Effect of Nickel Precursor on the Catalytic Performance of Graphene Aerogel‐Supported Nickel Nanoparticles for the Production of CO_x‐free Hydrogen by Ammonia Decomposition

Abstract

Graphene aerogel (GA), a promising porous material with high specific surface area and electrical conductivity, is utilized to disperse nickel nanoparticles to reach high catalytic activity in COx‐free hydrogen production from ammonia. Ni(NO3)2·6H2O and Ni (II) acetylacetonate (Ni(acac)2) were considered as metal precursors and the pH of the impregnation solution was varied to investigate the effects on the catalytic properties of the GA‐supported nickel catalysts. Data showed that the best dispersion and homogeneity, as well as the catalytic performance, is achieved with Ni(acac)2. An average Ni nanoparticle size of 13.6 ± 4.3 nm was obtained on the GA‐supported catalyst prepared by using Ni(acac)2 dissolved in an impregnation solution with a pH of 10.2. This catalyst with a Ni loading of 11.1 wt% provided an ammonia conversion of 70.2% at a space velocity of 30 000 mL NH3 gcat−1 h−1 and 600 °C corresponding to a hydrogen production rate of 21.5 mmol H2 gcat−1 min−1. Data illustrated that the difference between the point of zero charge of the support and the pH of the impregnation solution set by the type of the Ni precursor is a major parameter controlling the metal dispersion and the consequent catalytic activity.

Effect of Surface Characteristics of Graphene Aerogels and Hydrophilicity of Ionic Liquids on the CO2/CH4 Separation Performance of Ionic Liquid/Reduced Graphene Aerogel Composites

“…Figure shows the representative SEM images of the pristine rGAs and IL-loaded rGAs. The clear, randomly oriented, wrinkled-sheet structures of pristine rGAs shown in Figure a,b are consistent with the previous reports. , The wrinkled nature of the composites prepared with rGA500 was more prominent compared to rGA300 composites, consistent with its higher surface area and pore volume. With the impregnation of ILs, rGAs became smoother by losing their roughness as can be seen in Figure c,d for [BMPyr]­[DCA] and Figure e,f for [BMPyr]­[PF 6 ]-loaded rGAs.…”

“…The clear, randomly oriented, wrinkled-sheet structures of pristine rGAs shown in Figure 2a,b are consistent with the previous reports. 41,42 The wrinkled nature of the composites prepared with rGA500 was more prominent compared to rGA300 composites, consistent with its higher surface area and pore volume. With the impregnation of ILs, rGAs became smoother by losing their roughness as can be seen in Figure 2c,d Structures of the composites were further analyzed by XRD to check whether there was a change in the pristine material's crystal structure after IL impregnation.…”

“…These values are lower than those of the previously reported as-treated and untreated GAs prepared with similar synthesis methods. 13,41 The decrease in surface areas might be arising from the overlapping sheets and the collapse of the porous carbon structure due to thermal reduction and synthesis conditions. 19 The synthesis steps of IL/rGA composites are given in Figure 1, which encapsulates the fabrication of pristine rGAs from GO solution, the representative chemical structure of GA and rGAs, and the preparation of IL-loaded composites using the incipient wetness method.…”

Review on Ru-Based and Ni-Based Catalysts for Ammonia Decomposition: Research Status, Reaction Mechanism, and Perspectives

“…Graphene aerogel (GA), a promising porous material, is used to support nickel-based catalysts. Kocer et al 143 synthesized various GA-supported Ni catalysts by employing a series of Ni precursors; they concluded that the increase in the pH of the impregnation solution resulted in a smaller average particle size of the nickel particles and more homogeneous dispersion of nickel nanoparticles, which is beneficial for accelerating the catalytic reaction. In recent years, there have also been many studies on ammonia decomposition catalysts supported by natural clay with nickel.…”

One-Pot Synthesis of Menthol from Citral over Ni/H-β-38 Extrudates Containing Bentonite Clay Binder in Batch and Continuous Reactors

“…The effect of the nickel precursor on the surface properties of Ni/KL-supported catalysts prepared from nickel nitrate, nickel acetylacetonate, and nickel phthalocyanine was explored in hydrogenation of citral at 5 MPa and 50 °C, demonstrating different nickel species distribution in the zeolite and giving as the main reaction products always citronellal and citronellol . The prominent effect of Ni precursors was demonstrated, however, for various processes, e.g., ammonia decomposition for the production of CO x -free hydrogen (nickel nitrate, nickel acetylacetonate), CO 2 methanation (nickel acetate, nickel nitrate, nickel acetylacetonate, nickel sulfate, and nickel chloride) including over zeolite 5A and 13X supported catalysts (nickel nitrate, nickel citrate, and nickel acetate), 1,1,1,2-tetrafluoroethane pyrolysis to trifluoroethylene (nickel acetate, nickel nitrate, and nickel chloride), steam and enhanced steam methane reforming (nickel acetate, nickel nitrate), glycerol steam reforming (nickel nitrate, nickel chloride, nickel acetate, and nickel acetylacetonate), hydroisomerization of n -decane (nickel nitrate, nickel acetylacetonate, and (triethylenediamine)-nickel nitrate), hydrogenation and ring-opening of tetralin (nickel nitrate, nickel citrate), where formation of different surface Ni 0 species, amount of acid sites, adsorption of coordinating anions, and Ni particles’ distribution depending on precursors were shown to directly affect Ni dispersion and accessibility. Therefore, the choice of the metal salt precursor can also be significant when designing Ni-based catalysts for citral hydrogenation.…”