双金属表面上硼氢化物催化产氢的理论研究
发布时间：2019-04-04 20:31
【摘要】：近年来,硼氢化物(BH4-)水解反应产氢凭借其产氢效率高、原料廉价易得、能耗低等特点而来备受瞩目。BH4-水解催化剂的研究是将BH4-水解产氢技术进一步发展的重要环节。目前,常见的BH4-水解产氢催化剂多以贵金属为主,催化剂价格昂贵,不易推广。在本文工作中,采用量子化学方法,从原子尺寸上对两种合金催化剂进行了研究考察,以DFT计算为主要研究手段,系统阐述了 Ir-Ni、Ru-Ni金属表面催化体系的结构及对BH4-水解产氢反应的催化性能。本文主要进行了三方面的工作:一是利用DFT计算对BH4-在Ir-Ni合金表面上的吸附结构、吸附强度和H解离进行研究;二是利用DFT计算研究环境因素对BH4-在Ir-Ni合金表面上的吸附的影响;三是基于BH4-的水解机理,利用DFT计算对不同Ru-Ni合金结构的催化活性研究。本文研究主要获得以下结论:(1)通过DFT计算考察了 BH4-在不同合金表面的吸附结构。结果表示我们可以通过改变合金表面Ir原子的掺杂比例对BH4-吸附时的H原子解离情况进行调控。在吸附强度方面,我们得到几种合金表面对BH4-的吸附强度遵循 IrNi2-Ni (111) 2Ir-Ni (111) Ir2Ni-Ni (111) 1Ir-Ni (111) 1Ir-2Ir2Ni-Ni (111), 1Ir-Ni (111)和 1Ir-2Ir2Ni-Ni (111)两种合金表面所表现出的BH4-吸附强度接近甚至超过纯Ir表面。我们进一步通过对合金结构的电子结构的计算对这一结果进行了证实与解释。除此之外,我们还对1Ir-Ni(111)和1Ir-2Ir2Ni-Ni(111)表面上解离后的BH的进一步解H反应进行了机理研究,结果与纯Ir表面进行对比得到,1Ir-2Ir2Ni-Ni(111)结构上此解离反应的能垒最小,表明1Ir-2Ir2Ni-Ni(111)合金结构对BH4-的解离具有更高的活性。本项工作可对BH4-水解合计催化剂设计提供部分理论基础。(2)本文通过DFT方法系统的讨论的一系列环境因素对BH4-在金属催化剂表面吸附的影响。从吸附结构上来看,H2O分子的加入会促进BH4-中H原子的解离,当加入OH-存在时,H2O分子对H原子解离的促进效果将被削弱。不仅如此,当水分子以解离的形态(H + OH-)存在时,对BH4-吸附的影响则变得十分微弱。从吸附强度上进行考察发现,无论是H2O分子的存在还是OH-的存在都会使BH4-与表面的相互作用减弱,进一步的电荷分析证实,当有其他物质共吸附时,催化剂与BH4-之间的电荷迁移会相对减少,使得BH4-的吸附强度变弱。但这种影响在不同的合金表现上所表现出的强弱不尽相同,因此通过本项研究可以有助于我们更好的筛选稳定性更好的催化剂结构。(3)本文DFT计算对BH4-在Ru-Ni合金表面的水解机理进行了研究,并与纯Ru表面上的结果进行了对比。本项工作通过DFT计算探究了BH4-及其水解过程中各物质在Ru-Ni合金表面的吸附结构与吸附强度,发现在1Ru-2Ru2Ni-Ni(111)合金表面上BH4-中的H原子表现出了解离结构,这种结构在纯Ru表面并未发现。进一步探究金属催化剂催化活性发现,针对BH4-的第一步水解,1Ru-2Ru2Ni-Ni(111)合金表面表现出了比Ru(111)表面更好的催化活性。
[Abstract]:In recent years, the hydrolysis reaction of borohydride (BH4-) has attracted attention by the characteristics of high hydrogen production efficiency, cheap and easily available raw materials, low energy consumption and the like. The research of BH4-hydrolysis catalyst is an important part of the further development of BH4-hydrolyzed hydrogen-producing technology. At present, the common BH4-hydrolyzed hydrogen-producing catalyst is mainly a noble metal, the catalyst is expensive and is not easy to popularize. In this paper, a quantum chemical method was used to study the two kinds of alloy catalysts from the atomic size, and the structure of the catalyst system of the metal surface of Ir-Ni and Ru-Ni and the catalytic performance of the hydrogen-producing reaction to the BH4-hydrolysis were described. The first is to study the adsorption structure, adsorption strength and H dissociation of BH4-on the surface of Ir-Ni alloy by means of DFT. The second is to study the influence of environmental factors on the adsorption of BH4-on the surface of Ir-Ni alloy by means of DFT. Thirdly, based on the hydrolysis mechanism of BH4-, the catalytic activity of different Ru-Ni alloy structures was studied by means of DFT. The main results are as follows: (1) The adsorption structure of BH4-on the surface of different alloys is investigated by DFT. The results show that we can control the dissociation of H atoms at the time of BH4-adsorption by changing the doping ratio of the Ir atoms on the surface of the alloy. The adsorption of BH4-Ni (111) Ir2Ni (111) 2Ir-Ni (111) Ir2Ni-Ni (111) 1Ir-Ni (111) 1Ir-2Ir2Ni-Ni (111), 1Ir-Ni (111) and 1Ir-2Ir2Ni-Ni (111) on the adsorption strength is close to or above the pure Ir surface. We further confirm and explain this result by the calculation of the electronic structure of the alloy structure. In addition, the mechanism of the further deionization of BH in the surface of 1Ir-Ni (111) and 1Ir-2Ir2Ni-Ni (111) is studied. The results are compared with the pure Ir surface, and the energy barrier of the dissociation reaction on the 1Ir-2Ir2Ni-Ni (111) structure is the least, indicating that the structure of the 1Ir-2Ir2Ni-Ni (111) alloy has higher activity for the dissociation of BH4-. This work can provide some theoretical basis for the design of the BH4-hydrolysis total catalyst. (2) The influence of a series of environmental factors on the adsorption of BH4-on the surface of the metal catalyst is studied by means of the DFT method. The addition of H2O molecules can promote the dissociation of H atoms in the BH4-H from the adsorption structure. When OH-is added, the effect of H2O molecules on the dissociation of H atoms will be weakened. Furthermore, when water molecules are present in dissociated form (H + OH-), the influence on BH4-adsorption becomes very weak. It is found that the interaction of the BH4-with the surface is weakened by the presence of H2O molecules or the presence of OH-, and further charge analysis proves that the charge migration between the catalyst and the BH4-is relatively reduced when the other substances are co-adsorbed. Such that the adsorption strength of bh4-is weakened. But this effect is different in different alloy performance, so this study can help us to better screen the catalyst structure with better stability. (3) The hydrolysis mechanism of BH4-on the surface of Ru-Ni alloy is studied by DFT calculation, and the results are compared with the results on the pure Ru surface. The adsorption structure and adsorption strength of each substance on the surface of Ru-Ni alloy in BH4-and its hydrolysis process are investigated by means of DFT calculation, and it is found that the H atoms in BH4-in the surface of the 1Ru-2Ru2Ni-Ni (111) alloy show off-structure, and this structure is not found on the pure Ru surface. Further investigation of the catalytic activity of the metal catalyst found that the surface of the 1Ru-2Ru2Ni-Ni (111) alloy exhibited better catalytic activity than that of the Ru (111) surface for the first hydrolysis of BH4-.
【学位授予单位】：北京化工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ116.2
[Abstract]:In recent years, the hydrolysis reaction of borohydride (BH4-) has attracted attention by the characteristics of high hydrogen production efficiency, cheap and easily available raw materials, low energy consumption and the like. The research of BH4-hydrolysis catalyst is an important part of the further development of BH4-hydrolyzed hydrogen-producing technology. At present, the common BH4-hydrolyzed hydrogen-producing catalyst is mainly a noble metal, the catalyst is expensive and is not easy to popularize. In this paper, a quantum chemical method was used to study the two kinds of alloy catalysts from the atomic size, and the structure of the catalyst system of the metal surface of Ir-Ni and Ru-Ni and the catalytic performance of the hydrogen-producing reaction to the BH4-hydrolysis were described. The first is to study the adsorption structure, adsorption strength and H dissociation of BH4-on the surface of Ir-Ni alloy by means of DFT. The second is to study the influence of environmental factors on the adsorption of BH4-on the surface of Ir-Ni alloy by means of DFT. Thirdly, based on the hydrolysis mechanism of BH4-, the catalytic activity of different Ru-Ni alloy structures was studied by means of DFT. The main results are as follows: (1) The adsorption structure of BH4-on the surface of different alloys is investigated by DFT. The results show that we can control the dissociation of H atoms at the time of BH4-adsorption by changing the doping ratio of the Ir atoms on the surface of the alloy. The adsorption of BH4-Ni (111) Ir2Ni (111) 2Ir-Ni (111) Ir2Ni-Ni (111) 1Ir-Ni (111) 1Ir-2Ir2Ni-Ni (111), 1Ir-Ni (111) and 1Ir-2Ir2Ni-Ni (111) on the adsorption strength is close to or above the pure Ir surface. We further confirm and explain this result by the calculation of the electronic structure of the alloy structure. In addition, the mechanism of the further deionization of BH in the surface of 1Ir-Ni (111) and 1Ir-2Ir2Ni-Ni (111) is studied. The results are compared with the pure Ir surface, and the energy barrier of the dissociation reaction on the 1Ir-2Ir2Ni-Ni (111) structure is the least, indicating that the structure of the 1Ir-2Ir2Ni-Ni (111) alloy has higher activity for the dissociation of BH4-. This work can provide some theoretical basis for the design of the BH4-hydrolysis total catalyst. (2) The influence of a series of environmental factors on the adsorption of BH4-on the surface of the metal catalyst is studied by means of the DFT method. The addition of H2O molecules can promote the dissociation of H atoms in the BH4-H from the adsorption structure. When OH-is added, the effect of H2O molecules on the dissociation of H atoms will be weakened. Furthermore, when water molecules are present in dissociated form (H + OH-), the influence on BH4-adsorption becomes very weak. It is found that the interaction of the BH4-with the surface is weakened by the presence of H2O molecules or the presence of OH-, and further charge analysis proves that the charge migration between the catalyst and the BH4-is relatively reduced when the other substances are co-adsorbed. Such that the adsorption strength of bh4-is weakened. But this effect is different in different alloy performance, so this study can help us to better screen the catalyst structure with better stability. (3) The hydrolysis mechanism of BH4-on the surface of Ru-Ni alloy is studied by DFT calculation, and the results are compared with the results on the pure Ru surface. The adsorption structure and adsorption strength of each substance on the surface of Ru-Ni alloy in BH4-and its hydrolysis process are investigated by means of DFT calculation, and it is found that the H atoms in BH4-in the surface of the 1Ru-2Ru2Ni-Ni (111) alloy show off-structure, and this structure is not found on the pure Ru surface. Further investigation of the catalytic activity of the metal catalyst found that the surface of the 1Ru-2Ru2Ni-Ni (111) alloy exhibited better catalytic activity than that of the Ru (111) surface for the first hydrolysis of BH4-.
【学位授予单位】：北京化工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ116.2
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