摘要
催化剂的结构，是决定性能优劣的主要原因。合成结构清晰，性能优良的催化剂，构建清晰的构效关系，是催化剂研究的重要课题。表面分析技术实现在原子尺度上研究化学反应，为多相催化反应机理及催化剂结构剖析提供支持。扫描隧道显微镜，可以实现原子尺度的空间成像，而X射线光电子能谱则为催化剂表面元素组成及价态表征提供有力证据。基于模型体系和实际催化体系相结合，可以为催化剂结构构建提供重要参考。本文基于模型体系研究基础，合成不同结构催化剂，并将其应用于丙烷脱氢反应，探究其反应性能。
丙烯作为重要的化工中间体，随着其下游三大产品：聚丙烯，丙烯腈和环氧乙烷的需求不断上升，丙烯需求量逐年增长，传统的丙烯生产工艺（如炼厂催化裂化和石脑油裂解等）难以满足日益增长的丙烯需求。近年来，随着页岩气的开发，丙烷脱氢制丙烯（PDH）工艺日渐受到关注。丙烷脱氢制丙烯是强吸热反应，因此需要高温来促进反应进行。传统工业上常用的催化剂为Pt基催化剂和Cr系催化剂。然而对Pt基催化剂来说，高温积碳严重导致催化剂选择性低和不稳定是其亟待解决的问题。加入另一种助剂可有效改善Pt的催化反应性能。然而其具体结构，机理和相互作用还需进一步研究。本论文基于Pt基催化剂研究了不同助剂加入时其催化剂结构及相互作用以及由此产生的对于丙烷脱氢反应性能的影响，为以后催化剂的结构设计提供了参考。
首先，本文通过独特的合成方法，合成表面富集Pt亚表面3d过渡金属的Pt-skin结构的催化剂。研究发现，虽然表面3d过渡金属存在会导致丙烷脱氢丙烯选择性的降低，但是采用高温还原酸洗处理后得到Pt-skin结构的方法后，其丙烯选择性和纯Pt相比有很大的提升。首先结合TEM, EDS, ICP, XPS, XANFS等手段表征亚表面3d过渡金属，表面富集Pt的Pt-skin结构的形成，之后结合DFT 计算和红外，C3H6-TPD等发现，亚表面3d过渡金属的加入，降低表面Pt的d 带中心，减弱了对于丙烯的吸附，有利于形成丙烯而不利于其深度脱氢形成积碳，从而提高了丙烯的选择性。并且关联了丙烯选择性和表面Pt的d带中心的变化关系。
此外，本文还研究了高分散的可还原性氧化钨载体的加入对于Pt基催化剂丙烷脱氢性能的影响。当氧化钨的负载量低于单层负载量时，由于氧化钨和氧化铝的作用，使得氧化钨呈现高分散，大大促进Pt纳米粒子的分散。研究发现，加入高分散的可还原性氧化钨，Pt基催化剂丙烷脱氢性能得到提高，归因于可还原性氧化钨和贵金属Pt之间的强相互作用。
关键词：丙烷脱氢,d带中心，Pt-skin，强相互作用，表面分析技术
ABSTRACT
The structure of the catalyst is the main reason for determining the performance. Construction the clear relationship between the structure and performance is the important topic for catalyst rearch.
The surface analysis technique is ud to study chemical reaction on atomic scale and provides support for heterogeneous catalysis reaction mechanism analysis. Scanning atomic tunneling microscope can realize atomic scale imaging, and X-ray photoelectron spectroscopy can analyze the surface element composition and valence for catalyst. Bad on the combination of model catalytic system and supported catalytic system, it can provide important reference for the construction of the catalyst structure. Bad on the model system, this paper synthesizes different structural catalysts and applies them to propane dehydrogenation to explore its reaction properties.
Propylene is an important building intermediates for chemistry and the demand for propylene is increasing along with its down-stream products (polypropylene, propylene oxide, acrylonitrile, phenol, etc.). The traditional propylene producing technology (steam cracking and fluid catalytic cracking (FCC) of naphtha) is difficult to meet the increasing propylene demand. In recent years, with the growing production of shale gas the propane dehydrogenation process has attracted more and more attention. The propane dehydrogenation has gradually become the most promising new propylene production technology becau of its high efficiency of propylene production and considerable economic profit. Propane dehydrogenation requires high temperature to facilitate the reaction becau of the strong endothermic reaction process. The usually industrial catalysts in prop
hofane dehydrogenation are Pt and CrO x. The problem demanding prompt solution for Pt-bad catalysts are the low lectivity and instability caud by carbon deposition and particle aggregation. The addition of additives can effectively improve performance of Pt. However, the specific structure, mechanism and interaction need to be further studied. Bad on Pt-bad catalyst, In this paper, we studied different structure Pt-bad catalysts and the effect for the performance as different additives adding, which provides reference for later design the structure of the catalyst.
Firstly, we synthesized the special Pt-skin structure with subsurface 3d transition metal through a unique synthesis method. We found that the surface 3d transition metal would lead to decreasing for propylene lectivity. However, the obtained Pt-skin catalysts with subsurface 3d transition metal through high temperature reducing following by acid etching treatment can increasing the propylene lectivity
dramatically. With the aid of TEM, EDS, ICP, XPS and XANFS characterization methods, we demonstrate a facile construction of well-defined Pt-skin catalysts modified by different 3dTM atoms in subsurface regions. After that, combined with DFT calculations, CO-FTIR, and C3H6-TPD, we found that subsurface 3d transition metal, reduced the d-band center of surface of Pt and the adsorption of propylene. As a result, the Pt-skin structure catalysts with 3d transition metal in subsurf
ace region can facilitate the formation of propylene and prejudice deep dehydrogenation, which would improve the lectivity of propylene. In addition, we also established relationship between reactivity and d-band center shifting.
In addition, the effect of the high dispersion and reducible tungsten oxide addition on the dehydrogenation of propane was studied. When the capacity of tungsten oxide is lower than single layer capacity, the interaction between tungsten oxide and alumina makes tungsten oxide highly disperd, which greatly promotes the dispersion of Pt nanoparticles. We found that the addition of high dispersion and reducible tungsten oxide would improve the performance of Pt-bad catalysts due to the strong interaction between the reducible tungsten oxide and the metal Pt.
KEY WORDS: Propane dehydrogenation, D-band center, Pt-skin, SMSI, Surface analysis technique
目录
第1章绪论 (1)
1.1表面结构对催化剂性能的调变 (1)
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1.2Pt-skin结构催化剂的研究 (2)
1.3贵金属载体强相互作用的研究 (3)
1.4丙烯的用途，丙烷脱氢主要工艺及催化剂 (4)
1.5丙烷脱氢催化剂现状 (7)
江畔独步寻花的诗意是什么
1.5.1Pt基催化剂 (7)
1.5.2Cr系催化剂 (9)
1.5.3其他丙烷脱氢催化剂 (10)
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1.6本论文选题意义及工作设想 (10)
第2章实验总述 (13)
2.1超高真空仪器设备 (13)
2.1.1扫描隧道显微镜 (13)
2.1.2带有高压反应腔的X射线光电子能谱 (13)
2.2表面分析技术及基本原理 (14)
2.2.1扫描隧道显微镜 (14)
other什么意思2.2.2X射线光电子能谱 (16)
2.3纳米粒子实验方法 (17)
2.3.1实验原料 (19)
2.3.2催化剂制备 (20)
2.3.3催化剂表征 (21)
2.3.4催化反应性能评价 (23)
2.3.5产物分析方法 (24)
2.3.6催化剂活性评价指标 (24)
第3章基于亚表面3d过渡金属修饰的Pt基双金属催化剂丙烷脱氢性能的研究 (25)
peter gade3.1引言 (25)
3.2催化剂的制备 (26)
3.3实验结果与讨论 (26)
3.3.1催化剂结构表征 (27)
3.3.2催化剂丙烷脱氢活性测试 (31)
michael phelps3.3.3反应机理的研究 (33)
few怎么读3.4本章小结 (35)
第4章高分散部分还原的氧化钨对于Pt基催化剂丙烷脱氢性能的影响 (39)
4.1引言 (39)
4.2催化剂的制备 (40)
4.3催化剂的表征 (40)
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4.3.1催化剂性能测试 (40)
4.3.2催化剂性能提升原因的探究 (42)vul
4.4本章小结 (44)
第5章表面超高真空系统的维修和调试 (45)
5.1引言 (45)
5.2扫描隧道显微镜的拓展 (45)
5.2.1原有的扫描隧道显微镜 (46)
5.2.2拓展后的扫描隧道显微镜系统 (47)
5.3表面分析和制备系统的维修和改良 (48)
第6章结论与展望 (51)
6.1结论 (51)
6.2展望 (52)
参考文献 (55)
发表论文和科研情况说明 (63)
致谢 (65)
