Yolk-shell Catalysts Research Articles

Highly efficient hydrogenation of levulinic acid into γ-valerolactone over modified bifunctional yolk-shell catalyst

Highly efficient hydrogenation of levulinic acid into γ-valerolactone over modified bifunctional yolk-shell catalyst

Improving the anti-coking ability in the Ni-M(M = Ce, Zr, Co)@SiO2 yolk-shell catalysts for dry reforming of methane

Dry methane reforming (DRM) represents a highly promising approach to greenhouse gas conversion (CO2 and CH4) to valuable byproducts. However, severe carbon deposition and catalyst deactivation inhibit large-scale applications. The work designed new catalysts with a yolk-shell structure using the water-in-oil microemulsion method. The catalysts were composed of a yolk-shell structure, with Ni-M as the active point and silica as the shell. The catalytic performance evaluation indicates that the Ni-M @SiO2 catalysts show higher CH4 and CO2 conversion compared with the Ni@SiO2 and conventional catalysts at 750 ℃, suggesting the yolk-shell structure and added M species enhance the DRM activity. The XRD, HRTEM, XPS, BET, H2-TPR, and CO2-TPD analysis confirmed the existence of yolk-shell configuration and evident electronic effect among Ni, M species, and SiO2. The long term measurements indicate that the added M species also bring higher carbon deposition tolerance for DRM, where Ni-Ce@SiO2 and Ni-Zr@SiO2 exhibit good structural and catalytic stability for DRM over 100 h. Through XRD, TEM, and TGA characterizations of the exhausted catalysts, it is determined that the coke deposition resistance of the catalyst is improved as a result of increased oxygen mobility and enhanced Ni dispersion on the catalytic surface, both of which are enhanced by the added Ce species. The structural analysis of the spent catalysts indicates that the tolerance of carbon deposition is improved by the yolk-shell samples. This study can offer valuable insights for the development of Ni-based catalysts with exceptional carbon deposition capability for DRM.

Catalytic decomposition of methane for controllable production of carbon nanotubes and high purity H2 over LTA zeolite-derived Ni-based yolk-shell catalysts

Catalytic decomposition of methane for controllable production of carbon nanotubes and high purity H2 over LTA zeolite-derived Ni-based yolk-shell catalysts

Unveiling the in-situ formation mechanism of nano-fir tree-like architecture: Yolk-shell structure enables the development of an advanced multifunctional template

The combination of electronic regulation and architectural engineering within a multifunctional material is a combination that can yield a potent strategy for simultaneously enhancing its catalytic performance and electrochemical response. We herein developed MIm@Ni-Co@CoCH/IL nanocomposite material that was used to construct a three-dimensional (3D) Fir tree-like structure grown on a magnesium alloy substrate as a highly efficient multifunctional coating. The new network design is intended to improve the overall performance of the porous coating by utilizing pulsed plasma electrolysis (PPE), in combination with a layered double hydroxide (LDH) backbone and zeolitic imidazolate framework (ZIF), which is known to increase electrochemical efficiency and achieve an architectural upgrade that enhances the functionality of the coating. By interlocking the hybrid branches architecture with the surface motifs of the solid platform, we can create a hierarchical structure that resembles a fir tree-like structure grown on an inorganic bed. Interestingly, this new approach serves to create an efficient electron transport system that can act as a functionalized pathway for creating highly efficient and multifunctional materials. The tunable morphology of the hybrid architecture allows it to exhibit both electrochemical stability and catalytic activity toward the radical degradation of organic pollutants in various aqueous environments. This dual-functionality makes the hybrid architecture a promising material for addressing environmental pollution. Our findings shed light on the potential of exploring nanocomposites-modified yolk-shell catalysts as electrochemically stable and catalytically active materials, which can serve as the foundation for next-generation multifunctional frameworks.

Ni nanoparticles supported on Al2O3 + La2O3 yolk-shell catalyst for photo-assisted thermal decomposition of methane

Catalytic methane decomposition (CMD) has emerged as an appealing technology for large-scale production of H2 and carbon nanostructures from natural gas. As the CMD process is mildly endothermic, the application of concentrated renewable energy sources such as solar energy under a low-temperature regime could potentially represent a promising approach towards CMD process operation. Herein, Ni/Al2O3-La2O3 yolk-shell catalysts are fabricated using a straightforward single-step hydrothermal approach and tested for their performance in photothermal CMD. We show that the morphology of the resulting materials, dispersion and reducibility of Ni nanoparticles, and nature of metal-support interactions can be tuned by addition of varying amounts of La. Notably, the addition of an optimal amount of La (Ni/Al-20La) improved the H2 yield and catalyst stability relative to the base Ni/Al2O3 material, while also favoring base growth of carbon nanofibers. Additionally, we show for the first time a photothermal effect in CMD, whereby the introduction of 3 suns light irradiation at a constant bulk temperature of 500 °C reversibly increased the H2 yield of catalyst by about 1.2 times relative to the rate in the dark, accompanied by a decrease in apparent activation energy from 41.6 kJ mol−1 to 32.5 kJ mol−1. The light irradiation further suppressed undesirable CO co-production at low temperatures. Our work reveals photothermal catalysis as a promising route for CMD while providing an insightful understanding of the roles of modifier in enriching methane activation sites on Al2O3-based catalysts.

Ultra-stable porous yolk-shell Ni catalysts for the steam reforming of methane with alkali poisoning

Hydrogen, a clean energy carrier, can be produced from renewable sources such as biomass and waste, but it is needed to develop new catalysts with high resistance against impurities. Ni/Al2O3 yolk-shell catalysts were prepared by different procedure for the steam reforming of methane reaction with alkali poisoning. Yolk-shell (ys) and porous yolk-shell (pys) materials were synthesized using a spray pyrolysis process. The physicochemical and structural properties of the prepared catalysts on the reaction performance and alkali resistance were investigated. All the yolk-shell catalysts exhibited high resistance to carbon deposition. The Ni/pys-Al2O3 catalyst showed the highest CH4 conversion and the best stability at a gas hourly space velocity of 932,492 mL·g−1·h−1 even upon exposure to alkali hydroxide vapor. It also showed strong resistance to sintering, whereas the structures of the ys-Ni-Al2O3 and Ni/ys-Al2O3 catalysts were relatively degraded under the same conditions.

Hydrodesulfurization over NiMo Catalysts Supported on Yolk‐shell Silica Materials with Controllable Cavity Size

AbstractNovel yolk‐shell (YS) mesoporous silica materials with different cavity sizes were successfully synthesized. Aluminium was bridged into the yolk‐shell framework of silica by a post synthesis method to improve the acidity of YS, namely Al‐YS. The corresponding NiMo/Al‐YS catalysts were also fabricated and used in the hydrodesulfurization (HDS) reaction of dibenzothiophene (DBT) and 4,6‐dimethyldibenzothiophene (4,6‐DMDBT). The NiMo/Al‐YS catalyst with the cavity size of 154 nm (NiMo/Al‐YS‐154) exhibits the superior conversions of DBT (99.2 %) and 4,6‐DMDBT (96.1 %) at 340 °C, 4.0 MPa, 10 h−1, highest kHDS (13.4×10−4 mol g−1 h−1 for DBT and 8.9 mol g−1 h−1 for 4,6‐DMDBT) and highest TOF for DBT (3.7 h−1) and 4,6‐DMDBT (2.3 h−1) among the investigated catalysts. The appropriate cavity size of NiMo/Al‐YS‐154 catalyst plays the key role in obtaining its superior HDS catalytic performance. Furthermore, the possible reaction networks of DBT and 4, 6‐DMDBT HDS over NiMo/Al‐YS‐x catalysts were also presented.

Sintering resistant cubic ceria yolk Ni phyllosilicate shell catalyst for methane dry reforming

Methane dry reforming (DRM) reaction is an efficient strategy to achieve carbon neutralization. Whereas, nano-catalysts, which are highly active due to size effect, are prone to sinter under the relatively high reaction temperature conditions, leading to the degradation of catalytic performance and accumulation of carbon. Therefore, preventing sintering is highly desired. In this manuscript, we synthesize cubic CeO2 yolk Ni phyllosilicate shell (CeO2 @Ni-Ps YS) catalyst which exhibits superb catalytic performance for DRM reaction. This is because the Ni bearing Ps structure mitigates the agglomeration of Ni nanoparticles due to strong metal support interaction (MSI); whilst CeO2 still preserves cubic morphology due to the protection by yolk shell structure, isolating CeO2 from each other. In addition, the yolk shell structure also provides intimate interaction between reactant gases and catalyst, which is known as confinement effect and further contributes to its better catalytic performance than the CeO2 @Ni-Ps CS catalyst. By comparison, serious sintering of both Ni and CeO2 occurs for DP Ni-Ps/CeO2 catalyst, leading to its continuous degradation of DRM performance. This method is promising to synthesize other efficient yolk shell catalysts for use in sustainable reaction processes.

Bimetal Oxide Catalysts Selectively Catalyze Cellulose to Ethylene Glycol

Cellulose is an attractive and potential biomass material in nature. It has been studied for decades to convert it into high value-added chemical materials. In this article, we prepared a unique structure of a yolk–shell catalyst with uniform-sized Pd nanoparticles as the core and easily modified mesoporous silica as the shell, and the shell was modified by alumina and tungsten oxide. The modified Pd@W/Al-MSiO2 yolk–shell-structured nanosphere (YSNS) catalyst showed good catalytic activity in the conversion of cellulose to ethylene glycol: the conversion of cellulose was 96.1%, and the selectivity of ethylene glycol reached 56.5%. From XRD, XPS, and 27Al MAS NMR spectral analysis, it can be seen that the existence of tungsten species would lead to the formation of more extra framework aluminum, which increased the acid strength; meanwhile, aluminum made the tungsten oxide oligomer increase, which increased the dispersion of tungsten species on the catalyst. The interaction of the two metal oxides increased the acidity and the increase in tungsten oxide oligomers were the reasons for the higher selectivity of ethylene glycol. Due to the protective effect of the shell on the Pd nanoparticles, there was no sintering and serious loss of Pd during the reaction, and only small amounts of tungsten and aluminum distributed in the pores and surface were lost. Therefore, the Pd@W/Al-MSiO2 YSNS catalyst maintained 48.5% ethylene glycol selectivity after five cycles.

Yolk-shell silica dioxide spheres @ metal-organic framework immobilized Ni/Mo nanoparticles as an effective catalyst for formic acid dehydrogenation at low temperature

The novel catalyst with yolk-shell SiO2 NiMo/SiO2 spheres immobilized by zeolitic imidazolate framework (ZIF-67) materials has been successfully prepared. The experimental results indicated that the prepared catalyst exhibits superior performance for hydrogen generation from Formic acid (FA) dehydrogenation without any additives at low temperatures. The catalytic performances of the NixMo1−x/ZIF-67@SiO2 yolk-shell increased with Ni addition ratio increasing. In this research, Ni0.8Mo0.2/ZIF-67@SiO2 yolk-shell could provide the highest catalytic conversion efficiency. This is due to the uniform dispersion of fine metal nanoparticles (NPs) and synergistic effect between the NiMo NPs and ZIF-67@SiO2 supporter. The turn over frequency (TOF) value was approximately 13,183 h−1 at 25 °C through complete FA conversion. H2 selectivity was also approximately 100% with obvious CO-free hydrogen production at 25 °C. Meanwhile, the prepared NiMo/ZIF-67@SiO2 yolk-shell catalyst also shows superior catalytic stability with corresponding 99% activity after 10 cycles. In summary, the catalyst preparation and hydrogen generated from FA dehydrogenation obtained from this research could provide the important information for application in catalyst innovation and waste FA recycling and recovery in the future.

Yolk-Shell Nanocapsule Catalysts as Nanoreactors with Various Shell Structures and Their Diffusion Effect on the CO2 Reforming of Methane.

Well-geometric-confined yolk-shell catalysts can act as nanoreactors that are of benefit for the antisintering of metals and resistance to coke formation in high-temperature reactions such as the CO2 reforming of methane. Notwithstanding the credible advances of core/yolk-shell catalysts, the enlarged shell diffusion effects that occur under high space velocity can deactivate the catalysts and hence pose a hurdle for the potential application of these types of catalysts. Here, we demonstrated the importance of the shell thickness and porosity of small-sized Ni@SiO2 nanoreactor catalysts, which can vary the diffusional paths/rates of the diffusants that directly affect the catalytic activity. The nanoreactor with an ∼4.5 nm shell thickness and rich pores performed the best in tolerating the shell diffusion effects, and importantly, no catalytic deactivation was observed. We further proposed a shell diffusion effect scheme by modifying the Weisz-Prater and blocker model and found that the "gas wall/hard blocker" formed on the openings of the shell pores can cause reversible/irreversible interruption of the shell mass transfer and thus temporarily/permanently deactivate the nanoreactor catalysts. This work highlights the shell diffusion effects, apart from the metal sintering and coke formation, as an important factor that are ascribed to the deactivation of a nanoreactor catalyst.

A Mini Review on Yolk-Shell Structured Nanocatalysts.

Yolk-shell structured nanomaterials, possessing a hollow shell and interior core, are emerging as unique nanomaterials with applications ranging from material science, biology, and chemistry. In particular, the scaffold yolk-shell structure shows great promise as a nanocatalyst. Specifically, the hollow shell offers a confined space, which keeps the active yolk from aggregation and deactivation. The inner void ensures the pathway for mass transfer. Over the last few decades, many strategies have been developed to endow yolk-shell based nanomaterials with superior catalytic performance. This minireview describes synthetic methods for the preparation of various yolk-shell nanomaterials. It discusses strategies to improve the performance of yolk-shell catalysts with examples for engineering the shell, yolk, void, and related synergistic effects. Finally, it considers the challenges and prospects for yolk-shell nanocatalysts.

Yolk-shell ZIF-8@ZIF-67 derived Co3O4@NiCo2O4 catalysts with effective electrochemical properties for Li-O2 batteries

Metal−organic frameworks (MOFs) have attracted researchers’ attention because of its unique adjustable structure, large open space and high porosity. Herein, we design a yolk-shell catalyst of Co3O4@NiCo2O4, which selects ZIF-8@ZIF-67 materials with rhombic dodecahedron structure as the template, and is coated with NiCo2O4. Compared with the pure Co3O4, Co3O4@NiCo2O4 composite exhibits excellent ORR and OER performance as the adjustable structure, abundant active sites and open space. Furthermore, the discharge capacity of Co3O4@NiCo2O4 catalyst is 11672.8 mA h g−1, while Co3O4 cathode is 8636.3 mA h g−1, even at 600 mA g−1 current density, Co3O4@NiCo2O4 cathode retains the capacity retention of 48.2%, much higher than that of Co3O4, i.e., 21.6%. As for the cycle test, Co3O4@NiCo2O4 composite has much long cycle life of 280 cycles. In contrast, the Co3O4 electrode only has 77 cycles.

Self-templated fabrication of hierarchical hollow manganese-cobalt phosphide yolk-shell spheres for enhanced oxygen evolution reaction

Hierarchical nanostructures with hollow architectures can provide rich active sites, improved transport of ions, and highly robust structure for electrochemical applications. In this work, we report the self-templated fabrication of hierarchical manganese-cobalt phosphide (Mn-Co phosphide) yolk-shell spheres using highly uniform cobalt glycerate spheres as sacrificial templates. Through a simple exchange reaction with the manganese precursor solution at room temperature, these cobalt glycerate spheres are readily converted to hierarchical Mn-Co LDH yolk-shell spheres, which can be further phosphidized at 350 °C under inert atmosphere to generate hierarchical Mn-Co phosphide with distinct yolk-shell morphology. When tested as an electrocatalyst for oxygen evolution reaction (OER), the hierarchical Mn-Co phosphide yolk-shell spheres exhibit an overpotential of 330 mV at a current density of 10 mA cm−2 and a Tafel slope of 59.0 mV dec-1, which are higher than those of Mn-Co oxide yolk-shell spheres (480 mV and 113 mV dec-1) and hierarchical cobalt phosphide spheres (410 mV and 61.3 mV dec-1). Post-OER analysis by XPS reveals that the high activity of the hierarchical Mn-Co phosphide yolk-shell catalyst originates from the existence of Mn4+/Mn3+ and Co2+/Co3+ redox couples and the formation of active metal oxyhydroxide species on its surface. The proposed self-sacrificial templating strategy will provide useful guidance for future construction of hollow inorganic metal nanostructures with yolk-shell morphology for energy storage and conversion applications.

Facial fabrication of yolk-shell Pd-Ni-P alloy with mesoporous structure as an advanced catalyst for methanol electro-oxidation

High activity and long-term stability are necessary for the electro-catalysts to be used in fuel cells. Herein, we report the facile fabrication of a yolk-shell Pd-Ni-P alloy based on the thermal ripening of aggregated nanoparticles. The material has abundant nanopores in both the core and the shell parts. Size distribution analysis based on density functional theory shows the width of the nanopores is around 15 nm. Based on the electro-chemical active area of palladium, the supported yolk-shell Pd-Ni-P catalyst affords a high electro-catalytic activity (1.9 mA cm−2Pd) in methanol oxidation reaction which is 1.5, 3.1, 3.8, or 5.5 times higher than those of face-centered cubic Pd-Ni-P, amorphous Pd-Ni-P, PdNi, or Pd nanoparticles, respectively. Impressively, 87% of the current density remains after 2000 cycles' cyclic voltammetry with yolk-shell catalyst as the anode, which is much superior to those values with other related Pd-based nanoparticles.

A high-performance CeO2 @Pt-Beta yolk-shell catalyst used in low-temperature ethanol steam reforming for high-purity hydrogen production

A high-performance CeO₂ @Pt-Beta yolk-shell catalyst used in low-temperature ethanol steam reforming for high-purity hydrogen production

Synthesis of octahedral Pt-Ni-Ir yolk-shell nanoparticles and their catalysis in oxygen reduction and methanol oxidization under both acidic and alkaline conditions.

Fuel cells are expected to be one of the most promising alternatives to the increasingly scarce fossil fuels, and Pt is the most commonly used catalyst for anodic and cathodic electrochemical reactions. To realize large-scale commercialization, it is most urgent to improve the efficiency of Pt and reduce the cost. Here, we synthesized an octahedral Pt-Ni-Ir yolk-shell catalyst through stepwise co-deposition (SCD), surface-limited Pt deposition (SLPD) and Ni-coordinating etching (NCE) processes. Experimental studies showed that the catalytic activities of the as-prepared trimetal yolk-shell catalyst were several times higher than that of the commercial Pt/C towards oxygen reduction and methanol oxidization under both acidic and alkaline conditions. This work may be extended to designing other multimetallic functional materials with complex hierarchical nanostructures, which is conducive to greatly enhancing the performance.

Advantages of Yolk Shell Catalysts for the DRM: A Comparison of Ni/ZnO@SiO2 vs. Ni/CeO2 and Ni/Al2O3

Encapsulation of metal nanoparticles is a leading technique used to inhibit the main deactivation mechanisms in dry reforming of methane reaction (DRM): Carbon formation and Sintering. Ni catalysts (15%) supported on alumina (Al2O3) and ceria (CeO2) have shown they are no exception to this analysis. The alumina supported catalysts experienced graphitic carbonaceous deposits, whilst the ceria showed considerable sintering over 15 h of DRM reaction. The effect of encapsulation compared to that of the performance of uncoated catalysts for DRM reaction has been examined at different temperatures, before conducting longer stability tests. The encapsulation of Ni/ZnO cores in silica (SiO2) leads to advantageous conversion of both CO2 and CH4 at high temperatures compared to its uncoated alternatives. This work showcases the significance of the encapsulation process and its overall effects on the catalytic performance in chemical CO2 recycling via DRM.

Robust mesoporous bimetallic yolk–shell catalysts for chemical CO2 upgrading via dry reforming of methane

A new generation highly efficient and stable mesoporous ZnO/Ni@silica yolk–shell catalyst is designed for chemical CO2 recycling, to solve the coking and sintering issues of traditional catalysts.

Yolk-shell structured Pt-CeO2@Ni-SiO2 as an efficient catalyst for enhanced hydrogen production from ethanol steam reforming

A novel Pt-CeO2@Ni-SiO2 yolk-shell catalyst was fabricated through modified Stöber method and was applied to the ethanol steam reforming reaction. The catalyst structure was characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectrometry, X-ray diffraction, nitrogen adsorption-desorption and X-ray photoelectron spectroscopy. Compared with the mechanically mixed catalyst, the yolk-shell catalyst exhibited excellent catalytic performance and stability in ethanol steam reforming. The selection of hydrogen reached as high as 66%, and the conversion reached nearly 100% at 400°C for 28h.