Cesarini Alessia, Mitchell Sharon, Zichittella Guido, Agrachev Mikhail, Schmid Stefan P, Jeschke Gunnar, Pan Zeyou, Bodi Andras, Hemberger Patrick, Pérez-Ramírez Javier
Institute for Chemical and Bioengineering, Department of Chemistry and Applied Biosciences, ETH Zurich, Zurich, Switzerland.
Laboratory of Physical Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, Zurich, Switzerland.
Nat Catal. 2022;5(7):605-614. doi: 10.1038/s41929-022-00808-0. Epub 2022 Jun 27.
Understanding hydrocarbon generation in the zeolite-catalysed conversions of methanol and methyl chloride requires advanced spectroscopic approaches to distinguish the complex mechanisms governing C-C bond formation, chain growth and the deposition of carbonaceous species. Here operando photoelectron photoion coincidence (PEPICO) spectroscopy enables the isomer-selective identification of pathways to hydrocarbons of up to C in size, providing direct experimental evidence of methyl radicals in both reactions and ketene in the methanol-to-hydrocarbons reaction. Both routes converge to C molecules that transform into aromatics. Operando PEPICO highlights distinctions in the prevalence of coke precursors, which is supported by electron paramagnetic resonance measurements, providing evidence of differences in the representative molecular structure, density and distribution of accumulated carbonaceous species. Radical-driven pathways in the methyl chloride-to-hydrocarbons reaction(s) accelerate the formation of extended aromatic systems, leading to fast deactivation. By contrast, the generation of alkylated species through oxygenate-driven pathways in the methanol-to-hydrocarbons reaction extends the catalyst lifetime. The findings demonstrate the potential of the presented methods to provide valuable mechanistic insights into complex reaction networks.
了解甲醇和氯甲烷在沸石催化转化过程中的烃类生成，需要先进的光谱方法来区分控制碳 - 碳键形成、链增长和含碳物种沉积的复杂机制。在此，原位光电子光离子符合（PEPICO）光谱能够对尺寸达C的烃类生成途径进行异构体选择性鉴定，为两个反应中的甲基自由基以及甲醇制烃反应中的乙烯酮提供了直接实验证据。两条途径都汇聚到转化为芳烃的C分子。原位PEPICO突出了焦炭前驱体存在情况的差异，这得到了电子顺磁共振测量的支持，为累积含碳物种的代表性分子结构、密度和分布差异提供了证据。氯甲烷制烃反应中自由基驱动的途径加速了扩展芳烃体系的形成，导致快速失活。相比之下，甲醇制烃反应中通过含氧物驱动途径生成烷基化物种延长了催化剂寿命。这些发现证明了所提出方法为复杂反应网络提供有价值的机理见解的潜力。
