Abstract
The present study investigated the effects of Co addition on the surface structure and activity of Mo/Al 2 O 3 for the hydrogenation of C 6 -C 10 olefins. CoMo/Al 2 O 3 (Co/Mo atomic ratio: 0.56) had lower activity for the hydrogenation of 1-hexene, 1-octene and 1-decene than Mo/Al 2 O 3 , whereas CoMo/Al 2 O 3 had higher activity for the hydrogenation of 2-octene, 2,4,4-trimethyl-2-pentene and cyclohexene. Co/Al 2 O 3 showed no activity for the hydrogenation of 1-octene and 2,4,4-trimethyl-2-pentene. NO uptake measurements over Mo/Al 2 O 3 suggested that the coordinatively unsaturated sites of Mo atoms located at the edges of MoS 2 clusters were active for the hydrogenation of both 1-octene and 2,4,4-trimethyl-2-pentene. Diffuse reflectance FTIR measurements of NO adsorbed on CoMo/Al 2 O 3 (Co/Mo atomic ratio: 0.56) indicated that Co atoms blocked Mo atoms located at the edges of MoS 2 clusters almost completely, i.e. formation of the Co-Mo-S structure. Therefore, formation of the Co-Mo-S structure depressed the activity for hydrogenation of 1-octene. The addition of Co promoter also increased the stacking number of MoS 2 clusters. Presumably the increase in the stacking number of MoS 2 clusters facilitated the adsorption of bulky olefins and promoted the hydrogenation. This may be the main reason for the promoting effect of Co for the hydrogenation of 2,4,4-trimethyl-2-pentene.
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