In this work, the hydrogenation of cyclohexene over Ru–Zn/Ru(0 0 0 1) surface alloy was investigated by a DFT study so as to improve the understanding of the catalytic mechanism of the partial hydrogenation of benzene to cyclohexene over Ru–Zn alloy catalyst. Calculation results show that the presence of Zn atoms on the surface alloy results in not only a direct decrease in sites for the chemisorption of cyclohexene but also a depressed adsorption capability of the neighboring surface Ru sites. For an adsorbed cyclohexene molecule, whether the subsequent hydrogenation can be readily performed actually is determined by the relative position among the Zn atom, the H atom, and the adsorbed cyclohexene molecule. In most cases, the hydrogenation is forbidden because of the repulsion from Zn atoms to the nearby H atoms. Only in the specific situations in which the H atom participating in the reaction is not immediately close to the Zn atom, can the hydrogenation be accomplished with a relatively lower activation energy compared with the reactions on the Ru(0 0 0 1) surface. From the perspectives of adsorption and reaction kinetics, Ru-based catalyst modified by metallic Zn is no longer suitable for the hydrogenation of cyclohexene, which is supposed to be crucial to the improvement of cyclohexene yield in the partial hydrogenation of benzene over Ru–Zn alloy catalyst.

From the adsorption point of view, partial hydrogenation of benzene to cyclohexene over the metallic Zn modified Ru-based catalyst was experimentally and theoretically investigated. A decreased hydrogenation activity but increased selectivity to cyclohexene over the prepared Ru-Zn/ZrO2 catalyst was observed in the partial hydrogenation of benzene. Theoretical calculations suggest that the above phenomena are mainly resulted from the depression of the chemisorption of benzene and cyclohexene on the modified catalyst, especially for the latter. Undesired deep hydrogenation from cyclohexene to cyclohexane in the middle and late reaction stage therefore is effectively retarded, by which an improved cyclohexene yield is guaranteed. An optimal Zn content of 2.72wt.% in the Ru-based catalyst was proposed by both the experiment and calculation for the partial hydrogenation of benzene, and a cyclohexene yield up to 44% was obtained over Ru-Zn/ZrO2 catalyst.

In this work, hydrophilic property of Ru (0001) with and without H adatoms was theoretically studied to increase the understanding of the partial hydrogenation of benzene to cyclohexene over ruthenium catalysts. Density functional theory based calculations suggest that formation of hydrogen bonding among the adsorbed H2O molecules results in a weakened interaction between the water adlayer and Ru (0001), while the calculated heat of adsorption containing the contribution of hydrogen bonding is no longer suitable for evaluating the hydrophilic property of the metal surface. The presence of H adatoms exerts an electrostatic repulsion on the adsorbed H2O molecules; thereby the latter can be in the state of chemisorption or physisorption on the Ru metal depending on the number of immediately adjacent H adatoms and on the relative distance to the H adatoms. By tuning the coverage of H adatoms, the surface hydrophilic/hydrophobic balance of the Ru metal can be effectively adjusted, which provides an approach to improve the selectivity to cyclohexene in the partial hydrogenation of benzene.

A high-performance liquid chromatography with ultraviolet detection method was established and validated for quantification of forsythoside concentrations in dog plasma. Following a single-step protein precipitation with perchloric acid, the forsythoside and internal standard were separated on a reversed-phase C18 column with water-glacial acetic acid-methanol as mobile phase at a flow rate of 1 mL/min with ultraviolet detection at 326 and 278 nm for forsythoside and IS, respectively. The calibration curve for forsythoside was linear over a range of 0.052–13.33 μg/mL with correlation coefficient of 0.999. The within- and between-batch precisions of analysis were <8 % and accuracy was 95–107%. After intravenous administration of forsythoside at the doses of 5, 10, and 20 mg/kg, theC max values for forsythoside were estimated to be of 12.33, 22.90 and 54.45 μg/mL, respectively. The AUC increased with the increasing of doses, and the mean AUC0-t values were 5.69, 11.80, and 18.66 mg·h/L, respectively. Forsythoside was eliminated quickly and the meanT m values at doses of 5, 10, and 20 mg/kg were 1.36, 1.49, and 0.71h, respectively. The pharmacokinetics of forsythoside in beagle dogs complied with linear kinetic course in the dose range.

Partial hydrogenation of benzene over Ru-Zn/ZrO2 was investigated with the theoretical and experimental approaches. Atomic state of Zn was introduced into the Ru-based catalyst by loading ZnSO4 into the water phase during the reduction of the precursor. The DFT calculation showed that the presence of Zn atoms on the Ru-based catalyst has an unfavorable effect on the chemisorption of benzene and cyclohexene. Furthermore, the whole Zn atoms-modified catalyst surface is partly passivated for the chemisorption of cyclohexene, which is considered essential to the improvement of the cyclohexene yield on the Ru-Zn/ZrO2 catalyst. The experimental results showed that an increase in the Zn content in the Ru-based catalyst results in a monotonically decreased hydrogenation activity and an improved selectivity for cyclohexene. Both the theoretical and experimental investigation confirm the optimal Zn content in the Ru-based catalyst.

In this paper,the adsorption of benzene on the Ru-Zn/Ru(0001) surface alloy was investigated by density functional theory in order to improve the understanding to the reaction mechanism of the partial hydrogenation of benzene on the Ru-Zn alloy catalyst.Calculation results show that the heat of adsorption of benzene on the Ru-Zn/Ru(0001) surface decreases by about 60% when the adsorption sites are directly related to the Zn atoms.The repulsion between the Zn atom and the carbon atoms of benzene distorts the spatial symmetry between the bonding orbitals of benzene and the valence orbitals of the surface Ru atoms,which is unfavorable to the adsorption of benzene on the alloy surface.When the adsorption site doesn't involve the Zn atom,the neighboring Zn atom actually has no influence on the adsorption of benzene on the alloy surface.

For the sake of improving the performance of Ru-based catalyst used in partial hydrogenation of benzene to cyclohexene, the effect of Zn2+/Zn layer on the adsorption and dissociation of H2 on Ru (0001) surface was investigated by applying density function theory (DFT) calculations. Calculation results show that the dissociation of H2 occurs only after its being chemisorbed horizontally at atop site. Because of the influence of Zn2+ on the electron delocalization between molecular orbit of H2 and valence orbits of atop Ru atom, a remarkable increase in the H2 dissociation barrier is noticed, which results in zones of sparse chemisorbed H around Zn2+. Adsorbed Zn2+ can be reduced by chemisorbed H, and the H2 dissociation kinetics varies little in the presence of Zn atoms at adjacent sites. Split zones of chemisorbed H are formed at a high coverage of Zn layer. The consecutive or synchronous hydrogenation of benzene is disturbed when benzene is adsorbed in zones of sparse chemisorbed H or split zones of chemisorbed H. It is therefore deducted that a high coverage layer of some transition metal atoms on catalyst surface should be helpful for maintaining the hydrogenation activity of the catalyst and improving the cyclohexene yield.