Preparation Of Palladium-based Nanocatalysts And Their Performance For Selective Hydrogenation Of Phenol

Cyclohexanone is widely used in medicine,pesticides,coatings and other chemical fields.It is the key intermediate for the synthesis of nylon 6 and nylon 66.In the reported synthesis methods of cyclohexanone,the selective hydrogenation of phenol for cyclohexanone has more advantage,such as mild reaction conditions,high atomic economy,and is regarded as the best method.However,its products are usually the mixture of cyclohexanol and cyclohexanone,which thereby affects the quality of cyclohexanone and its application.From this view,it is of great significance to prepare a highly efficient and green catalyst for the selective hydrogenation of phenol to cyclohexanone.In this context,a series of Pd-based nanocatalysts were designed,prepared and applied in phenol hydrogenation.The relationship between the structure and performance of these catalysts was studied based on necessary experiments and characterizations.Firstly,a novel sodium alginate-based Pd-3D double network hydrogel catalyst Pd/Ca-Alg-PAAS has been fabricated by adding sodium polyacrylate.The prepared catalyst showed excellent catalytic activity and high selectivity?99.8%?for cyclohexanone in the selective hydrogenation of phenol.Furthermore,this catalyst still kept a conversion of over80%with the selectivity for cyclohexanone being over 99%after 6 runs.The prepared catalysts were characterized by XRD,XPS,and TEM.The results indicate that the addition of sodium polyacrylate could enhance the interaction between the composite hydrogel and Pd²⁺,and thus inhibit the agglomeration and loss of Pd nanoparticles,which could improve the stability of the catalyst.Then,to improve the efficiency of the catalyst in the selective catalytic hydrogenation of phenol,a series of second metal modified Pd/M-SBA-15 catalysts was prepared by using the mesoporous SBA-15 molecular sieves as support.It was found that Pd/Mg-SBA-15 showed excellent activity and good stability.To study the reason of its high catalystic performance,the effect of a second metal was systematically investigated by means of several characterations such as H₂-TPR,XPS and TEM.In addition,the relationship between catalyst structure and the catalytic performance was also clarified.Finally,a Pd/NH₂-SBA-15 catalyst was prepared by using an amine-grafted SBA-15 as support for further improving the catalytic activity and stability of catalysts.A series of characterations including XRD,XPS and TEM was employed.The results revealed that there is a strong metal-molecular support between the amino groups and Pd nanoparticles,which can promote the dispersion of Pd nanoparticles and its particle size is only 1.7 nm.In addition,it was speculated that the amino groups can effectively inhibit the aggregation of Pd nanoparticles.This catalyst still kept excellent catalytic performance after being recycled 10times.