摘要
采用第一性原理方法,通过计算表面能确定Mg_3N_2(011)为最稳定的吸附表面,分别研究了H_2分子在Mg_3N_2(011)三种终止表面的吸附性质.研究发现H_2分子平行表面放置更有利于吸附,表面能最低的终止表面Model II上吸附H_2分子最稳定,主要存在三种化学吸附方式:第一种吸附方式,H_2分子解离成2个H原子分别吸附在N原子上形成双NH基,这是最佳吸附方式;此时H_2分子与Mg_3N_2表面间主要是H原子的1s轨道和N原子的2s、2p轨道发生作用,N—H之间为典型的共价键.第二种吸附方式中H_2分子部分解离,两个H原子吸附在同一个N原子上形成NH_2基.第三种吸附方式中H_2分子解离成两个H原子,一个H原子和表面N原子作用形成NH基,另一个H原子和表面Mg原子作用形成Mg H结构.三种吸附方式不存在竞争关系,形成双NH基的吸附方式反应能垒最低,最容易发生.除此之外H_2还能以分子的形式吸附在晶体表面,形成物理吸附.
The first principles density theory calculations have been performed to investigate different Mg3N2 surface and the corresponding properties of HE adsorption. The calculation of surface energy present that Mg3N2（011） is the most stable surface. The result show that the H2 parallel to the surface is a favorable adsorption and the most stable structure is Ha ad- sorbed onto the Model II surface, which have the lowest energy. There are three main modes of chemical adsorption： The first adsorption mode is that HE is dissociated into two H, and each H connect with N atom respectively to form double NH. This is the best adsorption model, which mainly results from the interaction between the H 1 s orbit and N ls, 2p orbits. By the analysis of the charge distribution variation H atom and N atom lose electrons, Mg obtain electrons. The second mode, H2 dissociated partly and the two H are adsorbed onto the same N forming one NH2, forms covalent bond. From the analysis of the bond population, we conclude that the covalent bonds strengthen the structure of NH. In other words, the hydrogen de- sorption of NH2 is easier than NH. H2 is fully dissociated in the third mode. One H atom is adsorbed onto N forming a NH group, which is connected by covalent bond, while the other H atom is adsorbed onto Mg forming MgH, which is forming ionic bond. The reaction energy barrier show that there is no competition among the three adsorption modes. The model of forming two NH is the easiest pathway, which have the lowest reaction energy barrier of 0.848 eV. The second is that the adsorption of H2 molecules on the surface forming NH2 have the reaction energy barrier of 1.596 eV. The most unlikely ad- sorption model is that H2 is dissociated and forming the structure of NH＋MgH, which have the reaction energy barrier of 5.495 eV. In addition, H2 also can be physically adsorbed onto Mg3N2（011） surface.
作者
陈玉红
刘婷婷
张梅玲
元丽华
张材荣
Chen Yuhong Liu Tingting Zhang Meiling Yuan Lihua Zhang Cairong(State Key Laboratory of Advanced Processing and Recycling of Non-ferrous Metals, Lanzhou University of Technology, Lanzhou 730050 School of Science, Lanzhou University of Technology, Lanzhou 730050)
出处
《化学学报》
SCIE
CAS
CSCD
北大核心
2017年第7期708-714,共7页
Acta Chimica Sinica
基金
国家自然科学基金(No.51562022)
省部共建有色金属先进加工与再利用国家重点实验室开放基金(No.SKLAB02014004)
甘肃省高校基本科研业务费项目(No.05-0342)
NSFC-广东联合基金(第2期)超级计算科学应用研究专项资助项目~~
