A Rietveld analysis of the transformation of (La–Sr–V–O)reduced to (La–Sr–V–O)oxidized solids and the effect on their surface catalytic properties Original Research Article

The transformation of the crystal phases of the system (La–Sr–V–O)reduced, having the general formula La1−xSrxVO3 (x=0.0, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, 0.9, 0.95, 1.0) and the perovskite structure, towards the (La–Sr–V–O)oxidized one, was studied using the Rietveld analysis. The oxidized system contains the crystal phases LaVO4, Sr2V2O7 and Sr3V2O8 which originate from the crystal phases LaVO3 and SrVO3 existing in the reduced system. The oxidized solids exhibits surface areas (BET) around 8–10 m2 g−1 while the reduced ones much lower ∼1 m2 g−1. SEM studies showed that the oxidized particles exhibits a much more irregular surface with pores, cracks, steps and similar features which lack in the reduced solids. The oxidized solids rich in Sr show also a platelet-like structure. The acid/base function of the surface was studied using the isopropanol decomposition as a test reaction towards propene or acetone. The oxidized forms of the solids exhibits stronger acidic properties as compared to the reduced one and lead to dehydration towards propene while the reduced solids exhibit also considerable dehydrogenation activity. The rest features of catalytic action, like reaction rate and apparent activation energies appear rather similar and a common compensation effect, for the reduced and oxidized solids, is observed. The variation of the reaction path towards dehydrogenation or dehydration is related to the intermediate electronegativity of the solids for both the reduced and the oxidized samples.