Hollow Sphere Catalysts Research Articles

Low-Overpotential Rechargeable Na-CO2 Batteries Enabled by an Oxygen-Vacancy-Rich Cobalt Oxide Catalyst.

Rechargeable sodium-carbon dioxide (Na-CO2) batteries have been proposed as a promising CO2 utilization technique, which could realize CO2 reduction and generate electricity at the same time. They suffer, however, from several daunting problems, including sluggish CO2 reduction and evolution kinetics, large polarization, and poor cycling stability. In this study, a rambutan-like Co3O4 hollow sphere catalyst with abundant oxygen vacancies was synthesized and employed as an air cathode for Na-CO2 batteries. Density functional theory calculations reveal that the abundant oxygen vacancies on Co3O4 possess superior CO2 binding capability, accelerating CO2 electroreduction, and thereby improving the discharge capacity. In addition, the oxygen vacancies also contribute to decrease the CO2 decomposition free energy barrier, which is beneficial for reducing the overpotential further and improving round-trip efficiency. Benefiting from the excellent catalytic ability of rambutan-like Co3O4 hollow spheres with abundant oxygen vacancies, the fabricated Na-CO2 batteries exhibit extraordinary electrochemical performance with a large discharge capacity of 8371.3 mA h g-1, a small overpotential of 1.53 V at a current density of 50 mA g-1, and good cycling stability over 85 cycles. These results provide new insights into the rational design of air cathode catalysts to accelerate practical applications of rechargeable Na-CO2 batteries and potentially Na-air batteries.

In situ aqueous phase hydrodeoxygenation of methyl palmitate on Ni–Co alloy particles embedded in mesoporous carbon hollow sphere catalysts

Ni–Co alloy particles embedded in mesoporous carbon hollow sphere (NiCo@MCHS) catalysts promote the internal diffusion and in situ aqueous phase hydrodeoxygenation of methyl palmitate.

Influence of Fe–N–C morphologies on the oxygen reduction reaction in acidic and alkaline media

AbstractThe development of nonnoble metal oxygen reduction reaction (ORR) catalysts for fuel cells has been motivated by the high cost and limited supply of noble metals, as well as the desire to improve the performance and durability of this type of energy conversion device. In this study, nonnoble Fe–N–C catalyst was synthesized using a zeolitic imidazole framework (ZIF‐8), poly (aniline), and 10,10′‐dibromo‐9,9′‐bianthry as precursors to produce Fe–N–C with hollow sphere (HS), amorphous bulky structure (B), and sheet‐like thin sheet (N) structure. The Fe–N–C catalyst was analysed in terms of their shape, crystal structure, pore characteristics, and elemental composition. Among all the Fe–N–C catalysts, Fe–N–C_HS had the highest total surface area, followed by Fe–N–C_B and Fe–N–C_N. To evaluate their ORR catalytic activity, a half‐cell electrochemical experiment with .1 M KOH and .1 M HClO4 as the alkaline and acidic electrolytes was conducted. This study revealed that Fe–N–C_HS exhibited the highest onset potential but the Fe–N–C_B has the highest limiting current density in alkaline medium; meanwhile, in acidic media, Fe–N–C_HS shows the best ORR performance with the highest onset potential and limiting current. This highly porous Fe–N–C_HS catalyst also demonstrated active site activation and excellent stability compared with the other samples as well as commercial Pt/C in acidic electrolyte, which suggests its potential for application in proton exchange membrane fuel cells (PEMFCs).

Promoting the electrocatalytic activity through the introduction of oxygen vacancies to core–shell NiO hollow sphere catalysts for efficient oxygen evolution

The contribution of oxygen vacancies for improving the OER activity of NiO.

A study on the catalytic performance of the ZrO2@γ-Al2O3 hollow sphere catalyst for COS hydrolysis

A nanoscale hollow sphere hydrolysis catalyst with low catalytic energy consumption, long catalytic lifetime and high conversion COS efficiency.

CO oxidation over the Cu2O/CuO hollow sphere heterojunction catalysts with enhanced low-temperature activities

In this work, a series of the Cu2O/CuO hollow sphere heterojunction catalysts with various Cu+/Cu2+ ratios were designed and synthesized to improve the low-temperature catalytic activity of CO oxidation. The physicochemical properties of all the catalysts were characterized by the SEM, TGA, N2-physisorption, XRD, FT-IR, XPS, and H2-TPR. The results revealed that the Cu2O hollow sphere catalyst had the large specific surface area due to the formation of the hollow structure, which could provid more accessible active sites for the gaseous reactants. Meanwhile, the Cu2O/CuO hollow sphere heterojunction catalysts possessed high concentration of the surface oxygen vacancies and further promoted the adsorption and activation of O2. As a result, the apparent activation energy of the CO oxidation was decreased and thus low-temperature activity of the CO oxidation was finally promoted. Therefore, the Cu2O/CuO hollow sphere heterojunction catalysts were considered as a series of high-efficient catalyst candidates for CO oxidation with promising low-temperature performance.

Effect of salt addition on morphology and activity of in situ synthesized silica–ruthenium–nickel hollow sphere catalyst for hydrolysis of ammonia borane

Effect of salt addition on morphology and activity of in situ synthesized silica–ruthenium–nickel hollow sphere catalyst for hydrolysis of ammonia borane

Fabrication of copper supported porous silica–alumina hollow spheres for catalytic decomposition of nitrous oxide

Copper supported porous silica–alumina hollow sphere catalysts were prepared using surfactant micelles to control the size distribution of interparticle spaces in the hollow sphere shells.

Degradation of Formaldehyde over MnO2/CeO2 Hollow Spheres: Elucidating the Influence of Carbon Sphere Self-Sacrificing Templates.

Here, we prepare a MnO2/CeO2 hollow sphere catalyst using the carbon sphere as a self-sacrificing template for formaldehyde (HCHO) removal. In the feed gas of 20 ppm of HCHO (balanced by N2) + 20 vol % O2, a HCHO removal efficiency of 70% was achieved at 20 °C and full conversion was reached at around 47 °C at GHSV = 50,000 mL (gcat h)−1 for MnO2/CeO2 hollow spheres. The catalytic performance and structural and chemical properties of MnO2/CeO2 hollow spheres for the removal of core carbon spheres were explored, and the influence of using the carbon sphere as a self-sacrificing template was proved by comparing with carbon@MnO2/CeO2 (a core carbon sphere with a MnO2/CeO2 shell) and nonmorphologic MnO2/CeO2. The properties of the MnO2/CeO2 hollow spheres are significantly improved compared to carbon@MnO2/CeO2 (removal efficiency of 45% at 150 °C) and MnO2/CeO2 (removal efficiency of 46% at 20 °C) as a result of an evolution in the interaction between Mn/Ce and carbon. This increase in the interaction strength seems to (i) increase the oxygen vacancy, (ii) promote the oxygen species mobility, and (iii) improve the chemical stability of the MnO2/CeO2 hollow spheres. We believe that these results are beneficial to the fabrication of binary transition metal oxides and applications of them in HCHO removal.

RETRACTED ARTICLE: Synthesis and Application of Double-Shelled CuCo2O4 Hollow Sphere Catalyst for Chemical Fixation of CO2

RETRACTED ARTICLE: Synthesis and Application of Double-Shelled CuCo2O4 Hollow Sphere Catalyst for Chemical Fixation of CO2

Synthesis and application of nanoporous triple-shelled CuAl2O4 hollow sphere catalyst for atmospheric chemical fixation of carbon dioxide

Designing complex hollow nano-/microspheres with multilayered structures of two or more metal oxides seems to be interesting to answer the request for novel catalytic structures. Herein, we develop a copper-alumina spinel hollow sphere with a triple-shell structure applied as a novel catalyst for the cycloaddition of CO2 at atmospheric pressure. Different operating conditions such as reaction temperature, various solvents and reaction time were studied in this reaction. Besides, different epoxides were converted at 80 °C, under bubbling of CO2 at atmospheric pressure, a catalyst loading of 3 wt.% and a reaction time of 24 h with isolated yields up to 100% of the carbonate. In addition, the kinetics of the reaction was investigated at different reaction temperatures by calculating the reaction rate constant and activation energy (based on the Arrhenius equation). The nanoporous triple-shell CuAl2O4 hollow microspheres reduce the mass transfer path of different reactant and product molecules along with better accessibility of interior active sites that improves the catalytic efficiency with suitable activity and remarkable cycling stability.

Highly Efficient NO Decomposition via Dual-Functional Catalytic Perovskite Hollow Fiber Membrane Reactor Coupled with Partial Oxidation of Methane at Medium-Low Temperature.

A novel dual-functional catalytic perovskite hollow fiber membrane reactor was fabricated by integrating BaBi0.05Co0.8Nb0.15O3-δ (BBCN) perovskite hollow fiber membrane with Ni-phyllosilicate hollow sphere catalysts for simultaneous NO decomposition and partial oxidation of methane (POM) reaction. With this novel catalytic membrane reactor, NO could be completely converted to N2 at a medium-low temperature (675 °C) owing to instantaneous oxygen removal from the NO decomposition reaction system. Coupled POM reaction on the other side of BBCN hollow fiber membrane not only increased the driving force for oxygen permeation but also produced valuable products (syngas). This novel membrane reactor showed high NO removal capacity at comparatively low temperatures (675-700 °C), which is 100-200 °C lower than those of other membrane reactors reported in literature. In addition, even with the presence of a 2-5% oxygen concentration in NO stream, NO could still be completely decomposed to N2 via this catalytic BBCN membrane reactor. Evidently, the application of this novel catalytic membrane reactor could overcome the inhibition of oxygen present atmosphere for NO decomposition and achieve a remarkably high efficiency for NO removal.

Facile Synthesis of Multi‐Ni‐Core@Ni Phyllosilicate@CeO2 Shell Hollow Spheres with High Oxygen Vacancy Concentration for Dry Reforming of CH4

AbstractA great challenge for cheap and active Ni‐based catalysts to be utilized for CO2 (dry) reforming of methane (DRM) reaction is their high‐carbon‐deposition problem. Herein, we designed multi‐Ni‐core@Ni phyllosilicate@CeO2 (Ni@NiPhy@CeO2) shell hollow sphere catalysts using a facile precipitation method. Compared with Ni@NiPhy without CeO2 shell, Ni@NiPhy@CeO2 exhibits high carbon resistance for the DRM reaction at both high GHSV value of 1880 L g−1 cat h−1 at 700 °C and a low reaction temperature of 600 °C. In addition, they show high and stable CH4 and CO2 conversions of 72.8 % and 79.1 % respectively at 700 °C under normal GHSV value of 36 L g−1 cat h−1. The good catalytic performance of Ni@NiPhy@CeO2 can be attributed to their high sintering resistance of both Ni and CeO2 which yields a high concentration of oxygen vacancies thereby a high catalytic performance and carbon resistance for DRM reaction. The facile synthesis method in this work can easily be applied to design other core–shell hollow catalysts such as Ni–M (M=Mg, Co, Cu, and Fe) silicate@CeO2 according to specific applications.

Hollow Structure and Electron Promotion Effect of Mesoporous Pd/CeO2 Catalyst for Enhanced Catalytic Hydrogenation

AbstractA hollow structured CeO2 spheres supported metallic Pd catalyst (Pd/CeO2‐H) was designed and prepared by a glucose hydrothermal method and impregnation method. The CeO2‐H consisted of an inner hollow cavity and an outer shell on which a large number of mesopores were formed. The Pd/CeO2‐H hollow sphere catalyst, which presented abundant surface oxygen vacancies, was investigated for catalytic hydrogenations of styrene and nitrobenzene to produce ethylbenzene and aniline. Activity tests indicated that the mesoporous Pd/CeO2‐H hollow sphere catalyst exhibited striking catalytic activity, which was attributed to the spatial core–shell structure that provided more active sites and facilitated reactant diffusion as well as surface defects (oxygen vacancies), which were capable of transferring electrons to metallic Pd. All of these advances are beneficial to give a higher catalytic hydrogenation performance.

Enhanced activity and stability of Co3O4-decorated nitrogen-doped carbon hollow sphere catalysts for microbial fuel cells

The unique hollow sphere structure, co-synergistic effect as well as ample macro/mesoporous lead to the superior ORR catalysis performance and outstanding MFCs practicability ability of HCN-Co3O4, even comparable to that of commercial Pt/C in the MFCs.

Degradation of acid scarlet 3R with CuO/SiO2 hollow sphere catalyst

Silica-supported copper catalyst materials have been synthesized via an incipient wetness impregnation. The resulting samples were characterized using X-ray diffraction (XRD) and Scanning electron microscope (SEM). The heterogeneous Fenton-like oxidation of reactive azo dye solutions by this catalyst was also investigated. The effects of various operating conditions on decolorization performance were evaluated, namely hydrogen peroxide dosage, initial pH, catalyst loading and initial dye concentration. The results indicated that by using 34 mmol/L of H2O2 and 6.0 g L-1 of the catalyst at 60°C, pH 3.5, 97% of decolorization efficiency was achieved within 90 min. CuO/SiO2 hollow sphere is shown a promising catalyst for degradation of azo dye aqueous solution by Fenton-like processes.

Preparation of Ag‐Modified (B,P)‐Codoped TiO2 Hollow Spheres with Enhanced Photocatalytic Activity

AbstractA series of TiO2 hollow sphere catalysts with or without nonmetal (B,P) dopants and Ag‐modification were prepared through a sol–gel process with styrene–methyl methacrylate copolymer (PSMMA) microspheres as the template. The samples were characterized by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), laser Raman spectroscopy (LRS), and UV/Vis diffuse reflectance spectroscopy (UV/Vis DRS), and their photocatalytic activities were evaluated by degradation of methylene blue (MB). Both B and P dopants could narrow the band gap of the TiO2 catalyst, and the loaded Ag only played the role of photoelectron transmitter. The two effects of the nonmetal dopants and the loaded Ag improved the photocatalytic activity of the TiO2 hollow spheres. Moreover, the hollow sphere structure and oxygen vacancies were beneficial to photocatalysis. Among all the catalysts prepared, Ag‐modified (B,P)‐codoped TiO2 hollow spheres exhibited the highest photocatalytic activity.

Novel aluminosilicate hollow sphere as a catalyst support for methane decomposition to COx-free hydrogen production

Novel Ni and Co supported on aluminosilicate hollow sphere catalysts were investigated to decompose methane into CO and CO2 free hydrogen and carbon nanotube. The hollow sphere structure was prepared by reverse microemulsion method and then Ni and Co were loaded by the impregnation method. The fresh catalysts and deposited carbon were characterized by several microscopic and spectroscopic techniques. The catalytic results showed that the Co based catalyst exhibited higher activity and durability at longer reaction time, due to the higher number and distribution of metal sites. The hollow sphere structure of the support could protect the metal particles against aggregation during the catalytic reactions. Accordingly, higher metal dispersion, stabilization and catalytic performance were achieved. The formation of nickel silicate is the main reason for the lower decomposition activity of Ni based catalyst at longer reaction time. TEM and Raman spectroscopic data revealed that the Co-based catalyst produced a relatively uniform diameter of MWCNTs with higher crystallinity and graphitization degree compared to the Ni-based catalyst.

Filter and buffer-pot confinement effect of hollow sphere catalyst for promoted activity and enhanced selectivity

To efficiently utilize the catalyst active sites and simultaneously enhance target hydrocarbon selectivity in Fischer–Tropsch synthesis (FTS), herein, we demonstrate a promising Co–Al2O3 hollow-sphere catalyst prepared by a two-pot route including hydrothermal carbonization and wet impregnation. Benefiting by plentiful mesopores on the shell, reactants could access the cavity inside and the active sites on the inner surface for further FTS reaction. Compared with conventional solid catalyst, the hollow structure provided a “buffer-pot” effect, where feed gas and preliminary product from the shell could mix completely at a low flow rate. Heavy hydrocarbons were further confined, leading to enhanced formation of lighter C5–C11 components, which more readily escaped out through the mesoporous shell, which thus played a “filter” role. Additionally, increased acidity on the shell generated more iso-paraffins and olefins in the final product. This concept displayed a great superiority in improving active metal activity and selective production from multiple products compared with conventional supported catalysts.

Ni-doped TiO2 hollow spheres as electrocatalysts in water electrolysis for hydrogen and oxygen production

This work represented the electrocatalytic properties of Ni-doped titania hollow sphere materials in hydrogen and oxygen evolution during water electrolysis from acidic media. Titania hollow sphere particles were synthesized using poly(styrene-methacrylic acid) latex as template material, and various amount of nickel were doped over the sphere using nickel (II) sulfate as the precursor of nickel. The presence of rutile TiO2 and NiO phases were revealed during XRD analysis, indicating the critical growth of nickel on the surface of the hollow sphere catalysts. BET surface area results also shown the 166.76 m2 g−1 value for 30 wt% Ni/TiO2 hollow sphere sample. The SEM and TEM images were confirmed the hollow sphere structure of the catalysts with diameter of 0.8–0.9 μm. The cyclic voltammetric studies proved the presence of both hydrogen and oxygen evolution peaks for all the hollow sphere samples. The anodic peak current density value, which usually represents the oxygen evolution phenomenon, was revealed as 13 mA cm−2 for 25 wt% Ni-loaded sample; whereas, the hydrogen evolution peak was most intense for 30 wt% Ni/TiO2 material with cathodic peak current density of 32 mA cm−2. The average value of −1.42 were determined as the reaction order of the system irrespective of the nickel loading and heating duration in the synthesis of hollow sphere materials. During photocatalytic water splitting, 30 wt% Ni/TiO2 hollow sphere sample yielded the highest amount of hydrogen in all irradiation time span.