Alkaline earth metal oxide modification of Ni/Al₂O₃ for hydrogen production from the partial oxidation and reforming of dimethyl ether

Abstract

The modification of Ni/Al₂O₃ catalyst by alkaline earth metal oxides including MgO, CaO, SrO and BaO was investigated for hydrogen production from the partial oxidation and reforming of dimethyl ether. MgO modification of the Ni/Al₂O₃ catalyst enhanced the formation of NiAl₂O₄. There was only one reduction peak from 700 to 950 °C, which is usually ascribed to the reduction of NiAl₂O₄. The Ni-containing species which are easily reduced at low temperature were removed. When the MgO modified Ni/Al₂O₃ was reduced at 750 °C in the performance evaluation, a small amount of Ni was produced from NiAl₂O₄ to give small and active Ni sites, resulting in better catalytic reforming performance than for the unmodified Ni/Al₂O₃. The H₂ yield of 88% and CO selectivity of 86% was obtained at 800 °C when MgO modified Ni/Al₂O₃ was adopted as a reforming catalyst, which was combined with 0.5 wt% Pt/Al₂O₃ to form a dual bed catalysts. The other metal (Ca, Sr, Ba) oxide modification of Ni/Al₂O₃ catalyst, however, did not enhance the formation of NiAl₂O₄ as well as MgO, and there were still certain amounts of low temperature reducible NiO species, resulting in a worse catalytic performance than the unmodified Ni/Al₂O₃. The variation of the amount of MgO modification had no obvious effect on the formation of NiAl₂O₄. However, the peak reduction temperature of 7.5 wt% MgO modified Ni/Al₂O₃ in H₂-TPR patterns was a little lower than that of 5.0 or 10.0 wt% MgO modified Ni/Al₂O₃, resulting in a little better catalytic performance by giving more active Ni sites reduced from NiAl₂O₄ at 750 °C.