Effects of Preparation Method on the Performance of Ni/Al2O3 Catalysts for Hydrogen Production by Bio-Oil Steam Reforming

Steam reforming of bio-oil derived from the fast pyrolysis of biomass is an economic and renewable process for hydrogen production. The main objective of the present work has been to investigate the effects of the preparation method of Ni/Al₂O₃ catalysts on their performance in hydrogen production by bio-oil steam reforming. The Ni/Al₂O₃ catalysts were prepared by impregnation, co-precipitation, and sol?Cgel methods. XRD, XPS, H₂-TPR, SEM, TEM, TG, and N₂ physisorption measurements were performed to characterize the texture and structure of the catalysts obtained after calcination and after their subsequent use. Ethanol and bio-oil model compound were selected for steam reforming to evaluate the catalyst performance. The catalyst prepared by the co-precipitation method was found to display better performance than the other two. Under the optimized reaction conditions, an ethanol conversion of 99% and a H₂ yield of 88% were obtained.     

Production of Hydrogen from Methane by a CO2 Emission-Suppressed Process: Methane Decomposition and Gasification of Carbon Nanofibers

Catalytic methane decomposition into hydrogen and carbon nanofibers and the oxidations of carbon nanofibers with CO₂, H₂O and O₂ were overviewed. Supported Ni catalysts (Ni/SiO₂, Ni/TiO₂ and Ni/carbon nanofiber) were effective for the methane decomposition. The activity and life of the supported Ni catalysts for methane decomposition strongly depended on the particle size of Ni metal on the catalysts. The modification of the catalysts with Pd enhanced the catalytic activity and life for methane decomposition. In particular, the supported Ni catalysts modified with Pd showed high turnover number of hydrogen formation at temperatures higher than 973 K with a high one-pass methane conversion (>70%). However, sooner or later, every catalyst completely lost their catalytic activities due to the carbon layer formation on active metal surfaces. In order to utilize a large quantity of the carbon nanofibers formed during methane decomposition as a chemical feedstock or a powdered fuel for heat generation, they were oxidized with CO₂, H₂O and O₂ into CO, synthesis gas and CO₂, respectively. In every case, the conversion of carbon was greater than 95%. These oxidations of carbon nanofibers recovered or enhanced the initial activities of the supported Ni catalysts for methane decomposition.     

Nickel hydrogen gas batteries: From aerospace to grid-scale energy storage applications

The challenging requirements of high safety, low-cost, all-climate and long lifespan restrict most battery technologies for grid-scale energy storage. Historically, owing to stable electrode reactions and robust battery chemistry, aqueous nickel–hydrogen gas (Ni–H₂) batteries with outstanding durability and safety have been served in aerospace and satellite systems for over three decades ever since their first development in the 1970s. Despite their satisfactory performances, this technology has difficulty to be applied for grid-scale energy storage primarily because of their high cost resulting from the utilization of expensive platinum as anode hydrogen catalyst. In recent years, with the extensive exploration of inexpensive hydrogen evolution/oxidation reaction catalysts, advanced Ni–H₂ batteries have been revived as promising battery chemistry for grid-scale energy storage applications. This mini-review provides an overview of the development activities of Ni–H₂ batteries and highlights the recent advances in the application of advanced Ni–H₂ batteries for grid-scale energy storage. New cost-effective hydrogen evolution/oxidation reactions catalysts, novel cathode materials, and advanced Ni–H₂ battery designs toward further development of Ni–H₂ batteries are discussed. The renaissance of advanced Ni–H₂ battery technology is particularly attractive for future grid-scale energy storage applications.     

Ru/Ni/MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> catalysts for steam reforming of methane: effects of Ru content on self-activation property

The effects of Ru on the self-reducibility of Ru-doped Ni/MgAl₂O₄ catalysts, which do not need pre-reduction treatment with H₂, were investigated in the steam reforming of methane (SRM). The Ru-promoted Ni/MgAl₂O₄ catalysts with various amounts of Ru (0–0.5 wt%) were prepared by stepwise impregnation and co-impregnation methods using hydrotalcite-like MgAl₂O₄ support. For comparison, Ru/MgAl₂O₄ catalysts with the same amount of Ru were also prepared by the impregnation method. The catalysts were characterized by the N₂-sorption, XRD, H₂-TPR, H₂-chemisorption, and XPS methods. Ni/MgAl₂O₄ catalyst in the presence of even the trace amount of Ru (Ru content ≥0.05 wt%) showed higher conversion without pre-reduction as compared to Ru/MgAl₂O₄ catalysts in SRM under the same conditions. The self-activation of Ru–Ni/MgAl₂O₄ catalysts is mainly attributed to the spillover of hydrogen, which is produced on Ru at first and then reduces NiO species under reaction conditions. Besides, Ru doping makes the reduction of NiO easier. The stepwise impregnated Ru/Ni/MgAl₂O₄ catalyst produced superior performance as compared to co-impregnated Ru–Ni/MgAl₂O₄ catalyst for SRM.     

Fast-Response Nickel-Promoted Indium Oxide Catalysts for Carbon Dioxide Hydrogenation from Intermittent Solar Hydrogen

Construction of a “net-zero-emission” system through CO₂ hydrogenation to methanol with solar energy is an eco-friendly way to mitigate the greenhouse effect. Traditional CO₂ hydrogenation demands centralized mass production for cost reduction with mass water electrolysis for hydrogen supply. To achieve continuous reaction with intermittent and fluctuating flow of H₂ on a small-scale for distributed application scenarios, modulating the catalyst interface environment and chemical adsorption capacity to adapt fluctuating reaction conditions is highly desired. This paper describes a distributed clean CO₂ utilization system in which the surface structure of catalysts is carefully regulated. The Ni catalyst with unsaturated electrons loaded on In₂O₃ can reduce the dissociation energy of H₂ to overcome the slow response of intermittent H₂ supply, exhibiting a faster response (12 min) than bare oxide catalysts (42 min). Moreover, the introduction of Ni enhances the sensitivity of the catalyst to hydrogen, yielding a Ni/In₂O₃ catalyst with a good performance at lower H₂ concentrations with a 15 times adaptability for wider hydrogen fluctuation range than In₂O₃, greatly reducing the negative impact of unstable H₂ supplies derived from renewable energies.     

Selective hydrogenation of 1,3-pentadiene over mono- and bimetallic sulfidized Ni(Cu)—S/SiO<Subscript>2</Subscript> catalysts

The activity and selectivity of the Ni/SiO₂ catalyst, as well as the mono- and bimetallic Ni(Cu)—S/SiO₂ systems were investigated in the selective hydrogenation of 1,3-pentadiene to pentenes. The presulfiding of the catalysts in a hydrogen sulfide flow substantially increases the selectivity to olefins in gas mixtures with a range of H₂/diene molar ratio of 2.5–10. The samples activated in hydrogen at elevated temperatures turned out to be more active. The effect of modification of the nickel—sulfide catalysts with copper, resulting in an increase in the activity and selectivity to olefins, was found. The weight ratio Ni/Cu = 4 was shown to be optimum for achieving the maximum conversion and selectivity on the surface.     

Oxidative addition of dihydrogen as the key step of the active center formation in the HDS sulfide bimetallic catalysts: ab initio MO/MP2 study

The electronic structure of Ni in the sulfide bimetallic species (SBMS), which is the active component of the sulfide HDS catalysts, is studied with the ab initio molecular orbital calculations. In the previous paper [I.I. Zakharov, A.N. Startsev, G.M. Zhidomirov, J. Mol. Catal. 119 (1997) 437], we have shown that the d⁸ Ni(II) electronic state in the SBMS composition cannot be active in HDS reaction because of the lack of possibility to coordinate S-containing molecule. Therefore, this paper deals with the study of the possibility to stabilize d⁶ electron configuration with the formal Ni(IV) oxidation state. With this in mind, the reaction of oxidative addition of dihydrogen to square–planar complex Ni(II)Cl₂(PH₃)₂ has been studied, which allowed to predict a stabilization of the octahedral complex Ni(IV)H₂Cl₂(PH₃)₂ with d⁶ configuration. This allows us to assume a possibility of an oxidative adsorption of dihydrogen to the Ni atom entering the SBMS composition. Ab initio calculations have shown that such type of oxidative addition is thermodynamically favorable resulting in stabilization of the Ni(IV) d⁶ electronic state. Consequently, the dihydrogen molecule is assumed to dissociate on the Ni atom resulting in the formation of `surface' H<sub>s</sub> and `occluded' H_o hydrogen, which is located under the Ni atom in the center of the trigonal sulfur prism. The structure of the active centers is optimized and the stretching modes of the hydrogen atoms are calculated, which appear to be close to the literature data. The H₂S adsorption on the active center was also investigated and it was shown that the hydrogen disulfide molecule benefits to stabilization of the active Ni(IV) d⁶ state. The conclusion is drawn that the deciding factor in the formation of the active centers of sulfide HDS catalysts is the `occluded' hydrogen.     

Development of Methane Decomposition Catalysts for CO<Subscript>x</Subscript> Free Hydrogen

Now-a-days, catalytic decomposition of methane (CDM) into hydrogen and carbon is a promising technique for production of fuel cell grade hydrogen. The Ni based catalysts seems promising particularly for the production of CO_x free H₂ by methane decomposition process. The CDM activity and longevity of the Ni based catalysts are mainly influenced by the amount of Ni and type of support material. In this paper the CDM activity results are correlated with NiO crystallite size, Ni metal surface area and acidity of the catalysts. In case of bimetallic catalysts addition of Cu to Ni catalysts lead to enhance the CDM activity at higher temperature thus resulting in the increased concentration of hydrogen in the outlet stream. Finally, some of the carbon-based catalysts are studied for methane decomposition activity at higher temperature. The surface changes over carbon catalysts with methane decomposition are studied using various characterization techniques.     

Ni-based olivine-type catalysts and their application in hydrogen production via auto-thermal reforming of acetic acid

Olivine is abundant in the Earth’s upper mantle; it has applications in catalysts to enhance their stability in structures. The olivine-type catalysts were prepared by co-precipitation and hydrothermal synthesis and tested in the auto-thermal reforming (ATR) of acetic acid (AC), a model compound from bio-oil, for hydrogen production. In the meantime, the natural olivine impregnated with Ni was also tested. Characterisations of XRD, nitrogen physisorption, temperature-programmed reduction, and SEM-EDX were used to find the structure-reactivity relationship. The results indicate that the natural olivine produced a low H₂ yield close to 0.17 mole of H₂ per 1 mole of AC, while the olivine impregnated with Ni produced a H₂ yield of from 2.19 mole to 2.73 mole of H₂ per mole of AC. The olivine catalyst prepared by hydrothermal synthesis performed better in both activity and stability: the H₂ yield achieved 3.06 mole of H₂ per mole of AC and remained stable, which could be attributed to the higher surface area and stability with Ni inserted in the skeleton of olivine.     

The influence of plasma chemical treatment of nickel and nickel-rhenium catalysts deposited on sibunite on their activity in dehydrogenation

The dehydrogenation of isopropanol was studied at 440–680 K to find that the activity of the Ni(1 wt %)/sibunite catalyst decreased after annealings and quenchings and was stabilized after subsequent treatment with an (I) O₂ glow-discharge or (II) H₂ high-frequency plasma. Treatments of both kinds decreased the activity of the catalyst below the Curie point (633 K) and increased it over the paramagnetic temperature range (635–680 K). The treatment of the (1 wt % Ni–1 wt %Re)/sibunite and (2 wt % Ni–2 wt % Re)/sibunite catalysts with plasma II weakly influenced their activity, whereas treatment with plasma I substantially increased it. The kinetic reaction parameters on the (2 wt % Ni–2 wt % Re)/sibunite catalyst were found to depend on the duration of treatment with plasma II. Treatment with plasma I much more effectively changed the state of the surface of all the catalysts studied than treatment with plasma II.     

Study of catalytic hydrodeoxygenation performance for the Ni/KIT-6 catalysts

Ni/KIT-6 catalysts loaded with different amounts of metallic Ni were prepared by impregnation method. The prepared catalysts and their precursors were investigated through wide- and low-angle XRD, TEM, BET, H₂-TPR, and H₂-TPD analyzes. The catalytic hydrodeoxygenation performance of the catalysts was evaluated using ethyl acetate as a model bio oil compound. Results indicate that the catalytic hydrodeoxygenation performance of the prepared catalysts was directly related to hydrogen storage properties, hydrogen desorption properties, dispersion of the active component Ni, and so on. The ethyl acetate conversion and ethane selectivity of 25?wt% Ni/KIT-6 catalyst were 100 and 96.8%, respectively, at 300?°C, which shows the best performance. The hydrodeoxygenation activity of ethyl acetate was higher than that of methyl acetate and isopropyl acetate because of the effect of molecular polarity and size. And, this reaction is a structure sensitive reaction.     

Catalytic amination of 2,6-dimethylphenol to 2,6-dimethylaniline over Ni–Cu–Cr/γ-Al2O3

A series of transition metal-based catalysts, other than Pd or Pt-based catalysts, were investigated for catalytic amination of 2,6-dimethylphenol to 2,6-dimethylaniline in a fixed-bed reactor. Ni–Cu–Cr/γ-Al₂O₃ yielded satisfactory results with 82.08 % conversion and 47.24 % selectivity. The catalysts were characterized by H₂-TPR and TEM, and the results obtained showed that the doped Cu and Cr could promote reduction of Ni/γ–Al₂O₃ and dispersion of the Ni. Reaction conditions, including reaction temperature, flow rate of hydrogen, and ammonia, were studied.     

Low-Temperature Direct Electrochemical Methanol Reforming Enabled by CO-Immune Mo-Based Hydrogen Evolution Catalysts

Hydrogen storage in the form of intermediate artificial fuels such as methanol is important for future chemical and energy applications, and the electrochemical regeneration of hydrogen from methanol is thermodynamically favorable compared to direct water splitting. However, CO produced from methanol oxidation can adsorb to H₂-evolution catalysts and drastically reduce activity. In this study, we explore the origins of CO immunity in Mo-containing H₂-evolution catalysts. Unlike conventional catalysts such as Pt or Ni, Mo-based catalysts display remarkable immunity to CO poisoning. The origin of this behavior in NiMo appears to arise from the apparent inability of CO to bind Mo under electrocatalytic conditions, with mechanistic consequences for the H₂-evolution reaction (HER) in these systems. This specific property of Mo-based HER catalysts makes them ideal in environments where poisons might be present.     

Complete and Rapid Conversion of Hydrazine Monohydrate to Hydrogen over Supported Ni–Pt Nanoparticles on Mesoporous Ceria for Chemical Hydrogen Storage

The development of active, selective, and robust catalysts is a key issue in promoting the practical application of hydrazine monohydrate (N₂H₄ ? H₂O) as a viable hydrogen carrier. Herein, the synthesis of a supported Ni–Pt bimetallic nanocatalyst on mesoporous ceria by a one‐pot evaporation‐induced self‐assembly method is reported. The catalyst exhibits exceptionally high catalytic activity, 100 % selectivity, and satisfactory stability in promoting H₂ generation from an alkaline solution of N₂H₄ ? H₂O at moderate temperatures. For example, the Ni₆₀Pt₄₀/CeO₂ catalyst enabled complete decomposition of N₂H₄ ? H₂O to generate H₂ at a rate of 293 h^?1 at 30 °C in the presence of 2 M NaOH, which compares favorably with the reported N₂H₄ ? H₂O decomposition catalysts. Phase/structural analysis by XRD, TEM, and Auger electron spectroscopy was conducted to gain insight into the excellent catalytic performance of the Ni–Pt/CeO₂ catalyst.     

Hydrogen production from simulated hot coke oven gas by catalytic reforming over Ni/Mg（Al）O catalysts

Hydrogen production by catalytic reforming of simulated hot coke oven gas (HCOG) with toluene as a model tar compound was investigated in a fixed bed reactor over Ni/Mg(Al)O catalysts. The catalysts were prepared by a homogeneous precipitation method using urea hydrolysis and characterized by ICP, BET, XRD, TPR, TEM and TG. XRD showed that the hydrotalcite type precursor after calcination formed (Ni, Mg)Al₂O₄ spinel and Ni-Mg-O solid solution structure. TPR results suggested that the increase in Ni/Mg molar ratio gave rise to the decrease in the reduction temperature of Ni²⁺ to Ni⁰ on Ni/Mg(Al)O catalysts. The reaction results indicated that toluene and CH₄ could completely be converted to H₂ and CO in the catalytic reforming of the simulated HCOG under atmospheric pressure and the amount of H₂ in the reaction effluent gas was about 4 times more than that in original HCOG. The catalysts with lower Ni/Mg molar ratio showed better catalytic activity and resistance to coking, which may become promising catalysts in the catalytic reforming of HCOG.     

SiO2气凝胶负载的Ni催化剂在甲烷部分氧化制合成气反应中的催化性能及稳定性

以常压有机溶剂置换(A)和溶剂置换-表面改性(B)方式制备的两种SiO₂气凝胶(SiO₂-A(或B)型气凝胶,记为SiO₂-A(or B)G)为载体, 采用常规浸渍法和聚乙烯吡咯烷酮(PVP)添加浸渍法合成不同SiO₂气凝胶负载的Ni/SiO₂催化剂, 并考察其催化的甲烷部分氧化(POM)制合成气的反应性能. 结果表明, 各催化剂的初始反应性能相近, 但Ni/SiO₂-BG的POM稳定性明显较Ni/SiO₂-AG的差, 而PVP添加制备的催化剂稳定性则获明显改善, Ni/SiO₂-AG-PVP、Ni/SiO₂-BG-PVP上POM稳定性相近. 结合X射线衍射(XRD)、程序升温还原反应(H₂-TPR)、高分辨透射电镜(TEM)和Brunauer-Emmett-Teller (BET)等表征结果的分析发现: (1) SiO₂-AG表面上存在一定量的羟基, 可促进亲水性金属物种与其的相互作用, 而SiO₂-BG表面上基本为有机基团, 与亲水性金属物种几乎无作用; (2) PVP的存在可使金属物种进入亲/疏水载体孔道深处, 抑制焙烧中载体骨架的收缩和金属颗粒的生长, 进而促进金属-载体的相互作用. 这二者均能有效地提高催化剂的POM反应稳定性.     

Combined hydrogenation of carbon oxides on catalysts bearing iron and nickel nanoparticles

The reaction of the hydrogenation of a mixture of carbon oxides on ultradisperse powder (UDP) catalysts containing Fe and Ni nanoparticles and their bimetallic mechanical mixtures was investigated. It was established that the main reaction product on UDP Ni is methane, while the main products on the bimetallic systems are methane and ethylene. A synergetic effect was observed on the bimetallic catalyst under investigation. It was revealed that the hydrogenation of a mixture of carbon oxides proceeds through the stage of dissociative adsorption of both components, CO and CO₂. The olefin selectivity of the process was explained by the participation of different forms of adsorbed hydrogen (H_I: H_II) at the catalyst surface. It is assumed that the hydrogenation of carbon oxides on iron-nickel catalysts proceeds either through the jumpover effect or via hydrogen spillover.     

负载Ni催化剂用于乙二醇蒸汽重整制氢催化性能研究

采用等体积浸渍法和共沉淀法制备了Ni催化剂,在固定床反应器上考察了Ni负载量、焙烧温度、反应温度等因素对乙二醇低温重整制氢反应活性和选择性的影响。应用X射线衍射、氮物理吸附、H₂程序升温还原等技术对负载型Ni催化剂进行了表征。结果表明,共沉淀法制备的Ni/CeO₂催化剂具有较小的NiO颗粒与CeO₂载体颗粒粒径,催化活性较高。添加少量氧化钴到Ni/CeO₂催化剂中可使H₂收率达72.6%,EG转化率达93.1%。在CeO₂中添加Al₂O₃能提高负载Ni催化剂的活性,乙二醇转化率达94.0%,H₂收率达67.0%;但添加SiO₂则使其活性明显变差。     

Interfacial Engineering of Ni/V2O3 Heterostructure Catalyst for Boosting Hydrogen Oxidation Reaction in Alkaline Electrolytes

Alkaline fuel cells can permit the adoption of platinum group metal-free (PGM-free) catalysts and cheap bipolar plates, thus further lowering the cost. With the exploration of PGM-free hydrogen oxidation reaction (HOR) catalysts, nickel-based compounds have been considered as the most promising HOR catalysts in alkali. Here we report an interfacial engineering through the formation of nickel-vanadium oxide (Ni/V₂O₃) heterostructures to activate Ni for efficient HOR catalysis in alkali. The strong electron transfer from Ni to V₂O₃ could modulate the electronic structure of Ni sites. The optimal Ni/V₂O₃ catalyst exhibits a high intrinsic activity of 0.038 mA cm⁻² and outstanding stability. Experimental and theoretical studies reveal that Ni/V₂O₃ interface as the active sites can enable to optimize the hydrogen and hydroxyl bindings, as well as protect metallic Ni from extensive oxidation, thus achieving the notable activity and durability.     

Metal Effect Meets Volcano Plots: A DFT Study on Tris(phosphino)borane-Transition Metal Complexes Catalyzed H2 Activation

Bifunctional transition metal complexes are of particular interest in metal-ligand cooperative activation of small molecules. As a novel type of bifunctional catalyst, Lewis acid transition metal (LA-TM) complexes have attracted increasing interest in hydrogen activation and storage. To advance the catalyst design, herein the metal effect of LA-TM complexes on the hydrogen activation has been systematically studied with a series of tris(phosphino)borane (TPB) complexes with V, Cr, Mn, Fe, Co, and Ni as metal centers. The metal effect not only influences the mechanism of hydrogen activation, but also notably casts a volcano plot for the activity. TPB complexes of V, Cr, Mn, Fe, and Co tend to activate H₂ through a stepwise mechanism, while TPB-Ni prefers a synergetic mechanism for H₂ activation. More importantly, the metal effect significantly influences the activity of H₂ activation and the formation of the LA-H-TM bridging hydride. The trend of changes in the LA-H-TM structures, the second-order perturbation stabilization energies, and the Laplacian bond orders, along with different metals (from V to Ni), are all interestingly constitute volcano plots for the performance of TPB-TM complexes catalyzed H₂ activation. TPB-Mn and TPB-Fe are found to be the optimal catalysts among the discussed TPB-TM complexes. The volcano plots disclosed for the metal effects should be informative and instructive for homogeneous and heterogeneous LA-TM catalysts development.