X-ray photoelectron spectroscopy, temperature-programmed desorption and temperature-programmed reduction study of LaNiO3 and La2NiO4 +δ catalysts for methanol oxidation

Abstract

An X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption (TPD) and reduction (TPR) study of LaNiO₃ and La₂NiO_4+δ perovskites has been carried out. The existence of at least two different forms of oxygen in these compounds is shown by both oxygen reactivity (TPD and TPR) and XPS characterisation. XP spectra have also revealed a surface enrichment in lanthanum and oxygen. TPR profiles have shown a reduction of LaNiO₃ through the formation of La₂Ni₂O₅ as an intermediate compound. Above 450 °C, LaNiO₃ and intergrowth nickelates (La₂NiO₄ and La₂NiO_{4 +δ}) undergo a final reduction to metallic Ni and La₂O₃. Between 200 and 400 °C all three compounds exhibit a high catalytic activity in the total catalytic oxidation of methanol.