Effects of Co Addition on the Surface Structure and the Activity of Mo/Al₂O₃ Catalyst for the Hydrogenation of Olefins

Abstract

The present study investigated the effects of Co addition on the surface structure and activity of Mo/Al2O3 for the hydrogenation of C6-C10 olefins. CoMo/Al2O3 (Co/Mo atomic ratio: 0.56) had lower activity for the hydrogenation of 1-hexene, 1-octene and 1-decene than Mo/Al2O3, whereas CoMo/Al2O3 had higher activity for the hydrogenation of 2-octene, 2,4,4-trimethyl-2-pentene and cyclohexene. Co/Al2O3 showed no activity for the hydrogenation of 1-octene and 2,4,4-trimethyl-2-pentene. NO uptake measurements over Mo/Al2O3 suggested that the coordinatively unsaturated sites of Mo atoms located at the edges of MoS2 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/Al2O3 (Co/Mo atomic ratio: 0.56) indicated that Co atoms blocked Mo atoms located at the edges of MoS2 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 MoS2 clusters. Presumably the increase in the stacking number of MoS2 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.

Effects of Acidic Properties on the Catalytic Performance of CoMo Sulfide Catalysts in Selective Hydrodesulfurization of Gasoline Fractions

“…Many studies have investigated the difference between HDS and HYD active sites and have suggested that HYD active sites have different properties to HDS active sites. 4-7, [14][15][16] Hatanaka et al proposed that CUS can be classified as follows: (i) n-olefin HYD active sites, (ii) isoolefin HYD active sites, and (iii) HDS active sites. 6 Although, they do not mention the difference in the structures among these active sites.…”

“…Similarly, CUS will be involved in HYD of unsaturated compounds. Many studies have investigated the difference between HDS and HYD active sites and have suggested that HYD active sites have different properties to HDS active sites – ,– . Hatanaka et al proposed that CUS can be classified as follows: (i) n -olefin HYD active sites, (ii) isoolefin HYD active sites, and (iii) HDS active sites.…”

Novel preparation method of highly active Co/SiO2 catalyst for Fischer-Tropsch synthesis with chelating agents

“…On the other hand, we have already found that HDS activities of Co(or Ni)Mo(or W)/A1 2 O 3 are highly improved when some chelating agents are added in impregnating solutions containing Co (or Ni) ions and Mo (or W) ions [17][18][19][20][21]. The role of chelating agents is considered to form stable chelate-Co complex and to control the timing of sulfiding of Co.…”

Development of Highly Active Co/SiO₂ Catalysts with Chelating Agents for Fischer-Tropsch Synthesis

“…The complexes between Co 2 and chelating agents used in this study have higher stabilities than those reported previously. Thermodynamic calculations in our previous study suggested that these complexes survive the drying step 32) . On the other hand, the present XPS analysis indicated the absence of carbonaceous compounds originating from the chelating agents after calcination (not shown here) 21) , suggesting the importance of the drying and calcination steps.…”