Effect of Water Vapor on the Reduction of Ru-Promoted Co/Al2O3

Abstract

The effect of water vapor on the reduction of a calcined Ru-promoted Co/Al2O3 catalyst was investigated by introducing water vapor during the standard reduction procedure (H2, 350°C, 10 h) and during TPR. The presence of added water vapor (up to 3%) during standard reduction resulted in a decrease in the amount of Co able to be reduced. A peak located at ca. 500°C was observed in the TPR profiles of the catalyst after standard reduction in the presence of water. The amount of cobalt reducible in this temperature range increased with water vapor concentration. The reduction of this cobalt species, which was probably due to Co interacting strongly with the Al2O3, was inhibited during standard reduction in the presence of water vapor. Addition of water vapor during standard reduction also led to a decrease in the total amount of reducible cobalt (<900°C). The “nonreducible” cobalt existed mainly in the form of a cobalt aluminate with a reduction temperature higher than 900°C during TPR. It was observed that introduction of water vapor during TPR of the calcined catalyst also had a significant effect on the TPR profile. Two peaks could be observed in either the presence or the absence of added water vapor. The first reduction peak at ca. 230°C remained essentially unchanged; however, the second reduction peak temperature (400–600°C) shifted up to 200°C higher and the peak area decreased to ca. one-third in the presence of increased water vapor pressures. The amount of cobalt able to be reduced during TPR to 900°C decreased with an increase in the amount of H2O added. The presence of water vapor during reduction appears to retard the reduction process by increasing the Co–alumina interaction and/or forming cobalt aluminates.