Core-shell Catalysts Research Articles

A convenient synthesis of core-shell Co3O4@ZSM-5 catalysts for the total oxidation of dichloromethane (CH2Cl2)

Core-shell structured Co3O4@ZSM-5 catalysts were successfully synthesized by a simple two-step microwave hydrothermal method and used for the catalytic oxidation of dichloromethane (DCM). Co3O4@ZSM-5 catalysts exhibited better CO2 yield and lower byproduct yield than pristine Co3O4 and ZSM-5. For pure ZSM-5 and Co3O4, dechlorinated byproducts CH3Cl formed more readily over ZSM-5 due to its higher acidity and lower redox property, while polychlorinated byproducts (CHCl3 and CCl4) formed more readily over Co3O4 due to its lower acidity and higher redox property. Thanks to its core-shell structure, Co3O4@ZSM-5 exhibited appropriate redox ability and a suitable distribution of acid sites, possibly explaining its lower byproduct yields and more efficient formation and desorption of HCl and Cl2. In situ Fourier transform infrared (FTIR) spectra analysis indicated that formaldehyde, formate and methoxy species were the main intermediates of the catalytic oxidation reaction. A pathway for the catalytic oxidation of DCM on 1.5-Co3O4@ZSM-5 was proposed based on the DCM degradation performance and physicochemical property analysis. The addition of water vapor to the DCM degradation process on core-shell structure Co3O4@ZSM-5 was shown to promote DCM conversion and CO2 yield. In addition, we concluded that core-shell catalysts exhibited good thermal stability and durability for DCM oxidation.

High-Temperature Fischer–Tropsch Synthesis of Light Olefins over Nano-Fe3O4@MnO2 Core–Shell Catalysts

A one-pot hydrothermal process was adopted to synthesize nano-Fe3O4@MnO2 core–shell catalysts with diverse thicknesses of MnO2 for the high-temperature Fischer–Tropsch (HTFT) synthesis of light ole...

Graphene layer encapsulated MoNi4-NiMoO4 for electrocatalytic water splitting

Developing active and cheap bifunctional electrocatalysts is crucial and challenging for overall water splitting. This work reports a core-shell structured catalyst supported on nickel foam, which is composed of hybrid MoNi4 alloy and NiMoO4 encapsulated in graphene shell layer. The core catalyst of MoNi4-NiMoO4 supplies robust intrinsic activity and high conductivity. The graphene shell accelerates the charge transfer and provides additional protection for core catalyst. Hence, the present G@MoNi4-NiMoO4/NF exhibits excellent catalytic properties for alkali water splitting, with low overpotentials of 55 mV and 206 mV at 10 mA cm−2 for HER and OER, respectively. The efficient activity for overall water splitting is further demonstrated by a low cell voltage of 1.44 V at 10 mA cm−2 in the bifunctional G@MoNi4-NiMoO4/NF electrodes assembled electrolyzer, showing great promise for practical application.

Performance of mesoporous HZSM-5 and Silicalite-1 coated mesoporous HZSM-5 catalysts for deoxygenation of straw fast pyrolysis vapors

•Catalytic treating of biomass fast pyrolysis vapors offers a promising route to convert many different types of lignocellulosic biomass into biofuels. Considerable research efforts have focused on using zeolite catalysts, especially the microporous HZSM-5 zeolite. Unfortunately, the zeolite’s initial high activity in forming coke and light gases reduces the overall oil yield. In this contribution, we synthesized conventional HZSM-5 zeolite, mesoporous HZSM-5 zeolite, and a core-shell catalyst consisting of mesoporous HZSM-5 zeolite coated with a thin layer (<20 nm) of silicalite-1 zeolite. The catalysts were characterized by inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 and Ar physisorption, temperature programmed desorption of ammonia (NH3-TPD), diffuse reflectance infrared fourier transform spectroscopy (DRIFT) spectra, and 27Al nuclear magnetic resonance (NMR). The catalysts were tested in a tandem micro-pyrolyzer system for deoxygenation of wheat straw derived fast pyrolysis vapors in a downstream catalytic fixed bed reactor and the quantitative product analysis was performed with GC-MS/FID/TCD and TGA-MS. The change in yields of different product groups was monitored during catalyst deactivation for an increasing number of pyrolysis vapor pulses and the cumulative carbon recoveries of all product streams (char, vapors, gas, and coke) were compared at different biomass-to-catalyst ratios (∼4 and ∼1) for catalyst loadings of 2 and 8 mg, respectively. In addition, the yields were compared for the same number of zeolitic acid sites. Even though the coking propensity was highest for the mesoporous HZSM-5 (5.1% carbon recovery of fed biomass at B:C = 1), it showed improved conversion of oxygenates (wt% O of vapors = 15) and a higher tolerance towards deactivation by coking compared to the conventional HZSM-5 (wt% O of vapors = 20). Coating of mesoporous HZSM-5 with silicalite-1 reduced the number of acid sites per mass of catalyst by ∼20%, which is attributed to the addition of the inert silicalite-1 layer and passivation of the external acid sites of the mesoporous HZSM-5. Compared to mesoporous HZSM-5, the added silicalite-1 shell reduced the coke yield by 43% (from 5.1–2.9 wt% of fed biomass carbon) for the same catalyst mass and by 8% (4.7 wt% of fed biomass carbon) for the same total number of acid sites. Furthermore, the tolerance towards deactivation observed for the mesoporous HZSM-5 core was largely preserved—especially for conversion of small oxygenates like acids, alcohols and aldehydes, resulting in vapors with 14 wt% O.

The Effect of CeO2 Dispersity and Active Oxygen Species on the SCR Reaction Over Fe-ZSM-5@Ce/meso-SiO2

A core–shell catalyst for SCR reaction, which consists of Fe-ZSM-5 core and meso-SiO2 shell, was synthesized by the step by step assembly method. The cerium species were introduced into the SiO2 shell by using different solvents to enhance the oxidation of NO, which is beneficial to the fast-SCR reaction. The meso-SiO2 shell inhibits the growth of CeO2 particles and enhances the dispersion of cerium oxide. The results of TEM, XPS and H2-TPR found that the higher dispersity and smaller size of cerium species endow catalyst with a high ration of Ce4+/Ce3+ and outstanding SCR activity. In addition, the evolution and role of chemisorbed and lattice oxygen were investigated by in situ DRIFTS and O2-TPD. The meso-SiO2 shell inhibits the growth of CeO2 particles and enhances the dispersion of cerium oxide, effectively increasing the activity of the SCR reaction.

Synthesis of Ni-Mg@HC catalyst derived from sugarcane bagasse and its application for producing syngas via CO2 dry reforming

ABSTRACT In this paper, sugarcane bagasse was used as the raw material to produce hydrochar (HC) through the hydrothermal carbonization (HTC) process, then Ni and Mg were loaded on HC by the impregnation method. Thus, a serial of Ni-Mg x @HC core-shell structural catalysts for CO2 dry reforming were synthesized. In order to evaluate the application of Ni-Mg x @HC catalyst derived from sugarcane bagasse, the catalytic performance for CO2 dry reforming were investigated. Experimental results showed that the hydrochar based catalyst (Ni-Mg15@HC) exhibited an excellent activity and stability at 750°C, CH4 and CO2 conversions were 63.7% and 76.9%, respectively. XRD, TEM, CO2-TPD and TG-DTG characteristic proved that the addition of Mg into Ni@HC would promote the active site formation and the adsorption capacity of CO2. Moreover, the coke deposition was also suppressed in the DRM process. The catalytic performance of Ni-Mg15@HC catalyst demonstrated that it was a practical candidate for the DRM reaction due to its unexpected activity and stability.

CO and CO2 methanation over Ni/Al@Al2O3 core–shell catalyst

Core–shell Al@Al2O3, which was obtained by hydrothermal surface oxidation of Al metal particles, was used as the support in supported Ni catalysts for CO and CO2 methanation. The core–shell micro-structured support (Al@Al2O3) helped develop a highly efficient Ni-based catalyst compared with conventional γ-Al2O3 for these reactions. Moreover, the deposition–precipitation method was shown to outperform the wet impregnation method in the preparation of the active supported Ni catalysts. The catalysts were characterized using various techniques, namely, N2 physisorption, H2 chemisorption, CO2 chemisorption, temperature-programmed reduction with H2, temperature-programmed desorption after CO2 adsorption, X-ray diffraction, inductively coupled plasma-atomic emission spectroscopy, high-resolution transmission electron microscopy, and in situ diffuse reflectance infrared Fourier transform spectroscopy. Higher Ni dispersion when using Al@Al2O3 as the support and the deposition–precipitation method resulted in better catalytic performance for CO methanation. Furthermore, the higher density of medium basic sites and enhanced CO2 adsorption capacity observed for Ni/Al@Al2O3 helped increase catalytic activity for CO2 methanation.

Electron penetration from metal core to metal species attached skin in nitrogen-doped core-shell catalyst for enhancing oxygen evolution reaction

Metal nanoparticles (NPs) encapsulated into nitrogen-doped carbon are proved to be an efficient way to enhance the catalytic activity, but the mechanism behind is still debatable. Here, we prepared metal-nitrogen doped carbon shield (Me-NC) NiFe nanoparticles (NiFe-NC/Me-NC) by simple template nanocasting, and then selectively removed metal species on the surface or destroyed the core-shell structure to investigate whether the metal core or the metal doped surface are responsible for the activity enhancement. We show that, for the first time, a synergistic effect together with the electron penetration from metal doped NC shell to metal core is responsible for the enhancement of surface catalytic reaction. The core/shell structure insulates the metal core from electrolyte and the metal core act as electron receptor to modify the surface electronic structure. The electrochemical evaluations show that the as-synthesized NiFe-NC/Me-NC exhibits high electrocatalytic activity, which affords the current density of 10 mA cm−2 at low overpotentials of 231 mV and 271 mV for oxygen and hydrogen evolution reactions as well as excellent stability in alkaline medium. While both the NiFe-NC/Me-NC sample after ball-milled with the core-shell structure destroyed and the sample after acid leached with surface metal NPs removed show a remarkably decreased activity, confirming the synergistic effect between NPs core and Me-NC-sheet for efficient catalytic performance.

Magnetic core–shell nanocatalysts: promising versatile catalysts for organic and photocatalytic reactions

ABSTRACTDuring the past decades, there have been enormous developments in catalysis in the form of great innovations such as precise structure characterization, surface functionalization, and effective utilization of active sites. In both academic and industrial sectors, the development of efficient nanosized catalysts has received considerable attention because it can improve the efficiency of the catalytic process and the selectivity of products, which can minimize the overall production cost and the amount of chemical wastes generated by improving the atomic efficiency. However, bulk-scale synthesis and utilization of nanocatalysts are hindered by the high synthetic cost, tedious synthesis procedure, and difficulty in the separation and recovery of the catalysts after the reactions. In this context, superparamagnetic nanoparticles have attracted much attention as a catalyst and as a support owing to their robust structure, low cost, environmental benignity, and easy separation under an external magnetic response. In this review, we focused on organic catalysis and photocatalysis using magnetically retrievable core–shell nanocatalysts with various functionalities. This review presents a comprehensive overview of the synthesis of magnetic core–shell nanocatalysts with suitable functionalities for catalysis, recent developments in organic and photocatalytic reactions using core–shell catalysts, and challenges to be addressed as part of future research activities. The first part summarizes the various synthetic methods of magnetic nanocores, and the second part overviews the detailed functionalization methods for the growth of shells on the surface of the magnetic nanocores, along with the merits and challenges to-date. In the last section, the efficiency, recoverability, and reusability of magnetic core–shell nanocatalysts are reviewed for a variety of organic and photocatalytic reactions.

Iron ore as precursor for preparation of highly active χ-Fe5C2 core-shell catalyst for Fischer-Tropsch synthesis

This work describes a novel method for the preparation of active and stable Fe-based catalyst from an iron ore, which was chemically treated with oxalic acid to obtain a mixture of iron oxides and oxalate. It was found that under CO atmosphere at 350 °C, this mixture can be effectively transformed into active iron carbide phase (χ-Fe5C2), which is highly desirable for FTS. The catalysts were characterized by SEM, TEM, TGA, Raman, XRD, BET, and CO-TPR-MS. The catalytic performance was evaluated under FTS conditions (280 °C, H2 / CO = 1, P =20 bar) and GHSV = 12 N L gcat−1 h−1 for 100 h. The results showed that the CO conversion (66.8%) was higher on the oxalic acid-treated iron ore than in the untreated iron ore (46.5%), obtaining a high C5+ hydrocarbon selectivity (> 60.0%) in all cases. The proposed method significantly reduced the catalyst preparation steps using an inexpensive and abundant raw material for the sustainable preparation of very active and stable Fe-based catalysts for the FTS.

Methanol electro-oxidation on Cu@Pt/C core-shell catalyst derived from Cu-MOF

Core-shell structured Cu@Pt/C catalyst was fabricated by a simple three-step procedure involving hydrothermal synthesis of copper-centered metal organic framework (Cu-MOF), carbon-supported copper nanoparticles (Cu/C) by direct carbonization at 600℃ and partial galvanic replacement of Cu particle layers by Pt in a chloroplatinate solution. The characterization of Cu@Pt/C catalyst is achieved by XRD (X-ray powder diffraction), SEM (scanning electron microscopy) and voltammetry techniques. Cu@Pt/C catalyst has shown much larger electrochemical active surface area (ECSA, 74.3 m2.g−1) than commercial Pt/C catalyst (50.4 m2.g−1). Furthermore, nearly four-fold enhancement of activity of Cu@Pt/C catalyst for methanol oxidation has been observed. Moreover, the charge transfer resistance of methanol oxidation for Cu@Pt/C catalyst is 22.8 Ω cm-2, lower than that for Pt/C catalyst (73.7 Ω cm-2). Additionally, Cu@Pt/C catalyst exhibits a superior catalytic stability. The electronic effect modification and large ECSA may be collectively responsible for the enhanced catalytic activity of Cu@Pt/C over Pt/C.

Controlling Near-Surface Ni Composition in Octahedral PtNi(Mo) Nanoparticles by Mo Doping for a Highly Active Oxygen Reduction Reaction Catalyst.

We report and study the translation of exceptionally high catalytic oxygen electroreduction activities of molybdenum-doped octahedrally shaped PtNi(Mo) nanoparticles from conventional thin-film rotating disk electrode screenings (3.43 ± 0.35 A mgPt-1 at 0.9 VRHE) to membrane electrode assembly (MEA)-based single fuel cell tests with sustained Pt mass activities of 0.45 A mgPt-1 at 0.9 Vcell, one of the highest ever reported performances for advanced shaped Pt alloys in real devices. Scanning transmission electron microscopy with energy dispersive X-ray analysis (STEM-EDX) reveals that Mo preferentially occupies the Pt-rich edges and vertices of the element-anisotropic octahedral PtNi particles. Furthermore, by combining in situ wide-angle X-ray spectroscopy, X-ray fluorescence, and STEM-EDX elemental mapping with electrochemical measurements, we finally succeeded to realize high Ni retention in activated PtNiMo nanoparticles even after prolonged potential-cycling stability tests. Stability losses at the anodic potential limits were mainly attributed to the loss of the octahedral particle shape. Extending the anodic potential limits of the tests to the Pt oxidation region induced detectable Ni losses and structural changes. Our study shows on an atomic level how Mo adatoms on the surface impact the Ni surface composition, which, in turn, gives rise to the exceptionally high experimental catalytic ORR reactivity and calls for strategies on how to preserve this particular surface composition to arrive at performance stabilities comparable with state-of-the-art spherical dealloyed Pt core-shell catalysts.

Enhancing catalytic CH4 oxidation over Co3O4/SiO2 core–shell catalyst by substituting Co2+ with Mn2+

Co3O4, a transition metal oxide with spinel structure, has attracted wide attention due to its high catalytic activity in the field of catalytic oxidation of low concentration methane. However, due to the harsh conditions of methane catalytic reaction on catalysts, of which the high reaction temperature and complex reaction environment often lead to the deactivation and sintering of Co3O4 catalyst, improving the comprehensive performance of Co3O4 catalyst has become the current research hotspot and urgent demand. Core-shell flower-spheroidal cobalt-manganese composite catalyst was prepared in this paper by hydrothermal method, which gave full play to the advantages of carrier, special morphology and doping modification, reduced the risk of sintering and deactivation of Co3O4, and showed higher catalytic activity. Through SEM, EDS, and BET test and analysis, Mn1/Co/SiO2 has better microstructure and structure than Co3O4/SiO2. For example, the dispersion of Mn1/Co/SiO2 and the uniform distribution of elements are higher, and the values of surface area and pore volume are larger (129.956 m2/g → 180.639 m2/g, 0.333363 cm3/g → 0.398030 cm3/g). Combined with XRD and XPS analysis, it is concluded that Mn2+ manganese ion replaces Co2+ and causes lattice distortion of Co3O4, which promotes the production and mobility of reactive oxygen species, further increasing catalytic activity. Compared with Co3O4/SiO2, methane conversion at 350 °C and 450 °C increased by 10% and 6%, respectively.

Degradation of core-shell Pt3Co catalysts in proton exchange membrane fuel cells (PEMFCs) studied by mathematical modeling

Understanding the degradation process of Pt-based catalysts is a crucial step to improve the durability of PEMFCs. A mathematical model is established to study the electrochemical surface area (ECA) loss and structural/compositional evolutions of core-shell Pt3Co catalysts along the cathode under a certain circumstance. Three major processes are included in this model: Pt dissolution and re-precipitation on the Pt shell, Co leaching from the bulk and deposition of Pt ions in the membrane due to crossover hydrogen. The results show that the significant ECA loss next to the membrane is mainly attributed to the severe particle corrosion rather than variation of the particle size distribution. The Pt shell thickness and Pt/Co atomic ratio decrease from gas diffusion layer (GDL)/CCL interface to the cathode catalysts layer (CCL)/membrane interface, while the Co mass loss shows an inverse trend. This work demonstrates that mathematical modeling is effective to predict the structural and compositional evolutions of the catalyst particles across the CCL, and therefore is useful to evaluate the complete performance degradation of Pt3M catalysts for PEMFCs in the future.

Electrochemical Stability Improvements By Ir for Ultra-High Vacuum Prepared Pt/Pd(111) Bimetallic Surfaces

Introduction Pt-shell-Pd-core nanoparticles are effective cathode catalysts for polymer electrolyte fuel cell (PEFC) from the view-points of a great potential to reduce Pt usage and to improve the oxygen reduction reaction (ORR) activity [1]. However, because of operating conditions of PEFC, e.g., low pH, and high positive potentials with severe fluctuations, the ORR activity of the core-shell type catalysts tend to decline through dissolution of the core elements, accompanying re-arrangements of shell layer’s Pt atoms. Considering standard electrode potentials, Ir is a stable element in the fore-mentioned PEFC conditions among the late 9-11 group transition metals. Therefore, Ir can be applied for surface-stabilizing elements of the core-shell type ORR catalysts for the PEFC. Indeed, to control dissolution behavior of the less-noble element, Li et al. investigated influence of Ir for the Pt–Ni nanostructures and showed that the surface modifications of Pt-Ni alloys by Ir improved electrochemical stability [2]. However, relation between locations of Ir in the core-shell nano-structures and ORR properties (activity and durability) has yet to be investigated. For developing the practical Pt/Pd core-shell type catalysts, to clarify a role of a modifying element Ir for the ORR properties are required. Therefore, in this study, we prepared well-defined, Ir-modified Pt/Pd(111) bimetallic surfaces by molecular beam epitaxy (MBE) of Pt and Arc-plasma deposition (APD) of Ir in ultra-high vacuum (UHV; ~10-8 Pa) and studied Ir-modified ORR activity and stability of Pt/Pd(111) bimetallic surfaces. Experimental Two Ir-modified Pt/Pd(111) bimetallic surfaces, (1) interlayer-modified Pt/Ir/Pd(111) and (2) surface-modified Ir/Pt/Pd(111) are fabricated as follows. The Pt/Pd(111) bimetallic surface was prepared through e-beam deposition of 4 monolayer (ML)-thick Pt on the UHV-cleaned Pd(111) substrate surface. As for the interlayer-modified sample (1), 1 monolayer (ML)-thick Ir was deposited by APD on the UHV-cleaned Pd(111), followed by 4ML-thick e-beam deposition of Pt at 573K. The surface-Ir-modified Pt/Pd(111) (2), sub-ML-thick Ir was deposited on the Pt/Pd(111) at room temperature. The UHV-prepared samples (Pt/Pd(111), Pt/Ir/Pd(111), Ir/Pt/Pd(111)) were transferred to the electrochemical evaluation system set in a N2-purged glove box without air exposure to avoid sample oxidation and contamination [3]. Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were performed in N2-purged and O2-saturated 0.1 M HClO4, respectively in the glove-box. The ORR activity was evaluated from kinetic-controlled current density (j k) values at 0.9 V vs. RHE by using Koutecky–Levich equation. The electrochemical stabilities of the samples were discussed based on change in the j k values during applying 5000 square-wave potential cycles (PCs) between 0.6 (3 s) and 1.0 V (3 s) in O2-saturated 0.1 M HClO4 at a room temperature. Results and Discussion Fig. 1 (a) summarizes CV curves of the Ir0.1ML/Pt/Pd(111)(blue), Pt/Ir1.0ML/Pd(111)(red) and the Pt/Pd(111)(black) [4] sample surfaces. As shown in Fig. 1(a), in comparison with the Pt/Pd(111), hydrogen adsorption and desorption charges (QH; 0.15-0.35V) for the both Ir-modified samples clearly decreased. Particularly, the hydrogen storage current for the Pd(111) substrate (0.15V marked *) remarkably suppressed by Ir modifications. Furthermore, the Ir-modified samples show positive on-set potential shifts of the OH adsorption feature (0.6V-1.0V). The results clearly reveal that electrochemical properties of the Pt/Pd(111) bimetallic surface are modified by the third element, Ir, located not only at the surface (Ir/Pt/Pd(111)) but also at the interlayer (Pt/Ir/Pd(111)). Fig.1 (b) shows changes in ORR activity of the Ir-modified samples during applying the 5000 PCs. The initial, pristine ORR activities of the Pt/Ir/Pd(111) and Ir/Pt/Pd(111) are lower than non-Ir-modified Pt/Pd(111). In contrast, the ORR activities of the former interlayer-Ir-modified and the latter surface-Ir-modified samples become higher than the corresponding Pt/Pd(111) after the 3000 and 2000 PCs, respectively: the ORR activity enhancement factors vs. initial ORR activity of the clean Pt(111) for the interlayer-Ir- and surface-Ir-modified samples can be estimated to be ×3, ×4, respectively, after the 5000 PCs. The results obtained reveal that Ir can be applied for the modifying element for durability improvements of the Pt-shell/Pd-core type ORR catalyst. Acknowledgement This study was supported by the new energy and industrial technology development organization (NEDO) of Japan.

A Non-Negligible Interface Effect for Alkaline Hydrogen Oxidation Reaction

In alkaline medium, the slow kinetics of the anodic hydrogen oxidation reaction (HOR) hinders the development of alkaline membrane fuel cells (AMFCs). Therefore, it is of great significance to explore the mechanism of HOR from establishing the "structure-activity relationship" and researching the main factor influencing the activity of the catalyst. Generally accepted viewpoint is the hydrogen binding energy (HBE) theory, a main descriptor of the catalytic activity, and regulation of the binding energy usually could be achieved by controlling the lattice strain. In our research, by taking advantage of the difference in the atomic radius of the 3d transition metals, a trimetal model (Pd3M@Pt (M=Fe, Co, Cu) core-shell structure) is constructed to study the HOR through the tuning of stress shrink degrees. By step-by-step electrochemical monitoring method and surface-controlled technology, the phase changes in the cycle were regulated and analyzed. Interestingly, it shows that the low-valence M(OH)x species formed in the electrochemical cycle obviously influenced the HOR activity rather than the HBE change caused by lattice shrink, mainly ascribed to strengthen the adsorption of OHad species and accelerate the Volmer step (Had+OH-→H2O+e-+*, rate-determined step, RDS). Meanwhile, It's worth noting the mass activity (MA) and specific activity (SA) of Pd3Co@Pt are significantly improved compared with Pt/C, close to 4 and 2 times. This Pd3M@Pt core-shell structure also improves the utilization of Pt and facilitates the design of efficient HOR catalyst. Figure 1. a) Schematic diagram of the mechanism exploration for HOR with the model of Pd3M@Pt (M=Fe, Co, Cu); b) CV curves of four core-shell structure catalysts Keywords: Hydrogen Oxidation Reaction, Pd3M@Pt core-shell structure, low-valence M(OH)x species, interface effect

Single Atoms for Energy Applications

Single Atoms for Energy Applications

Environmental TEM Study of NiMoO4 Nanorods Undergoing Thermal Reduction: Observing the Formation of a Ni–Mo Alloy@oxide Core-shell Catalyst

Environmental TEM Study of NiMoO₄ Nanorods Undergoing Thermal Reduction: Observing the Formation of a Ni–Mo Alloy@oxide Core-shell Catalyst

The importance of inner cavity space within Ni@SiO2 nanocapsule catalysts for excellent coking resistance in the high-space-velocity dry reforming of methane

Metal sintering and carbon deposition are acknowledged to be the foremost critical issues in the important energy storage process of high temperature Dry Reforming of Methane (DRM). For that process, so-called “core-shell catalysts” have exhibited outstanding catalytic performance. However, the intrinsic confined geometric space of the host core-shell structure not only inevitably limits the ability of the catalyst system to facilitate the critical rapid infusion and diffusion of reacting gases, but also enhances the accompanying conversion of carbon intermediates to inert, catalyst-deactivating carbonaceous deposits under high-space-velocity conditions. Herein, we present a study highlighting the importance of the inner cavity space, now of a quasi-zero-dimensional, tubular, yolk-shell structured Ni@SiO2 nanocapsule catalyst, in the DRM process. The tubular yolk-shell structured Ni@SiO2 nanocapsule catalysts having controlled inner cavities (5.0–13.0 nm × 5.0–50.0 nm dimensions) were synthesised via a water-in-oil micro-emulsion method by employing different aging times (i.e. 3 h, 6 h and 12 h). Compared with corresponding Ni@SiO2 nanosphere catalysts, the tubular nanocapsule catalysts displayed both excellent catalyst activity, stability, and (metal) anti-sintering ability with, equally important, negligible carbon deposition during the operating DRM process under high space velocity conditions (60 L g−1 h−1), most relevant for application in real industrial processes.

Cellulose nanocrystal shelled with poly(ionic liquid)/polyoxometalate hybrid as efficient catalyst for aerobic oxidative desulfurization

Immobilization of polyoxometalates (POMs) plays significant roles in their industrial applications. In this work, POM-supported catalyst has been developed with cellulose nanocrystal (CNC) as a sustainable carrier and employed in the aerobic oxidative desulfurization (AODS) of fuels. The catalyst was constructed by grafting a poly(ionic liquid) (PIL) onto CNCs and subsequently exchanging the counterions of the PIL into [Co(OH)6Mo6O18]3−, a kind of POM anionic clusters. The resulting CNC@PIL@POM was systematically characterized and utilized as a catalyst in the AODS of thiophenic compounds including benzothiophene (BT), dibenzothiophene (DBT), and 4, 6-dimethyldibenzothiophene (4, 6-DMDBT), with oxygen contained in air as oxidizing agent. The catalyst could achieve complete conversion of DBT in model diesel under mild condition and be reused five times without apparent losing of activity. As for the desulfurization of a real diesel, it was demonstrated that almost all of the original sulfides were completely converted. Based on these results, it is expected that the core-shell POM-supported catalyst may serve as an efficient, separable and sustainable catalyst for AODS of fuels.