Renewable hydrogen production via glycerol steam reforming over Ni/CeO2 catalysts obtained by solution combustion method: The effect of Ni loading

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 H-2 production. The as-prepared, reduced and spent catalysts were characterized by various analytical techniques such as XRD, N-2-physisorption, SEM-EDX, TEM-HAADF and SAED, H-2-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 Ni-0 particles after reduction by H-2. Significant fraction of NiO(Ni-0) 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, H-2 yield, selectivity to H-2 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 Ni-0 particles and encapsulation of amorphous nickel.

Automated summary

Nanocrystalline Ni/CeO2 catalysts prepared by urea-nitrate combustion synthesis showed good catalytic performance in glycerol steam reforming. Characterization of the catalysts revealed that NiO mainly existed in the X-ray amorphous state and remained in the Ni-0 particles after reduction. Increasing the Ni content inhibited the agglomeration of CeO2 crystallites and increased the defectiveness of CeO2. The sample with 6.8 wt% Ni exhibited the best catalytic performance.