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

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.

Automated summary

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.