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中国材料进展[ISSN:1674-3962/CN:61-1473/TG]

卷:

期数:

2020年第09期

页码:

048-60

栏目:

出版日期:

2020-09-30

文章信息/Info

Title:

CO methanation on La/Ni(111) Surface: Effect of La Electron Delocalization on Activity and Selectivity

作者:

智翠梅1; 章日光2; 王宝俊2

(1. 太原科技大学化学与生物工程学院，太原，山西030021) (2. 太原理工大学煤科学与技术教育部和山西省重点实验室，太原，山西030024)

Author(s):

ZHI Cuimei 1;  ZHANG Riguang 2;  WANG Baojun 2

(1. College of Chemistry and bioengineering, Taiyuan University of Science and Technology, Taiyuan, Shanxi 030021) (2. Key Laboratory of Coal Science and Technology of Ministry of Education and Shanxi Province, Taiyuan University of Technology, Taiyuan, Shanxi 030024)

关键词:

密度泛函理论; Microkinetic modeling; d-带中心; 差分电荷密度; La–Ni协同催化

Keywords:

DFT;  Microkinetic modeling;  Differential charge density;  Electron delocalization;  Synergistic effect

文献标志码:

A

摘要:

针对Ni(111)表面上因副产物CH3OH形成而导致CH4选择性低的问题，本论文采用量子化学密度泛函理论（Density functional theory，DFT）计算的方法，通过添加富电子的助剂La调节表面Ni原子的电子状态，增大Ni的d电子平均能而增加La@Ni(111)表面的反应性，实现La与Ni的协同催化，达到提高CO甲烷化活性和CH4生成选择性的目标。同时，基于DFT结果，以Microkinetic modeling模拟实验条件下CH4和CH3OH的生成速率，结果表明，反应速率r随着温度升高而增大；在同一温度下，CH4生成速率r(CH4)远大于CH3OH的生成速率r(CH3OH)，且 在反应温度550~750K内高达100%，表明La@Ni(111)表面上CO甲烷过程中没有副产物CH3OH的生成。究其原因，在电子水平上通过对CH4形成路径Path1、Path 4、Path 9和Path 10所对应的关键中间体CO、HCO、CH2O和COH进行Bader电荷和pDOS分析，发现导致C–O键明显弱化，C–O断键能垒显著降低，以至无CH3OH生成的微观机理是La→Ni电子离域和La与O强相互作用而产生的“给电子诱导”效应。进一步，通过La与邻近Ni原子的三维差分电荷密度分析得知，La原子的电荷损耗是沿着“La→Ni”方向，这就是助剂La与Ni协同催化CO甲烷化并高活性高选择性地生成CH4的微观解释。

Abstract:

In attempting to promote the activity and selectivity of CO conversion to CH4 and simultaneously suppress CH3OH formation, density functional theory calculation has been employed to insight into reaction mechanism and the effect of the promoter La on CO conversion to CH4 on La/Ni(111). Our results indicate that the promoter La could enrich the outer layer valence electron density of Ni, make the d-band center of La/Ni(111) upward, and thereby leads to a significant increase of the reactivity. Accordingly, the enhanced activity and selectivity to CH4 as well as CH3OH resistance mainly due to the electronic effect of the promoter La on La/Ni(111), where the synergistic effect between La and Ni plays an important role. Meanwhile, the microkinetic modeling was used to estimate the production rates of CH4 and CH3OH under the experimental conditions, and the result show that r(CH4) is larger than r(CH3OH) at the same temperature, and the relative selectivity of CH4 reaches almost as high as 100% in the temperature range of 550 to 750 K, and thereby no CH3OH is formed when La is doped. Further, to clarify the effect of La promoter on CH4 formation at electron level, Bader charges and the projected density of states have been examined for CO、HCO、COH and CH2O, which are the key intermediates of Path1, Path2, Path3 and Path4 for CH4 formation, respectively. The results indicate that, it is electron transfer from La to Ni and the strong interaction between La and O that weaken the C–O bond and promote the cleavage of C?O bond, and thereby lead to no CH3OH yield, which controls the selectivity to CH4. Through the analyzing the differential charge density of La atom and its surrounding Ni atoms over La/Ni(111), the result of the direction along La→Ni of charge transfer, has been shed light on furtherly. Conclusively, La/Ni(111) shows a significant increase of the activity and selectivity to CH4 compared to Ni(111), which is mainly originated from the synergistic effect between La and Ni.

备注/Memo

备注/Memo:

收稿日期：2019-09-18 基金项目：国家自然科学基金重点资助项目（21736007）；太原科技大学科研启动基金资助（20182003, 20182016）第一作者：智翠梅 ，女，讲师，zhicuimei@tyust.edu.cn 通讯作者：王宝俊，男，教授，博士生导师，Email: wangbaojun@tyut.edu.cn

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更新日期/Last Update: 2020-08-28