A series of Pd catalysts were prepared on different supports（Fe2O3,SiO2,ZnO,MgO,Al2O3,carbon,and Amberlyst-45） and used in the selective hydrogenation of phenol to cyclohexanone in water.The Amberlyst-45 supported Pd catalyst（Pd/A-45） was highly active and selective under mild conditions（40-100 ℃,0.2-1 MPa）,giving a selectivity of cyclohexanone higher than 89%even at complete conversion of phenol.Experiments with different Pd loadings（or different particle sizes） confirmed that the formation of cyclohexanone was a structure sensitive reaction,and Pd particles of12-14 nm on Amberlyst-45 gave better selectivity and stability.
Selective oxidation of glycerol is a hot topic.Increased biodiesel production has led to glycerol oxidation over Au- and Pt-based catalysts being widely studied.However,Pt catalysts suffer from deactivation because of weak metal-support interactions.In this study,multi-walled carbon nanotube（MWCNTs）-pillared nitrogen-doped graphene（NG） was prepared by direct pyrolysis of melamine on MWCNTs,and the synthesized NG-MWCNT composite was used as the support for Pt.Characterization results showed that the surface area（173 m^2/g） and pore volume of the NG-MWCNT composite were greater than those of bare MWCNTs and the separated melamine pyrolysis product（CH_x）.Pt（1.4±0.4 nm） dispersion on the NG-MWCNTs was favorable and the Pt/NG-MWCNT catalyst was highly active and selective in the oxidation of glycerol to glyceric acid（GLYA） in base-free aqueous solution.For example,the conversion of glycerol reached 64.4% with a GLYA selectivity of 81.0%,whereas the conversions of glycerol over Pt/MWCNTs and Pt/CN_x were 29.0% and 31.6%,respectively.The unique catalytic activity of the Pt/NG-MWCNTs is attributed to well-dispersed Pt clusters on the NG-MWCNTs and the electron-donating effect of the nitrogen dopant in the NG-MWCNTs.
