【作者】 陈静；

【导师】 张庆红； 万惠霖；

【作者基本信息】 厦门大学 ， 物理化学， 2008， 博士

【摘要】 本论文针对负载型多相Pd催化剂的液相醇氧化反应开展研究。研究主要涉及以氧气为氧化剂的苯甲醇选择氧化反应和在惰性气氛中无氢受体存在的条件下的苯甲醇氧化脱氢反应两部分。论文通过对Pd催化剂的详细的性能评价和结构表征,建立各催化反应体系中催化剂的构效关联。针对以氧气为氧化剂的苯甲醇氧化反应,选择以负载于SiO₂-Al₂O₃复合氧化物载体金属Pd为催化剂。利用Pd前驱体(PdCl₄^2-)和不同Si/Al比的载体之间相互作用的强弱,以氢气或正己醇还原的方法合成了金属Pd粒子的粒径分布集中且粒径在2.2-10 nm可控的的纳米金属Pd催化剂。研究发现对于以氧气为氧化剂的苯甲醇选择氧化反应,金属Pd是反应的活性相。该反应为结构敏感反应。当金属Pd粒径处于3.6-4.3 nm范围内时表面Pd原子的苯甲醇氧化本征转换频率（TOF）最高。以立方八面体为模型分析随粒径的变化Pd粒子表面平台原子与缺陷位原子的数目变化趋势给出了在以氧气为氧化剂的苯甲醇氧化反应同时需要平台Pd和缺陷位Pd两类Pd原子,当二者数目之比为2∶1-3∶1的Pd颗粒显示最佳催化性能。343 K反应10 h时,0.3 wt%Pd/SiO₂-Al₂O₃（Si/Al=1/1）、Pd粒径3.6 nm的催化剂上苯甲醇转化率可达97%,生成苯甲醛的选择性98%。Pd/SiO₂-Al2O₃催化剂能够多次重复使用,并可以催化多种醇的氧化反应。针对在惰性气氛下无氢受体时苯甲醇的脱氢反应,研究发现Pd/HT（Hydrotalcite,水滑石）催化剂具有较高的氧化苯甲醇生成苯甲醛的性能,反应中伴有氢气分子放出。Pd/HT、Pd/Al2O₃和Pd/MgO催化剂的对比研究发现,酸性载体催化剂Pd/Al₂O₃显示较高的苯甲醇转化活性,但生成苯甲醛的选择性低。碱性载体催化剂Pd/MgO催化剂上苯甲醇生成苯甲醛的选择性高,但苯甲醇转化率有限。碱性适当的Pd/HT催化剂兼具苯甲醇转化率和生成苯甲醛选择性的优势,显示高的苯甲醛收率。催化剂上的反应活性相可能是带有正电荷的Pd粒子。相比以氧气为氧化剂的苯甲醇的氧化反应,在惰性气氛下苯甲醇更易于生成甲苯。我们推测Al₂O₃上L酸位易于吸附苯甲醇,并促进其脱去苯甲醇羟基生成副产物甲苯,降低了苯甲醛的选择性;采用碱性载体,可以加强苯甲醇的亲核性从而提高苯甲醛的选择性。更多还原

【Abstract】 This dissertation focuses on the studies of the liquid phase oxidation of alcohols catalyzed by palladium supported heterogeneous catalysts,including aerobic and anaerobic oxidation systems.From the detailed characterization,the correlation between the structure characters of palladium catalysts and their catalytic performance for the conversion of benzyl alcohol to benzyl aldehyde in both systems were discussed.For the aerobic oxidation of benzyl alcohol reaction,metallic palladium supported on the SiO₂-Al₂O₃ support was used as catalysts.Nano-sized Pd particles with its sized changed within 2.2-10 nm were prepared by controlling the interaction between the Pd precursor(PdCl₄^2-) and the supports followed by the reductions with H₂ or hexanol.It was found that the oxidation of benzyl alcohol using O₂ as oxidant was a structure sensitive reaction,and active phase was the metallic Pd.The highest catalytic activity（TOF） was found over the catalysts with Pd particles sized in 3.6-4.3 nm.We estimated the tendency of Pd atom numbers located in the surface sites and in the defect（edge and comer） sites changing along with the decreasing of the Pd diameter by using cuboctahedron as the geometrical model for Pd particles.The ratio of Pd atoms(Pd_surface/Pd_defect) in these two sites was found as 2:1-3:1 for the most effective catalysts where Pd diameters ranged in 3.6-4.3 nm.For this reaction,the best catalytic performance were 97%conversion of benzyl alcohol and 98%selectivity for benzyl aldehyde formation over 0.3 wt%Pd/SiO₂-Al₂O₃（Si/Al=I/1） catalyst with its Pd mean size of 3.6 nm.This kind of catalysts could be repeatedly used and was effective for oxidation of various alcohols.A novel catalytic system for anaerobic oxidation of alcohols over Pd/hydrotalcites（Pd/HT） catalyst was studied.Compared with Pd/Al₂O₃ and Pd/MgO catalysts,Pd/HT showed high catalytic performance in converting benzyl alcohol to benzyl aldehyde,and a hydrogen release was analyzed during the reaction.Over Pd/Al₂O₃ catalyst,although the high conversion of benzyl alcohol was achieved,the selectivity of benzyl aldehyde was only 60%,probably due to the acidity of the support.The main by-product was toluene.Over Pd/MgO catalyst,the selectivity to benzyl aldehyde formation was high probably conduced by the basicity of the support, although the conversion of the benzyl alcohol was limited.We speculate that the active species was positively charged Pd clusters.Benzyl alcohol prefers to adsorb onto Al₂O₃ and then were hydrogenolyzed into toluene and water over Pd.The basic supports can improve the nucleophilicity of benzyl alcohol to form Pd-alcoholate,and also promote theβ-H elimination,therefore the selectivity ofbenzaldehyde over basic support was increased.更多还原