【作者】 孙淼；

【导师】 张庆红； 万惠霖；

【作者基本信息】 厦门大学 ， 物理化学， 2009， 博士

【摘要】 本学位论文首先研究了不同铯取代量的磷钼杂多酸铯盐(Cs_xH_3-xPMo₁₂O₄₀，x=2．0-3．0)和一钒取代的磷钼钒杂多酸铯盐(Cs_xH_4-xPVMo₁₁O₄₀，x=2．0-4．0)催化剂上温和反应条件下（653 K）的丙烷氧化脱氢反应。研究发现，在这两系列催化剂上，随着铯含量的增加，丙烷的转化率均逐渐下降，丙烯的选择性逐渐上升。当铯量达到某一适合的值时，在这两系列催化剂上分别得到相对较高的丙烯收率。其中在CS_2．56H_0．44PMo₁₂O₄₀催化剂上得到最高的丙烯收率，为9．3％。磷钼杂多酸阴离子的一钒取代不能提高丙烷氧化脱氢反应中丙烷转化率和产物丙烯收率。关联两系列催化剂的催化活性与其物理化学性质发现，催化剂的酸性质在丙烷氧化脱氢反应中起到重要的作用。定量计算结果显示丙烷的转化速率与催化剂表面Br（?）nsted酸中心浓度呈正比，而丙烯的选择性随着催化剂表面酸中心浓度的增大而降低。在具有合适酸性质的催化剂上能够得到最高的丙烯收率。本学位论文中还针对常压下从氢气和氧气直接合成过氧化氢反应考察了在液相不共存任何酸和卤素助剂的情况下，磷钨杂多酸铯盐负载的金属Pd为催化剂的催化性能。研究结果显示，磷钨杂多酸铯盐可作为固体酸载体有效地促进过氧化氢的选择生成。磷钨杂多酸铯盐负载金属Pd催化剂的酸性质和金属Pd纳米粒子的尺寸决定了其催化生成过氧化氢的性能。具有3．8 nm Pd粒径和适宜酸性质的1．0 wt％Pd／Cs_1．5H_1．5PW₁₂O₄₀催化剂显示最高的H₂O₂生成效率。在283 K反应4小时之后，乙醇溶剂中H₂O₂的浓度可以达到1．1％，该结果与目前报道的相同反应条件下液相共存酸和卤素助剂的催化剂体系的H₂O₂生成能力相接近。直接合成H₂O₂反应中得到的H₂O₂浓度相接近。本工作为常压下氢气和氧气直接合成H₂O₂的反应提供了一条绿色环保的合成路线。更多还原

【Abstract】 This dissertation first studied the oxidative dehydrogenation of propane at a mildtemperature （653 K） over two series of Keggin-type polyoxometalates catalysts (i.e.,Cs_xH_3-xPMo₁₂O₄₀ and Cs_xH_4-xPVMo₁₁O₄₀) with different cesium contents.Theconversion of propane decreased while the selectivity to propylene formationincreased with the increase of cesium content in these samples,and the yield ofpropylene reaches a maximum at appropriate cesium content for both series ofcatalysts.The best yield of propylene （9.3%） was achieved over theCs_2.56H_0.44PMo₁₂O₄₀ catalyst and the vanadium substitution did not enhance the yieldof propylene.The correlation between catalytic behaviors and physicochemicalproperties of these catalysts suggests that the acidity plays crucial roles for theoxidative dehydrogenation of propane.It is clarified that the rate of propaneconversion increased proportionally to the concentration of Br（?）nsted acid sites,whereas the selectivity to propylene formation decreased with the increase of thesurface acidity.This dissertation also studied the direct synthesis of H₂O₂ from H₂ and O₂ undernormal pressure over polyoxometalates-supported Pd catalysts in the absence of anyliquid acid or halide additives in the liquid phase.It was confirmed that theCs-substituted 12-tungstophospharates could be used as solid acid catalyst whichbenefited for the direct synthesis of H₂O₂ from H₂ and O₂.The combination of thecharacterizations and the catalytic reactions shows that both the acidity of thepolyoxometalate and the size of Pd nanoparticles may determine the catalyticbehaviors of the catalyst.Over 1.0 wt% Pd/Cs_1.5H_1.5PW₁₂O₄₀ catalyst with Pdnanoparticles of 3.8 nm and a proper acidity,the concentration of H₂O₂ could reach upto 1.1% in ethanol after 4 h of reaction at 283 K.This result was close to that obtainedin the reaction systems containing both acid and halide additives under the samecondition.This work provided a green route for the direct synthesis of H₂O₂ from H₂and O₂ under normal pressure.更多还原