Department of Chemistry, Stanford University, Stanford, CA 94305, USA.
Department of Microbial and Molecular Systems, Centre for Sustainable Catalysis and Engineering, KU Leuven-University of Leuven, B-3001 Leuven, Belgium.
Science. 2021 Jul 16;373(6552):327-331. doi: 10.1126/science.abd5803.
Catalytic conversion of methane to methanol remains an economically tantalizing but fundamentally challenging goal. Current technologies based on zeolites deactivate too rapidly for practical application. We found that similar active sites hosted in different zeolite lattices can exhibit markedly different reactivity with methane, depending on the size of the zeolite pore apertures. Whereas zeolite with large pore apertures deactivates completely after a single turnover, 40% of active sites in zeolite with small pore apertures are regenerated, enabling a catalytic cycle. Detailed spectroscopic characterization of reaction intermediates and density functional theory calculations show that hindered diffusion through small pore apertures disfavors premature release of CH radicals from the active site after C-H activation, thereby promoting radical recombination to form methanol rather than deactivated Fe-OCH centers elsewhere in the lattice.
甲烷到甲醇的催化转化仍然是一个具有经济吸引力但从根本上具有挑战性的目标。目前基于沸石的技术由于失活过快而无法实际应用。我们发现，在不同的沸石晶格中承载的类似活性位在与甲烷反应时表现出明显不同的反应性，这取决于沸石孔口的大小。虽然具有大孔口的沸石在单个转化后完全失活，但具有小孔口的沸石中有 40%的活性位得以再生，从而实现了催化循环。对反应中间体的详细光谱表征和密度泛函理论计算表明，通过小孔口的扩散受阻不利于在 C-H 活化后从活性位过早释放 CH 自由基，从而促进自由基重组形成甲醇，而不是在晶格的其他地方形成失活的 Fe-OCH 中心。
