Abstract
Photocatalytic conversion of CO<sub>2<sub/> into fuels is an attractive option in terms of both reducing the increased concentration of atmospheric CO<sub>2<sub/> as well as generating renewable hydrocarbon fuels. It is necessary to investigate good catalysts for CO<sub>2<sub/> conversion and to clarify the mechanism irradiated by natural light. Layered Double Hydroxides (LDH) have been attracting attention for CO<sub>2<sub/> photoreduction with the expectation of sorption capacity for CO<sub>2<sub/> in the layered space and tunable semiconductor properties as a result of the choice of metal cations. This study first clarifies the effects of Cu doping to LDH comprising Zn and Al or Ga. Cu could be incorporated in the cationic layers of LDH as divalent metal cations and/or interlayer anions as Cu(OH)<sub>4<sub/><sup>2−<sup/>. The formation rates of methanol and CO were optimized for [Zn<sub>1.5<sub/>Cu<sub>1.5<sub/>Ga(OH)<sub>8<sub/>]<sup>+<sup/><sub>2<sub/>Cu(OH)<sub>4<sub/><sup>2−<sup/>·mH<sub>2<sub/>O at a total rate of 560 nmol h<sup>−1<sup/> g<sub>cat<sub/><sup>−1<sup/> irradiated by UV–visible light. Cu phthalocyanine tetrasulfonate hydrate (CuPcTs<sup>4−<sup/>) and silver were effective as promoters of LDH for CO<sub>2<sub/> photoreduction. Especially, the total formation rate using CuPcTs-[Zn<sub>3<sub/>Ga(OH)<sub>8<sub/>]<sup>+<sup/><sub>2<sub/>CO<sub>3<sub/><sup>2−<sup/>·mH<sub>2<sub/>O irradiated by visible light was 73% of that irradiated by UV–visible light. The promotion was based on HOMO–LUMO excitation of CuPcTs<sup>4−<sup/> by visible light. The LUMO was distributed on N atoms of pyrrole rings bound to central Cu<sup>2+<sup/> ions. The photogenerated electrons diffused to the Cu site would photoreduce CO<sub>2<sub/> progressively in a similar way to inlayer and interlayer Cu sites in the LDH in this study.
Highlights
Photocatalytic conversion of CO2 into fuels has emerged as an attractive option, in terms of both reducing the increased concentration of atmospheric CO2 as well as generating renewable hydrocarbon fuels that can be directly supplied to our present energy infrastructure (Costentin et al, 2013; Corma and García, 2013; Genevese et al, 2013; Habisreutinger et al, 2013; Indrakanti et al, 2009; Izumi, 2013; Kubacka et al, 2012; Lewis and Nocera, 2006; Lv et al, 2012; Roy et al, 2010)
The estimated Eg values for the Layered Double Hydroxides (LDH) used in this study were 5.6-3.0 eV (Tab. 1), indicating that only UV light was effective for CO2 photoreduction using LDH comprising Cu
Due to the wide band-gap nature Cavani F., Trifirò F., Vaccari A. (1991) Hydrotalcite-type anionic of these LDH, UV light was effective for CO2 photoreduc- clays: preparation, properties and applications, Catal
Summary
Photocatalytic conversion of CO2 into fuels has emerged as an attractive option, in terms of both reducing the increased concentration of atmospheric CO2 as well as generating renewable hydrocarbon fuels that can be directly supplied to our present energy infrastructure (Costentin et al, 2013; Corma and García, 2013; Genevese et al, 2013; Habisreutinger et al, 2013; Indrakanti et al, 2009; Izumi, 2013; Kubacka et al, 2012; Lewis and Nocera, 2006; Lv et al, 2012; Roy et al, 2010). The photocatalytic conversion of CO2 involves two reaction steps: 2H2OðgÞ ! 2H2ðgÞ þ O2ðgÞ; ÁGr 1⁄4 689 kJ molÀ1 ð1Þ. CH3OHðgÞ þ H2OðgÞ; ÁGr 1⁄4 2:9 kJ molÀ1 ð2Þ. It is important to investigate good catalysts for CO2 conversion into fuels using hydrogen as a reductant (Eq 2), which is potentially obtained from photocatalytic water splitting (Eq 1) (Izumi, 2013; Ahmed et al, 2011). Catalysts for converting CO2 into methanol using hydrogen and UV–visible light were investigated. To utilize visible light as the major part of the solar spectrum, dyes/nanoparticles were mixed with the LDH. The effects of Cu phthalocyanine tetrasulfonate hydrate (CuPcTs4À) combined with LDH were studied
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