Effect of initial nickel particle size on stability of nickel catalysts for aqueous phase reforming

摘要

The deactivation behavior by crystallite growth of nickel nanoparticles on various supports (carbon nanofibers,zirconia,SiC,α-Al2O3 and y-Al2O3) was investigated in the aqueous phase reforming of ethylene glycol.Supported Ni catalysts of ～10 wt％ were prepared by impregnation of carbon nanofibers (CNF),ZrO2,SiC,)γ-Al2O3 and α-Al2O3.The extent of the Ni nanoparticle growth on various support materials follows the order CNF～ZrO2 ＞ SiC ＞ y-Al2O3 ＞＞ α-Al2O3 which sequence,however,was determined by the initial Ni particle size.Based on the observed nickel leaching and the specific growth characteristics;the particle size distribution and the effect of loading on the growth rate,Ostwald ripening is suggested to be the main mechanism contributing to nickel particle growth.Remarkably,initially smaller Ni particles (～12 nm) supported on αα-Al2O3 were found to outgrow Ni particles with initially larger size (～20 nm).It is put forward that the higher susceptibility with respect to oxidation of the smaller Ni nanoparticles and differences in initial particle size distribution are responsible for this behavior.