Rh-ZSM-5分子筛吸附CO、H2O和O2的理论研究  

Theoretical investigation of adsorption of CO,H2O and O2 on Rh-ZSM-5 zeolite

作　　者：陈丹 吴安安 谭凯 吕鑫 CHEN Dan;WU An an;TAN Kai;L Xin(Fujian Provincial 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福建省理论与计算化学重点实验室

出　　处：《厦门大学学报（自然科学版）》2019年第6期833-839,共7页Journal of Xiamen University：Natural Science

基　　金：国家自然科学基金（91545105,21273177,21773193）

摘　　要：采用密度泛函理论(DFT)结合簇模型方法研究了小分子CO、H2O和O2在Rh交换的ZSM-5分子筛(Rh-ZSM-5)上的吸附.理论计算结果表明:H 2O和O2或CO可共吸附在Rh+上形成四配位铑配合物,其中Rh仅与ZSM-5表面的一个桥氧配位;在H 2 O和O 2共存时,最稳定的表面吸附物种为Rh(H 2O)2(O 2),含一个超氧离子;引入具有强配位能力的CO后,最稳定的表面吸附物种为Rh(CO)2(H 2O),阻碍了O 2的化学吸附.这暗示此前人们认为在CH 4/CO/H 2O/O2/Rh-ZSM-5混合体系中通过O 2的化学吸附活化甲烷的机理还有待进一步商榷.The adsorption of CO,H 2O and O 2 on Rh-exchange ZSM-5 zeolite(Rh-ZSM-5)is investigated using density functional theory(DFT)in combination with a cluster model.The theoretical computations reveal that H 2O can be readily co-adsorbed with O 2/CO onto the mononuclear Rh+cations,forming four-coordination of cationic Rh complexes,and the mononuclear Rh+cations anchored on a bridging oxygen atom(Al—O—Si)of ZSM-5 zeolite.The co-adsorption of H 2O and O 2 on Rh-ZSM-5 forms Rh(H 2O)2(O 2)as the most stable adspecies that contains a superoxide anion(O 2-).However,further introduction of strongly coordinating CO into the system gives rise to the formation of Rh(CO)2(H 2 O)as the most stable adspecies,which hinders the chemisorption of O 2.This finding implies that the mechanism previously proposed for the CH 4/CO/H 2 O/O 2/Rh-ZSM-5 system,i.e.,the oxygen species capable of activating the C—H bond of methane is formed by direct chemisorption of O 2 onto Rh+,is questionable and deserves further detailed investigation.

关 键 词：Rh-ZSM-5 羰基铑物种 化学吸附 簇模型 密度泛函理论 

分 类 号：O643.12[理学—物理化学]