Activity dependence of the binary vanadium oxide catalysts from specific surface area

Manganese oxide catalysts, including γ-MnO2, Mn2O3 and Mn3O4, were synthesized by a precipitation method using different precipitants and calcination temperatures. The catalytic oxidations of benzene and 1,2-dichloroethane (1,2-DCE) were then carried out. The effects of the calcination temperature on the catalyst morphology and activity were investigated. It was found that the specific surface area and reducibility of the catalysts decreased with the increase in the calcination temperature, and both the γ-MnO2 and Mn3O4 were converted to Mn2O3. These catalysts showed good activity and selectivity for the benzene and 1,2-DCE oxidation. The γ-MnO2 exhibited the highest activity, followed by the Mn2O3 and Mn3O4. The high activity could be associated with the large specific surface area, abundant surface oxygen species and excellent low-temperature reducibility. Additionally, the catalysts were inevitably chlorinated during the 1,2-DCE oxidation, and a decrease in the catalytic activity was observed. It suggested that a higher reaction temperature could facilitate the removal of the chlorine species. However, the reduction of the catalytic reaction interface was irreversible.

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Influence of vanadium content on structure and activity of V2O5–ZrO2–SiO2 catalyst for propane dehydrogenation

Voprosy Khimii i Khimicheskoi Tekhnologii ◽

10.32434/0321-4095-2021-135-2-117-125 ◽

2021 ◽

pp. 117-125

Keyword(s):

Specific Surface ◽

Vanadium Oxide ◽

Surface Area ◽

Specific Surface Area ◽

Average Pore Size ◽

Sol Gel ◽

Tetragonal Zirconia ◽

Propane Dehydrogenation ◽

Average Pore ◽

Zirconium Silicate

In order to create alternative vanadium oxide-supported catalysts for the process of non-oxidative propane dehydrogenation to propylene, we studied the effect of the increased content of vanadium oxide in the V2O5–ZrO2–SiO2 composition on its structure and catalytic properties. Zirconium silicate hydrogel in the form of finished spherical granules with the SiO2 content of more than 50% was prepared by direct sol-gel synthesis from zirconium oxychloride and sodium metasilicate using the droplet coagulation technology. Catalysts were fabricated by impregnation of hydrogel with an aqueous solution of vanadyl sulfate salt, hydrothermal treatment and calcination in air. By using scanning electron microscopy, X-ray diffraction analysis and low-temperature nitrogen adsorption/desorption method, we showed that amorphous samples with a developed mesoporous structure (with the pore diameter of ~6 nm and the specific surface area of ~300 m2 g–1) were formed when the content of the supporting V2O5 on zirconium silicate was 10, 20, 25, and 30 wt.%. In the course of temperature increase in the propane dehydrogenation reaction, the catalyst samples crystallized in the reaction mixture propane–inert gas with the formation of tetragonal zirconia. When the content of V2O5 was 25% or 30%, additional phases of reduced vanadium oxides and traces of the zirconium vanadate phase were formed. After the reaction, the specific surface area of the catalysts decreased significantly and the average pore size of the samples with 25% and 30% V2O5 increased to ~30 nm. The propylene yield reproducibly observed on the samples with 25% and 30% V2O5 was lower than that on the samples with 10% V2O5; however, it remained quite high, which was probably due to the expanded diameter of the pores and the appearance of additional ZrV2O7 sites that are active with respect to the dehydrogenation of light alkane.

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