Hydrogen production by steam reforming of ethanol using Ni catalysts based on ternary mixed oxides prepared by coprecipitation

摘要

Ni catalysts based on ternary mixed oxides, NiMAl (M = Mg, Ca, Zn) and NiMgN (N = La, Ce) were prepared by the coprecipitation method and characterized by N_2-sorption measurements, TGA, XRF, XRD, H_2-TPR and TEM. NiMAl (M = Mg, Ca, Zn) catalyst precursors exhibited a layered double hydroxide (LDH) structure, not observed in NiMgN (N = La, Ce) samples. NiMgAl mixed oxide exhibited well-stabilized nickel species needing high temperatures to be reduced (around 1100 K). The extent of Ni~(2+) reduction in the mixed oxides was improved with the replacement of Mg by Ca and Zn or Al by La and Ce. Catalysts were very active and selective in ethanol steam reforming although NiMgN (N = La, Ce) samples deactivate faster than NiMAl (M = Mg, Ca, Zn) having smaller Ni crystallites. In particular, the presence of Ca produced an important dispersing effect over the Ni species, favouring hydrogen production while keeping moderate coke formation. In the case of the reduced NiCaAl mixed oxide H_2 selectivity values above 87 mol % were reached.