Karatok Mustafa, Duanmu Kaining, O'Connor Christopher R, Boscoboinik Jorge Anibal, Sautet Philippe, Madix Robert J, Friend Cynthia M
Department of Chemistry and Chemical Biology, Harvard University Cambridge MA 02138 USA
Department of Chemical and Biomolecular Engineering, University of California Los Angeles California 90095 USA.
Chem Sci. 2020 Apr 20;11(25):6492-6499. doi: 10.1039/d0sc01461c.
The potential for tuning the electronic structure of materials to control reactivity and selectivity in heterogenous catalysis has driven interest in ultrathin metal films which may differ from their bulk form. Herein, a 1-atomic layer Ag film on Pd(111) (Ag/Pd(111)) is demonstrated to have dramatically different reactivity towards formic acid compared to bulk Ag. Formic acid decomposition is of interest as a source of H for fuel cell applications and modification of Pd by Ag reduces poisoning by CO and increases the selectivity for H formation. Formic acid reacts below room temperature on the 1-atomic layer Ag film, whereas no reaction occurs on pristine bulk Ag. Notably, 2 monolayer films of Ag again become unreactive towards formic acid, indicating a reversion to bulk behavior. A combination of infrared reflection absorption spectroscopy (IRRAS), X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) was used to establish that the Ag monolayer is continuous and electronically modified compared to bulk Ag. The work establishes a demonstration of the altered electronic structure of Ag monolayers on Pd(111) and an associated change in reactivity. The effect on reactivity only persists for the first layer, demonstrating the need for precise control of materials to exploit the modification in electronic properties.
在多相催化中，通过调整材料的电子结构来控制反应活性和选择性的潜力，引发了人们对可能与其块状形式不同的超薄金属薄膜的兴趣。在此，与块状银相比，Pd(111)上的1原子层银膜（Ag/Pd(111)）对甲酸的反应活性有显著差异。甲酸分解作为燃料电池应用中氢的来源备受关注，用银修饰钯可减少一氧化碳中毒并提高氢生成的选择性。甲酸在室温以下就能在1原子层银膜上发生反应，而在原始块状银上则不发生反应。值得注意的是，2个银单层膜对甲酸又变得无反应活性，这表明其行为又恢复到块状状态。结合红外反射吸收光谱（IRRAS）、X射线光电子能谱（XPS）和密度泛函理论（DFT），证实了与块状银相比，银单层是连续的且电子结构发生了改变。这项工作证明了Pd(111)上银单层的电子结构发生了改变以及相关的反应活性变化。对反应活性的影响仅在第一层持续存在，这表明需要精确控制材料以利用电子性质的改变。
