Structure and electronic properties of MoVO type mixed-metal oxides – a combined view by experiment and theory

Abstract

In this review we address recent efforts from experimental and theoretical side to study MoVO-type mixed metal oxides (MMOs) and their properties. We illustrate how structures of MMOs have been evaluated using a large variety of experimental techniques, such as electron microscopy, neutron diffraction, and X-ray diffraction. Furthermore, we discuss the current view on structure-catalysis correlations, derived from recent experiments. In a second part, we examine useful tools of theoretical chemistry for exploring MoVO-type systems. We discuss the need for using hybrid DFT methods and we analyze how, in the context of MMOs studies, semi-local DFT approximations can encounter problems due to a notable self-interaction error when describing oxidic species and reactions on them. In addition, we discuss various aspects of the model that are important when attempting to map complex MMO systems.

Probing the Positions of TeO Moieties in the Channels of the MoVNbTeO M1 Catalyst: A Density Functional Theory Model Study

“…Unless otherwise stated, all reported energies were obtained from electronic structure calculations using the software CRYSTAL14 [34], applying the hybrid DFT approach B3LYP [35], supplemented by the dispersion corrections D2 [36]. This electronic structure method offers a sufficient correction of self-interaction artifacts [37,38], otherwise typical of regular GGA DFT functionals [39], thus affording a suitable localization of electrons at reduced V and Mo complexes [40]. Integrations over the Brillouin zone were carried out with a 1 × 1 × 4 k-grid, following the scheme of Monkhorst-Pack [41].…”

Configurations of V4+ centers in the MoVO catalyst material. A systematic stability analysis of DFT results

“…The distribution of Mo/V at various metal sites [12][13][14][15][16][17] of the lattice and the location of V 4+ /V 5+ centers pose a tough challenge to modeling even the simpler material MoVO [11,18]. The metal sites exhibit mixed occupancies by Mo and V [7,11], which seem to vary with the synthesis approach [2,7,19]. A variation in Mo/V was revealed by scanning transmission electron microscopy using highangle annular dark-field imaging [11].…”

“…In modern chemical industry, acrylic acid and acrylonitrile are important functionalized raw chemicals for producing higher-value products [1,2]. Alkanes, in view of their better availability, are desirable raw materials for synthesizing these chemicals via selective partial oxidation or ammoxidation [1].…”

Hydrothermal synthesis of Mo-V mixed oxides possessing several crystalline phases and their performance in the catalytic oxydehydration of glycerol to acrylic acid

“…Although the catalysts did not possess high quantities of total acid sites, medium and strong acid sites were present, notably in the samples calcined in oxygen (> 50%), which could be beneficial in the dehydration step. Several studies have shown that adequate strength of the acid sites is important because the adsorption of glycerol on relatively moderate strength acid sites favors the production of 3-hydroxypropa-nal, which consequently dehydrates to acrolein [41,42]. In the glycerol oxydehydration, the formation of CO and CO 2 is commonly associated with (Mo,V)O X species, the pure oxide phases, that promote complete oxidation of intermediates such as acetol, 3-hydroxypropane, and acrylic acid [16,45].…”

“…(b) The formation of several phases of Mo-V oxides can lead to interfacial surfaces that create a unique reactivity. In order to elucidate this surface phenomenon, sophisticated techniques, in combination with theoretical studies, are needed to reveal the configuration and structure/morphology of the surface, as well as the composition of adsorbed species[42]. (c) The synthesis of pure-phase samples was attempted in order to correlate the catalytic performance individually, but this proved to be unfeasible due to the probable formation of V 2 O 5 and MoO 3 as products of decomposition of the mixed oxides.…”