Silica–Ceria sandwiched Ni core–shell catalyst for low temperature dry reforming of biogas: Coke resistance and mechanistic insights

• Published in: Applied catalysis. B, Environmental Vol. 230; pp. 220 - 236
• Main Authors: Das, S., Ashok, J., Bian, Z., Dewangan, N., Wai, M.H., Du, Y., Borgna, A., Hidajat, K., Kawi, S.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15-08-2018; Elsevier BV
• Subjects: Biogas; Carbon dioxide; Catalysis; Catalysts; Cerium; Cerium oxides; Coke; Coke resistance; Deactivation; DRIFTS; Dry reforming of methane; Gasification; Inhibition; Low temperature; Low temperature resistance; Nanoparticles; Nickel; Oxygen; Reaction mechanisms; Redox potential; Reforming; Sandwich structures; Silica; Silicon dioxide; Storage capacity; Temperature effects; DRIFTS; Dry reforming of methane; Coke resistance
• ISSN: 0926-3373; 1873-3883
• DOI: 10.1016/j.apcatb.2018.02.041

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•Novel Ni-SiO2@CeO2 catalyst with unique sandwiched core shell structure developed.•Coke formation prevented on Ni-SiO2@CeO2 in low temperature biogas dry reforming.•Excellent coke resistance due to confinement effect & redox capacity of CeO2 shell.•CeO2 shell increases activity by increasing reducibility and dispersion of Ni.•CeO2 shell changes reaction pathway from mono-functional to bifunctional mechanism.
In this paper, a novel sandwiched core–shell structured Ni-SiO2@CeO2 catalyst, with nickel nanoparticles encapsulated between silica and ceria, was developed and applied for dry reforming of biogas (CH4 / CO2 = 3/2) under low temperature conditions to test its coke inhibition properties. Ni-phyllosilicate was used as the Ni precursor in order to produce highly dispersed Ni nanoparticles on SiO2. Cerium oxide was chosen as the shell due to its high redox potential and oxygen storage capacity, that can reduce coke formation under severe dry reforming conditions. The core shell Ni-SiO2@CeO2 catalyst showed excellent coke inhibition property under low temperature (600 °C) reforming of biogas, with no coke detected after a 72 h catalytic run. Under the same conditions, Ni-SiO2 catalyst deactivated within 22 h due to heavy coke formation and reactor blockage, while Ni-CeO2 catalyst showed very low activity. The higher activity of the core–shell catalyst is attributed to its higher Ni dispersion and reducibility. TEM and XRD results show that the core–shell catalyst shows higher resistance to Ni particle sintering and agglomeration during the reaction than the Ni-SiO2 and Ni-CeO2 catalysts. In-situ DRIFTS on the Ni-SiO2@CeO2 catalyst indicate a change in the reaction mechanism from a mono-functional pathway on the Ni-SiO2 catalysts to a bi-functional route on the Ni-SiO2@CeO2 catalyst with active participation of oxygen species from CeO2 in carbon gasification. The confinement effect of the sandwich structure and the bifunctional mechanism of dry reforming are the primary reasons for the excellent coke resistance of the Ni-SiO2@CeO2 catalyst.