The kinetics of molecular adsorption and desorption can unveil the details of the adsorption potential that impact, for instance, the overall sticking probability. This information is of particular importance for catalysis and gas sensing. We investigate the room-temperature CO adsorption on a model single-atom catalyst consisting of single Co atoms trapped in graphene (Gr) double carbon vacancies during Gr growth by chemical vapor deposition (CVD) on Ni(111). The study is conducted by combining a thermal desorption spectroscopy (TDS) instrument that allows the study of systems with a very low surface density of active sites, of the order of 10^–3 monolayers (MLs) with variable-temperature scanning tunneling microscopy (VT-STM). Our findings show that CO adsorption onto the single Co atoms occurs mainly (up to 97%) through a reverse spillover mechanism, rather than through direct impingement from the gas phase. This mechanism involves CO physisorption and diffusion on pristine Gr, followed by lateral adsorption onto Co atoms. The reverse spillover channel effectively increases the sticking probability, by up to 2 orders of magnitude, compared with direct impingement. We use kinetic models to determine the relevant energies, such as the diffusion barrier for CO on Gr (68 ± 15 meV), the energy barrier for lateral CO adsorption on Co (174 ± 2 meV), and the chemisorption energy of CO on Co (0.97 ± 0.02 eV).

中文翻译：

---

石墨烯分离中单钴原子上 CO 吸附的反向溢出


分子吸附和解吸的动力学可以揭示影响总粘附概率等的吸附电位的细节。这些信息对于催化和气体传感尤为重要。我们通过在 Ni（111） 上进行化学气相沉积 （CVD），研究了在 Gr 生长过程中捕获在石墨烯 （Gr） 双碳空位中的单个 Co 原子组成的模型单原子催化剂上的室温 CO 吸附。该研究是通过结合热脱附光谱 （TDS） 仪器进行的，该仪器允许研究活性位点表面密度非常低的系统，大约 ^10-3 个单层 （ML） 与变温扫描隧道显微镜 （VT-STM）。我们的研究结果表明，CO 吸附到单个 Co 原子上主要（高达 97%）通过反向溢出机制发生，而不是通过气相的直接撞击。该机制涉及 CO 在原始 Gr 上的物理吸附和扩散，然后横向吸附到 Co 原子上。与直接撞击相比，反向溢出通道有效地增加了粘附概率高达 2 个数量级。我们使用动力学模型来确定相关能量，例如 CO 对 Gr 的扩散势垒 （68 ± 15 meV）、CO 对 CO 横向吸附的势垒 （174 ± 2 meV） 以及 CO 对 Co 的化学吸附能 （0.97 ± 0.02 eV）。