Effect of transition metals (Cr, Mn, Fe, Co, Ni, Cu and Zn) on the hydrogenation properties of benzene over Ru-based catalyst

Abstract The influence of transition metals on the hydrogenation properties of benzene over Ru-based catalysts had been investigated in the presence of ZnSO 4 acting as the reaction modifier. It was found that the (Zn(OH) 2 ) 3 (ZnSO 4 )(H 2 O) x salt ( x  = 1 or 3) chemisorbed on Ru surface played a key role in improving the selectivity of Ru catalysts to cyclohexene. The promoter Cr in Ru–Cr( x ) catalysts existed as Cr 2 O 3 . The amount of the (Zn(OH) 2 ) 3 (ZnSO 4 )(H 2 O) x salt ( x  = 1 or 3) chemisorbed on Ru surface slightly decreased with the increase of the amount of Cr 2 O 3 , resulting in a slight decrease of the selectivity to cyclohexene for the Ru–Cr(0.42) catalyst. Co and Ni promoters were present as Co 3 O 4 and Ni(OH) 2 in the Ru–Co( x ) and Ru–Ni catalysts, respectively. Increasing amounts of Co 3 O 4 and Ni(OH) 2 increased the chemisorption of (Zn(OH) 2 ) 3 (ZnSO 4 )(H 2 O) x salt ( x  = 1 or 3), leading to a slight decrease in activity and a slight increase in selectivity of the Ru–Co( x ) and Ru–Ni( x ) catalysts to cyclohexene. The promoters Mn, Fe and Zn existed as Mn 3 O 4 , Fe 3 O 4 and ZnO, respectively, in the Ru–Mn( x ), Ru–Fe( x ) and Ru–Zn( x ) catalysts. These could react with ZnSO 4 to form the (Zn(OH) 2 ) 3 (ZnSO 4 )(H 2 O) x salt ( x  = 1 or 3). The amount of chemisorbed (Zn(OH) 2 ) 3 (ZnSO 4 )(H 2 O) x salt ( x  = 1 or 3) was significantly increased with the content of Mn 3 O 4 , Fe 3 O 4 and ZnO, resulting in a prominent decrease in activity and a significant increase in cyclohexene selectivity of the Ru–Mn( x ), Ru–Fe( x ) and Ru–Zn( x ) catalysts. The Ru–Mn(0.23), the Ru–Fe(0.47) and the Ru–Zn(0.27) catalysts provided maximum cyclohexene yields of 55.3%, 56.7% and 53.4%, respectively. The Cu promoter in the Ru–Cu(0.49) catalyst was present as CuO. Part of the CuO could react with the ZnSO 4 in the slurry to form a Cu 4 (SO 4 )(OH) 6 (H 2 O) salt. The presence of the chemisorbed Cu 4 (SO 4 )(OH) 6 (H 2 O) and (Zn(OH) 2 ) 3 (ZnSO 4 )(H 2 O) x ( x  = 1 or 3) salts improved the selectivity of the Ru–Cu(0.49) catalyst to cyclohexene.