Kinetic Origins of High Selectivity of Metal Phosphides for Ethane Dehydrogenation

Abstract

Supercell density functional theory (DFT) calculations are used to create and exercise complete ethane dehydrogenation (EDH) reaction networks over Ni(111) and Ni 2 P(001). EDH intermediates are predicted to be more weakly bound to Ni 2 P than to Ni, with the differences being the greatest for deeply dehydrogenated intermediates. Both C−H and C−C bond cleavage activation energies are generally greater on Ni 2 P than Ni. The implications of these differences are explored through microkinetic models that incorporate a pathway for carbon growth. Ethylene formation rates and selectivities are predicted to be greater over Ni 2 P than Ni across a wide range of temperatures. Ni is predicted to be more susceptible to coke generation. Ethane activation exerts the greatest degree of rate control on both materials; in contrast, the competition between ethylene desorption and dehydrogenation controls selectivity on Ni, while no single step dominates selectivity on Ni 2 P. Results are consistent with previously reported observations, highlight the distinct and active contributions of phosphorus to phosphide surface chemistry, and highlight the role of coking pathways on predicted kinetics.

Computational screen of M2P metal phosphides for catalytic ethane dehydrogenation

“…18) improves EDH selectivity and durability. A density functional theory (DFT) comparison of EDH performance on Ni(111) and Ni 2 P(001) 17,51 showed that P atoms selectively participate in adsorbate binding and C-H bond breaking, increasing activation barriers for steps leading to deep dehydrogenation and promoting ethylene desorption over ethylene overactivation. In addition, P incorporation weakens binding of small hydrocarbons, imparting coke resistance to the surface.…”