双氧水对于单核铜分子筛催化甲烷直接氧化制甲醇反应性能的利弊  

Advantages and limitations of hydrogen peroxide for direct oxidation of methane to methanol at mono‐copper active sites in Cu‐exchanged zeolites

作　　者：程璐 陈许宁 胡培君 曹宵鸣[1] Lu Cheng;Xuning Chen;P.Hu;Xiao-Ming Cao(State Key Laboratory of Green Chemical Engineering and Industrial Catalysis,Centre for Computational Chemistry and Research Institute of Industrial Catalysis,East China University of Science and Technology,Shanghai 200237,China;School of Chemistry and Chemical Engineering,The Queen’s University of Belfast,Belfast BT95AG,United Kingdom)

机构地区：[1]华东理工大学计算化学中心和工业催化研究所,绿色化学工程与工业催化国家重点实验室,上海200237 [2]英国贝尔法斯特女王大学化学与化工学院,英国

出　　处：《Chinese Journal of Catalysis》2023年第8期135-144,共10页催化学报（英文）

基　　金：国家重点研发计划(2018YFA0208600);国家自然科学基金(22022302,92045303,91845111);111引智计划(B16017);中央高校基本科研业务费(JKVJ1211040).

摘　　要：直接催化甲烷(CH4)氧化转化制备甲醇(DMTM)是具有较高绿色化学原子经济性的反应过程,且可在常温下进行,是潜在的实现CH4转化升级的重要过程.作为“圣杯反应”,DMTM性能通常显著受氧化剂影响,使用氧气(O_(2))作为氧化剂一步实现DMTM仍然极具挑战性.至今,双氧水(H_(2)O_(2))仍是被报道最多的具有较高CH4转化速率和甲醇(CH3OH)选择性的绿色氧化剂.为了深入理解氧化剂如何影响DMTM反应性能,本文基于密度泛函理论计算和微观动力学分析研究了在Cu-ZSM-5,Cu-MOR和Cu-SSZ-13三种具有不同微孔尺寸的单核铜分子筛上DMTM反应机理,以确定H_(2)O_(2)作为氧化剂在DMTM反应中的优势和局限性.通过理论计算对比在反应条件下O_(2)和H_(2)O_(2)的O–O键活化以及CH4的C–H键活化过程,发现在单核Cu分子筛中,H_(2)O_(2)的O–O键通过水介导机制极易被活化,并形成活性Z[Cu(OH)_(2)]^(+)中心,该活性中心所含的表面羟基自由基能够在低温下活化CH4的C–H键,进而高效的形成CH3OH.随着分子筛微孔孔径增大,其更有利于表面羟基自由基的形成并促进C–H键的活化.相反,在低温下O_(2)的O–O键难以被具有不同微孔孔径的单核Cu分子筛催化断键,难以生成表面活性氧物种,进而抑制了CH4的C–H键活化.与O_(2)相比,H_(2)O_(2)能显著提升甲烷的活化转化.虽然H_(2)O_(2)能使得CH4被快速转化为CH3OH,但计算结果表明由于活性中心Z[Cu(OH)_(2)]^(+)上C–H键优先通过自由基机理活化,CH3OH较弱的C–H键更易断键,从而难以协调CH3OH选择性和CH4转化之间的竞争.同时,较弱的O–H键使得Z[Cu(OH)2]^(+)将优先催化H_(2)O_(2)自分解.尽管长期而言,使用H_(2)O_(2)作为氧化剂存在上述瓶颈,但动力学分析表明,相比于现有报道工作,以H_(2)O_(2)作为氧化剂时,通过改进催化剂和优化反应条件,仍能显著提升甲烷转化率和甲醇选择性.综上,本文研究了甲烷直接制甲�The efficiency of direct catalytic oxidation of methane to methanol(DMTM)is significantly influenced by oxidants.However,realizing a one-pot DMTM using dioxygen remains challenging.Hydrogen peroxide is still the most frequently reported green oxidant for DMTM,with high selectivity for methanol.To gain insight into the influence of oxidants on DMTM performance,we computationally investigated the reaction mechanisms involved in DMTM using H_(2)O_(2)at mono-copper sites in three types of Cu-exchanged zeolites with different micropore sizes.We identified the advantages and limitations of H_(2)O_(2)as an oxidant.In contrast to the O–O bond in O2,the O–O bond in H_(2)O_(2)can be easily broken to produce reactive surface oxygen species,which enable the facile C–H bond activation of methane at a low temperature.However,because of the radical-like process of C–H bond activation at mono-copper sites,actualizing the preferential C–H bond activation of methane is kinetically challenging compared to that of methanol.Moreover,the lower O–H bonding energy of H_(2)O_(2)would result in self-decomposition of H_(2)O_(2).Despite these bottlenecks,kinetic analysis shows that improving catalysts to boost the DMTM performance using H_(2)O_(2)is a promising approach.

关 键 词：密度泛函理论 单核铜分子筛 过氧化氢 甲烷部分氧化 甲醇 

分 类 号：O64[理学—物理化学]