【作者】 李仁宏；

【导师】 范杰；

【作者基本信息】 浙江大学 ， 催化化学， 2014， 博士

【摘要】 由于催化反应一般发生在催化剂的表面,因此,催化材料的表面性质直接决定了其活性、选择性、稳定性等催化性能。纳米催化材料近几十年来发展迅猛,在诸多研究领域已经崭露头角,尤其在C-H和C-C键活化方面有着特殊的应用。本文的研究思路将按下述几个方向进行。首先,在第二章中,我们利用纳米介孔Ti02材料在可见光激发下,将含活性C-H键的苯甲醇分子高效定向转化为苯甲醛。Ti02本身只能被紫外光激发才能发生光化学反应,但是经研究我们发现苯甲醇的分子轨道可以和Ti02晶体中的O2p轨道发生杂化,在禁带中引入施主能级,从而缩减了Ti02的禁带宽度。可见光激发可以诱导施主能级的电子向Ti02导带发生跃迁,产生空穴-电子对。空穴可以直接氧化吸附在Ti02表面的苯甲醇,生成苯甲醛。由于苯甲醛分子和Ti02作用不稳定,易于脱离表面变成自由分子,从而使得Ti02禁带间的施主能级消失。也就是说,Ti02在可见光照射下将会停止产生空穴。这样的空穴生成可控的反应体系,我们将之定义为自调节光氧化系统。在第三章,我们发现通过在无氧条件下,可见光驱动的苯甲醇定向氧化脱氢反应可以重构介孔Ti02的表面,人为制造出大量的表面氧空位以及在晶格氧上接枝氢原子,这样的改性使得Ti02表面层的禁带宽度减小,成为可见光催化剂。这类表面重构Ti02催化材料由于在接近导带位置处产生了新的受主能级,因此在可见光下表现出了一定的光氧化和还原能力。在第四章,通过紫外光诱导的光化学反应法,我们发现乙腈分子中的C-C键可以被活性氧物种打断,生成CN自由基。这些活泼的CN自由基可以直接加成反应体系中的Au和其它过渡金属原子,生成AuCN等氰化物。这是一种新型绿色的自由基氰化法,有望取代传统的山埃氰化冶金法。我们利用这类氰化物进行水杨醛和苯乙炔环化制备异黄烷酮的有机催化,在较低的反应温度下,即表现出了相对优异的催化活性。在第五章,我们利用改进的光诱导氰化法,采用H202作为活性氧物种引发剂进攻乙腈分子,生成大量CN自由基,来制备氰化金属以及对Pt表面进行CN基修饰。这个改进后的方法相对更为绿色而且经济,只需短时间光照即可生成所需金属氰化物以及对Pt表面进行改性。经过CN改性过的Pt/C催化剂在电催化氧还原反应中表现出了抗甲醇中毒效应和一定的稳定性。在第六章,我们利用FeCl3-CH3CN简单的络合物,即可在室温条件下高效转化乙醛制乙酸,这个催化过程符合酶催化反应动力学,而且只需调控FeCl3的浓度就能对反应速率进行控制。同时,根据DFT理论计算和实验结果,我们推测反应过程中产生了高活性的铁氧物种。这类铁氧物种在室温下可以将苯甲醇分子定向转化为苯甲醛。更多还原

【Abstract】 Catalytic reactions usually occur on catalysts surface. Therefore, the catalytic activity, selectivity, and stability of certain catalysts largely depend on their surface properties. Nanocatalysts are special catalysts that have been explored for decades, and they have unique activity for C-H and C-C bond activation and utilization. The present thesis will include the following aspects.First, we found that mesoporous TiO2is an efficient photocatalyst for benzyl alcohol selective oxidation into benzaldehyde under visible light irradiation. Usually TiO2can only be activated by UV light, however, due to the hybridization of the molecular orbital of benzyl alcohol with O2p orbital of TiO2, some donor levels can be introduced in the forbidden band, resulting in the narrowing of the band gap. Consequently, electron-hole pairs will be formed on these donor levels with visible light irradiation. The holes are able to oxidize absorbed benzyl alcohols into benzaldehydes, while benzaldehydes have limited interaction with TiO2and they are apt to desorb from TiO2surface. Therefore, the donor levels are disappeared, leading to the pristine band gap intact. The resulting controllable hole generation is thus termed as self-adjustable photo-oxidation system.Second, under anaerobic conditions, we found that the surface of TiO2experienced reconstruction during benzyl alcohol oxidation under visible light. Plenty of oxygen vacancies are formed, and hydrogen atoms are grafted onto the surface oxygen atoms, both of which lead to the narrowing of the band gap of TiO2, making itself visible light responsive. The resulting surface reconstructed TiO2has some acceptor levels just below the conduction band, thus it can be served as promising visible light photocatalyst for oxidation and reduction purposes.Third, it is found that reactive oxygen species resulted from the UV induced photochemical reaction can be used to break the C-C bond of acetonitrile, generating CN radicals.These radicals are able to react with Au or other transitional metals to form metal cyanides. This method has been demonstrated to be green, versatile and convenient, which potentially can replace the conventional cyaniding strategy. The AuCN oligomers derived from this photocyanation method showed promising catalytic activity during annulation of salicylaldehyde with phenylacetylene to afford isoflavanones.Fourth, by employing the similar photocyanation strategy, we used H2O2as a new reactive oxygen species generator to pattern Pt/C electrode with CN groups. The resulting CN patterned Pt/C catalysts hold a much enhanced methanol tolerate ability during oxygen reduction reactions.Last, we found that FeCl3-CH3CN complex can be used to efficient oxidation of acetaldehyde into acetic acid at room temperature, which proceeds rather rapidly and follows the enzymatic-like Michaelis-Menten kinetics, ased on the catalytic results, spectro-scopic evidences and successive DFT calculations, a reactant-initiated, putative mononuclear non-heme iron-oxygen complex,[FeCl(MeCN)4(O)]2+, is proposed as the active oxidizing species to conduct the room temperature reaction with relatively high TOF values (～1.2s-1). Finally, the putative iron-oxygen complexes are employed to the selective oxidation of benzyl alcohol under ambient conditions.更多还原