苯酚加氢反应高效催化剂的研制及其抗硫性能的研究

【作者】 庄莉；

【导师】 李和兴；

【作者基本信息】 上海师范大学 ， 物理化学， 2004， 硕士

【摘要】 非晶态合金是一类介于晶态和无定形物质之间的特殊材料，在结构上表现为长程无序而短程有序结构，其独特的结构导致了优良的催化性能，同时在制备和使用过程中环境污染少，符合现代化工生产要求的“原子经济性”和“绿色化”的发展趋势，因而引起人们的普遍关注。非晶态合金催化剂的制备及其催化性能的研究是当前催化领域的研究热点和前沿。 本论文通过化学还原法制备超细Ni-B和Pd-La-B两种非晶态合金催化剂，以具有重要工业应用价值的液相苯酚制备环己醇和环己酮为目标反应，系统考察了上述催化剂的催化性能，结合催化剂的系统表征和催化反应动力学，研究了非晶态合金的结构、表面电子态与催化性能及抗硫性能之间的关系；同时，通过改变修饰剂的用量，阐述其与非晶态合金的相互作用及其对催化性能的促进作用。主要研究工作如下： 一、催化剂的制备 1．超细Ni-B和Pd-B非晶态合金催化剂的制备：用化学还原法将一定量的KBH₄溶液逐滴加入到NiCl₂溶液或PdCl₂溶液中，得到黑色的Ni-B以及Pd-B非晶态合金催化剂。改变反应介质或滴加方式，可获得不同的非晶态合金催化剂。 2．双金属非晶态合金催化剂Pd-La-B的制备：将一定量的KBH₄溶液逐滴加入到配制好的PdCl₂和LaCl₃混合溶液中，得到Pd-La-B黑色非晶态合金催化剂，改变溶液中LaCl₃的量可获得调节Pd-La-B中的La含量。 二、催化剂的性能评价 在高压釜中加入一定量所制备的催化剂、0.5g／ml苯酚的乙醇溶液和溶剂乙醇，在1.0MPa H₂以及适当的温度下进行催化加氢，并通过加入一定量CS₂作为毒剂，进一步考察催化剂的抗硫性能。采用气相色谱测定苯酚转化率以及对目标产物的选择性，结果表明，Ni-B催化剂对环己醇的选择性接近100％，Pd-La-B催化剂对环己酮有高的选择性，调节La的含量，可使环己酮的最佳得率达到81.3%。同时，制备催化剂时采用较高浓度的KB风也能够提高催化剂的抗硫性能。三、催化剂的催化性能与结构的关系 1.非晶态合金比对应的晶态金属催化剂具有优良的催化活性，一方面归因 于其短程有序而长程无序的独特非晶态结构、活性位的均匀分布和高度 配位不饱和;另一方面，归因于金属和类金属（B）之间的相互电子作用， 导致金属呈富电子态，而类金属（B）为缺电子态。非晶态合金的抗硫性能 除由于其独特的电子效应之外，另一方面，也由于类金属的氧化态能够 有效吸附CSZ，达到保护活性位的目的。 2.在Pd一B催化剂中添加修饰剂La，改变了原有催化剂的结构和电子态，由 此促进了催化剂对苯酚加氢制备环己酮反应的活性和选择性。La对催化 活性和环己酮选择性的促进作用主要归因于LaZO3对催化剂酸碱性的调 节作用、分散作用和供电子效应。更多还原

【Abstract】 The amorphous alloy is a kind of material with short-range ordering while long-range disordering structure. Its unique structure can result in excellent catalytic properties, such as high catalytic activity and selectivity as well as strong resistance to the sulfur poison during many reactions, especially in various hydrogenation reactions. Meanwhile, little or even no environmental pollution may be caused during the preparation process of amorphous alloys and their application in catalysis, which represents the trend of modern chemical engineering production, i.e., the green chemistry and the economic reaction. Due to the industrial requirements and environmental considerations, amorphous alloy catalysts caused much attention by both chemists and chemical engineers. Even today, the preparation of amorphous alloy catalysts and the study on their catalytic performance are still in the forefront of recent catalysis research.In this thesis, both the Ni-B and Pd-La-B amorphous alloys in the form of ultrafine particles were prepared by chemical reduction. Their catalytic performance was evaluated using liquid phase phenol hydrogenation to cyclohexenol or cyclohexenone, both of them are of great industrial importance. According to a series of characterizations and kinetic studies, the correlation of the catalytic performance to both the structural properties and electronic characteristics was discussed. Furthermore, the promoting effect of the La-dopant on the catalytic behavior of the Pd-B amorphous catalyst was also investigated and the optimum content of the La-dopant was determined. The followings are in details: 1 .Catalyst preparationAll the Ni-B, Pd-B and Pd-La-B amorphous catalysts were prepared by chemical reduction of their corresponding metallic ions by KBH4 in aqueous solution, followed by thoroughly washing with distilled water and ethanol (EtOH) and finally kept in EtOH until the time of use. In most cases, the KBH4 solution was added dropwise into the solution containing the corresponding metallic ions. Only one Ni-B amorphousalloy was obtained by addition NiCl2 solution into KBH4 solution. Change the concentration of either the KBH4 or the LaCl3 in the solution resulted in the amorphous alloys with different content B or La-dopants. 2.Activity testPhenol hydrogenation was performed in a stainless steel autoclave containing certain amount of the as-prepared catalysts, phenol and EtOH, at 1.0 MPa hydrogen pressure and a desired temperature and under vigorous stirring (ca. 1200 rpm) to eliminate the diffusion effect. The reaction mixture was sampled every one hour for product analysis on a gas chromatograph (GC 9800) equipped with a FID. During poisoning test, trace CS2 was added initially into the reaction mixture as a poison. 3. Catalytic performance(1) The amorphous alloys exhibited much higher activity than their corresponding crystalline counterparts during the phenol hydrogenation. On one hand, this could be attributed to the unique amorphous structure (i.e., the short-range ordering and long-range disordering) and other structural parameters including homogeneous distribution of active sites and high un-saturation of coordination of these active sites. On the other hand, for all metal-B amorphous alloys, the metal always accepts partial electrons from B owing to the electronic interaction between metals and the boron. The electron-deficient B was favorable for phenol adsorption while the electron-enriched Ni favored desorption of the products, which could also account for their excellent sulfur resistance.(2) The La-dopant exhibited promoting effects on both the activity and selectivity to cyclohexanone as well as sulfur resistance, which could be mainly attributed to the high surface area of the catalyst resulted from La2O3 as a support, the stabilization of the amorphous alloy structure by the La-dopant, and the electron-donation of the La2O3 to the Pd active center.更多还原