Influence of Ag Metal Dispersion on the Catalyzed Reduction of CO2 into Chemical Fuels over Ag-ZrO2 Catalysts

Metal/metal oxide catalysts reveal unique CO₂ adsorption and hydrogenation properties in CO₂ electroreduction for the synthesis of chemical fuels. The dispersion of active components on the surface of metal oxide has unique quantum effects, significantly affecting the catalytic activity and selectivity. Catalyst models with 25, 50, and 75% Ag covering on ZrO₂, denoted as Ag₄/(ZrO₂)₉, Ag₈/(ZrO₂)₉, and Ag₁₂/(ZrO₂)₉, respectively, were developed and coupled with a detailed investigation of the electronic properties and electroreduction processes from CO₂ into different chemical fuels using density functional theory calculations. The dispersion of Ag can obviously tune the hybridization between the active site of the catalyst and the O atom of the intermediate species CH₃O^* derived from the reduction of CO₂, which can be expected as the key intermediate to lead the reduction path to differentiation of generation of CH₄ and CH₃OH. The weak hybridization between CH₃O^* and Ag₄/(ZrO₂)₉ and Ag₁₂/(ZrO₂)₉ favors the further reduction of CH₃O^* into CH₃OH. In stark contrast, the strong hybridization between CH₃O^* and Ag₈/(ZrO₂)₉ promotes the dissociation of the C-O bond of CH₃O^*, thus leading to the generation of CH₄. Results provide a fundamental understanding of the CO₂ reduction mechanism on the metal/metal oxide surface, favoring novel catalyst rational design and chemical fuel production.

In situ Dispersed Nano-Au on Zr-Suboxides as Active Cathode for Direct CO2 Electroreduction in Solid Oxide Electrolysis Cells

CO₂ electrochemical reduction in solid oxide electrolysis cells is an effective way to combine CO₂ conversion and renewable electricity storage. A Au layer is often used as a current collector, whereas Au nanoparticles are rarely used as a cathode because it is difficult to keep nanosized Au at high temperatures. Here we dispersed a Au layer into Au nanoparticles (down to 2 nm) at 800 °C by applying high voltages. A 75-fold decrease in the polarization resistance was observed, accompanied by a 38-fold improvement in the cell current density. Combining electronic microscopy, in situ near-ambient pressure X-ray photoelectron spectroscopy, and theoretical calculations, we found that the interface between the Au layer and the electrolyte (yttria-stabilized zirconia (YSZ)) was reconstructed into nano-Au/Zr-suboxide interfaces, which are active sites that show a much lower reaction activation energy than that of the Au/YSZ interface. The formation of Zr-suboxides promotes Au dispersion and Au nanoparticle stabilization due to the strong interaction between Au and Zr-suboxides.

A density functional theoretical study on the stability of Pt clusters in MOF-808

Metal organic framework (MOF)-encapsulated metal clusters have shown superior catalytic activity due to geometric and electronic properties of metal clusters, which are largely determined by adsorption sites and sizes and morphologies of encapsulated metal clusters. In the present work, anchoring sites, the stability, and the agglomeration probability of Ptn (n = 1-23) clusters over an MOF-808 framework structure were studied using density functional theory calculations and ab initio molecular dynamics simulation. It has been found that Ptn (n = 1-7) clusters bind more strongly at the Zr6 metal node sites than at the interface and linker sites. Upon adsorption, significant amounts of electrons (+0.92 to +1.96 |e|) are transferred from Ptn clusters to the MOF framework. The agglomeration of single Pt1 atoms at the Zr6 metal node to form a Ptn cluster is unlikely, while the agglomeration at the interface or the linker is energetically feasible. Compared with the single Zr6 node, the bonding of Ptn clusters with two Zr6 metal nodes is weaker, with less electron (+0.12 to +0.89 |e|) transfer. Finally, our calculations show that CO adsorption at the single Pt atom is stabilized at the interface site, preventing its further agglomeration with Ptn clusters between the two Zr6 metal nodes.