Study on carbon dioxide reduction with water over metal oxide photocatalysts

Abstract

Various metal oxides with 0.1 wt% Ag loaded as a cocatalyst were prepared by an impregnation method and examined their photocatalytic activity for CO2 reduction with water. Among all the prepared Ag‐loaded metal oxides, Ga2O3, ZrO2, Y2O3, MgO, and La2O3 showed activities for CO and H2 productions under ultraviolet light irradiation. Thus, metal oxides involving metal cations with closed shell electronic structures such as d0, d10, and s0 had the potential for CO2 reduction with water. In situ Fourier transform infrared measurement revealed that the photocatalytic activity and selectivity for CO production are controlled by the amount and chemical states of CO2 adsorbed on the catalyst surface and by the surface basicity, as summarized as follows: Ag/ZrO2 enhanced H2 production rather than CO production due to very little CO2 adsorption. Ag/Ga2O3 exhibited the highest activity for CO production, because adsorbed monodentate bicarbonate was effectively converted to bidentate formate being the reaction intermediates for CO production owing to its weak surface basicity. Ag/La2O3, Ag/Y2O3, and Ag/MgO having both weak and strong basic sites adsorbed larger amount of carbonate species including their ions and suppressed H2 production. However, the adsorbed carbonate species were hardly converted to the bidentate formate.

Synthesis of α-Ga2O3 by Water Oxidation of Metallic Gallium as a Photocatalyst for CO2 Reduction with Water

“…In addition, Ga 2 O 3 consisting of two phases, α- and γ-phases or β- and γ-phases, shows the photocatalytic activity for CO 2 reduction, for which their phase boundaries are reported to be active sites for CO 2 reduction. − Precipitation of gallium oxide hydroxide (GaOOH) on α- and β-phases is also reported to increase the photocatalytic CO 2 reduction . In most cases, noble metals such as Ag − and Pt have been employed as cocatalysts to enhance CO productivity in photocatalytic CO 2 reduction. However, it has been reported that without a cocatalyst, Ga 2 O 3 consisting of two phases, α- and β- or β- and γ-phases, exhibits high activity for the photocatalytic CO 2 reduction. ,, It should be noted that except for the β-phase, no single phase of Ga 2 O 3 is examined as a photocatalyst for CO 2 reduction with water because of the lack of thermal stability and difficulties in their synthesis.…”

Photocatalytic Reduction of CO2 to Methanol by Cu2O/TiO2 Heterojunctions

“…Thus, the recycling of CO 2 into low-carbon chemicals or fuels using solar energy is considered an economically attractive and environmentally friendly route. The desired photocatalysts for the photocatalytic reduction of CO 2 to chemicals or fuels under mild conditions are being developed to achieve the goal of CO 2 recycling [1][2][3].…”

Nitrogen Doping-Roused Synergistic Active Sites in Perovskite Enabling Highly Selective CO2 Photoreduction into CH4

“…For example, the absorption band at ∼1557 cm −1 was attributed to the COOH* group, 20 one of the most common intermediates during photocatalytic CO 2 reduction process. The peak at 1320 cm −1 was attributed to the b-CO 3 2− * group, 21,22 which originated from CO 2 dissolving in H 2 O. Importantly, the peaks at 1064 and 1020 cm −1 may correspond to the *CH 3 O and *CHO groups, 7 both of which were the key intermediates for photocatalytic CO 2 reduction toward CH 4 production.…”