Construction And Benzene-selective Hydrogenation Performance Control Of Novle Ru-based Composite Catalysts

Cyclohexene with an active double bond is a very important organic intermediate.Cyclohexene is widely used in the synthesis of pharmaceuticals and other high value-added fine chemicals.Benzene-selective hydrogenation has been identified as the key technology for the production of nylon 6 and nylon 66.Benzene-selective hydrogenation to cyclohexene has always been a great challenge in heterogeneous catalytic reactions due to unfavorable thermodynamic factors.In the past few decades,the domestic and foreign researchers have done a lot of research work on benzene-selective hydrogenation in the range from the development of new catalysts to the optimization of process conditions,and have made great breakthroughs.However,the quantitative relationship between the composition,structure,and morphology of catalyst and the cyclohexene selectivity is rarely reported.At present,Ru-Zn catalyst is mainly employed on the industrial line.The benzene conversion rate was controlled at 40%⁵0%,and the yield of cyclohexene was 30%⁴0%,which was still relatively low.Therefore,it is of great significance to reveal the reaction mechanism and develop green catalysts whicn can improve the selectivity and yield.In order to construct the effective modification of active center,as well as the quantitative relationship between the nature of active center and activity and selectivity,this artivle is focused on the liquid benzene-selective hydrogenation,the main conclusions are as follows:1.A series of novel surface-modified Ru-based catalysts with chemisorption of BZSS（Basic Zinc Sulfate Salts,3Zn（OH）₂·ZnSO₄·xH₂O）were prepared and applied in benzene-selective hydrogenation,which showed good activity and cyclohexene selectivity.The surface active sites on Ru nanoparticles（NPs）are reconstructed because the strong active sites are selectively occupied and blocked by BZSS nanoclusters.Lewis acid sites,which are introduced by BZSS and modified by the interaction between Ru（0）and BZSS,play an important role in increasing the proportion of asymmetric adsorption and hydrogenation of benzene and improving the selectivity of cyclohexene;on the other hand,BZSS nanoclusters are confirmed to regulate surface and electronic properties as well as geometric constructions of Ru NPs.Benefiting from the BZSS nanoclusters located on the Ru NPs,the surface-modified catalysts present high activity with excellent selectivity for the hydrogenation reaction.The catalyst（RuAD300）exhibited a cyclohexene selectivity of 87% at the benzene conversion of 40%,and the maximum yield of cyclohexene was up to 61%.Zn（OH）₂,ZnO,and NaOH can form BZSS in situ under reaction condition,and the catalytic performace can be adjusted to the same effect by adding their equivalent amount versus BZSS,respectively.The industrial application shows that the BZSS-modified Ru-based catalysts has stable performance.The activity and selectivity have good tunable properties,which ensured the long-term stable operation on industrial line.2.ZrO₂ HSNCs（heterophase structure nanocrystals）were synthesized with tunable ratios of monoclinic ZrO₂（m-ZrO₂）versus tetragonal ZrO₂（t-ZrO₂）.The phase mole ratio of m-ZrO₂ in ZrO₂ HSNCs was tuned from 40% to 100%.The ZrO₂ HSNCs were used as effective supports to fabricate Ru/ZrO₂ catalysts for benzene-selective hydrogenation.Due to m-ZrO₂ with higher concentration of the surface hydroxyl groups than that of t-ZrO₂,ZrO₂ HSNCs have heterogeneous surface hydroxyl groups.ZrO₂ HSNCs create more intimate synergistic effects than their single-phase counterparts.Ru NPs tend to support on the m-ZrO₂/t-Zr O₂ junction,the heterogeneous strong/weak hydrophilic interface resulted in a water/oil layer forming at the m-ZrO₂/t-ZrO₂ junction during reaction.The oil layer ensures the adsorption and activation of benzene,and the water layer ensures the high selectivity of cyclohexene.The excellent catalytic performance is attributed to the specific diffusion-restricted area at the heterophase junction.When the ratio of m-ZrO₂ in ZrO₂ HSNCs was 60%,the yield of cyclohexene was 55.3% at the 87.0% conversion of benzene.3.A simple PEG-assisting H2 reduction method was developed for the synthesis of Ru NPs and fabrication of polycrystal nanospheres（NSs）.The Ru NSs possess a size of 50⁶0 nm.Ru NSs catalyst exhibits superior catalytic performance than that of Ru bulk,Ru network and dendritic Ru.Ru NSs are favorable to stay in water drops in benzene-selective hydrogenation and then construct an instant SCS（soft core-shell）structure.Ru NSs have excellent catalytic performance,because the spherical morphology has a better controlling of the water film thickness and uniformity than that of non-spherical morphologies.The core of the SCS structure is the catalytic active center,the shell is a water layer containing ZnSO₄ electrolyte solution.The water layer can effectively restrict the formed cyclohexane on the surface of the catalyst,and inhibit its desorption from the catalyst surface to the oil phase.At the same time,the desorbed cyclohexene is prevented from re-adsorption for further hydrogenation.Ru NSs without any promoters gave the highest cyclohexene selectivity（S40 = 66.6%）and yield（Ymax = 37.5%）.We call this catalytic model “teardrop catalysis”.This model is suitable for the selective hydrogenation of cinnamyl aldehyde（CAL）reaction.The introduction of electrolyte solution can significantly improve the selectivity of the target product of cinnamyl alcohol（COL）.The order is Zn（CH₃COO）₂ < ZnBr₂ < ZnSO₄ < CoCl₂ < Zn（NO₃）₂ < ZnCl₂.According to this model,we determined the optimal electrolyte is 0.5 mol L^-1 of ZnCl₂.