Structural features of La1−xCexNiO3 mixed oxides and performance for the dry reforming of methane

Mixed oxides La1−xCexNiO3 (x = 0, 0.05, 0.4 and 0.7) have been prepared by the citrate method and tested, after reduction activation, in the CO2 reforming of methane reaction into synthesis gas. The compounds were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), specific surface area measurements, X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), transmission electron microscopy (TEM) and temperature-programmed oxidation (TPO). The LaNiO3 perovskite exhibited activity to methane reforming, but suffered a slow deactivation with time-on-stream. Nevertheless, substitution of the A site metal ion with a tetravalent metal cation (Ce) led to an increase in catalytic activity. Moreover, the insertion of Ce increased the stability of the catalysts with respect to the reforming reaction. The La0.95Ce0.05NiO3 catalyst showed the highest activity, with CO2 conversion of 62% at 1023 K. The XRD and TPR analyses confirmed that at high Ce contents, ceria appears as segregated CeO2 phase and interferes with the rate of perovskite structure formation, so that NiO and La2NiO4 are produced. As a consequence of the low solubility of cerium oxide, its insertion in the perovskite structure is also possible in the low Ce-content regions. This low amount of cerium incorporated is responsible not only for the enhancement of catalytic performance of the perovskite after its activation by reduction, but also for the inhibition of carbon formation.