The Effect of Water on the 2‐Propanol Oxidation Activity of Co‐Substituted LaFe_1−xCo_xO₃ Perovskites

Abstract

Perovskites are interesting oxidation catalysts due to their chemical flexibility enabling the tuning of several properties. In this work, we synthesized LaFe1−xCoxO3 catalysts by co‐precipitation and thermal decomposition, characterized them thoroughly and studied their 2‐propanol oxidation activity under dry and wet conditions to bridge the knowledge gap between gas and liquid phase reactions. Transient tests showed a highly active, unstable low‐temperature (LT) reaction channel in conversion profiles and a stable, less‐active high‐temperature (HT) channel. Cobalt incorporation had a positive effect on the activity. The effect of water was negative on the LT channel, whereas the HT channel activity was boosted for x>0.15. The boost may originate from a slower deactivation rate of the Co3+ sites under wet conditions and a higher amount of hydroxide species on the surface comparing wet to dry feeds. Water addition resulted in a slower deactivation for Co‐rich catalysts and higher activity in the HT channel state.

Structure‐Performance Relationship of LaFe1‐xCoxO3Electrocatalysts for Oxygen Evolution, Isopropanol Oxidation, and Glycerol Oxidation

“…A shift from orthorhombic to rhombohedral perovskites with increasing Co content is a common phenomenon. [63,64] The smallest fraction of the total phase composition was made up of the spinel phase, [61] which might derive from phase segregation in the precursor state where a layered double hydroxide is formed in the otherwise amorphous precursor at higher Co contents, presumably [a] The values for materials with x = 0-0.30 had been reported previously. [52,59] ChemElectroChem consisting mainly of Fe and Co which means the two elements segregate from La.…”

“…[52,59] ChemElectroChem consisting mainly of Fe and Co which means the two elements segregate from La. [61] Thus, a too high degree of segregation in the precursor state causes the formation of the spinel phase in the calcined materials. Rietveld refinement was conducted for which fit criteria (Table SI1) and patterns (Figure SI1) as well as a table with the exact percentages of the respective phases (Table SI2) are featured in the Supporting Information.…”

“…A shift from orthorhombic to rhombohedral perovskites with increasing Co content is a common phenomenon [63,64] . The smallest fraction of the total phase composition was made up of the spinel phase, [61] which might derive from phase segregation in the precursor state where a layered double hydroxide is formed in the otherwise amorphous precursor at higher Co contents, presumably consisting mainly of Fe and Co which means the two elements segregate from La [61] . Thus, a too high degree of segregation in the precursor state causes the formation of the spinel phase in the calcined materials.…”

“…Here, we used the coprecipitation approach to fabricate LaFe 1-x Co x O 3 samples with x = 0-0.70, mainly crystallising in the orthorhombic perovskite structure with contributions of rhombohedral perovskite and spinel oxide at high cobalt content. [61] We investigated the relation between the electrocatalytic activity of the resulting materials for the three different reactions, namely, the OER, iPOR and GOR, and their structure and metal composition. Furthermore, we conducted detailed GOR product analysis to observe the relation between structural characteristics in terms of cobalt content and oxide phase with respect to their potential to convert glycerol to value-added products.…”

“…In all three cases, these materials showed a strong activation of LaFeO 3 upon incorporation of cobalt in small amounts. Here, we used the coprecipitation approach to fabricate LaFe 1‐x Co x O 3 samples with x=0–0.70, mainly crystallising in the orthorhombic perovskite structure with contributions of rhombohedral perovskite and spinel oxide at high cobalt content [61] . We investigated the relation between the electrocatalytic activity of the resulting materials for the three different reactions, namely, the OER, iPOR and GOR, and their structure and metal composition.…”