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A novel process based on cyclohexene esterification–hydrogenation for the production of cyclohexanol, the key intermediate in the production of ε-caprolactam, was devised and validated for the first time. In this process, cyclohexene obtained from the partial hydrogenation of benzene is esterified with acetic acid to cyclohexyl acetate, followed by hydrogenation to cyclohexanol. The experimentally determined equilibrium conversion of cyclohexene for cyclohexene esterification at the stoichiometric ratio is always ≥68% in the temperature range of 333–373 K over the commercial Amberlyst 15 catalyst, which is substantially higher than that of cyclohexene hydration. The apparent activation energy (Ea) for the esterification of cyclohexene with acetic acid is 60.0 kJ mol−1, which is lower than that of cyclohexene hydration. In the hydrogenation of cyclohexyl acetate to cyclohexanol, high conversion of 99.5% and high selectivity of 99.7% are obtained on the La-promoted Cu/ZnO/SiO2 catalyst prepared by the co-precipitation method. This process shows both a high overall atom economy of 99.4% comparable to that of the cyclohexene hydration process and a much higher catalytic efficiency than the phenol hydrogenation process. On the basis of the above fundamental works, a pilot-scale demonstration unit with a capacity of 8000 tonnes per annum was developed and operated smoothly for more than 1000 h with no indication of deactivation. [ABSTRACT FROM AUTHOR]

Abstract: A strategy based on galvanic replacement between metallic Zn and Ru salt followed by acid treatment was developed to fabricate supported Ru–Zn/ZrO2 nanocomposite catalysts with controlled contents of Zn for the benzene partial hydrogenation to cyclohexene. The catalysts were systematically characterized by techniques such as extended X‐ray absorption fine structure, X‐ray photoelectron spectroscopy, and transmission electron microscopy. In benzene partial hydrogenation, with the decrease in the content of Zn, the turnover frequency (TOF) of benzene increased monotonically, whereas the selectivity to cyclohexene evolved in a volcanic trend, passing through a maximum of 72 %. Kinetic analysis indicated that with the depletion of Zn, the rate constant for benzene hydrogenation to cyclohexene and that for cyclohexene hydrogenation to cyclohexane increased simultaneously, but the extents of the increments were at variance. It was identified that the ratios of the rate constants were in parallel with the change in the selectivity to cyclohexene, which is attributed to the electronic effect of metallic Zn that modifies the interactions of Ru with benzene and cyclohexene. [ABSTRACT FROM AUTHOR]

Partial hydrogenation of benzene to cyclohexene is attractive in terms of feedstock accessibility, atomic economy, and operational simplicity. Herein, a series of Ru/ZrO2 catalysts were prepared by post-treatment of a binary Ru-Zn/ZrO2 catalyst using 5-30 wt % NaOH aqueous solutions. Alloying between Ru and Zn was evidenced for the catalyst post-treated only by water (Ru/ZrO2-0). Alkaline post-treatment removed metallic Zn, forming smaller Ru nanoparticles. Concomitantly, the hydrophilicity of the catalysts was increased and maximized on the 10 wt % NaOH-treated catalyst (Ru/ZrO2-10). In partial hydrogenation of benzene, the Ru/ZrO2-0 catalyst displayed the highest turnover frequency but the lowest initial selectivity to cyclohexene, whereas the Ru/ZrO2-10 catalyst exhibited the highest initial selectivity (86 %) and yield of cyclohexene (51 %) among the catalysts investigated. A quantitative relationship between the initial selectivity to cyclohexene and the hydrophilicity of these catalysts was identified, which rationalizes the significant impact of alkaline post-treatment on selectivity enhancement in partial hydrogenation of benzene to cyclohexene over Ru/ZrO2 catalysts. [ABSTRACT FROM AUTHOR]

Site-specific deposition of metal nanoparticles (NPs) on metal oxide surfaces is challenging but of particular importance for the development of catalytic materials with improved or new performance. We report here that Ru NPs can be directed to the rutile/anatase junction of P25 TiO 2 via a facile wetness impregnation–chemical reduction method at room temperature. In the partial hydrogenation of benzene to cyclohexene, the Ru/P25 catalyst outperformed the Ru NPs supported on phase-pure rutile and anatase as well as physically mixed Ru/rutile and Ru/anatase, both in activity and in selectivity. We identified a unique electron-deficient Ru species (Ru δ+ ) on the Ru/P25 catalyst originated from the Ru O linkages connecting the Ru NPs with the rutile/anatase junction. This interfacial Ru δ+ species gave rise to an especially tightly bonding benzene species while lowering the adsorption strength of cyclohexene, thus granting the Ru/P25 catalyst superior activity and unprecedented selectivity toward cyclohexene (initial selectivity 90%). [ABSTRACT FROM AUTHOR]

Highlights: [•] B-doped ZrO2 (B-ZrO2) with various acid amounts (n NH3) from NH3-TPD were prepared. [•] The Ru/B-ZrO2 catalysts were evaluated in benzene hydrogenation to cyclohexene. [•] The turnover frequency of benzene was linearly proportional to n NH3. [•] B doping enabled a maximum initial selectivity (S 0) of 88% toward cyclohexene. [•] A volcanic evolution trend between S 0 and n NH3 was unveiled. [ABSTRACT FROM AUTHOR]

Ru–B/ZrO2catalysts using monoclinic,amorphous,and tetragonal ZrO2as supports were prepared and usedfor liquid-phase hydrogenation of benzene to cyclohexene. It is identifiedthat both the Lewis acid sites and the Brønsted acid sites existedon monoclinic ZrO2(ZrO2-M), while there wereonly Lewis acid sites on amorphous (ZrO2-A) and tetragonalZrO2(ZrO2-T). The amount of acid sites on ZrO2-T was the lowest. In liquid-phase hydrogenation of benzeneto cyclohexene, the Ru–B/ZrO2-T catalyst exhibitedthe highest selectivity and yield of cyclohexene, with the maximumyield of cyclohexene being 47%. These results suggest that for ZrO2-supported Ru–B catalysts, the lower was the amountof acid sites on ZrO2, the higher was the selectivity tocyclohexene. Also, the presence of the Brønsted acid sites onZrO2is probably adverse to the selectivity toward cyclohexene. [ABSTRACT FROM AUTHOR]

A colloidal RuB/Al2O3·xH2O catalyst has been synthesized through a combined coprecipitation–crystallization–reduction strategy and characterized in detail with techniques including ICP-AES, N2 physisorption, XRD, TG/DTA, PSD and TEM. The catalytic behavior in liquid phase selective hydrogenation of benzene to cyclohexene was studied and compared with that of the RuB/γ-Al2O3 catalyst prepared by the incipient-wetness impregnation method. The RuB/Al2O3·xH2O catalyst is found more reactive than the RuB/γ-Al2O3 catalyst, and the maximum yield of cyclohexene is about four times as high as that over the latter. The better activity of the colloidal catalyst is assigned to the higher dispersion of the smaller RuB particles, whereas its superior selectivity is attributed to the improved hydrophilicity due to higher content of structural water and surface hydroxyl groups. [Copyright &y& Elsevier]

A Ru–Zn/m-ZrO2 nanocomposite catalyst for benzene partial hydrogenation to cyclohexene was prepared by coprecipitation of ruthenium trichloride and zirconium oxychloride with ammonia, followed by hydrogen reduction in an aqueous zinc sulfate solution. By use of transmission electron microscopy (TEM), powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), the reduction of zinc cation to metallic zinc and the transformation of zirconium hydroxide to monoclinic zirconia were proposed and explained. The hydrogenation parameters, such as the amount of zinc sulfate in the pretreatment process, the hydrogenation temperature, the stirring rate, and the hydrogen pressure, influenced the yield of cyclohexene. The pronounced positive effect of metallic zinc in enhancing the cyclohexene yield was discussed. [Copyright &y& Elsevier]

Some ultrafine Ni-B amorphous alloys with variable B contents were prepared by chemical reduction under different conditions. The effect of the B content on their activities was evaluated by using the liquid phase cyclohexene hydrogenation as a probe. Both the specific activity and the TOF value increased with the increase of the B content, showing the promoting effect of the alloying B on the hydrogenation activity, which was mainly attributed to its modification of the nature of the Ni active sites. Concerning the structural effect, the XRD patterns revealed that the amorphous degree of the as-prepared Ni-B alloy increased with the increase of the B content. Meanwhile, the DSC analysis demonstrated that increase of the B content could increase the thermal stability of the Ni-B amorphous alloy and in turn, delay its crystallization during the cyclohexene hydrogenation. Furthermore, the EXAFS also demonstrated that the Ni active sites became more highly unsaturated at higher B content. These structural modifications were favorable for the hydrogenation activity. Concerning the electronic effect, the XPS spectra demonstrated the electronic interaction between Ni and B in the Ni-B amorphous alloy, making Ni electron-enriched while B became electron-deficient. According to the DFT calculations, more electrons may transfer from the alloying B to Ni with the increase of the B content. Such electronic modifications may also facilitate the cyclohexene hydrogenation. [Copyright &y& Elsevier]