Department of Chemical Engineering, Stanford University, Stanford, CA 94305, USA.
Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
Science. 2021 Sep 24;373(6562):1518-1523. doi: 10.1126/science.abj5291. Epub 2021 Sep 23.
Defects may display high reactivity because the specific arrangement of atoms differs from crystalline surfaces. We demonstrate that high-temperature steam pretreatment of palladium catalysts provides a 12-fold increase in the mass-specific reaction rate for carbon-hydrogen (C–H) activation in methane oxidation compared with conventional pretreatments. Through a combination of experimental and theoretical methods, we demonstrate that an increase in the grain boundary density through crystal twinning is achieved during the steam pretreatment and oxidation and is responsible for the increased reactivity. The grain boundaries are highly stable during reaction and show specific rates at least two orders of magnitude higher than other sites on the palladium on alumina (Pd/AlO) catalysts. Theoretical calculations show that strain introduced by the defective structure can enhance C–H bond activation. Introduction of grain boundaries through laser ablation led to further rate increases.
缺陷可能表现出高反应性，因为原子的特定排列与晶体表面不同。我们证明，与传统预处理相比，高温蒸汽预处理钯催化剂可将甲烷氧化中碳-氢键 (C–H) 活化的比质量反应速率提高 12 倍。通过实验和理论方法的结合，我们证明在蒸汽预处理和氧化过程中通过晶界孪晶增加了晶界密度，这是增加反应性的原因。在反应过程中，晶界非常稳定，其反应速率至少比钯氧化铝 (Pd/AlO) 催化剂上的其他位点高两个数量级。理论计算表明，由缺陷结构引起的应变可以增强 C–H 键的活化。通过激光烧蚀引入晶界可进一步提高反应速率。
