甲醇在几类含铂二元合金上部分氧化反应机理的理论研究

发布时间：2018-01-24 21:42

本文关键词： 甲醇部分氧化催化活性密度泛函理论（DFT）反应机理铂钌合金直接甲醇燃料电池（DMFC）　出处：《吉林大学》2015年硕士论文　论文类型：学位论文

【摘要】：直接甲醇燃料电池（DMFC）是一种以液态的甲醇为燃料的特殊的质子交换膜燃料电池，是一种可以将甲醇的化学能直接有效地转化成电能的装置，因为结构简单、操作温度低、无污染、高效安全可靠等优点而受到人们的广泛关注，直接甲醇燃料电池的开发和应用可以有效地缓解能源危机，并减少环境污染。众所周知，金属Pt是用于DMFC中最有效的一元阳极催化剂，但是，，阳极催化剂存在的一些问题限制了DMFC的商业化应用。首先，Pt是贵金属，在地球上的存储量有限，而且价格昂贵、成本高；其次，甲醇在氧化过程中产生的一氧化碳容易使铂催化剂中毒，降低催化剂的催化活性，减少催化剂的利用率。因此，寻找催化活性好、抗一氧化碳中毒能力强的催化剂已经成为DMFC目前发展中急需解决的问题。研究甲醇在阳极催化剂上电化学氧化的反应机理，将有助于研发出更好的直接甲醇燃料电池催化剂。本文采用高水平的量子化学计算方法，研究了甲醇在阳极催化剂上的吸附和脱氢机理，比较了不同催化剂对甲醇部分氧化的催化活性，可以为进一步对高效的阳极催化剂的研究提供可靠的理论依据。主要研究内容如下：我们用Pt6M（M=Pt，Sn，Ru）二元合金模型来模拟DMFC阳极的催化剂，采用密度泛函理论（DFT）中的B3PW91方法，研究了甲醇在Pt6M（M=Pt，Sn，Ru）二元合金催化剂上吸附和脱氢反应的反应机理，并且比较了Pt6M（M=Pt，Sn，Ru）三种催化剂对于甲醇部分氧化的催化活性。甲醇的吸附和脱氢机理主要有两种：（1）用羟基H原子和甲基H原子分别进攻Pt6M团簇的Pt原子和M原子，形成甲基吸附复合物，进而发生C-H键断裂；（2）用羟基O原子和羟基H原子分别进攻Pt6M团簇的M原子和Pt原子，形成了羟基吸附复合物，进而发生O-H键的断裂。在B3PW91/LANL2DZ理论水平讨论了反应的吸附能、活化能垒、分解能、自然键轨道分析和前线分子轨道分析。通过计算得到的反应势能面（PES）表明，在纯铂催化剂Pt7上更有利的脱氢反应通道是甲基吸附复合物的分解；在Pt6Sn二元合金催化剂上更有利的反应通道是羟基吸附复合物的分解；在Pt6Ru二元合金催化剂上甲基吸附复合物的分解和羟基吸附复合物的分解都是主要的反应通道。我们可以得出结论，在纯Pt催化剂中引入的第二种金属Ru和Sn提高了对甲醇部分氧化反应的催化活性，对于DMFC中甲醇的吸附和脱氢反应，Pt6Ru二元合金是Pt6M（M=Pt，Sn，Ru）三种催化剂当中最有效的。
[Abstract]:Direct methanol fuel cell (DMFC) is a kind of liquid methanol as fuel special proton exchange membrane fuel cell is a methanol chemical energy directly and efficiently into electrical energy device, because of simple structure, low operation temperature, no pollution, the advantages of high efficiency, safety and attention the development and application of direct methanol fuel cell can effectively alleviate the energy crisis, and reduce environmental pollution. As everyone knows, Pt is a metal element for an anode catalyst, the most effective in DMFC but some problems of anode catalyst have limited commercial application of DMFC. First, Pt is a precious metal, storage in the face of the earth is limited, and the price is expensive, the cost is high; secondly, methanol produced during oxidation of carbon monoxide to platinum catalyst poisoning, reduce the catalytic activity of the catalyst, reduce the catalyst utilization Rate. Therefore, looking for good catalytic activity, resistance to carbon monoxide poisoning catalyst ability has become the urgent problems in the development of DMFC. The reaction mechanism of methanol oxidation on the anode catalyst in the electrochemical, will contribute to the development of direct methanol fuel cell is a better catalyst. By using high level quantum chemical calculation method, to study the adsorption and dehydrogenation mechanism of methanol in the anode catalyst, the catalytic activity of different catalysts for partial oxidation of methanol, can provide a reliable theoretical basis for further research on the anode catalyst efficiency. The main research contents are as follows:
We use Pt6M (M=Pt, Sn, Ru) catalyst two element alloy model to simulate the DMFC anode, using density functional theory (DFT) in the B3PW91 method, the study of methanol on Pt6M (M=Pt, Sn, Ru) reaction mechanism of adsorption and dehydrogenation of two alloy catalyst, and more than Pt6M (M=Pt, Sn, Ru) three catalysts for catalytic partial oxidation of methanol. There are two main types of adsorption and dehydrogenation mechanism of methanol: (1) Pt6M clusters were used to attack the H atom and hydroxyl methyl H atoms Pt and M atoms, forming methyl adsorption complexes, and cleavage of C-H (; 2) attack Pt6M clusters respectively with O atoms and hydroxyl hydroxyl H atoms M and Pt atoms, the formation of hydroxyl adsorption complexes, and then breaking O-H bonds. At the B3PW91/LANL2DZ level of theory was discussed and the adsorption energy, activation energy, dissociation energy, natural bond orbital analysis and frontier molecular orbital Division Through the analysis. The calculated potential energy surface (PES) show that in pure platinum catalyst Pt7 on the dehydrogenation reaction channel more favorable is the decomposition of methyl adsorption complexes; Pt6Sn two element alloy catalyst reaction channel more favorable is the decomposition of hydroxyl adsorption complexes; decomposition in Pt6Ru two alloy catalyst on the adsorption of methyl complex decomposition and hydroxyl adsorption complexes are the major reaction channel. We can conclude that the introduction of pure Pt catalyst in second kinds of metal Ru and Sn enhanced the catalytic activity of the methanol oxidation reaction, the adsorption and dehydrogenation of DMFC in methanol, Pt6Ru alloy Pt6M (M=Pt is two yuan Sn, Ru, three) the most effective catalyst.

【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：O621.254;TM911.4

【共引文献】