Methane decomposition and carbon deposition over Ni/ZrO_2 catalysts: Comparison of amorphous, tetragonal, and monoclinic zirconia phase

摘要

The influence of crystal phase of ZrO2 on the catalytic performance of methane decomposition and the properties of deposited carbon on Ni/ZrO2 catalysts was investigated. Ni/ZrO2 catalysts were prepared by incipient-wetness impregnation method with 5% Ni loading, using amorphous, monoclinic, and tetragonal ZrO2 as supports. It was found that Ni/am-ZrO2 exhibited high activity and superior stability for carbon dioxide reforming of methane during 50 h of TOS, which could be attributed to the smaller Ni particle size and the lower coking rate. Additionally, the results of O-2-TPO/TPH/CO2-TPO showed that the nature of carbon deposition via CH4 decomposition on Ni/ZrO2 catalysts was strongly influenced by both the Ni particle size and the crystal phase of zirconia. The lowest coking rate on Ni/am-ZrO2 for carbon dioxide reforming of methane was due to the lower CH4 decomposition rate and the higher gasification rate of carbon species by CO2. Carbon deposited on Ni/am-ZrO2 could be greatly removed by CO2, due to the presence of large amount of adsorbed oxygen species on the surface of amorphous ZrO2, For comparison, the imbalance of CH4 cracking and removal of coke by CO2 resulted in the accumulation of coke, leading to the deactivation of catalysts. (C) 2019 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.