(481e) Density Functional Theory (DFT) Analysis of C-H Bond Formation on Anatase TiO2-Supported Single-Atom Catalysts

Single-atom catalysts have demonstrated unique reaction properties otherwise unseen in their traditional nanoparticle catalyst counterparts. As the size of the active metal deposited on a catalyst support decreases toward the single atom limit, the homogeneity of active sites allows us to tune and isolate them for specific reaction pathways and products¹. Ag, which is typically perceived as a poor hydrogenation metal, has shown promising hydrogenation performance when deposited at the single-atom limit. Recent experimental studies of Ag single-atoms supported on anatase-TiO₂ have demonstrated hydrogen activation and spillover of nearly 675 H atoms per Ag adatom², and selective hydrogenation of guaiacol to phenolic products. However, the metal-surface interaction and structure, spillover mechanism, active form of surface hydrogen, and active site for C-H formation remain underdetermined at an atomistic level, limiting rational design of single-metal atom/support systems for hydrogenation catalysis.

We used density functional theory (DFT) to study hydrogenation over Ag single-atom catalysts on anatase TiO₂ (001). C₂H₂ was used as a probe reactant convenient to probe C-H bond formation. We have identified stable adsorption sites of Ag single atoms on both fully oxidized and reduced surfaces. We propose that the processes of hydrogen activation, hydrogen spillover, and C-H bond formation do not simultaneously occur on the single metal atom but instead require a unique combination of active sites at the support and metal-support interface. Reduced sites are required to facilitate C-H formation. We propose viable reaction mechanisms for the stepwise C-H bond formation from C₂H₂ to C₂H₄ on Ag single-atom catalysts.

1. Yang et al., Accounts of Chemical Research 2013, 46, 1740-1748

2. Liu et al., Journal of Catalysis 2019, 369, 396-404