Abstract
The conversion of CH4 and CO2 to syngas using low-cost nickel catalysts has attracted considerable interest in the clean energy and environment field. Nickel nanoparticles catalysts suffer from serious deactivation due mainly to carbon deposition. Here, we report a facile synthesis of Ni single-atom and nanoparticle catalysts dispersed on hydroxyapatite (HAP) support using the strong electrostatic adsorption (SEA) method. Ni single-atom catalysts exhibit excellent resistance to carbon deposition and high atom efficiency with the highest reaction rate of 1186.2 and 816.5 mol.gNi−1.h−1 for CO2 and CH4, respectively. Although Ni single-atom catalysts aggregate quickly to large particles, the polyvinylpyrrolidone (PVP)-assisted synthesis exhibited a significant improvement of Ni single-atom stability. Characterizations of spent catalysts revealed that carbon deposition is more favorable over nickel nanoparticles. Interestingly, it was found that, separately, CH4 decomposition on nickel nanoparticle catalysts and subsequent gasification of deposit carbon with CO2 resulted in CO generation, which indicates that carbon is reacting as an intermediate species during reaction. Accordingly, the approach used in this work for the design and control of Ni single-atom and nanoparticles-based catalysts, for dry reforming of methane (DRM), paves the way towards the development of stable noble metals-free catalysts.
Highlights
Dry reforming of methane (DRM) to generate synthesis gas is gaining more and more attention as a potential renewable system in the energy sector
Noble metal-based catalysts are relatively more resistant to the undesirable coking compared to non-noble metal catalysts [14], a large-scale commercialization is limited by their high cost and limited availability
Small loading (0.5 wt%) and high loading (5 and 10 wt%) of Ni were deposited on hydroxyapatite support to obtain single-atom and nanoparticle catalysts, respectively, by a simple method named strong electrostatic adsorption (SEA) at room temperature [36]
Summary
Dry reforming of methane (DRM) to generate synthesis gas is gaining more and more attention as a potential renewable system in the energy sector. It has been reported that the size of supported nickel particles is a critical parameter for the DRM performance in terms of intrinsic activity, stability, and resistance to carbon deposition [17,18,19]. According to many published papers, varying the Ca/P molar ratio leads to the formation of additional phases and induces significant changes in the textural and acid-base properties [33] The presence of both cations (Ca2+ and Ca1+ ) and anions (PO4 3− and/or OH− ) can be considered as important sites for anchoring and stabilizing metals single atoms [34,35]. We report a comparative study of nickel single-atom and nanoparticles deposited on hydroxyapatite support (Ni/HAP) for DRM reaction. The catalysts were characterized before and after reaction using numerous advanced techniques
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