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To overcome the drawbacks of high solubility and instability of polyoxometalates (POMs) in aqueous solution and to expand their application in the electrocatalytic reduction of CO2 (ECR), we assemble sandwich-type POMs, K10[(PW9O34)2M4(H2O)2] (M = Mn, Ni, Zn, shortened as P2W18M4), into the hexagonal channel of a porphyrin-based metal–organic framework (MOF) PCN-222 to form P2W18M4@PCN-222 composites. Their ECR behavior displays polyoxoanion-dependent activity. P2W18Mn4@PCN-222 demonstrates a faradaic efficiency of 72.6% for the CO product (FECO), more than four times that of PCN-222 (FECO = 18.1%), and exhibits exceptional electrochemical stability over 36 h. P2W18Ni4@PCN-222 and P2W18Zn4@PCN-222 slightly increase (26.9%) and decrease (3.2%) in FECO, respectively. We combine the results with density functional theory (DFT) calculations to help understand the intrinsic reasons which reveals that the rate-determining step (RDS) reaction energy of P2W18Mn4@PCN-222 and P2W18Ni4@PCN-222 is significantly reduced compared to that of PCN-222. It is different in P2W18Zn4@PCN-222. Frontier molecular orbitals electron distribution results hint at directional electron transfer from P2W18Mn4/P2W18Ni4 to the porphyrin ring active center in PCN-222, promoting the electro-reduction of CO2 activity. By contrast, P2W18Zn4 may accumulate electrons from PCN-222, thus facilitating the hydrogen evolution reaction (HER). This work reveals the critical role of sandwich-type POMs in manipulating the electron transfer pathway during the electrocatalytic process. Our findings would broaden the scope of POM applications in electrochemical carbon dioxide reduction. [ABSTRACT FROM AUTHOR]

To avoid the agglomeration of iron NPs and improve the dispersion of Fe SAs, we employed a mixed-ligand strategy to regulate the iron content in PCN-224(ZnxFey) and PCN-222(ZnxFey). Thanks to the sublimation of Zn and the Kirkendall effect, uniform dispersions of Fe SAs with 1.04–1.06 wt% were obtained in the pyrolysis products Zn0.5Fe0.5–N–C-224 and Zn0.5Fe0.5–N–C-222 with excellent CO2 → CO activity, super-stability, and recyclability. [ABSTRACT FROM AUTHOR]

In this study, we investigated the reduction of CO2 using magnesium and calcium hydride (AeH2, Ae = Mg or Ca), in the process of which clean H2‐mixed CH4 fuel is produced. The result of this investigation shows that the particle size of AeH2 and AeH2/CO2 molar ratio can greatly affect the molar percentage value and reaction yield of methane. In general, the magnesium or calcium hydride as‐milled for 2 hr is enough active for reduction of CO2 to CH4. When the molar ratio of AeH2/CO2 is set to 2:1, the methanation effect is optimal for both reaction systems. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Summary: We systematically studied the thermochemical behaviors of alkali metals under the carbon dioxide (CO2) atmosphere and first investigated the hydromethanation performance of the alkali metal carbonate@carbon product formed in the reaction of CO2 with alkali metals. The on‐set reaction temperature of alkali metals with CO2 is at about 466, 584, and 595°C, respectively, following Li < Na < K. The experimental results indicate that COx‐free methane can be selectively and efficiently generated by hydrogenation of these carbonate@carbon composites at 450°C without a catalyst. Among these carbonate@carbon composites, the Li2CO3@carbon composite shows superior methanation performance. The selectivity of methanation is near 100%. The yield and content of methane are able to reach 30.3% and 26.6 mol%, respectively. This work provides an alternative method to produce methane, utilizing CO2 resources. [ABSTRACT FROM AUTHOR]