Ru/SiO₂ Catalysts For The Hydrogenation Of Biphenyl To Bicyclohexyl

Liquid organic hydrogen carriers have been recently developed as the promising hydrogen storage materials,which exhibit significant advantages in hydrogen energy storage and utilization compared with the conventional hydrogen storage systems.Bicyclohexyl is an ideal hydrogen storage material with high economic value due to its low toxicity and high boiling point.In this work,the supported Ru based catalysts with highly dispersed metal nanoparticles were synthesized by the simple and effective strong electrostatic adsorption method and applied for the complete hydrogenation of biphenyl to bicyclohexyl.A large number of characterization techniques were used to study the relationship between the physicochemical properties and the catalytic performance.The effects of reaction time,reaction temperature,hydrogen pressure and catalyst dosage on the reaction performance were further investigated.The mechanism of complete hydrogenation of biphenyl was studied by the density functional theory(DFT)calculations.The effects of specific surface area and calcination temperature on the reaction performance were also studied.The research contents of this work mainly included the following aspects:(1)A series of Ru/SiO2 catalysts with different metal loadings were synthesized by the strong electrostatic adsorption method.The hydrogenation performance of biphenyl was compared with those synthesized by the conventional dry impregnation method and the commercial 5.0 wt.%Ru/C catalyst.XRD,TEM,XPS,H2-TPR,and FT-IR characterization techniques were used to investigate the physicochemical properties of the representative catalysts.The results showed that the catalysts synthesized by the strong electrostatic adsorption method possessed small-sized and well-dispersed Ru nanoparticles on the support.Especially,1.5 wt.%Ru/SiO2 catalyst exhibited excellent hydrogenation activity,where the conversion of biphenyl was up to 99.9%,and the yield of bicyclohexyl reached 99.9%.In addition,the hydrogenation activity of 1.5 wt.%Ru/SiO2 catalyst did not decrease significantly after twenty cycles,indicating that the catalyst had excellent stability and reusability.According to the DFT calculations,the adsorption properties of biphenyl and cyclohexylbenzene were strongly depended on the size of Ru nanoparticles,and their adsorption strength on smaller Ru nanoparticles were decreased,which can enhance the anti-poisoning ability and improve the catalytic activity.(2)A series of Ru/SiO2 catalysts were synthesized by the strong electrostatic adsorption method and the dry impregnation method using fumed silica with different specific surface areas as support.The effects of specific surface area on the hydrogenation of biphenyl to bicyclohexyl over Ru/SiO2 catalysts were investigated.The catalysts synthesized by the strong electrostatic adsorption method had smaller metal Ru nanoparticles and higher hydrogenation activity than the catalysts synthesized via the dry impregnation method.The experimental results showed that the catalyst synthesized by the strong electrostatic adsorption method with the specific surface area of 300 m2 g-1 fumed silica had the highest catalytic activity.Further,the effects of calcination temperatures on the hydrogenation performance of biphenyl to bicyclohexyl over Ru/SiO2 catalysts were studied.The results showed that the best calcination temperature of supported catalyst was 120℃.With the increase of calcination temperature,Ru nanoparticles were likely to agglomerate,which led to the decrease of the hydrogenation activity.