Co-SiO2 nanosphere-catalyzed hydrolytic dehydrogenation of ammonia borane for chemical hydrogen storage

Cobalt clusters-silica nanospheres (15-30 nm) were synthesized using a Co(NH₃)₆Cl₃ template method in a polyoxyethylene-nonylphenyl ether/cyclohexane reversed micelle system followed by in situ reduction in aqueous NaBH₄/NH₃BH₃ solutions. The cobalt clusters are located either inside or on the outer surface of the silica nanospheres as shown by the transmission electron microscope (TEM)/energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) measurements. The cobalt-silica nanospheres have a high catalytic activity for the hydrolysis of ammonia borane that generates a stoichiometric amount of hydrogen, and can be efficiently cycled and reused 10 times without any significant loss of the catalytic activity.     

Carbon nanotubes supported PtPd hollow nanospheres for formic acid electrooxidation

Carbon nanotubes (CNTs) supported PtPd hollow nanospheres have been prepared by a replacement reaction between sacrificial cobalt nanoparticles and PtCl₆²⁻, Pd²⁺ ions. The morphology, elemental composition, structure and electrocatalytic properties of the PtPd hollow nanospheres have been investigated by transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and typical electrochemical methods, respectively. The results indicate that the CNTs supported PtPd hollow nanospheres have excellent electrochemical properties for the electrooxidation of formic acid (high electrocatalytic activity and excellent stability) due to the high surface area resulted from the hollow nanosphere structure with porous shell.     

Carbon supported Pt hollow nanospheres as anode catalysts for direct borohydride-hydrogen peroxide fuel cells

The carbon supported Pt hollow nanospheres were prepared by employing cobalt nanoparticles as sacrificial templates at room temperature in aqueous solution and used as the anode electrocatalyst for direct borohydride-hydrogen peroxide fuel cell (DBHFC). The physical and electrochemical properties of the as-prepared electrocatalysts were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), cyclic voltammetry (CV), chronoamperometry (CA), chronopotentiometry (CP) and fuel cell test. The results showed that the carbon supported Pt nanospheres were coreless and composed of discrete Pt nanoparticles with the crystallite size of about 2.8 nm. Besides, it has been found that the carbon supported Pt hollow nanospheres exhibited an enhanced electrocatalytic performance for BH₄⁻ oxidation compared with the carbon supported solid Pt nanoparticles, and the DBHFC using the carbon supported Pt hollow nanospheres as electrocatalyst showed as high as 54.53 mW cm⁻² power density at a discharge current density of 44.9 mA cm⁻².     

CO2 hydrogenation over differently morphological CeO2‐supported Cu‐Ni catalysts

Differently morphological CeO₂‐supported Cu‐Ni catalysts utilized for carbon dioxide hydrogenation to methanol were prepared by the method of impregnation. The 100‐ to 300‐nm CeO₂ nanorod‐supported catalyst dominantly exposed low‐energy (100) and (110) facets, and the Cu‐Ni supported on 10‐ to 20‐nm CeO₂ nanospheres and on irregular CeO₂ nanoparticles were both enclosed by (111) facets owning high energy. Besides, all CeO₂‐supported Cu‐Ni catalysts possess oxygen vacancies, which can active and absorb CO₂ and is further beneficial for the reaction. Most oxygen vacancies were generated from the Ce⁴⁺ reduction to Ce³⁺ with the ceria lattice cell expansion, and small amount of oxygen vacancies resulted from the Ce⁴⁺ replacement by Cu or/and Ni atom. Because of the exposed (100) and (110) facets and numerous oxygen vacancies, well‐defined CeO₂ nanorod‐supported Cu‐Ni alloy showed more superior catalytic performance than on CeO₂ nanospheres and nanoparticles.     

Ni/Al2O3 catalysts for CO2 methanation: Effect of silica and nickel loading

Samples containing from 1 to 33 wt.% of NiO on silica and alumina doped with silica (1 and 20 wt.% silica in the support) have been prepared and characterized by BET, XRD, FT-IR, UV–vis–NIR, FE-SEM, EDXS, and TPR techniques. Catalysts have been pre-reduced in situ before catalytic experiments and data have been compared with Ni/Al₂O₃ reference sample. Characterization results showed that SiO₂ support has a low Ni dispersion ability mainly producing segregated NiO particles and a small amount of dispersed Ni²⁺ in exchange sites. Instead, for the Si-doped alumina a “surface spinel monolayer phase” is formed by increasing Ni loading and, only when the support surface is completely covered by this layer, NiO is formed. Moreover, H₂-TPR results indicated that NiO particles are more easily reduced compared to Ni species. Low loading Ni/SiO₂ catalysts show high selectivity and moderate activity for RWGS (reverse Water Gas Shift) reaction, likely mainly due to nickel species dispersed in silica exchange sites, as evidenced by visible spectroscopy. High loading Ni/SiO₂ catalysts show both methanation and RWGS but evident short-term deactivation for methanation, attributed to large, segregated Ni metal particles, covered by a carbon veil. Ni on alumina -rich carriers, where nickel disperses forming a surface spinel phase, show high activity and selectivity for methanation, and short-term catalyst stability as well. This activity is attributed to small nickel clusters or metal particles interacting with alumina, formed upon reaction. The addition of SiO₂ in Al₂O₃ support decreases the activity of Ni catalysts in CO₂ methanation, because it reduces the ability of the support to disperse nickel in form of the surface spinel phase, thus reducing the amount of Ni clusters in the reduced catalysts.     

Dehydrogenation mechanisms of ammonia borane catalyzed by Pd atoms adsorbed on an MgO(100) surface

The dehydrogenation of ammonia borane (BH₃NH₃) catalyzed by Pd supported on an MgO(100) surface was investigated using the DFT/UB3LYP method and an embedded cluster model. We found that BH₃NH₃ molecules can be initially adsorbed on 2-Pd atom clusters on the MgO surface (Pd₂/MgO) in two different configurations, and on 4-Pd atom clusters (Pd₄/MgO) in one configuration. One of the two BH₃NH₃–Pd₂/MgO configurations can dehydrogenate in a concerted pathway with a forward free energy barrier of 16.5 kcal/mol, and the other in a stepwise mechanism with forward barriers of 11.1 and 9.4 kcal/mol, respectively. However, only a stepwise dehydrogenation pathway was found for the single BH₃NH₃–Pd₄/MgO configuration, with a rate-controlling barrier of 12.6 kcal/mol. These results suggest that the BH₃NH₃ dehydrogenation mechanism and reaction barrier height can change with the size of the Pd clusters on the MgO(100) surface.     

The dispersed SiO2 microspheres supported Ru catalyst with enhanced activity for ammonia decomposition

Ru nanoparticles supported on SiO₂ microspheres (Ru/SiO₂-GUS) were prepared by the glucose-urea-metallic salt method and applied in the decomposition of ammonia. In the glucose-urea-metallic salt method, glucose as the carbon template plays a significant role in the formation of diffusion-beneficial structural properties of Ru/SiO₂-GUS, and also induceds the modification of the electronic state of Ru. Ru/SiO₂-GUS exhibited higher catalytic activity compared with the catalyst prepared with the impregnation method. The catalytic performance of Ru/SiO₂-GUS was further enhanced with the addition of either K or Cs——the addition order and amount strongly affecting the catalytic performance. When the ratio of K/Cs to Ru is 2, the alkali metal (KOH/CsOH) solution is added in the homogeneous solution of glucose, urea, RuCl₃ and the colloidal silica, the promotion effect of K/Cs is the strongest, particularly under lower reaction temperatures. However, the promotion effects of K and Cs are different as reveled by the combined results of H₂-TPR, XPS and NH₃-TPSR. More NH₃ can be absorbed on K–Ru/SiO₂-GUS and the electron density of Ru decreased. By contrast, more metallic Ru formed on Cs–Ru/SiO₂-GUS, facilitating N₂ recombination.     

Enhanced catalytic activity of methane dry reforming by the confinement of Ni nanoparticles into mesoporous silica

Nickel nanoparticles were immobilized in mesoporous silica by a polyethyleneimine (PEI)-aided route and their catalytic performance was evaluated in dry reforming of methane. NH₂ terminal groups of PEI strongly interacted with surface silanol groups of mesoporous silica and then, Ni-chelating PEIs were highly dispersed inside its ordered channel. The steric hindrance of PEI with a long hydrocarbon chain also restricted the aggregation of Ni-PEI complexes anchored in the porous framework. The catalysts prepared by the PEI-aided route showed the stable activity at 750 °C for 40 h because Ni particles were confined inside the pore and therefore, cannot be sintered more than the pore diameter of their parent support. The carbon deposit is much smaller in the catalyst prepared by the PEI-aided route than the reference catalyst synthesized via a traditional impregnation method, suggesting that the sintering of Ni particles is a main contribution to the generation of graphitic carbon.     

Non-noble metallic nanoparticles supported on titania spheres as catalysts for hydrogen generation from hydrolysis of ammonia borane under ultraviolet light irradiation

Herein, a report on non-noble metal (Ni, Co, Cu, and their combination) nanoparticles (NPs) supported on TiO₂ spheres as catalysts for hydrogen generation via hydrolysis of ammonia borane (NH₃BH₃, AB) is provided. The TiO₂ spheres were prepared through a template method by using polystyrene (PS). The metallic nanoparticles were synthesized by a redox replacement reaction. The structure, morphology, and chemical composition of the obtained samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) equipped with energy dispersive X-ray spectroscopy (EDX), and X-ray Photoelectron Spectroscopy (XPS). The characterization results showed that the metallic nanoparticles were well dispersed on the TiO₂ supports. The catalytic activity toward the hydrolysis of AB was found to correlate well with the amount of metallic elements in catalysts while for the multicomponent phases, a synergistic effect was noticed. Theoretical calculations revealed that Ni, Co, and Cu atoms significantly influenced the electronic behavior of TiO₂ and thereby, the catalytic properties of the materials.     

Carbon dioxide reforming of methane over nickel catalysts supported on TiO2(001) nanosheets

As we all know, the critical problem of nickel catalysts for carbon dioxide reforming of methane is the deactivation of catalysts due to the carbon deposition and sintering of the active components under high temperature. It was reported that anatase TiO₂ nanosheets with high-energy (001) facets had strong interaction with nickel, which was probably beneficial to resist sintering of nickel nanoparticles and to eliminate deposited carbon via oxygen migration. In this study, Ni nanoparticles were supported on TiO2 nanosheets with exposed high-energy (001) facets. The Ni/TiO₂(001) catalysts were characterized by means of X-ray diffraction, transmission electron microscopy, physisorption of N₂, X-ray photoelectron spectroscopy and H₂ temperature-programmed reduction, and the spent catalysts were characterized by Roman and thermogravimetry analysis. The catalytic performance of Ni/TiO₂(001) catalysts were measured for carbon dioxide reforming of methane reaction. It was found that the prepared Ni/TiO₂(001) catalysts showed reasonably higher catalytic activity and stability compared with the nickel catalyst supported on commercial titanium oxide (P25). The high dispersion of nickel nanoparticles of Ni/TiO₂(001) catalysts was helpful to the resistance towards carbon deposition and the strong metal-support interaction was helpful to the resistance towards nickel sintering on account of the unusual surface properties of TiO₂(001).     

Enhanced methanol oxidation on PtNi nanoparticles supported on silane-modified reduced graphene oxide

Developing low cost, highly efficient, and long-term stability electrocatalysts are critical for direct oxidation methanol fuel cell. Despite huge efforts, designing low-cost electrocatalysts with high activity and long-term durability remains a significant technical challenge. Here, we prepared a new kind of platinum-nickel catalyst supported on silane-modified graphene oxide (NH₂-rGO) by a two-step method at room temperature. Powder X-ray diffraction, UV–vis spectroscopy, Raman, FTIR spectroscopy and X-ray photoelectron spectroscopy results confirm that GO was successfully modified with 3-aminopropyltriethoxysilane (APTES), which helps to uniformly disperse PtNi nanoparticles. Cyclic voltammetry, chronoamperometry, CO-stripping and rotating disk electrode (RDE) results imply that PtNi/NH₂-rGO catalyst has significantly higher catalytic activity, enhance the CO toxicity resistance, higher stability and much faster kinetics of methanol oxidation than commercial Pt/C under alkaline conditions.     

Effect of preparation method and reaction parameters on catalytic activity for ammonia synthesis

MgO–CeO₂ support was prepared by three different methods and impregnated by 1% Ru. These mixed oxides supported Ru catalysts were applied to ammonia (NH₃) synthesis. NH₃ synthesis activity was highly dependent on the H₂/N₂ ratio, temperature, pressure conditions, and physical characteristics of the catalysts. NH₃ synthesis increased using a higher H₂ concentration in reactant stream at a relatively higher temperature and pressure conditions, while lower H₂ concentration was suitable at lower temperatures. Likewise, the effect of increasing pressure was more dominant at a higher temperature for higher H₂ concentration. Physical characteristics of the catalysts strongly influenced NH₃ synthesis activity, which varied for different methods. Increased surface area, high dispersion of Ru and CeO₂, and preferential deposition of Ru on CeO₂ were responsible for higher NH₃ synthesis activity of the catalyst prepared from the co-precipitation method.     

Mesostructured cellular foam silica supported bimetallic LaNi1-xCoxO3 catalyst for CO2 methanation

To address the metal sintering problem over the transitional one-dimensional-channel materials supported metal catalyst at high loadings, the 3-dimensional mesostructured cellular foam silica (MCF) supported bimetallic LaNi_1–xCo_xO₃ perovskite catalyst was prepared via a citric acid assisted impregnation method for CO₂ methanation. Highly dispersed La₂O₃ and bimetallic Ni–Co alloy nanoparticles with size of around 5.1 nm were immobilized inside the pores of the MCF silica with intimate contact, resulting in high catalytic activity at low temperature and superior stability at high temperature for CO₂ methanation. Among all catalysts, the LaNi_0.95Co_0.05O₃/MCF catalyst exhibited the highest catalytic activity due to its smallest Ni–Co alloy nanoparticles as well as the synergistic effect between Ni and Co species. In addition, LaNi_0.95Co_0.05O₃/MCF catalyst also showed high long-term stability without Ni sintering in a 100 h-lifetime test, which was attributed to the confinement effect of the MCF support as well as the physical barrier of La₂O₃ species nearby metallic Ni nanoparticles.     

Preparation of nickel catalysts supported on CaO.2Al2O3 for methane reforming with carbon dioxide

Nanocrystalline calcium aluminate (CaO.2Al₂O₃) was prepared by a simple co-precipitation method using Poly (ethylene glycol)-block-poly(propylene glycol)-block poly(ethylene glycol) (PEG-PPG-PEG, MW:5800) as surfactant and employed as catalyst support for nickel catalysts in methane reforming with carbon dioxide. The prepared samples were characterized by X-ray diffraction (XRD), N₂ adsorption (BET), Temperature programmed reduction and oxidation (TPR-TPO) and Scanning electron microscopy (SEM) techniques. The results showed that the prepared support has a high potential as support for nickel catalysts in methane reforming with carbon dioxide. The results showed high catalytic activity and stability for the prepared catalysts. Among the prepared catalysts 15% Ni/CaO.2Al₂O₃ was the most active catalyst and showed the highest affinity for carbon formation. In addition, 7% Ni/CaO.2Al₂O₃ possessed high catalytic stability during 50 h time on stream. The TPO analysis revealed that increasing in nickel content increased the amount of deposited carbon over the spent catalysts. SEM results detected only whisker type of carbon for all spent catalysts.     

The effect of NH3·H2O addition in Ni/SBA-15 catalyst preparation on its performance for carbon dioxide reforming of methane to produce H2

Three kinds of Ni catalysts loaded on SBA-15 were prepared by impregnation method, adding NH₃·H₂O or C₂H₂O₄ in the impregnant, and applied to CO₂ reforming (DRM) of methane to generate hydrogen at 750 °C. The results showed that the catalyst prepared with NH₃·H₂O addition exhibited high activity and stability. TEM, H₂-TPR, XPS, XRD, and TG-MS characterization indicated that with addition of NH₃·H₂O (0.1 mol L^?1) in the preparation process, small nickel oxide particles, with average size of about 7 nm, were obtained on the catalyst, and the strong association between support and Ni species made them uniformly dispersed, enabling the capacity to resist carbon deposition and metal sintering, which contributed to the excellent activity, stability and selectivity for the DRM to H₂ production.     

Synthesis gas production in the combined CO2 reforming with partial oxidation of methane over Ce-promoted Ni/SiO2 catalysts

A series of nickel-based catalyst supported on silica (Ni/SiO₂) with different loading of Ce/Ni (molar ratio ranging from 0.17 to 0.84) were prepared using conventional co-impregnation method and were applied to synthesis gas production in the combination of CO₂ reforming with partial oxidation of methane. Among the cerium-containing catalysts, the cerium-rich ones exhibited the higher activity and stability than the cerium-low ones. The temperature-programmed reduction (TPR) and UV–vis diffuse reflectance spectroscopy (UV–vis DRS) analysis revealed that the addition of CeO₂ reduced the chemical interaction between Ni and support, resulting in an increase in reducibility and dispersion of Ni. Over NiCe-x/SiO₂ (x = 0.17, 0.50, 0.67, 0.84) catalysts, the reduction peak in TPR profiles shifted to the higher temperature with increasing Ce/Ni molar ratio, which was attributed to the smaller metallic nickel size of the reduced catalysts. The transmission electron microscopy (TEM) and X-ray diffraction (XRD) for the post-reaction catalysts confirmed that the promoter retained the metallic nickel species and prevented the metal particle growth at high reaction temperature. The NiCe-0.84/SiO₂ catalyst with small Ni particle size exhibited the stable activity with the constant H₂/CO molar ratio of 1.2 during 6-h reaction in the combination of CO₂ reforming with partial oxidation of methane at 850 °C and atmospheric pressure.     

Steam reforming of dimethyl ether over Cu–Ni/γ-Al2O3 bi-functional catalyst prepared by deposition–precipitation method

Cu–Ni/γ-Al₂O₃ catalysts with different metal contents for dimethyl ether steam reforming (DME SR) were prepared by the method of deposition–precipitation. Characterization of specific surface area measurement (BET), X-ray diffraction (XRD) and hydrogen temperature-programmed reduction (H₂-TPR) revealed that nickel improved the dispersion of copper, increased the interaction between copper and γ-Al₂O₃, and therefore, inhibited the sintering of copper. Ammonia temperature-programmed desorption (NH₃-TPD) showed that metal particles could occupy the acid sites, leading to the decrease in acid amount and acid strength of Cu–Ni/γ-Al₂O₃ catalyst. Kinetic measurements indicated that γ-Al₂O₃ is vital for DME SR and a higher content of γ-Al₂O₃ in catalyst was needed. The addition of nickel suppressed the water gas shift (WGS) reaction. Initial durability testing showed that the conversion of DME over Cu–Ni/γ-Al₂O₃ catalyst was always almost complete during the 30 h experimental reaction time. Therefore, Cu–Ni/γ-Al₂O₃ could be a potential DME SR catalyst for the production of hydrogen.     

Synthesis of highly active and stable Pd/C catalysts toward HCOOH dehydrogenation by a simple NH3 adsorption method

Pd catalysts supported on activated carbon (Pd/C–NH₃) toward HCOOH dehydrogenation were prepared by a simple adsorption method using ammonia (NH₃) and Ar as the working gas. The results show that the TOF_initial of Pd/C–NH₃ was 459.8 h⁻¹ at 50 °C. When the reaction was carried out for 4 h, the HCOOH dehydrogenation ratio over Pd/C–NH₃ was about 81.2%, which was 1.15 and 1.13 times, respectively, as that of the as-prepared Pd/C catalyst without any treatment (Pd/C–As) and the Pd/C catalyst purchased from Sigma-Aldrich (Pd/C-CM). The total amount of H₂ and CO₂ produced by using Pd/C–NH₃ to decompose HCOOH in the third cycle was 99.4% of the gas produced by the first reaction cycle, and 1.80 and 12.60 times, respectively, as that of Pd/C–As and Pd/C-CM. The characterization results indicated that the Pd active species in Pd/C–NH₃ migrated to the outer surface of the carbon support during the reaction, and the pore volume of the carbon support became larger, which were beneficial to the reaction. These factors made Pd/C–NH₃ exhibit excellent HCOOH dehydrogenation activity and stability. NH₃ adsorption is a simple and effective method for preparing high-performance Pd/C HCOOH dehydrogenation catalysts, and has important guiding significance for the preparation of other carbon supported noble metal catalysts.     

Effect of synthesis conditions on characteristics of the precursor material used in NiO·OH/Ni(OH)2 electrodes of alkaline batteries

The synthesis of nickel hydroxide occurs by many stages. When the precipitating reagent is NH₄OH solution, the precipitation of nickel hydroxide occurs between pH 8.0 and 8.6. For pH between 8.6 and 10.0, a soluble complex such as [Ni(NH₃)₆]²⁺ is formed. The precipitation of nickel hydroxide happens again after the pH equals 10.0. Finally, there occurs the ageing of α-Ni(OH)₂. A mixture of α-Ni(OH)₂ and β-Ni(OH)₂ phases is formed when the solid state reaction is not totally completed. One adsorbed layer becomes very hard with the exit of the water intercalated in the α-Ni(OH)₂. In presence of KOH solution occurs the formation and the ageing of α-Ni(OH)₂. Synthesis was characterized by the following techniques: X-ray diffraction, Fourier transform infrared spectroscopy (FT-IR), differential thermal analysis (DTA) and gravimetric thermal analysis (GTA), and specific surface area and UV–vis spectroscopy.     

Preparation and improvement of nickel catalyst supported ordered mesoporous spherical silica for thermocatalytic decomposition of methane

The thermocatalytic alteration of CH₄ into highly pure hydrogen and filaments of carbon was investigated on a series of Ni-catalysts with various contents (25, 40, 55, and 70 wt%) supported mesoporous spherical SiO₂. The silica with ordered structure and high specific surface area (1136 m²/g) was synthesized using the Stöber technique with TEOS as a silica precursor and CTAB as the template in a simple synthesis system of aqueous-phase. This technique led to the preparation of mesoporous spherical silica. The prepared samples were characterized using BET, TPR, XRD, TPO, and SEM analyses. The prepared catalysts with different nickel loading showed the BET surface area ranging from 225.0 to 725.7 m²/g. These results indicated that an increase in nickel content decreases the surface area and leads to a subsequent collapse of a pore structure. SEM analysis confirmed a spherical nanostructure of catalysts and revealed that with the increase in loading of Ni, the particle size enlarged, because of the agglomeration of the particles. The results implied that the high methane conversion of 54% obtained over the 55 wt% Ni/SiO₂ at 575 °C and this sample had higher stability at lower reaction temperature than the other prepared catalysts, slowly deactivation was observed for this catalyst at a period of 300 min of time on stream.