Impact of mesoporous structure of acid-treated clay on nickel dispersion and carbon deposition for CO methanation

Nickel catalysts supported on different acid-treated clays were prepared by the impregnation method in order to investigate the effect of the pore structures of supports on the dispersion and the chemical states of nickel species, and thus on the carbon depositions resulted from the dissociation of the CO molecules adsorbed on different active nickel sites. The catalysts and supports were characterized by the X-ray diffraction (XRD), the transmittance electron microscopy (TEM), the H-2 temperature-programmed reduction (H-2-TPR), the nitrogen adsorption-desorption, and the thermogravimetry and differential thermal analysis (TG-DTA). The CO methanation performance of the catalyst was investigated at a temperature range from 300 degrees C to 500 degrees C. The results indicated that the dispersion and the states of the nickel species on the support were influenced strongly by the pore structures of the acid-treated clays, and only the mesopores composed by partly damaged clay layers were conducive to forming the active nickel species, and thus reducing the deposition of the inactive carbon and improving the stability of the catalyst. The carbon species deposited on different active sites was slightly different in the oxidative properties when it was oxidized in air. A fraction of aluminum in the clays was leached out by acid, which decreased the possibility of forming the spinel phase of nickel aluminate in the catalyst. The highly dispersed nickel species showed little relevance to the high activity of the catalyst, but it exhibited a strong relation to the nickel sites from the bulk nickel species. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved

Nickel on a macro-mesoporous Al2O3@ZrO2 core/shell nanocomposite as a novel catalyst for CO methanation

A novel nickel catalyst supported on Al2O3@ZrO2 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 degrees C to 500 degrees C. 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 Al2O3@ZrO2 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/Al2O3@ZrO2-15 exhibited the highest CO conversion and methane selectivity at 400 degrees C, but they decreased dramatically above or below 400 degrees C due to the temperature sensitivity of the catalyst. Ni/Al2O3@ZrO2-30 exhibited a high and constant rate of methane formation between 350 degrees C and 450 degrees C. 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. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved