(574g) Methane Activation over Transition Metal Single Atom Doped (211) Facets of Pt and Pd

Harold, M., University of Houston
Grabow, L., University of Houston
With a vast abundance of natural gas resources in the United States, transformative changes are possible in the energy and chemical industry. Methane (CH4), a key component of natural gas, is however energetically very stable and the activation of its C-H bonds has posed a pervasive challenge. Recent advances in single atom catalysis have demonstrated avenues for enhancing catalytic performance by exploiting the unique electronic structure of atomically dispersed active sites.

Here, we consider the high index facets of Pt(211) and Pd(211) doped with single transition metal atoms to (i) elucidate the intricacies of dopant-site specificity towards C-H activation, and (ii) explore earth abundant candidates that can enhance methane reactivity on precious metal catalysts. To this end, ab-initio density functional theory (DFT) calculations were performed on Pt(211) and Pd(211) metal slabs with single atoms dopants of 3d, 4d, and 5d elements. There are three major sites for dopant atom incorporation into the metal slab – edge sites, terrace sites, and subsurface sites. While edge and terrace sites present an opportunity for the dopant to directly interact with methane, dopants in the generally more stable subsurface positions indirectly tune the reactivity of the exposed surface metal atoms. As shown in Fig. 1, the energy of dissociative chemisorption of CH4, a critical descriptor for CH4 activation, was found to increase for most subsurface dopants and could be attributed to compressive lattice strain induced by the single atom dopants. On the contrary, edge site doping was prone to induce tensile strain, resulting in enhanced methane activation.

Overall, our comprehensive analysis indicates that strain effects outweigh ligand effects and that nearly any perturbation of the (211) surface geometry of Pt or Pd can enhance their ability to activate CH4 as long as subsurface dopant incorporation can be avoided.