Synthesis Of Cu-based Layered Double Hydroxides/mixed Metal Oxides As Catalysts For Epoxidation Of Styrenr

The epoxidation of styrene had attracted increasing interest since the epoxide was an important intermediate in organic synthesis,pharmaceutical and perfume industries.However,the traditional preparation method of styrene oxide led serious environmental pollution and high production cost.Therefore,under the action of catalyst,the green O2,H2O2 and tert-butyl hydroperoxide(TBHP)used as oxidant had become increasingly widespread attention for styrene epoxidation.Recent work on the synthesis of heterogeneous catalysts had chiefly covered noble metal catalysts,particularly Au-and Ag-based catalysts,because of their high catalytic performance.However,considering the low natural reserves and high prices of noble metals,vigorously developing non-noble-metal catalysts was more in accordance with the main tendencies of the sustainable chemical industry.However,the active components of single non-noble-metal catalysts were easy inactivation and agglomeration which caused poor catalytic activity and stability.Therefore,taking advantage of multi active components to design and synthesize high activity non-noble-metal catalysts to improve the yield of styrene oxide is of great significance.Layered double hydroxides(LDHs)was a kind of typical anionic layered materials.Because of its special structure characteristics,it had been widely used in the field of catalysis.In this paper,a series of non-noble-metal catalysts were prepared based on the cation-tunability,lattice orientation effect and tunable acid-base properties of LDHs,and then the catalysts were applied to the epoxidation of styrene in order to discuss the impact of structure of active components on the performances of catalyst.Cu and Mn as active metals were simultaneously introduced in to the layer of LDHs by co-precipitation method to synthesize a series of high-dispersed CuMnMgAl-LDHs-CP.The focus of this study was on revealing the effect of the different composition and structure on surface acidity and basicity,active metal dispersion and valence,as well as interaction between active components of catalysts.Experimental results showed that compared with CuO-MnOx/MgAl-LDHs-DP catalyst prepared by deposition-precipitation method,the Cu and Mn of CuMnMgAl-LDHs-CP catalyst were highly dispersed which increased the conversion of styrene largely.Furthermore,the surface suitable acidity and alkalinity as well as high content of Mn(?)and Mn(?)species of CuMnMgAl-LDHs-CP catalyst promoted the generation of styrene oxide,selectivity increased by 25.0%.When Cu/Mn=0.5/0.5,Cu and Mn had the strongest synergistic catalytic effect and the lowest apparent activation energy(22.5 kJ/mol).M2CrAl-LDHs(M2=Cu,Ni,Zn or Co)were used as precursor to obtain a series of M2CrAl-MMO catalysts which were applied to the epoxidation of styrene.Compared with MgCrAl-MMO catalyst,the introduction of Cu significantly improves the selectivity of styrene oxide,which increased from 66.0%to 88.4%.But the activity was relatively low,only 38.0%.In order to further improve the catalytic activity,the maximum increase of active metals Cr and Cu,thus CuCr-MMO catalyst were prepared and compared with MMO catalyst,its catalytic activity increased from 38.0%to 82.0%.Moreover,the alkaline sites of CuCr-MMO catalyst inhibited the ring opening of styrene oxide,so it had high selectivity of SO(83.6%).Furthermore,the acid sites of CuCr-MMO catalyst improved the stability in acid system,the yield of styrene oxide(69.2%)was much higher than other reported non-noble-metal and noble metal catalysts.