Effect of Pr, Sm, and Tb Doping on the Morphology, Crystallite Size, and N₂O Decomposition Activity of Co₃O₄ Nanorods

Abstract

Cobalt(II,III) oxide, Co3O4, is a promising catalyst for nitrous oxide direct decomposition. In this paper we report effect of doping with some rare earth (RE) elements (Pr, Sm, and Tb) on the morphology and crystallite size of Co3O4nanorods. The various precursors (RE/Co oxalates) were prepared via the microwave assisted method and subsequent calcination. The decomposition pathway of these precursors was followed using thermogravimetric analysis (TGA). Based on thermal analysis results, Pr-, Sm-, and Tb-doped Co3O4samples were obtained via the calcination in static air at 500°C for their oxalate precursors. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and hydrogen temperature programmed reduction (H2-TPR) were used to characterize the RE-doped cobalt oxide catalysts. The activity of the prepared catalysts was investigated for N2O direct decomposition and compared with that of the undoped Co3O4catalyst. It was shown that the promoted Co3O4catalysts revealed higher activity compared to the unpromoted one. The dependence of the activity on both the catalysts particle size and the reduction behaviour was discussed.

Rare Earth-Promoted Nickel Oxide Nanoparticles as Catalysts for N2O Direct Decomposition

“…Two other peaks can be observed at ~1485 cm −1 and ~1361 cm −1 , which are related to the metal carbonate structures [7,30]. The higher intensities of these two absorptions in the case of the RE-containing samples could be related to their high ability to form surface carbonate structures [21,22]. Inspection of Figure 3 reveals the absence of any peaks due to oxalate anion, suggesting complete decomposition of the precursors, which is in agreement with the XRD findings.…”

“…This picture suggests a significant textural change of bare NiO upon the incorporation of RE-oxides. In this context, we reported that the incorporation of various RE-oxides into CuO and Co3O4 results in a noticeable decrease in their particles sizes [21,22,31]. Concurrently, Xue et al [10] reported a decrease in the Co3O4 SEM-estimated particles size after the addition of 5% of CeO2.…”

“…Among a series of alkali-doped NiO catalysts, the K-and Cs-promoted catalysts (M/Ni molar ratio = 0.05) showed the highest activity levels [24]. The activity of the present catlysts is higher than that of the Gd-, La-, and Sm-promoted CuO catalysts prepared by the same procedure [21,22].…”

“…The diffractograms of the Gd-, La-and Sm-containing samples (Figure 2b-d, respectively) show the same reflections exhibited by the bare NiO sample, indicating the presence of NiO as a major phase component of these solids. Moreover, these diffractograms show the existence of weak reflections below 35˝, which could be related to the presence of the relevant RE-oxides in minor amounts [21,22]. It is obvious from Figure 2 that the NiO characteristic diffraction peaks are markedly broadened upon the addition of the various RE-oxides.…”

“…From the obtained morphological and textural features of the obtained catalysts, it is evident that the added REs play an important role in controlling these two processes. CTAB, which is a cationic surfactant, was reported to enhance the formation of rod-like structures of NiO [34] and Co3O4 [31] with reduced dimensions. During the NiC2O4 synthesis, Ni 2+ ions first interact with CTAB to produce the Ni-CTAB complex, which is transformed immediately to NiC2O4-CTAB complex upon the addition of oxalic acid solution.…”