Role of SiO2 in enhancing CO yield by using silica-supported La0.5Ba0.5FeO3 in reverse water–gas shift chemical looping†

Abstract

Perovskite oxides, such as La_0.5Ba_0.5FeO₃ (LBF), facilitate CO₂ conversion by reverse water–gas shift chemical looping (RWSG-CL) at moderate conditions by employing an oxygen vacancy at the surface to aid CO₂ adsorption and then to scavenge an oxygen atom from it to fill the vacancy. The formation of composites with silica is also known to enhance the perovskite oxide's performance. To better clarify this, experimental and computational methods are now combined to probe CO₂ adsorption for both unsupported and silica-supported LBF. Chemisorption tests showed the CO₂ adsorption sites increased from 12.4 to 60.6 μmol g_LBF⁻¹ after adding SiO₂ (75 wt%) to LBF (25 wt%). Spectroscopic studies (DRIFTS) indicated that the carbonate formation during CO₂ adsorption shifts from bidentate to monodentate because the surface morphology changes upon supporting on silica. Computational (DFT) results provide evidence for CO₂ adsorbed as a monodentate and a bidentate carbonate, respectively, on the (111) and (100) surfaces. Monodentate species required lower energy, as determined by DFT, to dissociate C–O bond than bidentate species. Since XRD results identified increases in the (111) relative to (100) planes upon supporting LBF on SiO₂, the combined DRIFTS and DFT approach revealed that the perovskite oxide restructures when in composite form, which explains the increased RWGS-CL process yield of CO.