Novel and effective surface enrichment of active species in Ni-loaded catalyst prepared from Mg–Al hydrotalcite-type anionic clay

Abstract

Egg shell-type Ni loaded catalysts have been prepared by adopting the “memory effect” of Mg–Al hydrotalcite and have been successfully used in the steam reforming of CH 4. Mg–Al(3/1) mixed oxide particles were first prepared as the catalyst support by the thermal decomposition of Mg–Al hydrotalcite. When the particles were dipped in aqueous solution of Ni(II) nitrate, Mg–Al hydrotalcite was reconstituted in the surface layer of the particles, and simultaneously Ni(II) substituted for the Mg(II) sites, leading to the formation of egg shell-type Ni-loading. The conditions of both preparation of Mg–Al(3/1) mixed oxide and dipping in Ni(II) nitrate solution were varied, and their influences on egg shell-type Ni-loading and on the catalytic activity were studied. The shape of egg shell-type Ni-loading was significantly affected by the rate of heating, the final calcination temperature of Mg–Al(3/1) mixed oxide, the pH of Ni(II) nitrate aqueous solution, and the dipping time of the mixed oxide in the aqueous solution. The smaller heating rate, the lower temperature calcination, and a dipping in the aqueous solution at the lower pH were preferable for the Ni-loading in egg shell-type. Under the mild heating conditions, periclase-like MgO structure was formed, on which the reconstitution of Mg–Al hydrotalcite was preferentially provoked in the surface layer of the particle by “memory effect” during the dipping at the lower pH. It is concluded that the activity of egg shell-type Ni-loaded catalyst was enhanced by the surface enrichment of well-dispersed Ni metal particles.