Perovskite La–St–Fe–O (St=Ca, Sr) supported nickel catalysts for steam reforming of ethanol: The effect of the A site substitution

The perovskite type oxides (PTO) supported Ni catalysts were prepared by one step citrate complexing method and were applied to steam reforming of ethanol (SRE). The catalysts were characterized by X-ray diffraction (XRD), oxygen temperature-programmed desorption (O2-TPD), temperature programmed reduction (TPR), thermal analysis (TG), mass spectrometer (MS), physical adsorption for specific surface areas and hydrogen chemical adsorption for metal surface areas. The perovskite oxide without substitution is LaFe1−yNiyO3. For the samples substituted by Sr or Ca, as indicated by the XRD results, the calcium and strontium were successfully introduced into the La site of the LaFe1−yNiyO3. The Ca substitution in LaFeyNi1−yO3 perovskite leads to the enrichment of oxygen vacancies, and some of released oxygen species is resulted from the reduction of the Fe4+ into Fe3+ in the perovskite. Although the enrichment of oxygen vacancies was also observed for the samples with Sr substitution, the insertion of Sr into the perovskite lowers the dispersion of metallic Ni, leading to a poor SRE activity. The correlation between the oxygen vacancies and the stability for SRE indicates that the surface oxygen vacancies and the promoted bulk oxygen species, as the results of the La site substitution, restrain the carbon formation and facilitate the carbon elimination. The surface oxygen vacancies as well as lattice oxygen vacancies are beneficial for the reaction between water and hydrocarbon species on the catalyst surface, reducing carbon containing intermediates and accelerating eliminating reaction of the deposited carbon. In sum, the A site doped perovskite La1−xCaxFe1−yNiyO3 supported nickel catalysts exhibit very good stability for SRE, due to the surface and bulk oxygen vacancies.