The reaction network in propane oxidation over phase-pure MoVTeNb M1 oxide catalysts

Abstract

MoVTeNb oxide catalysts exclusively composed of the M1 phase (ICSD no. 55097) have been studied in the direct oxidation of propane to acrylic acid applying a broad range of reaction conditions with respect to temperature (623-633-643-653-663 Highlights• Phase purity and homogeneity ensure high stability of MoVTeNbO x in C 3 H 8 oxidation• The catalyst bears a self-supported active layer in sub-nanometer dimension• Higher O 2 content in the feed increases the activity without loss of selectivity• Oxygen partial pressure affects surface oxidation state and number of active sites• Auxiliary steam changes performance by modifying the nature of the active sites 5

Characterization of MoVTeNbOx Catalysts during Oxidation Reactions Using In Situ/Operando Techniques: A Review

“…For example, V +5 /V +4 pairs are claimed to be responsible for active lattice oxygen in most publications [11,[25][26][27]50,76] but changes in oxidation states of Mo, Te(Sb), and Nb are debated based on techniques used (XPS vs. XANES/EXAFS, etc.) and the type of oxidation reactions [11,25,26].…”

“…This conclusion was later supported by in situ XRD studies which showed the remarkable stability of the bulk structure with no indication for segregation of any phases. However, the morphology of the M1 particles is damaged after prolonged periods due to reduction and evaporation of Te [76]. A debate remains in the literature surrounding the nature of the surface restructuring process and identifying Extensive in situ/operando XPS and XRD studies were performed by the same group in other papers to analyze the surface and bulk catalyst compositions/structures during the propane oxidation reaction [17,75,76].…”

“…However, the morphology of the M1 particles is damaged after prolonged periods due to reduction and evaporation of Te [76]. A debate remains in the literature surrounding the nature of the surface restructuring process and identifying Extensive in situ/operando XPS and XRD studies were performed by the same group in other papers to analyze the surface and bulk catalyst compositions/structures during the propane oxidation reaction [17,75,76]. In situ XPS indicates that the yield of acrylic acid increases with decreasing amount of Mo and increasing molar ratio of Te/V (V +5 oxo-species in close vicinity to Te +4 sites) at the surface.…”

“…This surface restructuring also indicates that active sites do not contain all the elements of the M1 phase and the surface composition of the M1 phase differs greatly from the bulk. The catalyst surface changes dynamically and reversibly with variations in feed compositions, but only in the outermost surface layer to a depth of around one nanometer [76]. The active sites are, therefore, proposed to be embedded in a thin surface layer 9 of 15 enriched in V, Te, and Nb, but depleted in Mo, as presented in Figure 6 [17].…”

The M1 Phase of MoVTeNbO as a Catalyst for Olefin Metathesis and Isomerization

“…4, 5 The multiple catalytic functions of the M1 phase capable of activating various functional groups (e.g., alkanes, alkenes, alcohols, aldehydes) are considered a key aspect that enables the direct formation of acrylic acid with high selectivity 6. 7 Structural assignment of the catalytic functions is not straightforward, as the catalytic functions of M1 are closely related to the dynamics of the M1 surface changes in response to the reaction atmosphere (e.g., gas composition, temperature) 8–10. It is likely that the gradient of the gas composition within the catalyst bed influences the catalytic properties of M1.…”