Mechanistic Insight into the Formation of Acetic Acid from the Direct Conversion of Methane and Carbon Dioxide on Zinc-Modified H-ZSM-5 Zeolite
Mechanistic Insight into the Formation of Acetic Acid from the Direct Conversion of Methane and Carbon Dioxide on Zinc-Modified H-ZSM-5 Zeolite
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DOI：
10.1021/ja406978q
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发表时间：
2013-09-11
影响因子：
15
通讯作者：
Wang, Wei
中科院分区：
文献类型：
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作者：
Wu, Jian-Feng;Yu, Si-Min;Wang, Wei
甲烷和二氧化碳是已知的温室气体，将这两种碳-1结构转化为有用的燃料和化学物质是一个非常重要的课题。通过固体核磁共振波谱分析，我们发现在523-773 K的低温范围内，甲烷和二氧化碳可以在锌改性的H-ZSM-5沸石（记为Zn/H-ZSM-5）上共转化生成乙酸。固态C-13和H-1 MAS NMR研究表明，双功能Zn/H-ZSM-5催化剂的独特性质是这种高选择性转化的原因。锌位点有效激活CH4形成甲基锌（-Zn-CH3），锌- c键进一步受到CO2的插入产生表面醋酸物质（-Zn-OOCCH3）。此外，Bronsted酸位点在质子转移到醋酸表面的过程中对醋酸的最终形成起着重要的作用。本研究结果为通过共转化策略实现甲烷的低温高效活化和选择性转化提供了新的可能性。此外，对这一过程的机理理解将有助于合理设计稳健的催化系统，将温室气体实际转化为有用的化学品。
Methane and carbon dioxide are known greenhouse gases, and the conversion of these two C-1-building blocks into useful fuels and chemicals is a subject of great importance. By solid-state NMR spectroscopy, we found that methane and carbon dioxide can be co-converted on a zinc-modified H-ZSM-5 zeolite (denoted as Zn/H-ZSM-5) to form acetic acid at a low temperature range of 523-773 K. Solid-state C-13 and H-1 MAS NMR investigation indicates that the unique nature of the bifunctional Zn/H-ZSM-5 catalyst is responsible for this highly selective transformation. The zinc sites efficiently activate CH4 to form zinc methyl species (-Zn-CH3), the Zn-C bond of which is further subject to the CO2 insertion to produce surface acetate species (-Zn-OOCCH3). Moreover, the Bronsted acid sites play an important role for the final formation of acetic acid by the proton transfer to the surface acetate species. The results disclosed herein may offer the new possibility for the efficient activation and selective transformation of methane at low temperatures through the co-conversion strategy. Also, the mechanistic understanding of this process will help to the rational design of robust catalytic systems for the practical conversion of greenhouse gases into useful chemicals.