Effect of calcium addition on catalytic ethanol steam reforming of Ni/Al2O3: I. Catalytic stability, electronic properties and coking mechanism

Ca-modified Ni/Al2O3 catalysts with various Ca loadings of 0, 3, 5 and 7 wt% were studied for low temperature catalytic ethanol steam reforming (ESR). Catalyst with 3 wt% of Ca remains stable at 673 K for at least 24h, while 0 wt%, 5 wt% and 7 wt% Ca modified catalysts deactivate easily. The addition of Ca increases the particle size of active Ni which promotes the formation of un-reactive and encapsulating carbons, undermining the stability of highly loaded (7 wt%) Ca-modified Ni catalyst. XPS valence band shows that the presence of Ca increases the density of Ni 3d band valence electrons which helps in dissociation of methane and deactivates the catalysts, as in the case of nickel catalysts supported on 7 wt% of Ca on Al2O3. Excellent catalytic performance of 10Ni/3Ca-Al2O3 is due to the effective coke removal and the amorphous nature of coke deposition. Optimized Ca loading was found to play a critical role in coke removal, through its effect on Ni particle size, valence band of catalyst and steam gasification of coke. (C) 2011 Elsevier B.V. All rights reserved.