How Nitrogen Doping Affects Hydrogen Spillover on Carbon-Supported Pd Nanoparticles: New Insights from DFT

Abstract

The process of hydrogen spillover on metal nanoparticle decorated carbon surfaces has been discussed for many years due to its importance for heterogeneous catalysis and hydrogen storage. The present density functional theory (DFT) study supports recent experimental observations of the hydrogen spillover process. By use of model systems of carbon-supported palladium nanoparticles, the details of hydrogen spillover are investigated and the effects of nitrogen doping on such processes are elucidated. It is found that graphitic nitrogen atoms and water molecules significantly facilitate the hydrogen spillover reaction and serve as anchoring sites for the spillover hydrogen atoms.

Multifunctional Catalytic Properties of Pd/CNT Catalysts for 4‐Nitrophenol Reduction

“…[58][59][60][61] The Hspillover can contribute to the reactivity through reversibly stored surface H-species that participate to Pd active site regeneration via reverse spillover. [62] Hydrogen spillover has already been reported for noble metal catalysts supported on O-doped, [63] N-doped [64,65] and S-doped [51,66] carbon materials. According to the heteroatom doping, different types of surface groups have been reported to facilitate the H-spillover on Pd catalysts, such as N-quaternary atoms for N-doped materials [65] and quinone groups for O-doped ones.…”

“…[62] Hydrogen spillover has already been reported for noble metal catalysts supported on O-doped, [63] N-doped [64,65] and S-doped [51,66] carbon materials. According to the heteroatom doping, different types of surface groups have been reported to facilitate the H-spillover on Pd catalysts, such as N-quaternary atoms for N-doped materials [65] and quinone groups for O-doped ones. [67] Interestingly, it was also reported that water molecules, present as solvent during 4-NP reduction, significantly facilitate the H-spillover reaction on carbon supports by acting as shuttle/stabilizer for the Hspecies.…”

“…[67] Interestingly, it was also reported that water molecules, present as solvent during 4-NP reduction, significantly facilitate the H-spillover reaction on carbon supports by acting as shuttle/stabilizer for the Hspecies. [63,65,68] H-spillover should not occur on undoped CNTs because of the low concentration of surface oxygen groups. [69][70][71][72] The Pd/CNT catalyst must therefore be the only catalyst whose activity (1.2 10 À 5 mol 4-NP /mg cat /h) results only from Pd NP .…”

“…Such synergistic effect was recently reported between Co NP and N-CNT for 4-NP reduction. [73] Thus, even if H-spillover has been regularly reported for Pd NP deposited on N-doped carbon materials, [64,[74][75][76] it seems that it should not be significantly operative under these conditions, presumably because the quaternary nitrogen atoms that have been identified as critical for H-spillover [65] are involved in 4-NP reduction. [56] It is worth noting that the interaction between Pd and N-CNT should occur through the pyridinic and not the N-quaternary atoms.…”

Hydrogen Storage in Untreated/Ammonia-Treated and Transition Metal-Decorated (Pt, Pd, Ni, Rh, Ir and Ru) Activated Carbons

“…Modifying carbonaceous structures by hetero-atoms, such as boron or nitrogen, before metal decoration, was suggested to enhance their catalytic effect in comparison to the unmodified ones [71,[79][80][81][82][83][84][85][86][87][88][89]. Previously, we tested platinum-decorated, ammonia-treated activated carbons for carbon dioxide and methane gas storage [90].…”