The role of La in improving the selectivity to cyclohexene of Ru catalyst for hydrogenation of benzene

Ru–La catalysts with different La/Ru molar ratios were prepared by co-precipitation. Characterizations revealed that the promoter La existed as La(OH)3 on the Ru surface. The La(OH)3 itself could not enhance the selectivity to cyclohexene of Ru catalyst. However, the La(OH)3 could react with ZnSO4 in slurry to form an insoluble (Zn(OH)2)3(ZnSO4)(H2O)3 salt. The chemisorbed (Zn(OH)2)3(ZnSO4)(H2O)3 salt on Ru surface played a key role in improving the selectivity to cyclohexene of Ru catalyst. Ru–La catalyst with the optimum La/Ru molar ratio of 0.14 gave a maximum cyclohexene yield of 59.5%. Besides, Ru–La(0.14) catalyst had a good reusability and an excellent stability.

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► The La in the catalyst existed as La(OH)3 on the surface of Ru particles.
► The La(OH)3 could react with ZnSO4 to form an insoluble (Zn(OH)2)3(ZnSO4)(H2O)3 salt.
► The (Zn(OH)2)3(ZnSO4)(H2O)3 salt improved the selectivity to cyclohexene of Ru catalyst.
► Ru–La(0.14) catalyst gave a maximum cyclohexene yield of 59.5%.