Kumar Pankaj, Meyerstein Dan, Mizrahi Amir, Kornweitz Haya
Chemical Sciences Department, The Radical Reactions Research Center, Ariel University, Ariel, Israel.
Chemistry Department, Ben-Gurion University, Beer-Sheva, Israel.
Chemphyschem. 2025 Apr 14;26(8):e202400979. doi: 10.1002/cphc.202400979. Epub 2025 Feb 25.
It was reported that adsorbed methyl radicals produce ethane with Ag- and Au-nanoparticles in aqueous media, whereas on Cu-powders, the product is methanol. The source of these differences was explored computationally, using the DFT method. The results indicate that up to six radicals can be adsorbed on Ag(111) and Au(111), (top site), while only four can be adsorbed on Cu(111) (fcc site), each surface containing eight atoms. The diffusion of the radicals on the surface is very easy on silver and copper, as this is achieved with a very low barrier (0.06 eV and 0.15 eV for Ag(111) and Cu(111), respectively), while on Au(111), the barrier is higher, 0.51 eV. The formation of ethane via a reaction of two adsorbed radicals is thermodynamically plausible for all studied coverage ratios on the three surfaces, but kinetically, it is plausible at room temperature only on Au(111) and Ag(111) at full coverage. Ethane can also be produced on Au(111) and Ag(111) by a collision of a solvated radical and an adsorbed radical. This is a barrierless process. On Cu(111), the yield of such a process is CH(aq), and an adsorbed CH which reacts further with a non-adsorbed water molecule to produce adsorbed CHOH.
据报道，在水介质中，吸附的甲基自由基与银和金纳米颗粒反应生成乙烷，而在铜粉上，产物是甲醇。使用密度泛函理论（DFT）方法通过计算探索了这些差异的来源。结果表明，在Ag(111)和Au(111)（顶位）上最多可吸附六个自由基，而在Cu(111)（面心立方位）上只能吸附四个自由基，每个表面包含八个原子。自由基在银和铜表面的扩散非常容易，因为实现这一过程的势垒非常低（Ag(111)和Cu(111)分别为0.06 eV和0.15 eV），而在Au(111)上，势垒更高，为0.51 eV。对于在三个表面上研究的所有覆盖比，通过两个吸附自由基的反应形成乙烷在热力学上是合理的，但在动力学上，只有在室温下Au(111)和Ag(111)完全覆盖时才是合理的。乙烷也可以通过溶剂化自由基与吸附自由基的碰撞在Au(111)和Ag(111)上产生。这是一个无势垒过程。在Cu(111)上，该过程的产物是CH(aq)，以及一个吸附的CH，它与一个未吸附的水分子进一步反应生成吸附的CHOH。
