乙烷在Fe110 Co111 Ni111表面吸附及解离的密度泛函理论研究

乙烷在Fe110 Co111 Ni111表面吸附及解离的密度泛函理论研究

乙烷在Fe(110)、Co(111)、Ni(111)表面吸附及 解离的DFT研究

专业：环境科学

研究生：张福兰

指导教师：李来才

摘要： 第一过渡金属催化乙烷裂解制备乙烯倍受广大研究者的关注， 受当前实验手段的限制，其反应机理尚不明确。本文采用基于密度泛函理论 的量子力学计算程序DMol3，计算并分析了乙烷在金属低指数面上的吸附和 解离过程，完善了反应机理。

本文基于第一性原理的密度泛函理论与周期平板模型相结合的方法，优化 TCzH6裂解反应过程各驻点在Fe(110)表面的top、hop、SB、LB位，在Co(111) 和Ni(111)表面的top、foe、hcp、bridge位的吸附模型；计算了能量，并对布居 电荷进行了分析，得到了各驻点的有利吸附位；研究了乙烷在Fe(110)、Co(111)、 Ni(11 1)表面解离的可能微观反应机理，使用完全LST／QST程序确定解离反应的 过渡态。结果表明：

(1)当C2H6在Fe(110)表面裂解时，C2H6、C2H5、C2H4、CI-14、CH3、CH2、

H2和H在Fe(110)表面稳定吸附位分别为LB、LB、top、SB、top、hcp、LB 和hcp，所对应的吸附能分别为．80．24、．178．89、．132．73、．38．14、．171．78、

．342．43、．19．50和．345．63 k．1·mol一：在吸附过程中，物种C2fi6、C2H5、C2H4、 CH2和H将电荷转移给Fe(1lO)表面，而CH4、CH3和H2是得到Fe(110)表面 的电荷，各物种均为化学吸附；C2战在Fe(110)表面C．C解离的速控步骤活

化能为而C．H解离的速控步骤活化能为，故C．C解离过程占优势，主反应通

道为Fe(1lo)+C2H矿Fe(110)．C21-16哼TS3--·M2呻TS4--,P2，其主产物为Cm

和CH2。

(2)当C2成在Co(I 1 1)表面裂解时，C2HF、C2H5、C2H4、C地、CH3、CH2、 H2和H在Co(111)表面稳定吸附位分别为bridge、bridge、top、top、top、bridge、 bridge和fcc，所对应的吸附能分别为．89。39、-243．98、．133．32、．60．35、．227．61、

．440．57、．40．24和．338．46 1(J-tool\，在吸附过程中，物种C2凰、C2I王4、CH4、 CH3、CH2和H将电荷转移给Co(111)表面，而C2H5和H2是得到Co(111)表 面的电荷，各物种均为化学吸附；C2H6在Co(111)表面C—C解离的速控步骤 活化能为223．8蚶·tool\C—H解离的速控步骤活化能为180．9 kJ·tool\ C-H解离占优势，主反应通道为Co(111)+C2H6--,'Co(111)-C2Hp TSl一-IMI--*

TS加P1，其主产物为C2H4和H2。

(3)当C2H6在Ni(111)表面裂解时，C2H6、C2H5、C2H4、CI-h、CH3、CH2、 H2和H在Ni(111)表面稳定吸附位分别为top、hq,、top、hcp、hcp、fcc、bridge 和fcc，所对应的吸附能分别为．36．41、．100．21、-48．62、．16．13、．126．18、一296．60、

。12．19和．352．13 kJ·tool\C2H5、C2H4、CH3、CH2和H 将电荷转移给Ni(111)表面，而C2玩、CI-h和H2是得到Ni(111)表面的电荷， 各物种均为化学吸附；C2H6在Ni(111)表面C．C解离的速控步骤活化能为257．9

kJ·tool～，而C．H解离的速控步骤活化能为159．8 U·tool一，故C．H解离占优势， 主反应通道为Ni(111)+C2H—Ni(111)．C2H—TSl-．．,D讧1·TS2呻P1，其主产物 为C2H4和H2。

综上所述，第一过渡金属Fe、C0、Ni活化’C2H6制备C2H4的最好催化剂

是Ni，Co次之，而Fe不宜采用。

关键词：乙烷；乙烯：吸附： Fc(110)表面；Co(111)表面；Ni(111)表面：密

度泛函理论：电子结构：过渡态

Theoretical on the and Study Decomposition AdsOrption

of Ethane over the Fe(110)，Co(111)

and Ni(111)Surface

Science Major：Environmental

Graduate Student． Zhang Fu-lan Supervisor：Professor Li lai·eai

Abstract

The investigation that the first transition-metal forming ethylene catalyzed by ethane is very concerned by researchers．The mechanism of ethane is still decomposition because experimental are finite．In this research，the Drool3 ambiguous apparatuses program module based on DFT has been used to compute and analyze the ethane．adsorption and decomposition on low index transition metal surface．And improve the reaction mechanism．

In this paper,the density functional theory fOFT)and self-consistent periodic calculation have been used to investigate that the species CxHy(x=o

之，y=l-q5)are The on the re(110)，Co(111)，and absorpt Ni(111)surface，respectively adsorption of the four energy,the optimized geometry species CxHy(x--0-2，y=l--6)absorpt on．the possible sites(top，hep，SB，and LB)ofFe(110)，Co(111)and Ni(111)surfaces have been calculated and compared．Mulliken charges have been analyzed，then the most stable site have got．A possible decomposition mechanism for ethane absorpting on the

Fe(110)，C0．(111)，and Ni(111)surfaces have been investigated

using DFT．The transition!’§fates have been defified using complete linear

and quadratic synchronous transit(LST／QST)methods．The synchronous transit

main results indicate the following：

1．'When the ethane decomposes on the most stable sites of Fe(1 10)surface，the

the are H species C2H6，C2Hs，C2H4，CH4，CH3，CH2，H2，and LB，LB，top，SB，top,hcp，LB， and hcp，respectively．The corresponding adsorption energy is一80．24，-178．89，

：

‘

一132．73，-38．14，-171．78，-342．43，一19．50，and-345．63 kJ‘mol～，respectively．The

have transfered from the H to 1 surface charges species C2H6，C2Hs，C2地，CH2，and Fe(1 o) the have the of HE during adsorption process．However,the charges species CH4，CH3， and transfered from l the Fe(1 adsorption 0)surface during process．All species adsorptions are chemisorptions on the Fe(1 l O)surface．In the C—C bond activation pathway,the activation energy of the activation rate—determining step is 122．9 k．r’tool～．、酮缸1e the the is 148．8 of U·tool。1 during the C—H bond activation energy rate—determining step activation pathway is preferred．The pathway,which suggests that the C-C bond on the mainly pathway of ethane decomposing Fe(1lO)surface is Fe(110)+C2H6÷Fe(1lO)一C2H6_TS3呻M2·TS4--,P2，and the

main products are CH4 and CH2．

2．Ⅵm％the ethane decomposes on the Co(1 l 1)surface，the most stable sites of the H are C2H6，C2H5，C2H4，CH4，CH3，CH2，H2，and bridge，species bridge，bridge，top，top， top，bridge，and fee，respectively．The corresponding adsorption energy is

一89．39，一243．98，-133．32，-60．35，一227．61，一440．57，-40．24，and一338．46 IO‘mol\ respectively．The charges have transfered from the species C2H6，C2H4，CH4，CH3，

the adsorption process．However,the to Co(1 l CI-12，and H charges 1)surface during

●

of the species C2H5

and H2血a．ye transferred from Co(111)surface during the

1 1) adsorption process．All speciSs。adsorptions are chemisorptions Oil the Co(1 surface．In the C—C bond activation pathway,the activation energy of the rate—determining step is 223．8灯’mol\1e the activation energy of the is only 1 80．9 ld‘tool—during the C—H bond activation pathway, which rate—determining step suggests that the C-H bofid activation pathway is preferred．The mainly pathway ofethane on is Co(111)+C2I-16---Co(111)‘ decomposing Co(111)surface