Supported single metal atoms embody active, efficient catalysts. Much effort in the literature has focused on late transition metals, but understanding the reactivity and stability trends across all metals is key to developing new metal catalysts.
Supported single metal atoms embody active, efficient catalysts. Much effort in the literature has focused on late transition metals, but understanding the reactivity and stability trends across all metals is key to developing new metal catalysts. Metal–support interactions are especially important since they determine stability. We used density functional theory (DFT) to model binding of all 29 transition metal atoms and 8 post-transition metal atoms to TiO2, a prototypical support. The binding energies ranged from very strong (up to −7.6 eV) for early transition metals to weak (>−1 eV) for late transition metals. Adsorbed early transition metals were strongly cationic while adsorbed later transition metals were slightly cationic. Stability calculations (aggregation, diffusion, and substitution) indicated that several metal atoms were stable on the surface. Statistical models demonstrate that metal–oxygen bond dissociation energies correlate well with the binding of the metal atoms to the surface, while statistical models using other parameters (electronegativity or group number) also predict metal adsorption energies well. Gap states consisted of predominantly TiO2 states for early transition metals and of predominantly metal adatom states for mid/late transition metals. To understand the reactivity trends, we modeled activation of CO2, or adsorption of bent CO2, which is an important initial step in the CO2 reduction reaction. We found that inexpensive and abundant early/mid transition metals could activate CO2 strongly. Using statistical learning methods, we also identified several descriptors that may explain the CO2 adsorption energies, such as workfunction, cohesive energy, and d-band center of metal adatom. We also briefly discuss CO2 dissociation calculations over M/TiO2 catalysts. Our work furthers understanding of single atom and atomically dispersed catalysts and provides motivation to synthesize and study a wider class of catalysts, including early and mid transition metals.
Iyemperumal, S., Pham, T., Bauer, J., & Deskins, N. (2018). Quantifying Support Interactions and Reactivity Trends of Single Metal Atom Catalysts over TiO 2. The Journal of Physical Chemistry C, 122(44), 25274–25289. https://doi.org/10.1021/acs.jpcc.8b05611
*denotes a WPI undergraduate student author