Passivation of a Co-Ru/γ-Al2O3 Fischer-Tropsch catalyst

Passivation of highly dispersed metal catalysts after reduction is necessary prior to exposure to air due to the exothermicity of metal oxidation. This exothermicity can result in a significant increase in temperature of the catalyst resulting in catalyst degradation and a potential fire hazard. This paper reports the results of a study of passivation of Ru-promoted Co/alumina. Passivations using CO and CO + H-2 mixtures were compared to the standard method of passivation using small concentrations of O-2. Passivation by CO + H-2 resulted in a lower temperature rise upon exposure to air than oxygen passivation. Passivation using CO/H-2 = 10 resulted in a catalyst whose catalytic activity for CO hydrogenation was able to be recovered after exposure to air by re-reduction similar to after oxygen passivation. CO passivation yielded a catalyst that was not able to be as well recovered upon re-reduction, probably due to the formation of graphitic carbon. Exposure of the CO/H-2 passivated catalyst to air for at least 90 min actually made it easier to recover the original activity upon re-reduction. This is probably related to the oxidation of the carbidic passivation layer during air exposure. (C) 2002 Elsevier Science B.V. All rights reserved.