The Preparation Of Hydrotalcite-supported PdCu Catalyst And Its Performance In The Oxidation Of Benzyl Alcohol

Pd-based nanocatalysts have high catalytic activity in the fields of petroleum,chemical industry,energy,biomedicine,and environmental protection,and thus have always been the focus of catalytic scientific research.While monometallic Pd catalysts generally have the disadvantages of high loadings,large particle size,and poor dispersion.To solve these problems,people usually introduce a second metal in the Pd catalyst in order to reduce the amount of Pd and change the electronic structure of the palladium atom,as well as control the size,surface morphology and dispersion of the Pd nanoparticle by a good preparation method,thereby improving the catalytic performance of the catalyst.Hydrotalcite is a layered compound,the chemical compositions of the layer are regulatable,and the interlayer anions are exchangeable.Based on these,we proposed to prepare supported PdCu bimetallic catalysts using Cu-doped hydrotalcite as support in this thesis.(1)A new method was proposed that can effectively control the particle size and the dispersion of bimetallic nanocatalysts.CuMgAl hydrotalcites(Cu-HTs)were prepared by co-precipitation method,and then PdCu/HTs catalyst was obtained by impregnating Pd on the surface of Cu-HTs and further reduction.Typically,Cu2+ was introduced on the MgAl hydrotalcite layer,and the highly dispersed constitutional Cull was used as positioning agent.Pd atom was directed and dispersed on the surface of the catalyst because of the strong effect between Cu and Pd,therefore,a highly dispersed PdCu bimetallic catalyst was obtained.For comparison,MgAl hydrotalcites(HTs)were similarly prepared,and then Pd and Cu were simultaneously impregnated on the surface of HTs to obtain the conventional PdCu/HTs-C catalyst.The structure,phase and composition of catalysts were characterized by XRD,TPR,STEM and XPS.It was showed that the size of PdCu/HTs nanoparticle was about 2.4 nm,the dispersion was up to 36.7%,and with the increase of Pd loadings,the size was still small and the dispersion was high.However,the particle size of PdCu/HTs-C was about 4.3 nm,the dispersion was only 25%,and the particle agglomeration was more serious.A series of characterization results indicated that Cu incorporated into hydrotalcite has a localization effect on metal Pd,which can effectively disperse the nanoparticles of the bimetallic catalyst.(2)The aerobic oxidation of benzyl alcohol was used as a probe reaction,and the performance of catalysts was investigated.Specifically,the effects of the reduction temperature,catalyst amount,Pd loading,and Cu content of the catalyst were all investigated.We also studied the optimal reaction temperature and reaction time.Finally,the reusability of PdCu/HTs catalysts was explored.When the reaction run 3 h at 110 ?and the amount of catalyst was 0.1 g,Pd loading of 1 wt%,as well as the ratio of Cu2+/Mg2+/Al3+ was 0.1:2:1,complete conversion of benzyl alcohol was achieved and the yield of benzaldehyde was reached to 97%for PdCu/HTs catalyst,which was much higher than the yield when using PdCu/HTs-C(72%).