Texture Properties of Undoped and Na 2 O-doped V 2 O 5 /Al 2 O 3,Catalysts

Abstract

Pure alumina, V₂O₅–Al₂O₃ and Na₂O-doped V₂O₅/Al₂O₃ samples have been obtained and roasted in air over the temperature range 400–750°C. The textural properties of all the calcination products have been determined from nitrogen adsorption studies at 77 K. The inclusion of V₂O₅ in alumina modifies the textural characteristics leading to an enhancement of activation at temperatures ≤450°C and to an enhancement of sintering at higher temperatures. Furthermore, AlV₂O₄ which formed at temperatures below 750°C resulted in a tremendous change in the textural properties. Three types of sintering were detected, i.e. particle-particle adhesion, pore widening and phase change. Doping with Na₂O retards sintering and at low calcination temperatures gave solids with higher surface areas compared to undoped samples. This has been attributed to activation brought about by the decomposition of NaNO₃ and the evolution of nitrogen oxides.