乙炔选择性加氢反应中Cu催化剂表面结构、价态及金属掺杂对乙烯选择性的影响

发布时间：2018-05-23 12:40

本文选题：乙炔选择性加氢 + Cu催化剂　；参考：《太原理工大学》2017年硕士论文

【摘要】：乙烯是工业生产聚合物和精细化学品的基础原料,是衡量一个国家石化行业生产水平的重要标志。工业上获得乙烯主要通过石油热裂解,热裂解过程在产生乙烯的同时会产生0.1~1%的乙炔,而乙炔会导致乙烯聚合反应催化剂不可逆失活。因此,乙炔含量必须降低到1 ppm以下才能符合乙烯聚合反应的要求。工业上广泛采用贵金属Pd基催化剂催化乙炔选择性加氢生成乙烯,该方法不仅可以脱除乙炔,而且能够增加乙烯产率。但贵金属Pd基催化剂存在生成乙烯选择性低、成本高等问题,故寻求一种催化性能优良的非贵金属催化剂成为研究重点。对于非贵金属Cu催化剂,尽管低温下选择性和活性较低,仅将其作为助剂添加到贵金属催化剂中,但高温下Cu催化剂却是乙炔选择性加氢反应的活性组分。本文采用密度泛函理论计算方法,以Cu催化剂上乙炔选择性加氢反应为研究对象,系统研究了Cu催化剂价态、表面结构和金属掺杂对其催化性能(选择性和活性)的影响。对于不同价态Cu催化剂,通过Cu、Cu2O和Cu O来反映Cu(0)、Cu(I)和Cu(II)催化剂;对于Cu的表面结构,通过Cu、Cu2O和Cu O的低指数表面(111)、(110)和(100)反映不同表面结构,同时考虑了这些表面的完美和缺陷表面;对于金属掺杂Cu催化剂,考虑了Ni、Pd、Pt和Au四种金属的掺杂。首先,研究了H2和H2O在不同表面结构Cu O(111)表面上(完美、缺陷、预吸附氧)的吸附和解离,从而阐明cu催化剂表面结构对乙炔选择性加氢反应关键起始步骤的影响。其次,详细研究了三种不同价态cu催化剂cu(0)、cu(i)和cu(ii)的不同表面结构(完美、缺陷)上乙炔选择性加氢反应来阐明cu催化剂价态和表面结构对乙炔选择性加氢反应的影响。进一步,研究了cu(0)/cu(i)双组分催化剂上乙炔选择性加氢来阐明cu催化剂组分对反应的影响。最后,考虑了金属ni、pd、pt和au掺杂改性的cu(0)和cu(i)催化剂上乙炔选择性加氢反应来阐明金属掺杂对反应的影响。通过上述研究进而获得cu催化剂价态、表面结构、组分和金属掺杂对乙炔选择性加氢反应生成乙烯的催化性能影响,为新型高效cu催化剂的设计提供重要理论依据。主要结论如下:1.cuo(111)表面结构对h2和h2o的吸附与解离表现出结构敏感性:a)h2在完美表面发生解离吸附,与表面晶格氧生成h2o,进而形成氧缺陷表面;由于活性位表层氧原子的减少,h2在氧缺陷表面以分子吸附形式存在;h2在预吸附氧表面同样为解离吸附;b)对于h2o的第一步解离反应(h2o→oh+h),氧缺陷表面较完美表面呈现出强的催化活性,预吸附氧表面是动力学和热力学上最有利的表面。oh在完美表面较难解离生成h和o,在氧缺陷和预吸附氧表面上h2o解离的h可促进oh解离。oh是h2o在不同cuo(111)表面解离的主要产物。2.cu催化剂价态、表面结构影响乙炔选择性加氢反应体系中生成乙烯的选择性和活性:a)cu催化剂对乙烯的选择性和活性随价态变化(cu(ii)→cu(i)→cu(0))而改变:cu(ii),cu(i)和cu(0)催化剂对乙烯的生成均呈现较好的选择性和催化活性,其中cu(i)具有最高的乙烯选择性,而cu(0)催化剂呈现最高的催化活性;b)对于cu(ii)催化剂,完美cuo表面呈现极低的乙烯选择性;缺陷cuo(111)表面具有较高的乙烯选择性和催化活性;c)对于cu(i)催化剂,完美cu2o表面对乙烯的生成表现出极低的选择性;缺陷cu2o(111)和cu2o(110)表面对乙烯的生成表现出较高的选择性和活性,二者选择性几乎相同,但cu2o(110)缺陷表面较cu2o(111)缺陷表面具有更高的催化活性;d)对于cu(0)催化剂,cu(111)和cu(211)表面对乙烯的生成表现出较高的选择性和催化活性,其中cu(111)表面较cu(211)表面表现更优的催化选择性和活性。3.cu催化剂活性组分影响乙炔选择性加氢反应体系中生成乙烯的选择性和活性:相对于单组分cu(0)和cu(i)催化剂,cu(0)/cu(i)双组分催化剂因表现较低的催化活性,不能将其作为乙炔选择性加氢反应的理想催化剂;对于乙炔选择性加氢反应体系,cu催化剂应仅存在单一价态组分。4.金属ni、pd、pt和au掺杂改性影响cu催化剂上乙炔选择性加氢反应体系中生成乙烯的选择性和活性:a)对于金属ni、pd、pt和au掺杂的cu(111)表面,生成乙烯的选择性排序:pdcu(111)cu(111)ptcu(111)nicu(111)aucu(111)pd(111);活性顺序:pdcu(111)ptcu(111)pd(111)cu(111)nicu(111)aucu(111);pdcu(111)具有最高的乙烯选择性和催化活性,并且远高于cu(111)和pd(111)表面上的催化性能;而Au Cu(111)表面表现最低的催化活性;b)Ni、Pd、Pt和Au金属的掺杂改变了Cu(111)表面金属原子的d带中心,进而影响乙炔选择性加氢反应的乙烯选择性和催化活性,根据不同掺杂型表面以及Cu(111)、Pd(111)表面的选择性和催化活性与金属表层原子d带中心所形成的近似火山型曲线,得出如下结论:较比其他表面,Au Cu(111)和Pd(111)分别具有最小和最大的表层金属原子d带中心,故而呈现最低的乙烯选择性;PdCu(111)表层金属原子的d带中心位于中间位置,呈现最高的乙烯选择性和催化活性;c)Pd金属掺杂的缺陷Cu2O(111)和Cu2O(110)表面,因掺杂金属Pd占据缺陷位而使得掺杂后的表面表现出与相应完美表面相似的乙炔加氢特性,即Pd金属掺杂的Cu(I)催化剂具有极低的乙烯选择性和催化活性。5.Cu催化剂价态、表面结构、组分和金属掺杂四个主要结构因素影响乙炔选择性加氢反应生成乙烯的催化性能,通过调变这些结构因素进而调控其催化性能,实现乙炔选择性加氢反应中高选择性、高活性生成乙烯进而脱除乙炔。本文的理论计算工作能够为乙炔选择性加氢反应体系中新型高效Cu催化剂的改性和设计提供基本理论线索和方法。
[Abstract]:Ethylene is the basic raw material for the production of polymer and fine chemicals in industry. It is an important symbol to measure the production level of a national petrochemical industry. The industrial ethylene is mainly pyrolytic by petroleum, and the process of pyrolysis produces ethylene at the same time, while acetylene will lead to the irreversible deactivation of the ethylene polymerization catalyst. Therefore, the content of acetylene must be reduced to less than 1 ppm to meet the requirements of ethylene polymerization. The noble metal Pd based catalyst is widely used in industry to catalyze ethene selective hydrogenation to generate ethylene. This method can not only remove acetylene, but also increase ethylene production. However, the Pd based catalyst for noble metals has low selectivity and cost of producing ethylene. In order to find a non noble metal catalyst with excellent catalytic performance, the non noble metal Cu catalyst is added to the noble metal catalyst, although the selectivity and activity are low at low temperature, but the Cu catalyst is the active component of the selective hydrogenation reaction of acetylene at high temperature. The degree functional theory calculation method is used to study the selective hydrogenation of acetylene on Cu catalyst. The effects of the valence state of Cu catalyst, surface structure and metal doping on its catalytic performance (selectivity and activity) are systematically studied. For different valence Cu catalysts, Cu (0), Cu (I) and Cu (II) catalysts are reflected by Cu, Cu2O and Cu O; The surface structure, through the low exponential surface (111), (110) and (100) of Cu, Cu2O and Cu O, reflects the perfect and defective surfaces of these surfaces; for metal doped Cu catalysts, the doping of four metals, Ni, Pd, Pt and Au, is considered. First, the H2 and H2O on the surface of the different surface structure Cu (111) surface (perfection, defect, preconditioning) The adsorption and dissociation of adsorbed oxygen is used to elucidate the influence of the surface structure of Cu catalyst on the critical initial step of acetylene selective hydrogenation. Secondly, the valence state and surface junction of Cu catalysts are clarified in detail with three different valence Cu catalysts Cu (0), Cu (I) and Cu (II) on the different surface structures (perfect, defects). Further, the effect of acetylene selective hydrogenation on Cu (0) /cu (I) dual component catalyst was studied to clarify the effect of Cu catalyst components on the reaction. Finally, the selective hydrogenation of acetylene on Ni, PD, Pt and Au doped modified Cu (0) and Cu (I) catalysts was considered to clarify the effect of metal doping on the reaction. The effect of the valence state of Cu catalyst, surface structure, composition and metal doping on the catalytic performance of ethylene in acetylene selective hydrogenation, which provides an important theoretical basis for the design of a new efficient Cu catalyst, is obtained through the above study. The main conclusions are as follows: the structure sensitivity of 1.cuo (111) surface structure to the adsorption and dissociation of H2 and H2O shows the structure sensitivity. Sensibility: a) H2 occurs dissociation adsorption on the perfect surface, forming H2O with surface lattice oxygen to form an oxygen defect surface; due to the decrease of oxygen atom on the surface of the active surface, H2 exists in the form of molecular adsorption on the surface of oxygen defect; H2 is also dissociated on the surface of the preadsorbed oxygen; b) the first step dissociation reaction (H2O to oh+h), the surface of oxygen defect on the H2O. The most favorable surface of the oxygen surface is the most favorable surface.Oh on the perfect surface, which is difficult to dissociate and produce H and O on the perfect surface. The h of the dissociation of H2O on the oxygen defect and the preadsorbed oxygen surface can promote the oh dissociation.Oh is the main product of H2O on the different CuO (111) surface, the valence state of the.2.cu catalyst, and the surface junction. The selectivity and activity of ethylene production in acetylene selective hydrogenation reaction system: the selectivity and activity of a) Cu catalyst changes with the change of valence state (Cu (II), Cu (I) to Cu (0)): Cu (II), Cu (I) and Cu (0) catalysts show good selectivity and catalytic activity to ethylene production. The Cu (0) catalyst presents the highest catalytic activity; b) for the Cu (II) catalyst, the perfect CuO surface presents extremely low ethylene selectivity; the defective CuO (111) surface has high ethylene selectivity and catalytic activity; c) shows extremely low selectivity for the formation of ethylene with the Cu (I) catalyst and the perfect Cu2O table; the defect Cu2O (111) and Cu2O (110) The surface has higher selectivity and activity for the generation of ethylene, and the selectivity of the two is almost the same, but the surface of the Cu2O (110) defect has higher catalytic activity than the Cu2O (111) defect surface; d) for Cu (0) catalyst, Cu (111) and Cu (211) surface showed high selectivity and catalytic activity to ethylene production, of which the Cu (111) surface was compared with Cu (21). 1) the selectivity and activity of the catalytic selectivity and active.3.cu catalyst on the selective hydrogenation of acetylene in the selective hydrogenation reaction system of acetylene can not be used as an acetylene selective hydrogenation reaction compared to the single component Cu (0) and Cu (I) catalysts, and the Cu (0) /cu (I) dual component catalyst has a lower catalytic activity. Ideal catalyst; for the acetylene selective hydrogenation reaction system, the Cu catalyst should have only a single valence group of.4. metal Ni, PD, Pt, and Au doping modification affecting the selectivity and activity of ethylene production in the acetylene selective hydrogenation reaction system on the Cu catalyst: a) for the selective discharge of the metal Ni, PD, Pt, and Au doped (111) surfaces. Order: PdCu (111) Cu (111) ptcu (111) NICU (111) aucu (111) Pd (111); active order: PdCu (111) ptcu (111) Pd (111) Cu (111) NICU (111) aucu (111)); The doping changes the center of d band of metal atoms on the surface of Cu (111), and then affects ethylene selectivity and catalytic activity of acetylene selective hydrogenation reaction. According to the approximate volcanic curve formed by the selectivity and catalytic activity of different doped surface and Cu (111), Pd (111) surface and the D zone of metal surface atoms, the following conclusions are drawn: Compared with other surfaces, Au Cu (111) and Pd (111) have the minimum and maximum surface metal atom d band center, thus presenting the lowest ethylene selectivity; PdCu (111) surface metal atom's d band center is located in the middle position, showing the highest ethylene selectivity and catalytic activity; c) Pd metal doped defects Cu2O (111) and Cu2O (110) surface, due to doping. The metal Pd occupies the defect position and makes the doped surface exhibit acetylene hydrogenation characteristics similar to the corresponding perfect surface. That is, the Pd metal doped Cu (I) catalyst has very low ethylene selectivity and catalytic activity.5.Cu catalyst valence state. The four main structural factors of surface structure, composition and metal doping influence the acetylene selective hydrogenation reaction. The catalytic performance of ethylene is generated by regulating these structural factors and regulating its catalytic performance, achieving high selectivity in acetylene selective hydrogenation, high activity to generate ethylene and then removing acetylene. The theoretical calculation of this paper can provide the basis for the modification and design of a new efficient Cu catalyst in the acetylene selective hydrogenation reaction system. The theoretical clues and methods.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36;TQ221.211

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