化学
催化作用
甲醇
甲烷
催化循环
扩展X射线吸收精细结构
分子
多相催化
蒸汽重整
部分氧化
X射线吸收光谱法
甲醛
铜
甲烷单加氧酶
无机化学
吸收光谱法
制氢
有机化学
物理
量子力学
作者
Ying Yang,Siriluk Kanchanakungwankul,Suman Bhaumik,Qing Ma,Sol Ahn,Donald G. Truhlar,Joseph T. Hupp
摘要
Activating the C-H bonds of alkanes without further oxidation to more thermodynamically stable products, CO and CO2, is a long-sought goal of catalytic chemistry. Inspired by the monocopper active site of methane monooxygenase, we synthesized a Cu-doped ZIF-8 metal-organic framework with 25% Cu and 75% Zn in the nodes and activated it by heating to 200 °C and dosing in a stepwise fashion with O2, methane, and steam. We found that it does oxidize methane to methanol and formaldehyde. The catalysis persists through at least five cycles, and beyond the third cycle, the selectivity improves to the extent that no CO2 can be detected. Experimental characterization and analysis were carried out by PXRD, DRUV-vis, SEM, and XAS (XANES and EXAFS). The reaction is postulated to proceed at open-coordination copper sites generated by defects, and the mechanism of methanol production was explicated by density functional calculations with the revMO6-L exchange-correlation functional. The calculations reveal a catalytic cycle of oxygen-activated CuI involving the conversion of two molecules of CH4 to two molecules of CH3OH by a sequence of hydrogen atom transfer reactions and rebound steps. For most steps in the cycle, the reaction is more favored by singlet species than by triplets.
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