石墨烯负载单原子Mo上合成气催化转化机理:碳组分和Mo-C作用的影响  

Mechanism upon Conversion of Syngas Catalyzed by Single Atom Mo Supported on Graphene:Role of Carbon Component and Impact from Mo-C Interactions

作　　者：孔雪 张海平 夏文生[1] 张庆红[1] 万惠霖[1] KONG Xue;ZHANG Haiping;XIA Wensheng;ZHANG Qinghong;WAN Huilin(State Key Laboratory of Physical Chemistry of Solid State Surface,National Engineering Laboratory for Green Chemical Productions of Alcohols-Ethers-Esters,Fujian Province Key Laboratory of Theoretical and Computational Chemistry,College of Chemistry and Chemical Engineering,Xiamen University,Xiamen 361005,China)

机构地区：[1]厦门大学化学化工学院,固体表面物理化学国家重点实验室,醇醚酯化工清洁生产国家工程实验室,福建省理论与计算化学重点实验室,厦门361005

出　　处：《高等学校化学学报》2024年第7期101-110,共10页Chemical Journal of Chinese Universities

基　　金：国家重点研发计划项目(批准号:2019YFE04400);教育部创新团队发展计划项目(批准号:IRT1036)资助.

摘　　要：金属在合成气转化反应中的催化性能与其在反应中的碳化密切相关,然而所形成的金属碳化物的组成和结构十分复杂,使得催化剂活性相的鉴定变得极为困难,因而催化剂中碳组分的作用具有研究意义.本文采用密度泛函理论(DFT)计算研究了单原子Mo负载在无缺陷石墨烯(Mo/pri-graphene)和单碳空位石墨烯(Mo/sv-graphene)上合成气转化制醇的反应机理,以探究碳组分对钼基催化剂上C—O活化的调控作用.结果表明,具有较弱Mo-C作用的Mo/pri-graphene和具有较强Mo-C作用的Mo/sv-graphene上的合成气转化机理存在明显差别.Mo/pri-graphene上最优途径为CO→HCO→CH_(2)O→CH_(3)O→CH_(3)/CH_(4),物种CH_(3)O因转化为CH_(3)/CH_(4)的活化自由能垒偏高而具有一定的稳定性;Mo/sv-graphene上最优途径则为CO→HCO→CH_(2)O→CH_(2)OH→CH_(3)OH/CH_(3)(CH_(4)),共存的产物CH_(3)OH和CH_(3)(CH_(4))为后续的碳链增长提供了可能.Mo/sv-graphene上CO加氢反应的各基元步骤的活化自由能垒总体低于Mo/pri-graphene,其原因是Mo/sv-graphene与反应底物分子间的作用强度低于Mo/pri-graphene与底物分子的作用,Mo/sv-graphene中碳组分可以参与底物分子的活化与转化.因此,催化剂中的碳组分可以调控(和/或参与)底物分子与催化剂间的作用,继而改变反应的活性和选择性.The catalytic behaviors of metal for syngas conversion are related to the carbonization of the metal,however,the formed metallic carbides are of complicated composition and structures,making the identification of the active phase of the catalysts be challengeable,so it is significant to investigate the role of the carbon component of the catalysts.In this work,we studied computationally mechanisms of syngas conversion to alcohols on single atom Mo supported on pristine graphene(Mo/pri-graphene)and single-carbon vacant graphene(Mo/sv-graphene)by means of density functional theory(DFT)method to explore the regulated effect of carbon component on C—O activation.The results show that it is significantly different for mechanisms of syngas conversion on Mo/pri-graphene with weak Mo-C interactions and Mo/sv-graphene with strong Mo-C interactions.On Mo/pri-graphene the preferred pathway is CO→HCO→CH_(2)O→CH_(3)O→CH_(3)/CH_(4),and species CH_(3)O is of some stability due to high activation free energy of its further transformation into CH_(3)/CH_(4),while on Mo/sv-graphene the preferred pathway is CO→HCO→CH_(2)O→CH_(2)OH→CH_(3)OH/CH_(3)(CH_(4)),and the coexistence of species CH_(3)OH and CH_(3)(CH_(4))provides a possibility for the following carbon chain propagation.The activation free energy of the elementary steps of CO hydrogenation on Mo/sv-graphene is generally lower than that on Mo/pri-graphene.The reasons are the lower interactions between Mo/sv-graphene and the substrate,and the participation of the carbon component of Mo/sv-graphene during the activation/transformation of the substrate.Thus,the carbon component of catalysts can regulate(and/or take participate in)the interaction of the catalysts with the substrates,and then make an improvement on the activity and selectivity.

关 键 词：单原子 钼/石墨烯 合成气转化 碳 反应机理 

分 类 号：O641[理学—物理化学] O643[理学—化学]