【作者】 项益智；

【导师】 李小年；

【作者基本信息】 浙江工业大学 ， 工业催化， 2010， 博士

【摘要】 化学工程为人类社会提供了最基本的生产手段与技术。催化加氢(还原)是最基本的化工过程,自1897年由Paul Sabatier提出至今(特别是近六七十年)已在能源、环境、材料和精细化工等各个领域发挥了举足轻重的作用。但是催化加氢必须在H2(高压)气氛下完成,工业上存在一定的安全隐患；而且由于H2较强的还原性,如何实现提高加氢过程目标产物的选择性则是近年来的研究重点和热点。然而却少有人想到“不用H2”的催化加氢,或通过选用弱还原剂代替H2来提高加氢选择性。早在1954年由Braude和Linstead提出的催化氢转移加氢,使用含氢的多原子分子(如仲醇“异丙醇等”、肼、甲酸/盐等)为氢供体,实现一类不用H2的液相还原方法；但是从机理上看,转移加氢和催化加氢存在本质的区别,前者是“H原子”在分子(供体与受体)间的相互转移,而后者是H2在催化剂表面活化形成“吸附H”从而实现加氢。此外,转移加氢的“H原子”利用率较低,且普遍使用均相金属络合物为催化剂,目前在不对称选择性加氢中有较多的应用。本论文从苯乙酮(羰基)和苯酚(苯环)两类不同有机物的加氢反应入手,结合脂肪醇的“水相重整制氢”技术,提出了一类以“小分子脂肪醇：甲醇或乙醇”为氢源的液相催化加氢反应体系。脂肪醇的水相重整/脱氢反应在催化剂表面形成“活化H”并原位地用于有机物的催化加氢反应,因此与催化氢转移加氢不同。而且这种由“活化H”参与的催化加氢与传统的H2催化加氢又有不同,因为由脂肪醇原位产生的“活化H”无论在数量、分布还是吸脱附性能上均与H2催化加氢过程不同,这就为提高一些复杂有机物或反应体系的加氢选择性提供了新的可能。本论文的具体研究结果如下：对苯乙酮加氢合成α-苯乙醇研究发现,Pd/CNTs催化剂上α-苯乙醇选择性明显高于Pd/AC催化剂(～95% vs～5%)。通过对反应机理的探讨和密度泛函理论(DFT)对α-苯乙醇在Pd/CNTs和Pd/AC催化剂上的吸附研究表明,引起两个催化剂上的选择性差异在于：当α-苯乙醇吸附在Pd/CNTs上时,分子中的羟基远离载体(有效地避免了羟基的氢解反应),而吸附在Pd/AC上时α-苯乙醇分子中的羟基靠近载体(羟基在载体与活性金属的界面上发生氢解反应生成了副产物乙苯)。对苯酚催化加氢研究发现,以水为溶剂时显著地提高了加氢反应的活性和环己醇选择性。巧妙地利用苯酚在339 K以下为疏水性有机物,而在339 K以上与水任意比互溶的特点,提出了“温控型”水-有机两相苯酚加氢反应体系。苯酚加氢反应温度高于339 K(苯酚与水互溶),反应速率不受传质过程限制,反应结束后(温度低于339 K),原料和产物均不溶于水,简化了溶剂的分离。此外,本论文实验还证明Raney Ni在水中比在甲醇中吸附更多的H和苯酚。针对“以脂肪醇为氢源的催化加氢反应”这一新体系,本论文详细地介绍了该体系的提出和验证过程。以“苯酚原位加氢反应”为例,研究了该反应在RaneyNi催化剂上的表观动力学(苯酚与吸附氢对生成环己醇和环己酮的的浓度级数a1和a2分别为0.93和1.09,β1和β2分别为3.82和3.47,表观活化能Ea1和Ea2分别为67.8和80.2kJ.mol-1)。考察了La修饰的Pd/Al2O3催化剂在苯酚液相原位加氢合成环己酮反应中的性能,并揭示了La的修饰作用提高了Pd/Al2O3催化剂在苯酚液相原位加氢反应中的活性和选择性的原因。考察了“以脂肪醇为氢源的加氢反应体系”的普适性；通过催化剂的设计实现了“原位氢化-烷基化”和“原位氢化-胺化”等以脂肪醇为氢源的加氢耦合反应体系(如：在不用H2的情况下,以Pd/Al2O3或Fe-Pd/Al2O3,和Au-Pd/Al2O3为催化剂,分别实现了吡啶加氢/烷基化直接合成N-烷基哌啶,和以甲醇为氢源的芳香硝基物和羰基化合物直接合成亚胺)。更重要的是在这些体系的研究中均发现,利用脂肪醇水相重整/脱氢的方式为加氢反应提供“活化H”比H2催化加氢具有更高的选择性。最后,本论文对“以脂肪醇为氢源的加氢反应体系”的催化机制,特别是脂肪醇在该反应中的供氢机理进行了研究。脂肪醇原位产生的催化剂表面“活化H”的程序升温脱附(TPD)和苯酚的液相程序升温表面反应(Liquid phase-TPSR)研究表明,由不同氢源(H2和脂肪醇)产生的催化剂表面“活化H”的脱附及还原性能存在差异,通过氢源种类及供氢方式的改变可以有效地调控催化剂表面的吸附氢浓度及“活化H”在催化剂表面的分布；以脂肪醇为氢源向催化剂表面供氢可以在催化剂表面形成低浓度的吸附氢(催化剂表面对H的吸附未达到饱和),这种H的不饱和吸附/不均匀分布是提高复杂有机物/加氢体系选择性的主要原因。利用D20同位素跟踪实验研究表明,以脂肪醇为氢源加氢反应的供氢受反应条件和催化剂的影响,主要包括：水相重整、脱氢氢转移,以及这两条途径的结合。更多还原

【Abstract】 Chemical engineering throughout the time enabled many of the fundamental breakthroughs in human society. Catalytic hydrogenation is one of the most important chemical processes, since its first observation by Paul Sabatier (1912 Nobel Prize), have already plays a tremendous role in energy generation, environmental protection, materials and fine chemical production etc. However, catalytic hydrogenation uses pure gaseous H2 as the reactant which makes it a quite risky process in industry. Catalytic transfer hydrogenation (CTH), proposed by Braude and Linstead in 1954, carries out reduction of organics by hydrogen donor (such as secondary alcohols "isopropanol", hydrazine, formic acid/formates etc.) rather than using H2-gas. But CTH is different from catalytic hydrogenation in terms of mechanism, i.e., the CTH is the exchange/transfer of "H atom" between molecules, hydrogen donor and acceptor, while the catalytic hydrogenation forms "adsorbed H" on the surface of catalyst. The CTH using homogeneous metal complex as the catalyst, and present industry application mainly limited to the asymmetry selective hydrogenation.In this thesis, based on the study of acetophenone and phenol hydrogenation, and the recent literature work on aqueous-phase reforming for H2 production, we proposed a novel liquid system of catalytic hydrogenation using "aliphatic alcohols:methanol or ethanol" as the hydrogen source. This system is different from that CTH, which also using alcohols (mainly secondary one) as hydrogen donor, because "activated H", as in the catalytic hydrogenation using H2-gas, was identified as the key intermediate for the reaction in the proposed system (desorption of "activated H" result in the production of H2). Although the proposed system involving "activated H" as the catalytic hydrogenation with H2-gas, they are also different since the properties of the "activated H" in terms of amounts, distribution, and adsorption/desorption behavior are different between these two processes. Therefore, the catalytic hydrogenation using aliphatic alcohols as hydrogen source also a potential way improving the catalytic selectivity. The detailed results for the present thesis are shown below.The carbon nanotube and activated carbon supported Pd catalyst (Pd/CNTs and Pd/C) shown dramatic selectivity difference (～95% vs～5%) in the hydrogenation of acetophenone to a-phenylethanol. The catalytic mechanism and DFT studies on the adsorption of a-phenylethanol suggested that the different selectivity can be explained by the different adsorption model of a-phenylethanol. When a-phenylethanol adsorbed on Pd/CNTs, the hydroxyl-group point-up, far away from the support, which inhibited the occurrence hydrogenolysis. While, when a-phenylethanol adsorbed on Pd/C, the hydroxyl-group point-down, close to the support, which favors the occurrence of hydrogenalysis (usually taken place at the interface between metal and support).The hydrogenation of phenol in water solvent shown quite higher activity than that in methanol. "Thermo-regulable" water-organic biphasic system was proposed for the hydrogenation of phenol in aqueous solvent, because phenol is hydrophobic below 339 K, but it is hydrophilic above 339 K. Catalytic hydrogenation of phenol usually carried out at hydrophilic temperature (>339 K), therefore, the reaction rate should not be limited by the solubility problem. While in this thesis, we also observed that the Raney Ni adsorbs more phenol in water than the methanol. After reaction (<339 K), both reactant and products are hydrophobic; the separation of solvent (water) was simplified.For the system of "catalytic hydrogenation using aliphatic alcohols as hydrogen sources", the combination of "catalytic hydrogenation of nitrobenzene and phenol" and "aqueous-phase reforming of methanol" was investigated over the commercial Raney Ni catalyst. The feasibility of the proposed system "aliphatic alcohols as hydrogen source for catalytic hydrogenation:liquid phase in-situ hydrogenation" was proved with this initial test/try. In order to understand well of the proposed system, apparent kinetics of phenol in-situ hydrogenation over Raney Ni catalyst were investigated (the reaction order with respect to phenol and hydrogen for cyclohexanolα1 andβ1 are 0.93 and 3.82, respectively, and for cyclohexanoneα2 andβ2 are 1.09 and 3.47, respectively. The activation energy of phenol in-situ hydrogenation for cyclohexanol (Ea1) and cyclohexanone (Ea2) are 67.8 and 80.2 kJ.mol-1, respectively). Additionally, a series of La-promoted Pd/Al2O3 catalyst was prepared for the liquid phase in-situ hydrogenation of phenol to cyclohexanone. The role of lanthanum on the Pd/Al2O3 catalyst was characterized by BET, CO chemisorption, XRD, and H2-TPR. The presence of lanthanum improves the Pd particle dispersion and the TOF for phenol in-situ hydrogenation over the Pd/Lax-Al2O3 catalyst was observed. Moreover, we also observed that the "aliphatic alcohols as hydrogen source for catalytic hydrogenation" is of general applicability. Based on the design of multifunctional catalyst, hydrogenation involved combination reactions, such as "in-situ hydrogenation coupled with alkylation" and "in-situ hydrogenation coupled with amination" etc. were also realized. For example, pyridines hydrogenation/alkylation for N-alkylpiperidines using aliphatic alcohols as hydrogen source was realized over the Pd/Al2O3 or Fe-Pd/Al2O3 catalyst; the use of methanol as hydrogen source for the direct synthesis of imines from nitroarenes and carbonyl compounds was realized over Au-Pd/Al2O3 catalysts. Among these studies, the superiority of using aliphatic alcohols as hydrogen source was well established in terms of the catalytic selectivity.Finally, the catalytic mechanism, in particular the hydrogen providing manner, of the "catalytic hydrogenation using aliphatic alcohols as hydrogen source" was investigated. The desorptions and reduction properties of the "activated H" from different hydrogen source were investigated by means of temperature-programmed desorption (TPD) and phenol-temperature programmed surface reaction in liquid phase (liquid phase-TPSR). The results indicated that the amounts of the hydrogen adsorbed on the catalyst could be regulable through the change of hydrogen source and hydrogen providing manner. The use of aliphatic alcohols as hydrogen source could provide limited amount/unsaturated of hydrogen (inhomogeneously distributed) on the surface of the catalyst through the aqueous-phase reforming or dehydrogenation. Isotope tracking studies using D2O suggest that hydrogen providing manner using aliphatic alcohols as hydrogen source including, aqueous phase reforming, dehydrogenation, and the coupling of the two manners, which could also depending on the reaction conditions and properties of the catalyst.更多还原