Abstract
Nickel catalysts supported on γ-Al2O3 were synthesized in the presence of polyvinylpyrrolidone (PVP) using both alkaline polyol method and hydrazine reduction method while fixing the weight ratio of [(PVP)]/[Ni(CH3COO)2·4H2O] at 2. The effects of hydrazine [N2H5OH]/[Ni] and [NaOH]/[Ni] molar ratios on the structural properties of the catalysts were characterized by transmission electron microscopy (HRTEM) and by X-ray diffraction (XRD). The average of monodispersed Ni nanoparticles ranged between 8.0 and 13.0 nm. The catalytic tests were performed for the partial oxidation of methane in the temperature range of 600–800 °C under a flow rate of 157,500 L kg–1 hr–1 with CH4/O2= 2. At the molar ratio of [NaOH]/[Ni] = 2, the resultant nickel nanoparticles on alumina was established completely without impurities; thus, it demonstrated the highest catalytic activity, 88% for CH4 conversion, and H2 selectivity, 90.60%. The optimum [N2H5OH]/[Ni] ratio was determined as 4.1, which means a good catalytic performance and 89.35% selectivity to H2 for the partial oxidation of methane.
Highlights
Nanosized nickel particles have been mainly preferred as catalysts in the catalytic partial oxidation of methane (CPOM), which is one of the basic H2 production processes
Since the morphology of Ni nanoparticles synthesized in our study is closer to spherical particles, obtaining up to 86% methane conversions in the partial oxidation reaction of methane may be related to more limited hydrogen storage, that is, limited nickel dispersion
highresolution transmission electron microscopy (HRTEM) images show that the non-agglomerated Ni nanoparticles are well-dispersed on alumina support, and the average particle size was determined in the range of 8.4–8.5 nm
Summary
Nanosized nickel particles have been mainly preferred as catalysts in the catalytic partial oxidation of methane (CPOM), which is one of the basic H2 production processes. Various performances of catalysts such as mechanical strength, microporous structure, reactivity and stability can be significantly improved [12,23] Supports such as ZrO2, MgAl2O4 and Al2O3 are frequently used in industry for many catalytic reactions and have desirable properties such as high surface area and high mechanical strength. The reduction step can be assisted by adding an additional reducing agent such as N2H5OH (hydrazine hydroxide) along with NaOH In this way, the formation of smaller metallic particles is usually achieved in the presence of a capping agent such as PVP. ; in this study, we used the advantages of two types of polyol processes and reported on the effects of reaction parameters on Ni nanoparticles’ morphologies and tested their performances in the catalytic partial oxidation of CH4 to syngas in the medium-high temperature range 600–800 °C at the atmospheric pressure. The pore volume and specific surface area of catalyst samples were calculated by the Barrett–Joyner–Halenda (BJH) and Bru- nauereEmmette Teller (BET) methods, respectively
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