E. V. Ishchenko

Effect of preparation conditions on the phase composition of the MoVTe(Nb) oxide catalyst for the oxidative conversions of propane

The replacement of expensive propylene by propane, which requires the development of catalysts for the direct oxidation of propane into acrylonitrile, is an important and insufficiently studied problem. Multicomponent MomVnTekNbx oxide systems are promising in one-stage ammoxidation of propane to acrylonitrile. Despite considerable attention of various authors to the preparation methods for these catalysts, the reproducibility of their physicochemical and catalytic properties is low. To optimize the technology of catalyst synthesis, we studied the effect of drying method (evaporation or spray drying) for the aqueous suspension of the initial compounds on the formation of the Mo1V0.3Te0.23(Nb0.12) oxide catalyst. It is shown that the method of drying determines the chemical and phase composition of solid catalyst precursors and the phase composition of the final catalyst in high-temperature treatment. The use of spray drying provides the required physicochemical characteristics of the catalyst (the specific surface area and the phase composition) that determine the high activity and selectivity in the selective conversion of propane. These catalysts contain two crystalline phases: orthorhombic M1 and hexagonal M2 in an optimal ratio of 3: 1.

Heterogeneous catalytic oxidative conversion of ethane to ethylene

Multicomponent and multiphase oxide catalysts with a uniform composition Mo1V0.3Te0.23Nb12 but different phase contents were studied in the oxidative conversion of ethane to ethylene and characterized by X-ray diffraction analysis. The phase composition of the samples was varied by modifying such conditions of catalyst preparation as the pH of raw precursor, the drying of the wet precursor, and the conditions of solid precursor calcination. The content of the detected phase is determined via Rietveld refinement. The catalytic activity of MoVTeNb oxide catalysts studied in the oxidative conversion of ethane was found to be determined by the content of the orthorhombic M1 phase (the layered four-component compound (TeO)0.23(Mo,V,Nb)5O14).

Effect of SiO2 on the physicochemical and catalytic properties of VMoTeNbО catalyst in oxidative conversion of ethane

Supported oxide catalysts of the overall composition V0.3Mo1Te0.23Nb0.12/n SiO2 (n = 0, 10, 25, 35, and 50 wt %) were tested in oxidative conversion of ethane to ethylene and were characterized by chemical analysis, X-ray diffraction, and high-resolution transmission electron microscopy. On introducing SiO2, coarse crystals of the active М1 phase become partially coated with layers of amorphous SiO2. The support does not influence the selectivity with respect to the reaction products. The catalysts with 10–25 wt % SiO2 content exhibit the highest activity owing to the presence of nanodomains of the M1 phase.

Effect of pressure on the oxidative conversion of ethane on VMoTeNbO catalyst

Study of the catalytic properties of the VMoTeNbO catalyst in the oxidative conversion of ethane to ethylene at pressures of 0.1 to 2.1 MPa demonstrated that the pressure positively affects the conversion of ethane and favors formation of oxygen -containing products of deep and partial oxidation: carbon oxides and acetic acid, respectively. With increasing pressure, the yield of the product of oxidative dehydrogenation of ethane, i.e., ethylene, decreases.

Structural features of promoted MoVTeNbO catalysts for the oxidative dehydrogenation of ethane

The morphology, crystal structure, and phase composition of MoVTeNbO catalysts modified with K, Ca, Zr, or Bi were studied, and the effects of promoters on their catalytic properties in the oxidative conversion reaction of ethane were examined. With the use of high-resolution transmission electron microscopy (HRTEM), it was found that Bi and K were inserted into the structure of the active phase M1 and potassium changed its morphology. Zr and Ca formed individual oxides and molybdates. Changes in the structure of the promoted models affected their catalytic properties.

A tem study of MoVTe(Nb) oxide catalysts for the selective conversion of propane

The structure of X-ray amorphous precursors of MoVTeO and MoVTeNbO oxide catalysts and their conversion at high-temperature treatment and under exposition in the reaction medium is studied by analytical transmission electron microscopy (TEM) in combination with the local energy dispersive X-ray (EDX) microanalysis of the elemental composition. At thermal treatment in the range of 300–450 °C the presence of both true amorphous phases and nanosized crystallites of the orthorhombic M1 and pseudohexagonal M2 phases is detected in the MoVTe(Nb)O catalysts. An increase in the annealing temperature results in the formation of well-crystallized particles of the M1 and M2 phases in the MoVTeNbO catalyst. The four-component M1 phase is stable at 550 °C and it is maintained under the reaction conditions. At an increase in the temperature of thermal treatment the successive crystallization of nanosized particles occurs in the three-component MoVTeO system with the formation of mainly the M2 phase. The nanostructured three-component M1 phase formed at low temperatures cannot crystallize into the full M1 phase in the absence of Nb and decomposes with the formation of the M2 phase that is inactive in the conversion of propane. The calculation procedure for EDX, which was developed specially for these catalysts, enabled the refinement of the chemical composition of separate phases.

Oxidative dehydrogenation of ethane on VMoTeNbО/Al–Si–O catalysts: Effect of the support on the physicochemical and catalytic properties

Supported oxide catalysts of the overall composition V0.3Mo1Te0.23Nb0.12/nAl–Si–O (n = 0, 10, 25, 35, 50, and 70 wt %) were tested in oxidative dehydrogenation of ethane and were characterized by chemical analysis, X-ray diffraction analysis, and transmission electron microscopy. The use of the Al–Si–O support in a wide range of its content (from 10 to 50 wt %) favors formation of nanodomains of the active М1 phase ensuring higher, compared to the bulk catalysts, activity in oxidative dehydrogenation of ethane. The formation of secondary phases of aluminum molybdate and vanadium–molybdenum double oxide, observed at the support content increased over 35 wt %, leads to worsening of the catalytic properties.

Oxidative conversion of ethane over VMoTeNb oxide catalyst

The oxidative conversion of ethane over a multicomponent oxide catalyst with the composition V0.3Mo1Te0.23Nb0.12 was studied in the temperature range of 360–450°C. It was found that temperature did not affect the contribution from the parallel and consecutive paths of reaction product formation. The obtained data could be useful in developing applications for the process, particularly in choosing the type and design of a reactor (tubular fixed bed, fluidized bed, and so on).

Role of MoVTeNb oxide catalyst constituent phases in propane oxidation to acrylic acid.

Abstract The catalytic activity of MoVTeNbO catalyst and its constituent phases (M1, M2 and Mo5O14-like) in the oxidation of propane, as well as propylene and acrolein, which are intermediates of acrylic acid formation from propane, was studied. In all the reactions, the М1 phase shows higher activity and selectivity, compared to M2 and Mo5O14-like phases; its presence being sufficient for efficient proceeding the propane oxidation to acrylic acid.