Synergistic effect of manganese on zirconia and ceria supports for improving photoreduction of CO₂

Photocatalytic CO2 reduction in the liquid phase at neutral pH conditions has been studied employing high surface area Mn-modified cubic CeO2 and amorphous ZrO2 catalysts. Results of the photocatalytic reduction of CO2 to methane are promising on Mn-modified ZrO2 and comparable with the noble metal-based photocatalysts. The surface area of both supports CeO2 and ZrO2 increased with Mn addition. Two broad diffraction peaks in Xray diffractograms indicate that the ZrO2 support is in the amorphous phase and Mn addition showed no considerable change. High intense diffraction peaks for CeO2 support illustrated the cubic fluorite phase and Mn addition to CeO2 support decreased the crystallite size due to the incorporation of Mn ions into the CeO2 lattice. XPS study revealed the stabilization of Mn in a lower oxidation state i.e., Mn2+ and Mn3+, with ZrO2 support than with CeO2 support. The superior specific capacitance of the Mn-modified ZrO2 catalyst indicates the enhanced synergy of active Mn species and support. Among the studied catalysts, Mn-modified ZrO2 photocatalyst exhibited the highest activity and selectivity for photoreduction of CO2 to methane and CO.