The Effect of Co Incorporation on the CO Oxidation Activity of LaFe1−xCoxO3 Perovskites

Abstract

Perovskite oxides are versatile materials due to their wide variety of compositions offering promising catalytic properties, especially in oxidation reactions. In the presented study, LaFe1−xCoxO3 perovskites were synthesized by hydroxycarbonate precursor co-precipitation and thermal decomposition thereof. Precursor and calcined materials were studied by scanning electron microscopy (SEM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), thermogravimetric analysis (TG), and X-ray powder diffraction (XRD). The calcined catalysts were in addition studied by transmission electron microscopy (TEM) and N2 physisorption. The obtained perovskites were applied as catalysts in transient CO oxidation, and in operando studies of CO oxidation in diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). A pronounced increase in activity was already observed by incorporating 5% cobalt into the structure, which continued, though not linearly, at higher loadings. This could be most likely due to the enhanced redox properties as inferred by H2-temperature programmed reduction (H2-TPR). Catalysts with higher Co contents showing higher activities suffered less from surface deactivation related to carbonate poisoning. Despite the similarity in the crystalline structures upon Co incorporation, we observed a different promotion or suppression of various carbonate-related bands, which could indicate different surface properties of the catalysts, subsequently resulting in the observed non-linear CO oxidation activity trend at higher Co contents.

The Effect of Water on the 2‐Propanol Oxidation Activity of Co‐Substituted LaFe1−xCoxO3 Perovskites

“…Within the phase-pure orthorhombic perovskites, a volcano-like behavior was observed with a maximum of 15 % Co, which might be superimposed to the composition effect in both channels. A similar non-linear activity increase was reported before in CO oxidation and exhaust gas decomposition on LaFe x Co 1À x O 3 , [19,50] Co-doped NiO in CO oxidation, [51] and LaFeO 3 with Co and Sr doping. [23] For all catalysts, acetone was the main product.…”

“…As reported in our previous study, the (112) reflection shifted to higher angles, indicating the incorporation of the smaller Co 3 + cations into the perovskite lattice. [19,30] For x � 0.40, no phase pure materials were synthesized. Instead, a mixture of three crystalline phases was observed.…”

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

“…[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. [61] Thus, a too high degree of segregation in the precursor state causes the formation of the spinel phase in the calcined materials.…”

“…A suitable candidate class of materials for anodic reactions in water electrolysis are perovskites, [12,[51][52][53][54][55][56][57][58] metal oxides with the general formula ABO 3 consisting typically of rare-earth metals on the A-site, and transition metals on the B-site. The latter directly affects their electrocatalytic properties and changes therein may impact the reaction mechanism.…”

Dynamics of Reactive Oxygen Species on Cobalt-Containing Spinel Oxides in Cyclic CO Oxidation

“…Catalytic oxidation in several temperature cycles is frequently used in the literature to show catalyst stability [18,19]. However, some studies indicated further effects of either pretreatment or subsequently performed catalytic runs.…”