The Synthesis Of Bn Supported Catalysts And Their Applications In Oxidative Dehydrogenation Of Ethylbenzene

Oxidative dehydrogenation of ethylbenzene to styrene is considered as an alternative to the traditional direct dehydrogenation process.Due to the strong exothermic characteristics,the reaction is not restricted by the thermodynamic equilibrium and a higher conversion rate can be obtained at a lower temperature（400-500°C）.At the same time,the use of superheated water vapor is avoided and the energy consumption of the reaction is reduced.However,the reaction usually suffer from the lower styrene selectivity due to the oxygen insertion and deep-oxidation of ethylbenzene or styrene into CO_X.Therefore,we need to develop highly selective and active catalysts for oxidative dehydrogenation.In recent years,hexagonal boron nitride,with high selectivity and excellent catalytic activity,has been discovered as novel catalysts in the oxidative dehydrogenation of light alkanes.However,a low styrene formation rate is usually observed in ODH of ethylbenzene over BN.An efficient strategy to solve this problem is to fabricate hybrid catalysts with multi-component showing specific functions.In this thesis,boron-based and metal oxide-based composite catalysts were synthesized,respectively.The unique advantages of composite catalysts were revealed through performance test.A series of characterization methods were used to analyze the structure and surface properties of the catalysts,and the active site of boron-based catalysts were also analyzed.The specific research content and results are as follows:（1）Using ball-milling and washing treated hexagonal boron nitride as support,a series of BPO₄/BN composite catalysts were prepared showing high selectivity for oxidative dehydrogenation to styrene.High selectivity of styrene（95.1%）was achieved at 27.7%ethylbenzene conversion level over the optimized BPO₄/BN catalyst.The optimized BPO₄/BN catalyst shows a higher styrene formation rate of 4.0 mmol g^-1_cat h^-1,compared individually to BPO₄(2.8 mmol g^-1_cat h^-1)and BN(0.5 mmol g^-1_cat h^-1).The tetra-coordinated boron（BO₄）species of BPO₄ was speculated to be responsible for the ODH of ethylbenzene,and a synergistic effect between BPO₄ and BN can remarkably improve the catalytic performance of the BPO₄/BN catalyst.（2）Using ball-milling and washing treated hexagonal boron nitride as support,a series of CuO/BN and CuO-ZnO/BN composite catalysts were prepared showing high activity for oxidative dehydrogenation to styrene.High selectivity of styrene（90.1%）was achieved at 38.9%ethylbenzene conversion level over the optimized CuO/BN catalyst.The optimized CuO/BN catalyst shows a higher styrene formation rate of 5.3 mmol g^-1_cat h^-1,compared individually to BN(0.5 mmol g^-1_cat h^-1).The presence of ZnO in the catalyst further improve the catalytic performance in the oxidative dehydrogenation of ethylbenzene.The optimized CuO-ZnO/BN catalyst showed a higher styrene formation rate of 6.1 mmol g^-1_cat h^-1 under the same conditions,but the selectivity also decreased to 84.2%.