Abstract
The effect of cobalt addition on Mo/Al2O3 hydrodesulfurization catalyst was investigated by 129Xe NMR. Both the amount of adsorbed xenon and the peak width of 129Xe NMR were almost constant at various cobalt loadings. This result indicates that the cobalt species on the catalyst surface had little effect on the motion of xenon in the micropores. The chemical shift δ of the 129Xe NMR peak varied nonlinearly with the amount of adsorbed xenon. Presumably this is due to a strong interaction between xenon and coordinatively unsaturated anion vacancy sites. The curvature of δ increased further at cobalt loadings of more than 2.2 mass%, which suggests that the electrons of xenon were strongly attracted by the cobalt species. Moreover, the parameter δ0 calculated from fitting of the theoretical equation gradually increased with Co/Mo ratio and reached the maximum value at Co/Mo = 0.71. This is caused by an increase in the term δM that depends on the magnetic susceptibility and strongly suggests that antiferromagnetic Co-Mo-S phases were formed. On the other hand, a small decrease in δ0 at Co/Mo = 0.99 originated from a decline in the magnetic susceptibility of the whole sample due to the formation of diamagnetic Co9S8. 129Xe NMR is useful for analysis of the formation of the Co-Mo-S phase on CoMo/Al2O3 hydrodesulfurization catalyst.
