Nickel on a macro-mesoporous Al_2O_3@ZrO_2 core/shell nanocomposite as a novel catalyst for CO methanation

摘要

A novel nickel catalyst supported on Al_2O_3@ZrO_2 core/shell nanocomposites was prepared by the impregnation method. The core/shell nanocomposites were synthesized by depositing zirconium species on boehmite nanofibres. This contribution aims to study the effects of the pore structure of supports and the zirconia dispersed on the surface of the alumina nanofibres on the CO methanation. The catalysts and supports were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), H_2 temperature-programmed reduction (H_2-TPR), nitrogen adsorption-desorption, and thermogravimetry and differential thermal analysis (TG-DTA). The catalytic performance of the catalysts for CO methanation was investigated at a temperature range from 300 ℃ to 500 ℃. The results of the characterization indicate that the metastable tetragonal zirconia could be stably and evenly dispersed on the surface of alumina nanofibres. The interlaced nanorods of the Al_2O_3@ZrO_2 core/shell nanocomposites resulted in a macropore structure and the spaces between the zirconia nanoparticles dispersed on the alumina nanofibres formed most of the mesopores. Zirconia on the surface of the support promoted the dispersion and influenced the reduction states of the nickel species on the support, so it prevented the nickel species from sintering as well as from forming a spinel phase with alumina at high temperatures, and thus reduced the carbon deposition during the reaction. With the increase of the zirconia content in the catalyst, the catalytic performance for the CO methanation was enhanced. The Ni/Al_2O_3@ZrO_2-15 exhibited the highest CO conversion and methane selectivity at 400 ℃, but they decreased dramatically above or below 400 ℃ due to the temperature sensitivity of the catalyst. Ni/Al_2O_3@ZrO_2-30 exhibited a high and constant rate of methane formation between 350 ℃ and 450 ℃. The excellent catalytic performance of this catalyst is attributed to its reasonable pore structure and good dispersion of zirconia on the support. This catalyst has great potential to be further studied for the future industrial use.