Preparation Of Multistage Porous Alumina Supported Palladium Catalysts And The Catalytic Performance For Hydrogenation Of Styrene

The Pd/Al₂O₃ supported catalyst is the most commonly used hydrogenation catalyst in the industry.The Pd particles in the catalyst prepared by the traditional chemical impregnation method are easy to agglomerate and the dispersion is not high.At the same time,the acid sites and pore structures on the surface of Al₂O₃ affect the activity and longevity of catalyst.In order to solve the above problems,Pd-based catalysts with different structures supported on precious metals were prepared and their catalytic performance for hydrogenation of styrene was investigated.X-ray diffraction?XRD?,field emission scanning electron microscopy?SEM?,high resolution transmission electron microscopy?HR-TEM?,low temperature N₂ physical adsorption and desorption,hydrogen temperature programmed reduction?H₂-TPR?,and X-ray photoelectron spectroscopy?XPS?characterizes its physicochemical properties and analyzes the composition and properties of the catalyst.The following conclusions were obtained:1?The effect of the preparation method on the particle size and dispersion of Pd/?-Al₂O₃ supported catalyst Pd shows that the Pd particles of the reduction-sodium method after immersion are more uniform in size,better in dispersion and active component Pd and strong interactions occur between the carriers,and the activity is superior to other methods.2?In order to investigate the effect of pore structure on the activity of Pd-based catalysts,a three-dimensional ordered-macroporous double-channel supported Pd/3DOM Al₂O₃ catalyst was synthesized by double template method.F127 played a better structural orientation than P123.The carrier 3DOM Al₂O₃-F has a richer pore structure and a suitable specific surface area.The interconnected three-dimensional ordered macroporous structure plays a good mass transfer role in the hydrogenation reaction of styrene,accelerates the reaction rate,and enables the conversion of styrene to reach 100%within 100 min.3?In order to further improve the catalytic activity of the Pd-based catalyst,a series of three-dimensional Pd-Al₂O₃ catalysts with different loadings were prepared by introducing the active metal into the meso-macroporous double-channel network structure.The results showed that the diameter of Pd particles is about 10 nm.The catalyst has good stability.When the loading is increased and the calcination temperature is increased,the morphology of the catalyst is still not destroyed,and the Pd nanoparticles are highly dispersed in the pores and on the pore walls.When the loading is less than 6 wt%,the catalytic activity and the loading amount are linearly related,wherein the Pd particles are monodispersed on the carrier;when the loading is greater than or equal to 6 wt%,the Pd nanoparticles exhibit a small amount of agglomeration,and some particles enter the alumina.Compared to conventional supported catalysts,this method is more active when the loading is increased,and all samples can completely convert styrene in 120 minutes.