LiOH改性对铂钨锆催化剂的影响

Effects of lithium hydroxide modification on platinum supported tungsten-zirconium composite oxide catalysts

采用共浸渍-焙烧法制备不同LiOH质量分数改性的铂钨锆催化剂(Pt-WZr),通过N2等温吸附-脱附、X线衍射(XRD)、NH3-程序升温脱附(NH3-TPD)、H2程序升温还原(H2-TPR)、CO脉冲吸附、H2-程序升温脱附(H2-TPD)对催化剂的理化性质进行表征。使用连续流动的固定床反应器考察催化剂对甘油氢解制备1,3-丙二醇的催化性能,使用高温水热釜考察钨锆复合氧化物的水热稳定性。结果表明:适量LiOH的引入能够显著调节催化剂的酸强度,减少强酸量、增大弱酸量,有利于提高催化剂表面活性组分Pt的分散度,增强Pt与钨锆载体间的相互作用,促使催化剂中的四方相ZrO2向单斜相ZrO2转变。LiOH的引入显著提高了甘油转化率和1,3-丙二醇收率,当LiOH质量分数为1.0%时,甘油转化率和1,3-丙二醇收率达到最优,分别为85.8%和39.7%。与未改性的钨锆复合氧化物相比,LiOH改性后的钨锆复合氧化物水热稳定性得到显著提高。

A series of platinum supported tungsten-zirconium composite oxide(Pt-WZr)catalysts modified with different lithium hydroxide mass fraction were prepared through the method of co-impregnation calcinations.The physical-chemical properties of catalysts were characterized by N2 physical adsorption and desorption,X-ray diffraction(XRD),NH3-temperature programmed desorption(NH3-TPD),H2-temperature programmed reduction(H2-TPR),CO pulse adsorption and H2-temperature programmed desorption(H2-TPD).The catalytic performance of glycerol hydrogenation to 1,3-propanediol over the prepared catalysts was investigated with a continuous flow fixed-bed reactor,and a high temperature hydrothermal kettle was used to study the hydrothermal stability of tungsten zirconium composite oxide.Results showed that the appropriate amount of LiOH could significantly adjust the acid strength of catalysts,reduce the strong acid content,increase the weak acid content,improve the dispersion of active component platinum in catalyst surface,strengthen the interaction between platinum and the tungsten-zirconium support,and promote tetragonal zirconia transform into monoclinic zirconia in Pt-WZr catalysts.The addition of LiOH could obviously increase the conversion of glycerol and the yield of 1,3-propanediol.When the loading of LiOH was 1.0%mass fration,the conversion of glycerol and the yield of 1,3-propanediol achieved the optimal,which was 85.8%and 39.7%,respectively.Compared to the unmodified tungsten-zirconium composite oxide,the appropriate amount of LiOH addition could increase hydrothermal stability remarkably.