Effect of metal loading sequences in CO2 methanation activity on samarium-doped ceria supported bimetallic catalysts

Abstract

A bimetal-supported catalyst, lanthanum and nickel (La and Ni) on samarium-doped ceria (SDC), was synthesized by a sequential microwave heating process for the CO₂ methanation reaction. The effect of altering orders of metal addition to SDC on the methanation activity was investigated. The La/Ni/SDC catalyst obtained in co-microwave synthesis (all precursors were added at the same time) had the best methanation activity with a CO₂ conversion of approximately 60% at 353 °C, compared to the catalyst that either La or Ni is loaded first on SDC. The better activity of the co-microwave catalyst was attributed to a synergistic function of the carrier and metals due to intimate contact, thus provoking a unique metal–support interaction and optimal CO₂ affinity. This was evidenced by surface characterisation including XRD, TEM and XPS analysis, revealing that La/Ni/SDC exhibits low crystallinity in nanoscale size and contains more active oxygen species, as well as Ce³⁺/Ce⁴⁺ redox couples. Besides, working mechanisms of the La/Ni/SDC catalyst were postulated according to in situ infrared studies. The result demonstrated that sequences of metal loading in the synthesis of the catalyst are critical to the metal–support interaction for the methanation activity. Accordingly, this will allow the design of effective bimetallic catalysts capable of conducting potential reactions with optimised synthesis conditions.