铬氧化物团簇负离子(CrO_(3))_(1-4)O^(-)活化烷烃的尺寸效应  

Size-Dependent Reactivity of Chromium Oxide Cluster Anions (CrO_(3))_(1−4)O^(−) towards Alkanes

作　　者：魏龚平 赵艳霞[1,3] 何圣贵[1,2,3] Gong-Ping Wei;Yan-Xia Zhao;Sheng-Gui He(State Key Laboratory for Structural Chemistry of Unstable and Stable Species,Institute of Chemistry,Chinese Academy of Sciences,Beijing 100190,China;.University of Chinese Academy of Sciences,Beijing 100049,China;Beijing National Laboratory for Molecular Sciences,CAS Research/Education Center of Excellence in Molecular Sciences,Beijing 100190,China)

机构地区：[1]中国科学院化学研究所,分子动态与稳态结构国家重点实验室,北京100190 [2]中国科学院大学,北京100049 [3]北京分子科学国家研究中心和中国科学院分子科学科教融合卓越创新中心,北京100190

出　　处：《Chinese Journal of Chemical Physics》2023年第3期279-288,I0007-I0017,I0099,I0100,共23页化学物理学报（英文）

基　　金：supported by the National Natural Science Foundation of China(No.92161205 and No.92061115);the Youth Innovation Promotion Association CAS(No.2018041).

摘　　要：本文采用自行研制的耦合船闸式反应装置的飞行时间质谱,研究了铬氧化物团簇负离子(CrO_(3))_(1-4)O^(-)与低碳烷烃(C1~C4)在298 K温度下的反应.结果表明CrO4-和Cr2O7-团簇可以分别抽取乙烷和甲烷中的氢原子,而Cr3O10-和Cr4O13-团簇在检测下限范围内仍对正丁烷呈惰性.理论计算结果表明CrO4-和Cr2O7-团簇具有离域的铬氧自由基(Cr-O^(-·)),与实验中观测到的CrO_(3)_(1,2)O^(-)团簇可以与烷烃发生氢抽取反应相一致.然而,CrO_(3)_(3,4)O^(-)团簇的活性位点转化为相对于O^(-·)自由基活性较低的过氧物种(O_(2)^(2-)).团簇尺寸减小导致CrOy单元具有更负的电荷环境,进而诱使Cr-3d轨道能量升高,可能是引起小尺寸CrO_(3)_(1,2)O^(-)团簇中O_(2)^(2-)位点更倾向于被还原并选择性生成高活性O^(-·)自由基的原因.本工作不仅丰富了人们对与金属键合的O一自由基在温和条件下活化烷烃的化学认识,而且提供了金属氧化物中O_(2)^(2-)物种和O^(-·)自由基之间相互转化的新见解.The reactivity of chromium oxide cluster anions(CrO_(3))_(1−4)O^(−)towards low carbon(C1−C4)alkanes has been experimentally investigated at 298 K by employing a homemade ship-lock-type reactor coupled with a time-of-flight mass spectrometer.The results demonstrate that while CrO4−and Cr2O7−clusters could abstract a hydrogen atom from C2H6 and CH4,respectively,Cr3O10−and Cr4O13−clusters were found to be inert towards n-C4H10 within the detection limit.Theoretical results reveal that CrO4−and Cr2O7−clusters possess delocalized chromium-bonded oxygen radicals(Cr−O−·),which rationalizes the hydrogen atom abstraction reactions between(CrO3)1,2O−clusters and alkanes.However,the active sites of(CrO_(3))_(3,4)O^(−)clusters evolve to peroxide species(O_(2)^(2−)),which exhibit inferior activity compared to O^(−·)radicals.The increase of Cr-3d orbital energy driven by the more negative charge around CrOy unit formed via downsizing the cluster size has been proposed to account for favorable reduction of O_(2)^(2−)and selective generation of reactive O^(−·)radicals in small-sized(CrO_(3))_(1,2)O^(−)clusters.This study not only enriches the chemistry of metal-bonded O−·radicals toward alkane activation under mild conditions,but also provides a new insight into the conversion between O_(2)^(2−)and O^(−·)radicals over metal oxides.

关 键 词：活性氧物种 烷烃活化 铬氧化物团簇 质谱 密度泛函理论计算 

分 类 号：O641.4[理学—物理化学]