Selective Photoconversion of Carbon Dioxide into Methanol Using Layered Double Hydroxides at 0.40 MPa

Abstract

CO2 photoconversion is a promising method to reduce atmospheric CO2 concentrations and mitigate energy problems simultaneously. Among the various efficient and stable semiconductor photocatalysts used for this purpose, layered double hydroxides (LDHs) have attracted attention as catalysts for CO2 photoconversion into CO and/or methanol. In this study, various LDHs of the formula [MII3GaIII(OH)8]2A⋅m H2O (MII=ZnII, CuII; A2−=CO32−, [Cu(OH)4]2−) were synthesized and used for CO2 photoconversion at a reaction pressure of 0.40 MPa in the presence of H2 to result in the exclusive production of methanol. Furthermore, the pretreatment of carbonate‐type LDHs at 423 K boosted the reaction rates by a factor of 7.5–20. Interestingly, [Zn3Ga(OH)8]2CO3⋅m H2O was the only LDH that produced methane primarily by an eight‐electron reduction (rather than the production of methanol by a six‐electron reduction) at a total formation rate of 2.7 μmol h−1 gcat−1 after it was preheated at 423 K and protected by an Ar atmosphere. Conversely, the methanol photogeneration rates of tetrahydroxycuprate‐type LDHs were suppressed to less than 0.1 μmol h−1 gcat−1 at 0.40 MPa. In summary, the contribution of the interlayer reaction space created by the partial removal of water molecules and/or carbonate ions of LDHs was suggested.

Engineering Layered Double Hydroxide–Based Photocatalysts Toward Artificial Photosynthesis: State‐of‐the‐Art Progress and Prospects

“…Equation ()–() describes the mechanism of intercalated CO 3 2− in CO 2 RR. [ 190 ] CO 2 reacts with the water molecules in the LDH interlayer to form H + and CO 3 2− , which replaces the CO 3 2− in the LDH interlayer. [ 191 ] Hence, carbonate anion functions as a proton generator for CO 2 RR.…”

“…Reaction space and products of CO 2 photoconversion at a) low pressure for pretreated LDHs at 373 K, b) high pressure for pretreated LDHs at 373 K, and c) high pressure for pretreated LDHs at 423 K. Reproduced with permission. [ 190 ] Copyright 2017, Wiley‐VCH. d) The Gibbs free energy diagrams for photocatalytic CO 2 reduction to CH 4 on m‐NiAl‐LDH (no defect), m‐NiAl‐LDH (VNi), m‐NiAl‐LDH (VAl), and m‐NiAl‐LDH (VOH), respectively, without driving force.…”

“…An in‐depth understanding of the impact of reaction conditions toward photocatalytic reactions is vital, which is anticipated to momentously influence the type of desired product obtained. [ 190,200 ] Importantly, isotopic labeling experiment is necessary to rule out any impurities from the photocatalytic reactions, which may stem from the photodissociation of LDH catalysts or organic residues. Furthermore, there are many considerations, which need to be considered when conducting CO 2 RR using LDH‐based photocatalysts in determining the product yield and selectivity such as the reaction condition, the type of intercalated anion, the presence of photosensitizer and sacrificial agent, and so forth.…”

Supported Porous Nanomaterials as Efficient Heterogeneous Catalysts for CO2 Fixation Reactions

“…[93] In this contextIzumi and co-workershave recently reported Zn/Cu-Ga-containing layered double hydroxidesa s an efficient photocatalyst in the selective photoreduction of CO 2 to methanol at 0.40 MPa pressure of CO 2 . [94] Nile red, a known fluorescents olvatochromic dye, embedded on TiO 2 electrode has been used in the selectivep hotoreduction of CO 2 to methanol with oxygen as the only other product, [95] which mimic the photosyntheticp athway with or without the presenceo fP da sa na dditional component of the electrode material. Co II -phthalocyanine complexes immobilized on porousg raphene oxide surfaces howedh igh recycling efficiency in the photoreduction of CO 2 ,i nw hich methanol is obtained as am ajor product.…”

“…On the other hand 3D hollow nanostructures of Bi 2 WO 6 quantum dots synthesized solvothermally by using ethylene glycol as solvent can selectively catalyze the photoreduction of CO 2 to methanol . In this context Izumi and co‐workers have recently reported Zn/Cu–Ga‐containing layered double hydroxides as an efficient photocatalyst in the selective photoreduction of CO 2 to methanol at 0.40 MPa pressure of CO 2 . Nile red, a known fluorescent solvatochromic dye, embedded on TiO 2 electrode has been used in the selective photoreduction of CO 2 to methanol with oxygen as the only other product, which mimic the photosynthetic pathway with or without the presence of Pd as an additional component of the electrode material.…”