蒸氨压力对Cu/SiO_2催化剂的影响及其草酸二甲酯加氢性能

以Si O2为载体,铜氨溶液为前驱体,采用蒸氨法在不同蒸氨压力下制备了系列铜负载量质量分数为20.0%的Cu/Si O2催化剂。采用X射线衍射(XRD)、H2-程序升温还(H2-TPR)、高分辨透射电子显微镜(HRTEM)、X射线诱导俄歇电子能谱(XAES)等技术手段对催化剂的物理化学性能进行了表征。考察了蒸氨速率对催化剂物化结构及其草酸二甲酯催化加氢制乙二醇的催化性能影响。在反应温度200℃、压力3.0 MPa、液时空速LHSV=0.4 h-1、氢气草酸二甲酯摩尔比80∶1的反应条件下测定了催化剂的活性。结果表明,在蒸氨压力为31.3 k Pa条件下制备的催化剂表现出了最佳活性和选择性,草酸二甲酯转化率达到了99.9%,乙二醇选择性达94.4%。H2-TPR、XRD、TEM、FTIR及XAES表征结果表明,较低蒸氨压力有利于铜氨离子快速分解负载在载体上,避免铜粒子聚集长大,还原后形成Cu2O和Cu0物种颗粒尺寸较小,分散比较均匀,催化活性,尤其是乙二醇的选择性更佳。

Influences of the Ammonia Evaporation Pressure on the Structure of Cu/SiO2 Catalysts and Catalytic Performances for Dimethyl Oxalate Hydrogenation to Ethylene Glycol

A series of Cu/SiO₂ catalysts with 20.0% mass fraction of Cu loading was prepared by the ammonia evaporation method using SiO₂ as the support and Cu(NH₃)₄²⁺ aqueous solutions as the precursor. The catalysts were characterized through X-ray diffraction(XRD), H₂-temperaure programmed reduction(H₂-TPR), transmission electronic microscopy(TEM) and X-ray Auger spectra(XAES) to investigate the influence of the ammonia evaporation rate on the catalyst physical and chemical structure and its catalytic performance for the hydrogenation of dimethyl oxalate(DMO) to ethylene glycol(EG). The catalytic activity measurement experiments were performed under working conditions of 200 ℃, p=3.0 MPa, LHSV=0.4 h^-1 and the molar ratio of hydrogen to DMO(n(H₂):n(DMO)=80:1). The results indicate that the catalyst prepared under high vacuum during ammonia evaporation has better catalytic performance. For the catalyst prepared under ammonia evaporation pressure of 31.3 kPa, 99.9% conversion of DMO and 94.4% selectivity to EG are obtained. Characterizations through XRD, H₂-TPR, TEM and XAES suggest that the higher the ammonia evaporation rate, the faster and more uniform distribution of copper precursors upon the SiO₂ support, and the coagulation and growth of the Cu particles during calcination and reduction can be reduced, which guarantees the high catalytic activity, particularly the selectivity to EG.