Redox behaviour of La-Cr compounds formed in CrOx/La2O3 mixed oxides and CrOx/La2O3/ZrO2 catalysts Original Research Article

The redox behaviour of chromium oxide in CrOx/La2O3, CrOx/La2O3/ZrO2 and CrOx/ZrO2 mixed oxide systems has been investigated by temperature-programmed reduction (TPR), photoelectron spectroscopy (XPS) and Raman spectroscopy (RS). The formation of La-Cr compounds such as La2CrO6, LaCrO4 was shown to occur by calcination of CrOx/La2O3 and CrOx/La2O3/ZrO2 at 600 °C. With a Cr content of ca. 4 wt.%, it was revealed that, having been reduced to Cr3+-containing compounds, La2CrO6 and/or LaCrO4 in both systems may be restored by reoxidation at 600 °C. In the case of CrOx/La2O3/ZrO2 catalysts, it is suggested that these compounds were real surface species anchored as an overlayer on zirconia. Such a structure may stabilise, on the one hand, the tetragonal modification of zirconia and, on the other hand, highly dispersed state of Cr species in calcined as well as in reduced catalysts.