Multilayer Catalyst Research Articles

Synergistic effect between CoSx and MoS2 at the micrometer scale: Considerable promotion of the hydrodesulfurization of DBT

The future implementation of ultralow sulfur fuel regulations requires researchers to have an excellent understanding of the mechanism of the synergistic effect between the Co(Ni) and (Mo)W sulfides in supported Co(Ni)Mo(W)S hydrodesulfurization (HDS) catalysts. This synergistic effect occurs when the distance between two metals is on the mm or nm scale. To investigate the promotion of HDS on the µm scale, a series of Co and Mo multilayer flake catalysts with a thickness of 1 mm were prepared by laminate molding. The distance between CoSx and MoS2 in these specially structured catalysts was adjustable on the µm scale by controlling the order and quality of the catalyst powder. The results for the HDS of dibenzothiophene (DBT) demonstrate that there is an obvious synergistic effect between CoSx and MoS2 on the µm scale. The results of pyridine IR spectroscopy indicate that this synergy is due to CoSx and MoS2 synergistically generating more coordinatively unsaturated sites (CUSs) and -SH active sites at the μm scale, thus increasing the HDS activity. Moreover, the catalyst activity increases as the distance between CoSx and MoS2 decreases, and the fact that the feed comes into contact with CoSx first greatly improves the activity.

Mn/Co bimetallic MOF-derived hexagonal multilayered oxide catalysts with rich interface defects for propane total oxidation: Characterization, catalytic performance and DFT calculation

Several hexagonal layered Mn/Co oxide catalysts were synthesized from Mn/Co-based metal–organic framework (MOF) precursors. The molar ratio of Mn/Co affects the physicochemical properties of catalysts, further affects their catalytic performance. The Mn/CoOx-3/2 sample with wide interlayer spacing exhibited the highest catalytic activity for total oxidation of propane, with a T90 of 270 °C at 120 L g−1 h−1. Low-temperature reducibility, oxygen mobility, water vapor tolerance, and oxygen defects play the key roles for improving catalytic activity. Oxygen defects were calculated using the density functional theory (DFT). The results show that the doping of Mn on Co oxide is conducive to the formation of oxygen vacancies. Therefore, benefiting from the layered structure and metal-doping for the catalysts, the formation of more abundant interfacial defects can further improve the catalytic performance. This study offers a simple way to synthesize regular layered multi-metal oxide, which can expose abundant interface defects and active sites.

Pyrolysis–catalysis upcycling of waste plastic using a multilayer stainless-steel catalyst toward a circular economy

Current un-sustainable plastic management is exacerbating plastic pollution, an urgent shift is thus needed to create a recycling society. Such recovering carbon (C) and hydrogen (H) from waste plastic has been considered as one practical route to achieve a circular economy. Here, we performed a simple pyrolysis-catalysis deconstruction of waste plastic via a monolithic multilayer stainless-steel mesh catalyst to produce multiwalled carbon nanotubes (MWCNTs) and H2, which are important carbon material and energy carrier to achieve sustainable development. Results revealed that the C and H recovery efficiencies were as high as 86% and 70%, respectively. The unique oxidation-reduction process and improvement of surface roughness led to efficient exposure of active sites, which increased MWCNTs by suppressing macromolecule hydrocarbons. The C recovery efficiency declined by only 5% after 10 cycles, proving the long-term employment of the catalyst. This catalyst can efficiently convert aromatics to MWCNTs by the vapor-solid-solid mechanism and demonstrate good universality in processing different kinds of waste plastics. The produced MWCNTs showed potential in applications of lithium-ion batteries and telecommunication. Owing to the economic profits and environmental benefits of the developed route, we highlighted its potential as a promising alternative to conventional incineration, simultaneously achieving the waste-to-resource strategy and circular economy.

Design of multi-layered gradient catalysts for efficient proton exchange membrane fuel cells

Efficient catalyst layers (CLs) in proton exchange membrane fuel cells (PEMFCs) should possess a highly active surface for electrochemical reaction and an ideal platform for simultaneous mass transfer. Efforts have been devoted to lower the widely used Pt and Nafion loading due to their high cost. However, the increase in gas transport resistance and decrease in transfer ability of protons and electrons result in a degraded fuel cell performance. Therefore, CL design with optimal efficiency is important for high performance and stability of PEMFCs. In this study, we design gradient multi-layered CLs in which the loadings of Pt–C catalyst and Nafion ionomer are set differently for each layer to increase efficiency. For ideal cell performance, the ionomer loading should be higher near the membrane layer and Pt–C loading should be higher near the gas diffusion layer. In addition, we confirm that if the loading difference between layers in the gradient CL becomes excessively large, performance can degrade due to the non-uniform Pt active surface. Thus, we compared 1-layer, 3-layer and 5-layer CLs, and designing more layers to reduce the difference in loading between layers results in higher electrochemical surface area (ECSA) and improved performance.

Development of Low Iridium Catalyst Layer Structure for a Water Electrolysis Cell

1.Introduction P2G is viewed as a solution essential for achieving carbon neutrality by 2050. It uses electrolysis to convert electricity from renewables into hydrogen, ready for storage and transportation. The key technology in the process is the water electrolyzer that converts energy into hydrogen without emitting CO2. A PEM water electrolyzer offers excellent adaptability to power fluctuations and high durability. PEM water electrolyzers use membrane electrode assemblies (MEAs) that integrate the electrolyte membrane and electrode. However, the MEA electrode relies on a large amount of iridium to ensure sufficient electrolytic efficiency. Iridium is one of the rarest precious metals and it is four to five times as costlyas platinum. Toshiba has developed a multilayer catalyst that uses a sputtering technology to deposit alternate layers of iridium oxide nanosheet films and void layers, which at low iridium loading achieved a performance superior to that of IrO2 powder anode. 2 ． Experimental The sputtering process was executed in a large chamber that can accommodate electrodes up to a maximum of 5 m2 in size. First, iridium together with pore-forming metal was sputtered onto a commercially available PTL substrate and then only pore-forming metal was sputtered, and this process was repeated to deposit multiple layers. Next, the pore-forming metal was removed to prepare the anode (Fig. 1). The loading of iridium metal was adjusted by the number of iridium layers. Then, a small electrode was cut from a large electrode and a 4 cm2 MEA was made by hot pressing of the anode, Nafion115®, and the Pt/C cathode. A conventional iridium oxide powder layer was sprayed on Nafion115 and a platinum-coated PTL substrate was prepared for reference. Water electrolysis performance of the MEAs was measured in a single-cell configuration by supplying water to the anode side and applying current to the cell under atmospheric pressure. 3 ． Results and discussion Figure 2 shows the water electrolysis IV curves at 80℃ for each type of anode. This novel catalyst structure successfully reduces the iridium to 0.15 mg/cm2, while maintaining the water electrolysis performance and durability. This superior performance is due to the homogeneity of the catalyst layer, which is achieved by a sputtering process enabling nanometer- thick coatings, and the high diffusivity of oxygen and water due to the multilayer structure of the iridium nanosheets and void layers. Our structure also has the advantage of reducing the amount of precious metals by dispensing with the need for Pt coating on the PTL. It was also found that there was no significant variation in water electrolysis performance within a 5 m2 electrode. Thus, the technology for production of large-scale electrodes has been developed. 600 cm2 MEA has also been tested. Figure 1

Multilayer mesoporous carbon catalysts for the efficient synthesis of 5-hydroxymethylfurfural in glucose-derived natural deep eutectic solvent

In this work, different multilayer mesoporous carbon solid catalysts were prepared and applied for 5-hydroxymethylfurfural (HMF) synthesis in carbohydrate-derived natural deep eutectic solvents (NADES). The structure of the carbon carriers and solid acids were systematically detected by various characteristics such as BET, SEM, TEM, XRD, FT-IR, and TGA, and stated the formation processes of the soft-templating copolymers and the multilayer mesoporous carbons. The carbon solid acidic catalysts showed effective performance conversion of carbohydrates such as fructose and glucose, with high 5-hydroxymethylfurfural (HMF) yields of 91.3 % and 60.1 % obtained from the NADES, respectively. Based on the proposed catalytic mechanism, the critical energy barriers and rate-limiting steps in glucose isomerization were demonstrated using Density Functional Theory (DFT) method. Both the carbon-based catalyst and the NADES reaction system could be easily recycled. This work provided a novel method for carbon catalyst synthesis and suggested a practical pathway from carbohydrates to value-added chemicals.

Design of Multi-Layered Gradient Catalysts for Efficient Proton Exchange Membrane Fuel Cells

Design of Multi-Layered Gradient Catalysts for Efficient Proton Exchange Membrane Fuel Cells

Electrodeposited Pd nanoparticles on polypyrole/nickel foam for efficient methanol oxidation

The present work describes the Ni foam (Ni–F)/polypyrrole (PPy)/palladium (Pd) (Ni–F/PPy/Pd) multilayered catalysts via a facile electrochemical technique. Potentiostatic deposition of PPy on the surface of Ni–F is followed by galvanostatic deposition of Pd nanoparticles on Ni–F/PPy acted as supports for electrochemical deposition of Pd nanoparticles. The produced catalysts are utilized for electrocatalytic methanol oxidation in alkaline media. Chronoamperometry (CA), cyclic voltammetry (CVs), and electrochemical impedance spectroscopy (EIS) techniques are used to examine the electrocatalytic performance of Ni–F/PPy/Pd based electrodes for methanol oxidation. The polypyrrole modification on Ni–F leads to an improvement in the electrocatalytic activity of the Ni-F/PPY-Pd catalysts toward methanol oxidation. As an open-pored, porous metal with high electrical conductivity, nickel foam produces a substantial amount of active area during the modification of Pd and polypyrrole, which results in significant catalytic activity and a rapid rate charge transfer reaction kinetics on methanol oxidation. The Ni–F/PPy/Pd10 catalyst exhibits enhanced specific activity than its counterparts and a reduced onset potential for methanol oxidation, as well as a low Tafel slope. Based on these results, Ni–F/PPy/Pd10 is suggested as a good material for the anode in the electrocatalytic oxidation of methanol.

Fabrication of multi-layered Co3O4/ZnO nanocatalysts for spectroscopic visualization: Effect of spatial positions on CO2 hydrogenation performance

Controlled fabrication of spatial positions of different active sites on catalyst structures is critical to exploring the reaction mechanisms for CO2 hydrogenation. Herein, two isomorphous zeolitic imidazolate frameworks (ZIF-67 and ZIF-8) were used as sacrificial templates to synthesize multi-layered Co3O4/ZnO catalysts with tunable core-shell structures and well-controlled spatial positions. The multi-layered catalysts were then evaluated for the catalytic performance for CO2 hydrogenation. A series of characterization techniques were applied to investigate the morphology and structure of the Co3O4/ZnO composites with different spatial locations. Due to the unique multi-layered structure, the distinct interfacial structures, and the synergistic effects, the resultant core-shell structured Co3O4/ZnO nanocatalysts exhibited significantly enhanced activity as compared to their monometallic counterparts (pure Co3O4 and ZnO). In addition, the ZnO@Co3O4 with Co3O4 as shell showed significantly higher CO2 conversion (25%) than that of Co3O4@ZnO with ZnO as shell (0.82%). Furthermore, in-situ Diffuse Reflection Fourier Transform Infrared Spectroscopy (DRIFTS) analysis suggested that formate (HCOO*) and methoxy (CH3O*) species were the crucial intermediates in the CO2 hydrogenation over the Co3O4/ZnO composite nanocatalysts. However, pure ZnO could not activate the CO2; consequently, the use of the Co3O4/ZnO nanocatalysts derived from multiple-layered ZIFs structures provides new insights into improving the catalytic efficiency of CO2 hydrogenation.

Bolstering the Alliance for a Trilateralism‐Based Security Strategy for South Korea in Times of US–China Rivalry*

As the strategic competition between the United States and China intensifies, South Korea is facing growing pressure to chart an optimal diplomatic strategy to navigate the convoluted geopolitics and foster lasting peace on the Korean Peninsula and beyond. At this crucial juncture, this study examines multi‐faceted, capacity‐building measures for peace aimed at precluding Sino–US friction in the East and South China Seas from spilling over into the Korean Peninsula. This article presents a road map to stimulate and reinvigorate security cooperation among South Korea, the United States, and Japan and economic cooperation among South Korea, China, and Japan in a virtuous cycle, and by extension to craft a dialogue channel among South Korea, the United States, and China. It also puts forward a three‐stage program for the evolution of the South Korea–US alliance whereby South Korea secures flexibility in its approach to China based on the robust trust of the alliance. This is to enable South Korea to assume a key role in connecting the three trilateral cooperation channels with the development of the Seoul–Washington alliance being a key driver to expand Seoul's diplomatic capacity. In the end, this study envisions a foreign policy model for South Korea that would allow the middle‐power country to punch above its weight by expanding the framework of cooperative security. It aims to ultimately pursue a multilateral, common security architecture in Northeast Asia, including China, which will serve as a multilayered catalyst to promote lasting peace on the Korean Peninsula.

FePc nanoclusters modified NiCo layered double hydroxides in parallel with Ti3C2 MXene as a highly efficient and durable bifunctional oxygen electrocatalyst for zinc-air batteries

Boosting the bifunctional oxygen activity of layered double hydroxides (LDHs) is a frontier but challenging issue for metal-air batteries. Herein, an iron phthalocyanine (FePc) nanocluster modified NiCo LDH in parallel with Ti3C2 (FePc-NiCo-LDH/Ti3C2) two-dimensional multilayer structured bifunctional oxygen catalyst is engineered by growing NiCo-LDH in parallel with Ti3C2 followed with adsorbing FePc via electrostatic interaction approach. Thanks to the abundant retained Fe-Nx active sites, the FePc-NiCo-LDH/Ti3C2 catalyzes the oxygen reduction reaction (ORR) with a half-wave potential (E1/2) of 80 mV positive compared to Pt/C. Besides, the current density only drops 5% after 33,000 s of chronoamperometry test, confirming the robust ORR stability. On the other hand, there are electronic interactions formed between FePc nanocluster and NiCo-LDH/Ti3C2 which boosts the OER activity as demonstrated by the negatively shifted potential of 89 mV at 10 mA cm−2 versus RuO2. The overall ORR/OER activity makes FePc-NiCo-LDH/Ti3C2 ranking top among the most active analogous samples. The Zn-air battery (ZAB) assembled with FePc-NiCo-LDH/Ti3C2 as air electrode exhibits a peak power density of 148 mW cm−2 and can be charge-discharged continuously for 80 h. This direct engineering ORR/OER active center strategy offers a unique facile direction for the fabrication of oxygen electrode catalysts for renewable clean energy devices.

Encapsulation of atomically dispersed Pt clusters in porous TiO2 for semi-hydrogenation of phenylacetylene.

The synthesis of atomically dispersed metal clusters with strong interaction with the support is attractive for the design of high-efficiency catalysts. Here, we report a multilayered catalyst (1.91%Pt@TiO2), in which atomically dispersed Pt clusters are encapsulated in the porous TiO2. As a result, 1.91%Pt@TiO2 exhibited high activity, selectivity (92.9%), and excellent stability in the semi-hydrogenation of phenylacetylene.

Solvent-free synthesis of 14-aryl-14H-dibenzo[a-j]xanthenes using Fe3O4@Al2O3@SiO2@Fe2O3 as a green catalyst

We report, a novel, green, nano-sized particles as a sandwich nano-capsule multilayer catalyst (SNC@MC) [Fe3O4@Al2O3@SiO2@Fe2O3] for the efficacious one-pot synthesis of 14-aryl-14H- dibenzo[a-j]xanthenes in high yields, under mild and solvent-free conditions at room temperature. The catalyst structure characterized by using various analytical techniques such as SEM, EDS, FT-IR, thermogravimetric analysis (TGA) and UV-visible spectroscopy. Environmentally friendly, availability, high catalytic activity, high efficiency, mild reaction conditions and ease of separation are the main reasons in using this green sandwich nano-capsule multilayer catalyst.

CeO2- and CaO-Promoted Precipitation Method for One-Step Preparation of Vermiculite-Based Multilayer Mesoporous Ni-Based Catalysts for Dry Reforming of Methane.

In this paper, a molecular sieve (VSiO2) prepared from modified vermiculite is used as a support, and a multilayer mesoporous catalyst, Ni-VSiO2, is prepared while the active components are loaded in one step by the precipitation method. The catalyst is further modified by adding additives Ca and Ce to prepare the catalyst Ni-5x-VSiO2 (x = Ce, Ca) and is used for the dry reforming of methane reaction. The catalyst is characterized by X-ray fluorescence, Brunauer–Emmett–Teller analysis, scanning electron microscopy, hydrogen temperature-programmed reduction test, transmission electron microscopy, thermogravimetric analysis, and other technical means. The result shows that under a normal pressure of 750 °C, the catalyst Ni-Ca-VSiO2 has good stability. The catalyst Ni-Ce-VSiO2 has good activity, stability and carbon deposition resistance, and the conversion rates of CO2 and CH4 are 88% and 78%, respectively. This is because the mesoporous structure allows Ni nanoparticles to enter the pores of the catalyst support, thereby inhibiting the aggregation of the active component Ni and improving its sintering resistance. CeO2 additives provide more oxygen vacancies to inhibit the formation of carbon deposits. At the same time, the strong interaction between the active component Ni and the additive CeO2 is also beneficial to improve its sintering resistance.

Influence of the Catalyst Layer Structure Formed by Inkjet Coating Printer on PEFC Performance.

In this study, we investigated the influence of the Catalyst-Layer (CL) structure on Polymer Electrolyte Fuel Cell (PEFC) performance using an inkjet coating printer, and we especially focused on the CL thickness and the electrode area. In order to evaluate the influence of CL thickness, we prepared four Membrane Electrode Assemblies (MEAs), which have one, four, five and six CLs, respectively, and evaluated it by an overpotential analysis. As a result, the overpotentials of an activation and a diffusion increased with the increase of thickness of CL. From Energy Dispersive X-ray spectroscopy (EDX) analysis, because platinum twines most ionomers and precipitates, the CL separates into a layer of platinum with a big grain aggregate ionomer and the mixing layer of platinum and ionomer during the catalyst ink drying process. Consequently, the activation overpotential increased because the three-phase interface was not able to be formed sufficiently. The gas diffusivity of the multilayer catalyst electrode was worse than that of a single layer MEA. The influence of the electrode area was examined by two MEAs with 1 and 9 cm2 of electrode area. As a result, the diffusion overpotential of 9 cm2 MEA was worse than 1 cm2 MEA. The generated condensate was multiplied and moved to the downstream side, and thereafter it caused the flooding/plugging phenomena.

Synthesis of Vertical Carbon Nanotube Interconnect Structures Using CMOS-Compatible Catalysts.

Synthesis of the vertically aligned carbon nanotubes (CNTs) using complementary metal-oxide-semiconductor (CMOS)-compatible methods is essential to integrate the CNT contact and interconnect to nanoscale devices and ultra-dense integrated nanoelectronics. However, the synthesis of high-density CNT array at low-temperature remains a challenging task. The advances in the low-temperature synthesis of high-density vertical CNT structures using CMOS-compatible methods are reviewed. Primarily, recent works on theoretical simulations and experimental characterizations of CNT growth emphasized the critical roles of catalyst design in reducing synthesis temperature and increasing CNT density. In particular, the approach of using multilayer catalyst film to generate the alloyed catalyst nanoparticle was found competent to improve the active catalyst nanoparticle formation and reduce the CNT growth temperature. With the multilayer catalyst, CNT arrays were directly grown on metals, oxides, and 2D materials. Moreover, the relations among the catalyst film thickness, CNT diameter, and wall number were surveyed, which provided potential strategies to control the tube density and the wall density of synthesized CNT array.

Investigation of Multilayered Catalyst Layers for Polymer Electrolyte Fuel Cells by Electrospray Deposition

In this study, multilayered catalyst layers with ionomer/carbon ratio (I/C ratio) were formed using electrospray deposition (ESD). The formed catalyst layer was used as the cathode of proton exchange membrane fuel cells (PEMFCs) for polarization measurements and electrochemical impedance measurements. The structures were observed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), and the maximum power densities for the homogeneous and three-layer catalyst layers at 100% MEA humidity were 274 mW/cm2 and 312 mW/cm2, respectively, indicating the effectiveness of the multilayered catalyst layer in ESD. SEM-EDS observations showed that larger aggregates were observed at higher I/C ratios, which also affected the thickness of the layers, suggesting that multilayered I/C ratios may be accompanied by multilayered physical structures.

Role of surface coverage of alumina with Pt nanoparticles deposited by laser electrodispersion in catalytic CO oxidation

This work elucidates the role of surface coverage of alumina with Pt nanoparticles on the catalyst efficiency in CO oxidation. Size-selected Pt nanoparticles were deposited on the outer surface of alumina pellets by the laser electrodispersion technique. The alumina surface coverage with Pt varied from 0.04 to 3.5 nanoparticle layers and affected the Pt electronic state and catalyst efficiency. Even in the multilayer coatings nanoplatinum particles remained isolated. The catalysts were tested in CO oxidation at CO/O2 ratios of 0.2, 1 and 2 in the temperature-programmed and pulse reaction modes. At CO/O2 = 0.2 the temperature of 50% CO conversion increased with decreasing the surface coverage with Pt particles. At CO/O2 = 2 the decrease in the surface coverage enhanced the catalyst activity. Pt0 dominates only in multilayer catalysts, however, approximately half of platinum remained non-oxidized even at such a low metal loading as 0.01 wt%. The change in the electronic state of platinum under the thermal treatment in the reaction mixture affected the catalyst efficiency. The oxidation state of Pt depended on the metal loading, reaction temperature, CO/O2 ratio in the reaction mixture, mode of its feeding and surface coverage with Pt nanoparticles that influenced the interparticle and particle – support interactions.

Investigation of gas diffusion phenomena in porous catalyst support pellets based on microstructure

Catalytic performance is influenced by the effective gas diffusivity in a heterogeneous catalyst. The diffusivity is dependent on the microstructure of the catalyst. Therefore, the microstructure of a catalyst must be characterized, and the effective gas diffusivity should be predicted using the microstructural properties. Mercury intrusion porosimetry (MIP) is a popular technique to characterize microstructure and subsequently predict the effective gas diffusivity with the random pore model (RPM) using the MIP results. However, this methodology cannot be used for multilayered catalysts such as automotive catalysts due to the difficulty of microstructure characterization. Three-dimensional (3D) image analysis is expected to be an informative technique to characterize the porous structure of multilayered catalysts because each layer can be analyzed independently. In this research, X-ray nano computed tomography (nano-CT), 3D-transmission electron microscopy (TEM) and MIP were employed to characterize porous Al2O3 pellet samples. A series of samples with different microstructures were prepared. The effective diffusion coefficient of CO2 was evaluated experimentally for each sample. The effective diffusion coefficient was also predicted with the RPM or by simulation. Pore properties obtained by MIP were applied for the RPM. 3D images obtained by nano-CT and 3D-TEM were used for application of the simulation. A strong correlation between the experimentally evaluated effective diffusion coefficient and the predicted diffusion coefficients was thus confirmed.

Miniature Fuel cell with Monolithically Fabricated Si Electrode -First prototype with Au-Pd-Pt multilayer catalyst-

Our first fuel cell prototype with a novel Au-Pd-Pt catalyst successfully demonstrated power generation. In order to reduce amount of platinum group metals and obtain high CO tolerance, electrochemical atomic layer depositions of Pd and Pt were applied on the porous Au. 5 ML Pd and sub-ML Pt deposition was attempted and amounts of Pd and Pt were electrochemically estimated to be 125 μg/cm2 and 6 μg/cm2, respectively. No catalyst poisoning to 100 ppm CO was observed during the power generation. Though the peak power was poor around 100 mW/cm2, results were satisfying for the first prototype.