidizing and reducing environments. By applying in situ spectroscopic [31][32][33] and atomic-resolution imaging [34][35][36] techniques to monitor redox properties under a reaction environment, new ways are opened to move towards a more complete understanding of the reactivity in oxide-catalyzed processes.…”

Vanadium Oxide Oligomers and Ordered Monolayers Supported on CeO2(111): Structure and Stability Studied by Density Functional Theory

“…Bañares and coworkers for a ternary VOx/CeO2/SiO2 system. 17 The activity in selectively oxidizing methanol to formaldehyde at ceria-supported vanadia catalysts depends on the amount of vanadium deposited on the surface. 9,[18][19] To understand this behavior at the atomic level, model studies are indispensable.…”