Preparation of Ni-based egg-shell-type catalyst on cylinder-shaped alumina pellets and its application for hydrogen production via steam methane reforming

Abstract

Nickel-based ‘egg-shell-type’ catalysts were prepared using cylinder-shaped alumina pellets as supports. In the egg-shell-type catalysts, nickel was selectively located in the outer region of the alumina pellets. Ethylene glycol or 1-octanol were used as hydrophobic solvents to retard internal penetration of the alumina pellets by the nickel nitrate solution. Without hydrophobic solvent, a ‘homo-type’ catalyst with even nickel distribution inside the alumina pellets was achieved. Cross-sectional images and SEM-EDS analysis of the cylinder-shaped alumina pellets showed that nickel concentration in the egg-shell-type catalyst was higher in the outer region and decreased towards the inner region of the alumina pellets. The egg-shell-type nickel distribution was maintained after subsequent magnesium impregnation and calcination processes. X-ray diffraction patterns and temperature programmed reduction profiles showed that the only difference between homo-type and egg-shell type catalysts, when their nickel loading was the same, was the nickel distribution inside pellets; and this was shown to cause significant difference in their catalytic activity in the steam methane reforming (SMR) reaction. For the homo-type catalyst, nickel loading of 3.5 wt% was insufficient for the SMR reaction, as metallic nickel particles were evenly distributed through the entire alumina pellet. However, nickel loading of 3.5 wt% was sufficient for the egg-shell-type catalyst, because active sites with metallic nickel particles were concentrated in the outer region of the pellets. These experimental results confirmed that the egg-shell-type nickel distribution is a favorable design for an SMR reaction catalyst.