Thermal solid–solid interactions and catalytic properties of V 2O 5/Al 2O 3 system treated with Li 2O and Ag 2O

Abstract

The effects of doping with Li 2O and Ag 2O (0.40–4.58 mol%) and thermal treatment on solid–solid interaction and physicochemical properties of 0.20V 2O 5/Al 2O 3 system were investigated. The pure and variously doped solids were subjected to heat treatment at 350, 550, 750 and 1000 °C. Thermal analyses (TG, DTG and DTA) techniques were used to study the thermal behaviour of pure and doped solids. The thermal products were identified using X-ray diffraction (XRD) analysis. The catalytic behaviour of pure and variously doped solids was tested in hydrogen peroxide decomposition as a model reaction at 30–50 °C. The results revealed that both of dopants enhanced the thermal decomposition of pure mixed solids. Crystalline AlOOH and V 2O 5 phases were detected for all solids preheated at 350 °C. Increasing calcination temperature up to 550 °C for all solids resulted in formation of γ-Al 2O 3 beside V 2O 5 phase. Poorly crystalline AgVO 3 phase was formed at 350 °C for solid heavily doped with Ag 2O. Crystalline LiVO 3 phase was detected for solid heavily doped with Li 2O and calcined at 550 °C. Crystalline AlVO 3 phase formed at 750 °C as a result of solid–solid interaction between the corresponding oxides. The doping with Li 2O or Ag 2O hindered this process. V 2O 5 enhanced the crystallization of γ-Al 2O 3 into α-Al 2O 3 for various solids preheated at 1000 °C. The catalytic activity of pure mixed solids treated with Li 2O or Ag 2O and preheated at 350 and 550 °C increased up to certain extent. The observed increase in activity is attributed to increasing concentration of catalytically active constituents and/or formation of new active sites. The activity decreased with increasing concentration of dopants and increasing calcination temperature up to 1000 °C. The decrease in activity is due to formation of inactive compounds as AlVO 3, LiVO 3, AgVO 3, α-Al 2O 3 and/or sintering process.