4.5 Article

The Annealing Effect of Arranged Nickel Octahedra Nanoparticles on the Performance of NiO Supported in Silica in Combined Steam and Dry Reforming of a Model Biogas Mixture

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SPRINGER HEIDELBERG
DOI: 10.1007/s13369-023-08108-w

Keywords

Octahedral nanoparticles; Biogas reforming; Annealing effect; Carbon gasification

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The study evaluated the effect of a mesoporous Ni60%SiO2(Comm) catalyst, which has octahedral-shaped NiO particles, on the synthesis gas production via steam and dry reforming of a model biogas mixture. Compared to a standard Ni5%SiO2 catalyst, Ni60%SiO2(Comm) showed different reducibility behavior and shape transformation, resulting in higher reactivity and lower carbon deposition. The high-coke resistance of Ni60%SiO2(Comm) was attributed to the annealing effect during H-2(g) treatment, which yielded mesoporous metallic Ni-0 nanorods with H-2(g) storage capacities.
The octahedral family of NiO nanoparticles is gaining significant attention as an assembly with unique physicochemical properties and outcomes in electromagnetics, shielding and absorption applications. In this study, a mesoporous Ni60%SiO2(Comm), chosen owing to its NiO species existing in an octahedral shape, was evaluated for synthesis gas (syngas: H-2(g) and CO(g) mixtures) production via combined steam and dry reforming of a model biogas mixture (T = 800 & DEG;C, (H2O(g) + CO2(g))/CH4(g) = 1.2). In comparison with a standard Ni5%SiO2 (Aerosil)-based catalyst, a different family of NiO species was deposited on the silica matrix with an average particle size being 4.5 times greater. This led to a completely different reducibility behavior with the majority of NiO species (around 80%) undergoing reduction at low temperatures, while around 66% of those impregnated on the Aerosil silica underwent reduction at higher temperatures. This has been accompanied by a major shape transformation from arrays of octahedral NiO geometries into metallic grids of metallic Ni-0 appearing over Ni60%SiO2(Comm). In terms of reactivity outcomes, slightly higher reactivity levels along with significantly lower amounts of carbonaceous deposits were obtained over Ni60%SiO2(Comm) for 10 h on stream, under harsh conditions of temperature and steam-rich atmosphere. The high-coke resistance of originally shaped NiO octahedra was ascribed to an annealing effect, generated during H-2(g)-treatment (prior to catalysis), yielding mesoporous metallic Ni-0 nanorods with H-2(g)-storage capacities. Stored hydrogen within Ni-0 layers acted as active centers for continuous in situ coke gasification, preventing thus C-(s) accumulation while keeping Ni-0 sites accessible for catalysis.

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