Abstract
The Fe-substituted Ba-hexaaluminates (BaFeHAl) are active catalysts for reverse water-gas shift (RWGS) reaction conducted in chemical looping mode. Increasing of the degree of substitution of Al3+ for Fe3+ ions in co-precipitated BaHAl from 60% (BaFeHAl) to 100% (BaFe-hexaferrite, BaFeHF), growing its surface area from 5 to 30 m2/g, and promotion with potassium increased the CO capacity in isothermal RWGS-CL runs at 350–450 °C, where the hexaaluminate/hexaferrite structure is stable. Increasing H2-reduction temperature converts BaFeHAl to a thermally stable BaFeHF modification that contains additional Ba-O-Fe bridges in its structure, reinforcing the connection between alternatively stacked spinel blocks. This material displayed the highest CO capacity of 400 µmol/g at isothermal RWGS-CL run conducted at 550 °C due to increased concentration of oxygen vacancies reflected by greater surface Fe2+/Fe3+ ratio detected by XPS. The results demonstrate direct connection between CO capacity measured in RWGS-CL experiments and calculated CO2 conversion.
Highlights
CO2 can be converted to syngas, a key intermediate in production of green chemicals and fuels [1,2], by reverse water-gas shift (RWGS)
Chemical looping (CL) combined two separate steps: hydrogen reduction of metal oxide catalyst followed by CO2 oxidation of the catalyst to produce CO (Scheme 1)
The crystollagraphic positions of X-Ray diffraction (XRD) reflections recorded with our BaFeHF material corresponded to the same structure were shifted to lower angles
Summary
CO2 can be converted to syngas, a key intermediate in production of green chemicals and fuels [1,2], by reverse water-gas shift (RWGS). Catalysts for this reaction are Cu, Ce, Ni, Fe-based oxides as well as supported noble metals (Pt, Rh), and multicomponent metal oxides [1,2,3,4,5,6]. Metal oxide catalytic materials suitable for RWGS-CL should have the ability to eliminate oxygen from materials surface for efficient splitting of C–O bond of CO2 during adsorption on O-vacancies at surface of the catalyst. It is important to maximize the surface area and surface concentration of suitable O-vacancies governed by cationic environment of precursor oxygen ions
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