Abstract
Perovskites LaNi0.8Fe0.2O3 and LaNi0.8Mn0.2O3 were synthesized using the co-precipitation method by substituting 20 mol.% of the Ni-site with Fe and Mn, respectively. Temperature programmed reduction (TPR) showed that the exsolution process in the Fe- and Mn-substituted perovskites followed a two-step and three-step reduction pathway, respectively. Once exsolved, the catalysts were found to be able to regenerate the original perovskite when exposed to an oxygen environment but with different crystallographic properties. The catalytic activity for both materials after exsolution was measured for the methane dry reforming (DRM) reaction at 650 °C and 800 °C. Catalyst resistance against nickel agglomeration, unwanted phase changes, and carbon accumulation during DRM were analyzed using X-ray diffraction (XRD), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The presence Fe alloying in the catalyst particles after exsolution from LaNi0.8Fe0.2O3 led to a lower methane conversion compared to the catalyst derived from LaNi0.8Mn0.2O3 where no alloying occurred.
Highlights
The dry reforming of methane (DRM, Reaction 1) has gained considerable attention due to its ability to produce synthesis gas via the simultaneous consumption of two greenhouse gases, methane (CH4 ), and carbon dioxide (CO2 ) [1,2]
The X-ray diffraction (XRD) pattern of LaNi0.8 Mn0.2 O3 showed a slight shift towards a lower angle side as compared to that of LaNi0.8 Fe0.2 O3 due to the fact that the size of Mn+3 is larger than that of Fe+3 [33,34]
scanning electron microscopy (SEM) images in Figure 1c,d show that both LaNi0.8 Fe0.2 O3 and LaNi0.8 Mn0.2 O3 perovskites had a spheroid morphology
Summary
The dry reforming of methane (DRM, Reaction 1) has gained considerable attention due to its ability to produce synthesis gas via the simultaneous consumption of two greenhouse gases, methane (CH4 ), and carbon dioxide (CO2 ) [1,2]. Synthesis gas generated by this process can be converted to synthetic liquid hydrocarbon fuels through the industrially well-known Fischer–Tropsch reaction [3]: o CH4 + CO2 = 247.3 kJ/mol. The DRM reaction is typically accompanied by side-reactions which serve both to decrease the H2 :CO ratio (reverse water–gas shift reaction, RWGS) as well as lead to solid carbon accumulation (e.g., deep methane cracking, Boudouard reaction, etc.) as shown in Equations (2)–(4): CO2 + H2 CH4. CO + H2 O, C(s) + 2H2 , C(s) + CO2 , o ∆H298K = 41.2 kJ/mol, (2) = 74.9 kJ/mol,
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