La_0.6Sr_0.4Co_1−yFe_yO_3−δ Perovskites: Influence of the Co/Fe Atomic Ratio on Properties and Catalytic Activity toward Alcohol Steam-Reforming

Abstract

La0.6Sr0.4Co1−y FeyO3−δ (y = 0.2, 0.5, 0.8) perovskite-type oxide powders were prepared by the citrate gel method with the aim of investigating the influence of cobalt/iron atomic ratio on the chemical and structural properties as well as on the catalytic activity. The samples were characterized by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermal analysis, Kr physisorption surface area, scanning electron microscopy (SEM), and temperature programmed reduction (TPR). XRD outcomes reveal the formation of perovskite phase after calcination at 873 K. Depending on the Co/Fe atomic ratio, the perovskite exhibits two different structure: rhombohedral for y < 0.5, orthorhombic for y ≥ 0.5. However, other phases are also observed. The crystallite size increases with the calcination temperature, while decreases with the iron content. The specific surface area of the La0.6Sr0.4Co1−y FeyO3-δ perovskites (calcined at 1073 K) is low, but increases with the iron amount: it varies between 4.1 and 6.6 m2 g−1 moving from y = 0.2 to y = 0.8. XPS results reveal the presence of traces of Co(II) in the sample with lower cobalt amount. The scanning electron micrographs reveal nanoscaled near spherical particles which are clustered together, forming a highly porous microstructure. However, the samples with higher iron content show a more compact morphology due to the enhanced agglomeration. The perovskite phase is rather stable even after aggressive treatment as high temperature reduction. The influence of cobalt/iron atomic ratio on the catalytic activity toward alcohol steam reforming was investigated. All the samples present good alcohol dehydrogenation activity, as resulting from the methanol steam reforming experiments. In the steam reforming of ethanol, the La0.6Sr0.4Co0.5Fe0.5O3-δ presents the better performance (especially after reduction at 873 K) with the complete conversion of ethanol into syngas above 850 K and the almost complete suppression of the ethylene formation at lower temperature. The differences of the activity toward ethanol steam reforming are attributable to a different stabilization of Co(0) nanoparticles produced during the reduction at 873 K.

La0.6Sr0.4Co0.8Ga0.2O3‐δ (LSCG) hollow fiber membrane reactor: Partial oxidation of methane at medium temperature

“…52 BE values about 133.0-133.7 eV coincides well with the SrCO 3 component. 53,54 The higher BE about 133.8-135.8 eV suggests presence of SrO species. 54,55 Based on Figure 8 and Table 1, for the fresh LSCG hollow fiber membrane, the external surface shows that the Sr element exists mainly in the form of SrCO 3 (due to atmospheric contamination) and Sr 21 .…”

“…53,54 The higher BE about 133.8-135.8 eV suggests presence of SrO species. 54,55 Based on Figure 8 and Table 1, for the fresh LSCG hollow fiber membrane, the external surface shows that the Sr element exists mainly in the form of SrCO 3 (due to atmospheric contamination) and Sr 21 . The internal surface, however, consists mainly of SrO species with a lesser percentage of Sr 21 in the perovskite phase.…”

Catalytic Hydrogen Production from Bioethanol

“…The introduction of Ca creates oxygen vacancies, which is beneficial for the enhancement of oxygen mobility [70,71]. Besides, the perovskite-type oxides such as LaAlO 3 , SrTiO 3 , and BaTiO 3 have been used as the support for BESR catalysts due to their highly labile lattice oxygen [72,73]. The cobalt precursor was proved by several authors [60,74,75] to have prominent effect on catalytic performance, which was proposed to be related to the cobalt dispersion.…”

High catalytic activity of Co-Fe/α-Al2O3 in the steam reforming of toluene in the presence of hydrogen

“…Recently, various Co-based catalysts have been reported to show the high performance in the steam reforming of oxygenates [11][12][13][14][15][16] hydrocarbons [17,18] and biomass-derived tar [19][20][21][22] as well as Ni-based catalysts [23][24][25][26][27][28][29][30][31][32][33][34][35][36]. In addition, the promoting effect of Fe addition to Ni catalysts in the steam reforming has been reported [37][38][39][40], and the additive effect of Fe to Co catalysts has been investigated [41][42][43][44][45]. We have also reported that Co-Fe/␣-Al 2 O 3 catalyst with optimum composition (Fe/Co = 0.25) showed higher catalytic activity and resistance to coke deposition than Co/␣-Al 2 O 3 in the steam reforming of tar derived from cedar wood [41].…”