Mechanisms of Pyrrole Hydrogenation on Ru(0001) and Hydrogen Molybdenum Bronze Surfaces

Hydrogenation of pyrrole and its derivatives is of fundamental importance in chemical and pharmaceutical processes for which a mechanistic understanding is still lacking. The objective of the present study is to unveil the energetic profiles of pyrrole hydrogenation on Ru(0001) along the prescribed routes by periodic density functional theory (DFT) calculations. It was found that the activation energy of the rate-limiting step of the hydrogenation process is 1.05 eV. The calculated desorption energy of the hydrogenated product is 1.24 eV. We also found hydrogen molybdenum bronze (HxMoO3) to be an efficient catalyst material for pyrrole hydrogenation via detailed mechanistic investigations. HxMoO3 is expected to outperform ruthenium owning to the lower hydrogenation barrier and more facile desorption of the product. We rationalize the more favorable energetics of pyrrole/HxMoO3 by the lower adsorption energy of pyrrole and the protonic nature of H in HxMoO3. The chemistry revealed in this work provides meaningful insight into the design of low-cost hydrogenation catalysts.