Renewable hydrogen production via glycerol steam reforming over Ni/CeO2 catalysts obtained by solution combustion method: The effect of Ni loading
2022
Omarov, Shamil O. | Martinson, Kirill D. | Matveyeva, Anna N. | Chebanenko, Maria I. | Nevedomskiy, Vladimir N. | Popkov, Vadim I.
A series of nanocrystalline Ni/CeO₂ catalysts with various Ni content was prepared by urea-nitrate combustion synthesis and evaluated in glycerol steam reforming for renewable H₂ production. The as-prepared, reduced and spent catalysts were characterized by various analytical techniques such as XRD, N₂-physisorption, SEM–EDX, TEM–HAADF and SAED, H₂-TPR, XPS, Raman, and DTA–TGA. NiO is predominantly in the X-ray amorphous state (particle size 2–4 nm regardless of the Ni amount), which is retained for Ni⁰ particles after reduction by H₂. Significant fraction of NiO(Ni⁰) is localized between CeO₂ aggregates. An increase in the Ni content leads to inhibition of the agglomeration of CeO₂ crystallites and increase in CeO₂ defectiveness up to 6.8 wt% Ni; formation of CeO₂(Ni²⁺) solid solution at 8.7 wt% Ni, which decomposes upon reduction. The sample containing 6.8 wt% Ni exhibits the best combination of Ni content and dispersion, CeO₂ defectiveness, glycerol conversion, H₂ yield, selectivity to H₂ and CO₂ and has low selectivity to hydrocarbons. TEM and DTA–TGA revealed the formation of amorphous, graphite-like, and fibrous coke depending on the Ni amount. This formation leads to accelerated deactivation due to partial agglomeration of Ni⁰ particles and encapsulation of amorphous nickel.
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