Detailed Investigation of Sm₂O₃ Catalysts with Different Morphologies for Oxidative Coupling of Methane

Abstract

Sm 2 O 3 catalysts with different morphologies (nanoparticle, nanorod, hollow nanosphere, nanofiber, flower-like) were synthesized and tested for the oxidative coupling of methane. The results obtained showed that increasing specific surface area reduced the activity, C 2 selectivity and, thus the yield. It was observed that the reaction initiation temperature was dependent on the total or partial oxidation of methane, which produced the heat for the initiation of the reaction. The effect of temperature on catalytic performance was relatively low at lower temperatures (< 600°C) than at higher temperatures (> 700°C). High reaction temperatures (> 700°C) decreased the C 2 selectivity, lower temperatures were found beneficial to achieve higher C 2 selectivity and yield as expected. Hollow nanosphere morphology showed the highest activity and selectivity at 450°C and yielded 10.5 % C 2 under high space velocity. The highest C 2 yield (11.8 %) was obtained at 600°C with nanoparticle morphology. Considering the results at the conditions that full oxygen conversion was attained, it was found that the C 2 selectivity and yield decreased with the nanoparticle > flower-like > nanorod and nanosphere > nanofiber sequence.

Recent Advances in the Use of Controlled Nanocatalysts in Methane Conversion Reactions

“…Additionally, the temperature at which the reaction initiated increased with the binding energy of lattice oxygen [111]. An increase in the binding energy of lattice oxygen suggests a shift in its nature from nucleophilic to electrophilic [113,114]. Consequently, a more nucleophilic O 2− and a more electrophilic La 3+ pair could lower the activation energy required for C-H bond cleavage, initiating the reaction at lower temperatures.…”