Stability of highly dispersed Ni/Al2O3 catalysts: Effects of pretreatment

Oxidic and reduced and passivated Al2O3-supported nickel catalysts with loa ding up to 19.3 wt% were characterized by temperature-programmed sulfiding (TPS), temperature-programmed reduction (TPR), and X-ray photoelectron spec troscopy. The oxidic catalyst precursors contain a highly disperse nickel s pecies consisting of either an oxidic core and a hydroxide outer layer or a hydroxide as a whole, dependent on the Ni loading. The crystallite size of the active phase varies between 0.4 and 1.6 mn. This high dispersion was m aintained during sulfidation. From TPR and TPS, it is inferred that no nick el aluminate is present. During reduction and passivation the crystallite s ize increases to 1.3-2.5 mn. From TPR of the oxidic catalyst it was conclud ed that the active phase contained more oxygen than that corresponding to t he stoichiometry of NiO since an excess of hydrogen of 20-50% was consumed for the removal of the reactive oxygen species. (C) 2000 Academic Press.