Encapsulation
of metal nanoparticles by support-derived materials
known as the classical strong metal–support interaction (SMSI)
often happens upon thermal treatment of supported metal catalysts
at high temperatures (≥500 °C) and consequently lowers
the catalytic performance due to blockage of metal active sites. Here,
we show that this SMSI state can be constructed in a Ru–MoO3 catalyst using CO2 hydrogenation reaction gas
and at a low temperature of 250 °C, which favors the selective
CO2 hydrogenation to CO. During the reaction, Ru nanoparticles
facilitate reduction of MoO3 to generate active MoO3–x
overlayers with oxygen vacancies,
which migrate onto Ru nanoparticles’ surface and form the encapsulated
structure, that is, Ru@MoO3–x
.
The formed SMSI state changes 100% CH4 selectivity on fresh
Ru particle surfaces to above 99.0% CO selectivity with excellent
activity and long-term catalytic stability. The encapsulating oxide
layers can be removed via O2 treatment, switching back
completely to the methanation. This work suggests that the encapsulation
of metal nanocatalysts can be dynamically generated in real reactions,
which helps to gain the target products with high activity.
CO 2 electrolysis via solid oxide electrolysis cell (SOEC) has shown promising practical applications in CO 2 conversion and renewable electricity storage due to low overpotential, large current density, high Faradaic efficiency, and energy efficiency facilitated by high-temperature operation. [1] Perovskites have been extensively investigated as cathode materials for direct CO 2 electrolysis in SOEC in the absence of protective gas [2] ; however, the perovskites still suffer from insufficient CO 2 electrolysis performance. [3] In situ exsolving metal nanoparticles on the perovskite surface have been explored as an efficient strategy to improve CO 2 electrolysis performance due to the exsolution of highly active metal nanoparticles and the simultaneous generation of oxygen vacancies within perovskite, where abundant metal-oxide interfaces are generated for highly efficient CO 2 electrolysis. [4] In addition, reversible exsolution and dissolution of metal nanoparticles in perovskite have been proposed as vital properties for resolving the possible particle agglomeration and coke formation during a long-term operation of SOECs. [2b,5] To date, although some perovskites have demonstrated redox reversibility with exsolution and dissolution of metal nanoparticles in reducing and oxidizing atmosphere, [6] fundamental understanding of these phenomena is still scarce. [7] Ex situ scanning/transmission electron microscopy (SEM/ TEM) and X-ray diffraction (XRD) techniques have been employed to investigate the morphology and crystalline evolution after reducing and oxidizing treatments. [8] Irvine et al. found that a decrease in the stoichiometry of perovskite from A/B = 1 to A/B<1 could break the bottleneck of exsolution level and facilitate high-population exsolution of metal nanoparticles. [7,9] Kim et al. investigated the reducibility of different cations in perovskite using co-segregation energy as a descriptor. The co-segregation energy of B-site dopant and oxygen vacancies plays a critical role in the exsolution. [10] Furthermore, Luo et al. used in situ TEM to investigate the exsolution of Co nano particles in Pr 0.5 Ba 0.5 Mn 0.9 Co 0.1 O x (PBMCo) perovskite, excluding the possibility of metal nanoparticles Reversible exsolution and dissolution of metal nanoparticles in perovskite has been investigated as an efficient strategy to improve CO 2 electrolysis performance. However, fundamental understanding with regard to the reversible exsolution and dissolution of metal nanoparticles in perovskite is still scarce. Herein, in situ exsolution and dissolution of CoFe alloy nanoparticles in Co-doped Sr 2 Fe 1.5 Mo 0.5 O 6-δ (SFMC) revealed by in situ X-ray diffraction, scanning transmission electron microscopy, environmental scanning electron microscopy, and density functional theory calculations are reported. Under a reducing atmosphere, facile exsolution of Co promotes reduction of the Fe cation to generate CoFe alloy nanoparticles in SFMC, accompanied by structure transformation from double perovskite to layer...
In situ exsolved FeNi3 nanoparticles on nickel doped Sr2Fe1.5Mo0.5O6−δ perovskite greatly enhance the performance of the electrochemical CO2 reduction reaction.
Metal nanoparticles anchored on perovskite through in situ exsolution under reducing atmosphere provide catalytically active metal/oxide interfaces for CO2 electrolysis in solid oxide electrolysis cell. However, there are critical challenges to obtain abundant metal/oxide interfaces due to the sluggish diffusion process of dopant cations inside the bulk perovskite. Herein, we propose a strategy to promote exsolution of RuFe alloy nanoparticles on Sr2Fe1.4Ru0.1Mo0.5O6−δ perovskite by enriching the active Ru underneath the perovskite surface via repeated redox manipulations. In situ scanning transmission electron microscopy demonstrates the dynamic structure evolution of Sr2Fe1.4Ru0.1Mo0.5O6−δ perovskite under reducing and oxidizing atmosphere, as well as the facilitated CO2 adsorption at RuFe@Sr2Fe1.4Ru0.1Mo0.5O6−δ interfaces. Solid oxide electrolysis cell with RuFe@Sr2Fe1.4Ru0.1Mo0.5O6−δ interfaces shows over 74.6% enhancement in current density of CO2 electrolysis compared to that with Sr2Fe1.4Ru0.1Mo0.5O6−δ counterpart as well as impressive stability for 1000 h at 1.2 V and 800 °C.
Na 3 V 2 (PO 4 ) 2 F 3 has been emerging as one of the most promising cathodes for sodium-ion batteries due to its stable NASICON structure and fast Na + diffusion. However, present methods for preparation of Na 3 V 2 (PO 4 ) 2 F 3 suffer from either high energy consumption or generating poor rate performance. Herein, a costeffective solvothermal−ball-milling method is proposed to solve the problem. In the solvothermal process, the morphology of Na 3 V 2 (PO 4 ) 2 F 3 varies from 0D to 3D with changing pH, in which 3D Na 3 V 2 (PO 4 ) 2 F 3 at pH = 3 shows optimal purity due to the fastest growth rate. With Ketjenblack (KB) coating by short-time ball-milling, the Na 3 V 2 (PO 4 ) 2 F 3 can be further nanosized with a highly graphited carbon coating layer. The purest Na 3 V 2 (PO 4 ) 2 F 3 @KB from pH = 3 exhibited an initial capacity of 138 mAh g −1 @ 0.5 C and 122 mAh g −1 @ 40 C. Moreover, ultrahigh dosage over an 80 mmol of V source in one 100 mL Teflon-lined autoclave has been achieved for the first time.
An ionic‐liquid‐assisted method is developed for the preparation of noble metal nanoparticles supported on multi‐walled carbon nanotubes (MWCNTs). The addition of a small amount of ionic liquids to the reaction solution leads to a production of well‐crystallized metallic nanoparticles with tunable diameter and narrow size distribution, uniformly dispersed on MWCNTs. The obtained Pt nanoparticles supported on MWCNTs show superior catalytic performance. Both the catalytic activity and stability for the electrochemical oxidation of methanol is remarkably improved. The uniform size of Pt nanoparticles in the composites makes it possible to study the size dependence of the catalytic performance in the selective oxidation of glycerol. The turnover frequency (TOF) has the maximum value at the size of ≈4 nm and the selectivity to glyceraldehyde increases with the particle size.
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