Alloying Ni-Cu Nanoparticles Encapsulated in SiO2 Nanospheres for Synergistic Catalysts in CO2 Reforming with Methane Reaction

Bimetallic Cu-Ni Catalysts Derived from Phyllosilicates for Synergistically Catalyzing CO2 and CH4 Dry Reforming

Methane dry reforming reaction offers an attractive route to simultaneously convert two kinds of greenhouse gases into clean fuels and highly valuable chemicals. Nevertheless, the inactivation of nickel-based catalysts due to sintering and coking in dry reforming has severely limited its industrial application. In this study, we proposed a step-by-step strategy to prepare a series of bimetallic xCu-Ni/SiO2 catalysts derived from phyllosilicate precursors. The optimized catalyst shows exceptional performance, with no deactivation during the 50 hour stability test, and the CH4 and CO2 conversion were 88.8% and 94.0%, respectively. This was attributed to the synergistic catalysis of Cu-Ni alloy, which effectively inhibits coke formation. Additionally, the distribution of copper species between nickel species inhibited the mobility and enlargement of nickel particles and thus enhanced the resistance to sintering. The preparation strategy offers valuable insights for designing and preparing highly efficient and stable bimetallic catalysts under high-temperature conditions.

Highly efficient Ni/Ac-Al2O3 catalysts in the dry reforming of methane: influence of acetic acid treatment and Ni loading

The presence of abundant hydroxyl groups on the surface of Al2O3 can promote the dispersion of Ni species but produce an inactive NiAl2O4 phase at high temperatures. Moreover, the catalysts prepared by the conventional incipient wetness impregnation method lack the sites for the activation of CO2, which leads to coke deposition and thus affects the catalyst activity. The above restricts the utilization of Ni in conventional Ni/Al2O3 catalysts. In this paper, Al2O3 support was pre-treated by acetic acid to selectively remove hydroxyl groups without affecting the coordination environment of Al. Results revealed that the Al2O3 support after hydroxyl removal not only showed moderate metal-support interaction but also produced more sites for the adsorption and activation of the reactant, which significantly improves the utilization of nickel species and the stability of the catalyst. The conversion of CH4 and CO2 at 700 °C was as high as 88% and 90%, respectively, and has an excellent stability of 50 h. This study provides a feasible strategy for the design of highly active methane dry-reforming catalysts.

Ag-Mediated Growth of Au/Ag-Cu Ternary Heterostructures for Selective Electrochemical CO2 Reduction

Copper (Cu)-based nanocatalysts play crucial roles in the electrochemical CO2 reduction reaction (ECO2RR) for sustainable energy resources. Particularly, Cu-based nanostructures incorporating Au and Ag are promising, offering enhanced activity, selectivity, and stability. However, precise control over the structure and composition of heterostructures remains challenging, hindering the development of highly efficient catalysts. Herein, we present a silver (Ag) transition-layer-mediated approach to synthesize ternary heterostructures with two specific morphologies, namely, Au/Ag-Cu-side and Au/Ag-Cu-tip, which exhibit different Ag-Cu interface epitaxial patterns. The two heterostructures achieve high C2 product selectivity in ECO2RR. Especially, the Au/Ag-Cu-side structure achieves 50.3% C2 selectivity with 35.5% ethanol, while the tip structure shows higher ethylene selectivity. Our study reveals the impact of the Ag layer in directing deposition sites on heterostructure growth and further facilitating the design of multicomponent Cu-based catalysts with enhanced structural integrity and ECO2RR performance.

Catalytic combustion of lean methane over different Co3O4 nanoparticle catalysts

Three types of Co3O4 catalyst, namely Co3O4 nanoparticles (denoted as Co3O4-NPs, ∼12 nm in diameter), Co3O4 nanoparticles encapsulated in mesoporou s SiO2 (denoted as Co3O4@SiO2), and Co3O4 nanoparticles inside microporous SiO2 hollow sub-microspheres (denoted as Co3O4-in-SiO2), were explored to catalyze the combustion of lean methane. It was found that the methane conversion over the three catalysts has the order of Co3O4-NPs ≈ Co3O4@SiO2 > Co3O4-in-SiO2 due to the different catalyst structure. The comparison experiments at high temperatures indicate the Co3O4@SiO2 has a significantly improved anti-sintering performance. Combined with the TEM and BET measurements, the results prove that the presence of the mesoporous SiO2 layer can maintain the catalytical activity and significantly improve the anti-sintering performance of Co3O4@SiO2. In contrast, the microporous SiO2 layer reduces the catalytical activity of Co3O4-in-SiO2 possibly due to its less effective diffusion path of combustion product. Thus, the paper demonstrates the pore size of SiO2 layer and catalyst structure are both crucial for the catalytical activity and stability.

Regulating the Pt-MnO2 Interaction and Interface for Room Temperature Formaldehyde Oxidation

Formaldehyde (HCHO) is a hazardous pollutant in indoor space for humans because of its carcinogenicity. Removing the pollutant by MnO₂-based catalysts is of great interest because of their high oxidation performance at room temperature. In this work, we regulate the Pt-MnO₂ (MnO₂ = manganese oxide) interaction and interface by embedding Pt in MnO₂ (Pt-in-MnO₂) and by dispersing Pt on MnO₂ (Pt-on-MnO₂) for HCHO oxidation over Pt-MnO₂ catalysts with trace Pt loading of 0.01 wt %. In comparison to the Pt-in-MnO₂ catalyst, the Pt-on-MnO₂ catalyst has a higher Brunauer-Emmett-Teller surface area, a more active lattice oxygen, more oxygen vacancy activating more dioxygen molecules, more exposed Pt atoms, and noninternal diffusion of mass transfer, which contribute to the higher HCHO oxidation performance. The HCHO oxidation performance is stable over the Pt-MnO₂ catalysts under high space velocity and high moisture humidity conditions, showing great potential for practical applications. This work demonstrates a more effective Pt-dispersed MnO₂ catalyst than Pt-embedded MnO₂ catalyst for HCHO oxidation, providing universally important guidance for metal-support interaction and interface regulation for oxidation reactions.

Ni-Cu Alloy Nanoparticles Confined by Physical Encapsulation with SiO2 and Chemical Metal-Support Interaction with CeO2 for Methane Dry Reforming

Fabrication of sintering- and carbon-free Ni catalysts for methane dry reforming (MDR), which is attractive to upgrade greenhouse gases CH₄ and CO₂, is challenging. In this work, we innovatively synthesized Ni-Cu alloy nanoparticles confined by physical encapsulation and chemical metal-support interaction (MSI); the synergism of alloy effect, size effect, MSI, and confinement effect in the catalysts gave high rates of CH₄ and CO₂ of 6.98 and 7.16 mmol/(g_Nis), respectively, at 1023 K for 50 h. The rates were 2-3 times enhanced compared to those in the literature. XRD, TEM, H₂-TPR, and so forth revealed that the alloy effect, size effect, and MSI of Ni-Cu and CeO₂ enhanced the MDR activity; MSI promoted the ceria surface lattice oxygen mobility and generated more oxygen vacancies, almost completely gasifying carbon deposits; chemical confinement from MSI and physical confinement from SiO₂ nanospheres realized sintering-free alloys and CeO₂ nanoparticles. The synergistic approach provides a universal strategy for sintering- and carbon-free Ni catalyst design for MDR reaction.