Nanocrystallites-forming hierarchical porous Ni/Al2O3–TiO2 catalyst for dehydrogenation of organic chemical hydrides

Dehydrogenation of organic chemical hydrides has been improved by reconstructing the catalyst in the form of hierarchical porous structure nanocatalyst, in which the economical Ni was adopted as catalytic component and nano Al₂O₃–TiO₂ hybrid composite as support. The Al₂O₃–TiO₂ composite was prepared by spontaneous self-assembly of nano Al₂O₃ and TiO₂ aggregates by hydrolysis of tetra-n-butyl-titanate under continuous agitation. The multi-scaled distribution of Al₂O₃–TiO₂ aggregates with hierarchy could be observed in dynamic light scattering spectrometer. The aggregates are comprised of nano-sized γ-Al₂O₃ and anatase TiO₂ crystallites with sizes of about 5 and 7 nm, respectively. The surface modulation by TiO₂ could be verified in FTIR Spectra. The migration of Ti species and crystallite growth were hindered by the Al₂O₃ skeleton and the hierarchical porous structure was sustained during the thermal related process. The multi-scaled distributed pores were confirmed by both TEM analysis and N₂ adsorption results. The results of dehydrogenation experiments showed that the hierarchical porous structure nano Ni/Al₂O₃–TiO₂ exhibited superior catalytic performance to Ni/Al₂O₃ with the optimum conversion of 99.9% at 400 °C, while the catalyst of Ni/Al₂O₃ exhibited only 16.5% under the same condition.     

Preparation and catalytic activity of PVP-protected Au/Ni bimetallic nanoparticles for hydrogen generation from hydrolysis of basic NaBH4 solution

Poly(N-vinyl-2-pyrrolidone)(PVP)-protected Au/Ni bimetallic nanoparticles (BNPs) were prepared in one-vessel via chemical reduction of the corresponding ions with dropwise addition of NaBH₄, and their catalytic activity in the hydrogen generation from hydrolysis of a basic NaBH₄ solution was examined. The structure, particle size, and chemical composition of the resultant BNPs were characterized by Ultraviolet–visible spectrophotometry (UV–Vis), X-ray photoelectron spectroscopy (XPS), Transmission electron microscopy (TEM) and High-resolution transmission electron microscopy (HR-TEM). The effects of processing parameters such as metal composition, metal ion concentration, and mole ratio of PVP to metal ion on the hydrolysis of a basic NaBH₄ solution were studied in detail. The results indicated that as-prepared Au/Ni BNPs showed a higher catalytic activity than corresponding monometallic NPs (MNPs) in the hydrogen generation from the hydrolysis reaction of a basic NaBH₄ solution. Among all the MNPs and BNPs, Au/Ni BNPs with the atomic ratio of 50/50 exhibited the highest catalytic activity, showing a hydrogen generation rate as high as 2597 mL-H₂ min⁻¹ g-catalyst⁻¹ at 30 °C, which can be ascribed to the presence of negatively charged Au atoms and positively charged Ni atoms. Based on the kinetic study of the hydrogen generation from the hydrolysis reaction of a basic NaBH₄ solution over the PVP-protected Au/Ni BNPs, the corresponding apparent activation energy was determined as 30.3 kJ/mol for the BNPs with the atomic ratio of 50/50.     

CO2 reforming of methane on Ni/γ-Al2O3 catalyst prepared by dielectric barrier discharge hydrogen plasma

Ni/γ-Al₂O₃ catalyst was prepared by direct treatment of Ni(NO₃)₂/γ-Al₂O₃ precursor with dielectric barrier discharge (DBD) hydrogen plasma at different input powers, characterized by XRD, H₂-TPR, CO₂-TPD, N₂ adsorption and TEM, respectively, and used as the catalyst for CO₂ reforming of methane (CRM). The results showed that the input power obviously affected the reduction degree and catalytic performances of catalysts. Low input power under 40 W mainly resulted in the decomposition of nickel nitrate into Ni oxides. The reduction degree, catalytic activity and stability increase with the input power. Similar catalytic performances in CRM reaction can be obtained when the power exceeds 80 W. Compared with the Ni/Al₂O₃ catalyst prepared by traditional method, Ni/γ-Al₂O₃ samples prepared by H₂ DBD plasma exhibit better activities, stability and anti-carbon deposit performances. It is mainly ascribed to smaller Ni particle size, more basic sites and weaker basicity. The increase of Ni particle sizes due to the sintering at high temperature results in the decrease of catalytic activities and coke formation.     

High-surface-area Ce0.8Zr0.2O2 solid solutions supported Ni catalysts for ammonia decomposition to hydrogen

Three kinds of Ce_0.8Zr_0.2O₂ solid solutions synthesized via surfactant-assisted route, co-precipitation, and sol–gel method were used as supports of Ni-based catalysts by impregnation. Their catalytic activities in ammonia decomposition to hydrogen were tested, and the structural effect of support and the influence of nickel content on catalytic activity were evaluated. Mesoporous/high-surface-area Ce_0.8Zr_0.2O₂ support synthesized by surfactant-assisted method exhibited better promoting effect than other supports when the same content of Ni was loaded. The interactions between Ni species and Ce_0.8Zr_0.2O₂ supports were found to greatly affect the chemical properties of catalysts, including redox, H₂ adsorption, and catalysis. The promoting effects of Ce in catalysts, plentiful vacancies in the solid solutions due to the doping of Zr⁴⁺, and high surface areas of the supports were discussed on the ammonia decomposition activities of the resultant catalysts, as well as the influence of hydrogen spillover. The ammonia conversion of 95.7% with the H₂ producing rate of 89.3 mL/min·g_cat was achieved at 550 °C over the Ni catalysts supported on the mesoporous/high-surface-area Ce_0.8Zr_0.2O₂.     

High temperature water gas shift reaction over promoted iron based catalysts prepared by pyrolysis method

In this work the effects of different promoters (Cr, Al, Mn, Ce, Ni, Co and Cu) on the structural and catalytic properties of Nanocrystalline iron based catalysts for high temperature water gas shift reaction were investigated. The catalysts were prepared in active phase (Fe₃O₄) via a facile direct synthesis routs without any additive and characterized using X-ray diffraction (XRD), N₂ adsorption (BET), temperature-programmed reduction (TPR), transmission and scanning electron microscopies (TEM,SEM) techniques. The obtained results indicated that synergic effect of Mn and Ni promoters can lead to obtain a Cr-free catalyst with high activity. In addition, the effect of Ni content on the structural and catalytic properties of the Fe–Mn–Ni catalysts was investigated. It was found that Fe–Mn–Ni catalyst with Fe/Mn = 10 and Fe/Ni = 5 weight ratios showed the highest catalytic activity among the prepared catalysts and possessed a stable catalytic performance without any decrease during 10 h time on stream. Moreover, the effect of GHSV and steam/gas ratio on the catalytic performance of this catalyst was investigated.     

Ni-based catalysts for reforming of methane with CO2

Ni catalysts supported on different carriers like δ,θ-Al₂O₃, MgAl₂O₄, SiO₂–Al₂O₃ and ZrO₂–Al₂O₃ were prepared. The solids were characterized by chemical analysis, N₂ adsorption–desorption isotherms, X-ray powder diffraction, UV–vis diffuse reflectance spectroscopy, temperature-programmed reduction, high-resolution transmission electron microscopy and temperature-programmed oxidation. The catalytic properties of the samples were evaluated in the reaction of reforming of methane with CO₂ at 923 K. It was shown that this kind of support greatly affects the structure and catalytic performance of the catalysts. Ni catalyst supported on MgAl₂O₄ showed the highest activity and stability due to the presence of small well dispersed Ni particles with size of 5.1 nm. It was shown that the lowest activity of Ni catalyst supported on SiO₂–Al₂O₃ oxide was caused by the agglomeration of nickel particles and formation of filamentous carbon under reaction conditions detected by the high resolution transmission electron microscopy.     

Hydrogen production by steam reforming of ethanol over P123-assisted mesoporous Ni–Al2O3–ZrO2 xerogel catalysts

A series of mesoporous Ni–Al₂O₃–ZrO₂ xerogel (denoted as X-NAZ) catalysts were prepared by a P123-assisted epoxide-driven sol–gel method under different P123 concentration (X, mM), and they were applied to the hydrogen production by steam reforming of ethanol. The effect of P123 concentration on the physicochemical properties and catalytic activities of X-NAZ catalysts was investigated. All the catalysts retained a mesoporous structure. Pore volume of the catalysts increased with increasing P123 concentration. Ni surface area and ethanol adsorption capacity of X-NAZ catalysts exhibited volcano-shaped trends with respect to P123 concentration. The trend of hydrogen yield was well matched with the trend of Ni surface area and ethanol adsorption capacity. Thus, Ni surface area and ethanol adsorption capacity of the catalysts served as important factors determining the catalytic performance. Among the catalysts tested, 12-NAZ catalyst with the highest Ni surface area and the largest ethanol adsorption capacity showed the best catalytic performance in the steam reforming of ethanol. In conclusion, an optimal P123 concentration was required for maximum production of hydrogen in the steam reforming of ethanol over X-NAZ catalysts.     

CO2 dry-reforming of methane over La0.8Sr0.2Ni0.8M0.2O3 perovskite (M = Bi,Co, Cr,Cu, Fe): Roles of lattice oxygen on C–H activation and carbon suppression

La_0.8Sr_0.2Ni_0.8M_0.2O₃ (LSNMO) (where M = Bi, Co, Cr, Cu and Fe) perovskite catalyst precursors have been successfully developed for CO₂ dry-reforming of methane (DRM). Among all the catalysts, Cu-substituted Ni catalyst precursor showed the highest initial catalytic activity due to the highest amount of accessible Ni and the presence of mobile lattice oxygen species which can activate C–H bond, resulting in a significant improvement of catalytic activity even at the initial stage of reaction. However, these Ni particles can agglomerate to form bigger Ni particle size, thereby causing lower catalytic stability. As compared to Cu-substituted Ni catalyst, Fe-substituted Ni catalyst has low initial activity due to the lower reducibility of Ni–Fe and the less mobility of lattice oxygen species. However, Fe-substituted Ni catalyst showed the highest catalytic stability due to: (1) strong metal–support interaction which hinders thermal agglomeration of the Ni particles; and (2) the presence of the abundant lattice oxygen species which are not very active for C–H bond activation but active to react with CO₂ to form La₂O₂CO₃, hence minimizing carbon formation by reacting with surface carbon to form CO.     

An investigation on the role of ytterbium in ytterbium promoted γ-alumina-supported nickel catalysts for dry reforming of methane

Addition of low quantities of ytterbium to sol–gel prepared Ni/γ-Al₂O₃ catalysts has been shown to lead to significant increases in catalytic activity and long term stability in the catalytic conversion of CO₂ and CH₄ into syngas (H₂ and CO). The role of ytterbium in these catalysts was investigated in this study through detailed investigations on the structure and composition of ytterbium promoted Ni/γ-Al₂O₃ catalysts using the following techniques: synchrotron X-ray diffraction, X-ray Photoemission Spectroscopy, Transmission Electron Microscopy, Scanning Electron Microscopy/Energy Dispersive X-ray analysis, Temperature Programmed Reduction techniques and N₂ adsorption–desorption isotherms. The results obtained indicated that ytterbium, at small quantities (up to 2 wt%), interacted strongly with the support which in turn altered the interaction between nickel and the support (most notably it was found to completely inhibit the formation of NiAl₂O₄). This decreased interaction between Ni and the support also led to a higher quantity of Ni being present in the catalyst in the form of Ni.     

Ordered mesoporous MgO–Al2O3 composite oxides supported Ni based catalysts for CO2 reforming of CH4: Effects of basic modifier and mesopore structure

A series of ordered mesoporous MgO–Al₂O₃ composite oxides with various Mg containing were facilely synthesized via one-pot evaporation induced self-assembly strategy. These materials with advantageous structural properties and superior thermal stabilities were used as the supports of Ni based catalysts for CO₂ reforming of CH₄. These mesoporous catalysts behaved both high catalytic activities and long term stabilities toward this reaction. The effects of the mesopore structure and MgO basic modifier on catalytic performances were carefully studied. Specifically, their mesoporous frameworks could accommodate the gaseous reactants with more “accessible” Ni active centers; the “confinement effect” of the mesopores would effectively suppress the thermal sintering of the Ni nanoparticles; the modified MgO basic sites would enhance the chemisorption and activation of CO₂. Consequently, the catalytic activities and stabilities of these catalysts were greatly promoted. Therefore, the present materials were considered as promising catalyst supports for CO₂ reforming of CH₄.     

Catalytic effect of Ni, Mg2Ni and Mg2NiH4 upon hydrogen desorption from MgH2

MgH₂ is a perspective hydrogen storage material whose main advantage is a relatively high hydrogen storage capacity (theoretically, 7.6 wt.% H₂). This compound, however, shows poor hydrogen desorption kinetics. Much effort was devoted in the past to finding possible ways of enhancing hydrogen desorption rate from MgH₂, which would bring this material closer to technical applications. One possible way is catalysis of hydrogen desorption. This paper investigates separate catalytic effects of Ni, Mg₂Ni and Mg₂NiH₄ on the hydrogen desorption characteristics of MgH₂. It was observed that the catalytic efficiency of Mg₂NiH₄ was considerably higher than that of pure Ni and non-hydrated intermetallic Mg₂Ni. The Mg₂NiH₄ phase has two low-temperature modifications below 508 K: un-twinned phase LT1 and micro-twinned phase LT2. LT1 was observed to have significantly higher catalytic efficiency than LT2.     

Effects of Y2O3-modification to Ni/γ-Al2O3 catalysts on autothermal reforming of methane with CO2 to syngas

The effects of Y₂O₃-modification to Ni/γ-Al₂O₃ catalysts on autothermal reforming of methane to syngas were investigated. It was found that the introduction of Y₂O₃ (5%, 8%, 10%) lead to significant improvement in catalytic activity and stability, and the H₂/CO ratio could be adjusted via controlling the O₂/CO₂ ratio of the feed gas. According to the characterization results of catalysts before and after reaction, it was found that the Y₂O₃·γ-Al₂O₃ supported Ni catalysts had higher NiO reducibility, smaller Ni particle size, higher Ni dispersion and stronger basicity than those of the Ni/γ-Al₂O₃ catalysts. The analysis of catalysts after reaction showed that the addition of Y₂O₃ inhibited the Ni sintering, changed the type of coke and decreased the amount of coke on the catalysts. All the experimental results indicated that the introduction of Y₂O₃ to Ni/γ-Al₂O₃ resulted in excellent catalytic performances in autothermal reforming of methane, and Y₂O₃ played important roles in preventing metal sintering and coke deposition via controlling NiO reducibility, Ni particle size and dispersion, and basicity of catalysts.     

Hydrogen production by steam reforming of ethanol over mesoporous Ni–Al2O3–ZrO2 aerogel catalyst

A mesoporous Ni–Al₂O₃–ZrO₂ aerogel (Ni–AZ) catalyst was prepared by a single-step epoxide-driven sol–gel method and a subsequent supercritical CO₂ drying method. For comparison, a mesoporous Al₂O₃–ZrO₂ aerogel (AZ) support was prepared by a single-step epoxide-driven sol–gel method, and subsequently, a mesoporous Ni/Al₂O₃–ZrO₂ aerogel (Ni/AZ) catalyst was prepared by an incipient wetness impregnation method. The effect of preparation method on the physicochemical properties and catalytic activities of Ni–AZ and Ni/AZ catalysts was investigated. Although both catalysts retained a mesoporous structure, Ni/AZ catalyst showed lower surface area than Ni–AZ catalyst. From TPR, XRD, and H₂–TPD results, it was revealed that Ni–AZ catalyst retained higher reducibility and higher nickel dispersion than Ni/AZ catalyst. In the hydrogen production by steam reforming of ethanol, both catalysts showed a stable catalytic performance with complete conversion of ethanol. However, Ni–AZ catalyst showed higher hydrogen yield than Ni/AZ catalyst. Superior textural properties, high reducibility, and high nickel surface area of Ni–AZ catalyst were responsible for its enhanced catalytic performance in the steam reforming of ethanol.     

Synthesis and characterization of bimetallic Cu–Ni/ZrO2 nanocatalysts: H2 production by oxidative steam reforming of methanol

Cu/ZrO₂, Ni/ZrO₂ and bimetallic Cu–Ni/ZrO₂ catalysts were prepared by deposition–precipitation method to produce hydrogen by oxidative steam reforming of methanol (OSRM) reaction in the range of 250–360 °C. TPR analysis of the Cu–Ni/ZrO₂ catalyst showed that the presence of Cu facilitates the reduction of the Ni at lower temperatures. In addition, this sample showed two reduction peaks, the former peak was attributed to the reduction of the adjacent Cu and Ni atoms which could be forming a bimetallic Cu-rich phase, and the second was assigned to the remaining Ni atoms forming bimetallic Ni-rich nanoparticles. Transmission Electron Microscopy revealed Cu or Ni nanoparticles on the monometallic samples, while bimetallic nanoparticles were identified on the Cu–Ni/ZrO₂ catalyst. On the other hand, Cu–Ni/ZrO₂ catalyst exhibited better catalytic activity than the monometallic samples. The difference between them was related to the Cu–Ni nanoparticles present on the former catalyst, as well as the bifunctional role of the bimetallic phase and the support that improve the catalytic activity. All the catalysts showed the same selectivity toward H₂ at the maximum reaction temperature and it was ∼60%. The high selectivity toward CO is associated to the presence of the bimetallic Ni-rich nanoparticles, as evidenced by TEM–EDX analysis, since this behavior is similar to the one showed by the monometallic Ni-catalyst.     

Stability, durability, and reusability studies on transition metal-doped Co–B alloy catalysts for hydrogen production

In addition to high catalytic efficiency the catalyst must also comprise important features like high stability in severe conditions, ability to be recycled several times and should have high tolerance against deactivation. This work is oriented specifically to study these properties of already developed efficient transition-metal doped Co–B alloy catalyst. Various transition metals, namely Ni, Fe, Cu, Cr, Mo, and W, were singly added as dopants in Co–B catalyst by chemical reduction of the corresponding metal salts. These alloy catalysts were calcinated, in Ar atmosphere, at 673, 773, and 873 K in order to investigate the stability of the powders at elevated temperatures. The catalytic performances of these treated catalyst powders were tested for H₂ generation by catalytic hydrolysis of sodium borohydride (NaBH₄). The alloy powders were exposed to ambient condition for several days to test their tolerance against deactivation and self life. After separation from the reaction course and after rinsing, the catalyst powders were tested for several cycles to evaluate the reusability property. The observed changes in the catalytic activity were discussed on the basis of structural and morphological variations. The Co–B catalyst, when doped with Ni, Mo, and W metals showed high stability and resistance against deterioration, as function of both time and use, as compared to Cr- and Fe-doped alloy powders. A much lower performance with respect to calcination temperature, holding time, and number of cycles was established for Cu doped Co–B catalyst powder.     

Carbon dioxide reforming of methane to synthesis gas over Ni/Si3N4 catalysts

Silicon nitride supported nickel catalyst prepared by impregnation using nickel nitrate solution was employed for the carbon dioxide reforming of methane. The catalyst was tested at 800 °C under atmospheric pressure. The influences of Ni loading and calcination temperature on the catalytic performance were investigated. It was found that the nickel loading and calcination temperature strongly influenced the catalytic performance. Over the 7 wt. % Ni/Si₃N₄ catalyst calcined at 400 °C, the conversions of CH₄ and CO₂ can achieve 95% and 91%, respectively. Appropriate interaction between the metal and the basic support makes the catalyst more resistant to sintering and coking, and thus an excellent stability.     

Catalytic CO2 reforming of CH4 over Cr-promoted Ni/char for H2 production

The objective of the study is to investigate the catalytic performance of Cr-promoted Ni/char in CO₂ reforming of CH₄ at 850 °C. The char obtained from the pyrolysis of a long-flame coal at 1000 °C was used as the support. The catalysts were prepared by incipient wetness impregnation methods with different metal precursor doping sequence. The characterization of the composite catalysts was evaluated by XRD, XPS, SEM-EDS, TEM, H₂-TPR, CO₂-TPD, CH₄-TPSR, and CO₂-TPO. The results indicate that the catalyst prepared by co-impregnation of Ni and Cr possess higher activity than those by sequential impregnation. The optimal loading of Cr on 5 wt% Ni/char is 7.8 wt‰. Moreover, the molar feed ratio of CH₄/CO₂ has a considerable effect on both the stability and the activity of Cr–Ni/char. The main effect of Cr is the great enhance of the adsorption to CO₂. It is interesting that the conversions of CH₄ and CO₂ over Cr-promoted Ni/char and Ni/char decrease initially, following by a steady rise as the reaction proceeds with time-on-stream (TOS). In addition, cyclic tests were conducted and no distinct deterioration in the catalytic performance of the catalysts was observed. On the basis of the obtained results, nickel carbide was speculated to be the active species which was formed during the CO₂ reforming of CH₄ reaction.     

Ni–CeO2 composite cathode material for hydrogen evolution reaction in alkaline electrolyte

In this work, nickel-based electrodes were prepared using composite electrodeposition technique in a nickel sulphamate bath containing suspended micro- or nano-sized CeO₂ particles. The prepared Ni–CeO₂ composite electrodes exhibit an enhanced high catalytic activity toward hydrogen evolution reaction (HER) in alkaline solutions. X-ray diffraction patterns indicated that the CeO₂ particles have been successfully incorporated into the Ni matrix and altered the texture coefficient (TC) of the Ni layer. The morphology of the obtained coatings was characterized by Scanning Electron Microscopy, and the CeO₂ content was determined by coupled energy dispersive X-ray spectrometry. The thermal stability of the composite electrodes was analyzed by thermogravimetric and differential scanning calorimetry, showing a good thermal stability. The catalytic activity of the composite electrodes for HER was measured by steady-state polarization and electrochemical impedance spectroscopy techniques in 1.0 M NaOH solution at room temperature. The exchange current density of HER on the Ni–CeO₂ composite electrodes was much higher than that on Ni electrode. EIS results suggested that a synergetic effect on HER may exist between CeO₂ particles and Ni matrix. Compared to nano-CeO_2, the micro-CeO₂ derived composite electrodes showed higher electrochemical activity. The possible correlation among particle size, content and catalytic activity is discussed.     

Properties of Ni/Y2O3 and its catalytic performance in methane conversion to syngas

Ni/Y₂O₃, with Y₂O₃ support prepared by the conventional precipitation method, was prepared by an impregnation method. The physicochemical properties of Y₂O₃ and Ni/Y₂O₃ were characterized by BET, CO₂-TPD, NH₃-TPD, TPR, XRF and TGA, and compared with those of γ-Al₂O₃ and Ni/γ-Al₂O_3, respectively. The catalytic performance of Ni/Y₂O₃ in the reaction of partial oxidation of methane (POM) to syngas was evaluated and compared with that of Ni/γ-Al₂O₃ catalyst, too. The results showed that, Y₂O₃ was a basic support with few acidic sites while γ-Al₂O₃ was an acidic support. NiO particles supported on Y₂O₃ were more easily to be reduced than those supported on γ-Al₂O₃. In the partial oxidation of methane, Ni/Y₂O₃ catalyst showed high catalytic activity and exhibited better catalytic stability than Ni/γ-Al₂O₃. After POM reaction at 700 °C for 550 h, methane conversion decreased little and only 2.2 wt% carbon was deposited on Ni/Y₂O₃ catalyst. Ni/Y₂O₃ was stable in POM even after a series of reaction temperature variations within the temperature range of 400 ∼ 800 °C.     

The effect of Ni content on a highly active Ni-Al2O3 catalyst prepared by the homogeneous precipitation method

Highly active Ni-Al₂O₃ catalysts were prepared by the homogeneous precipitation method with a variety of high nickel contents ranging from 30 to 70 wt.%. The effects of nickel content on the physicochemical properties and catalytic activities of the Ni-Al₂O₃ catalysts were investigated. XRD measurements showed that the catalyst with 30 Ni wt.% only had a diffraction peak corresponding to NiAl₂O₄, whereas the catalysts of 50, 60 and 70 Ni wt.% had diffraction peaks corresponding to NiO and NiAl₂O₄. Hydrogen chemisorption results showed that the nickel surface area increased with increasing nickel content in the order: 30 < 40 < 50 < 60 < 70 Ni wt.%. Specifically, the nickel surface area increased steadily from 11 to 22 m²/g with increasing the nickel content from 30 to 50 wt.%, after which it stayed nearly constant at 22 m²/g despite the increase in nickel content from 50 to 70 wt.%. TEM images of the reduced Ni-Al₂O₃ catalysts revealed that the average sizes of the Ni particles were 12, 13 and 16 nm for the catalysts with 30, 50 and 70 Ni wt.%, respectively, suggesting that a higher nickel content yielded a larger Ni particle. The catalytic performance of methane steam reforming showed that the catalytic reaction rate increased steadily with increasing nickel content from 30 to 50 wt.%, after which it stayed nearly constant despite that the nickel content increased to over 50 wt.%. As a result, about 50 wt.% of nickel was found to be a reasonable nickel content to obtain the maximum catalytic activity.