A DFT Investigation of the Dehydrogenation of Tetrahydropyrrole on Pt(111)

Abstract

van der Waals (vdW) corrected periodic density functional theory (DFT) calculations and microkinetic modeling were employed to elucidate the mechanism and energetics of dehydrogenation of tetrahydropyrrole, a model organic hydrogen carrier, on Pt(111). The overall dehydrogenation is endothermic while individual dehydrogenation steps can be endothermic or exothermic. The calculations indicate that the first dehydrogenation step proceeds via the C–H scission of an α-carbon (with respect to nitrogen). Subsequently, the remaining α- and two β-C–H bonds can be dissociated via multiple energetically similar pathways, wherein the second dehydrogenation step is rate controlling. The inclusion of vdW forces shifts the potential energy surface (PES) downward by an average 0.6 eV indicating that while the activation barriers remain unaffected, there can be significant influence on the overall rate due to increased coverage of intermediates. N-methylation of tetrahydropyrrole weakens adsorption of initial intermediates, indicating that the PES may generally be shifted up thereby affecting the overall kinetics. Finally, there exists a generally linear relationship between the transition state and final state energies of the dehydrogenation reaction.