Hydrogen Spillover on Carbon-Supported Metal Catalysts Studied by Inelastic Neutron Scattering. Surface Vibrational States and Hydrogen Riding Modes

Abstract

Hydrogen spillover on carbon-supported precious metal catalysts has been investigated with inelastic neutron scattering (INS) spectroscopy. The aim, which was fully realized, was to identify spillover hydrogen on the carbon support. The inelastic neutron scattering spectra of Pt/C, Ru/C, and PtRu/C fuel cell catalysts dosed with hydrogen were determined in two sets of experiments: with the catalyst in the neutron beam and, using an annular cell, with carbon in the beam and catalyst pellets at the edge of the cell excluded from the beam. The vibrational modes observed in the INS spectra were assigned with reference to the INS of a polycyclic aromatic hydrocarbon, coronene, taken as a molecular model of a graphite layer, and with the aid of computational modeling. Two forms of spillover hydrogen were identified: H at edge sites of a graphite layer (formed after ambient dissociative chemisorption of H 2 ), and a weakly bound layer of mobile H atoms (formed by surface diffusion of H atoms after dissociative chemisorption of H 2 at 500 K). The INS spectra exhibited characteristic riding modes of H on carbon and on Pt or Ru. In these riding modes H atoms move in phase with vibrations of the carbon and metal lattices. The lattice modes are amplified by neutron scattering from the H atoms attached to lattice atoms. Uptake of hydrogen, and spillover, was greater for the Ru containing catalysts than for the Pt/C catalyst. The INS experiments have thus directly demonstrated H spillover to the carbon support of these metal catalysts.

Molecular Dynamics Simulations of the Interactions between Platinum Clusters and Carbon Platelets

“…Interestingly, this is the opposite effect to hydrogen spillover 70 from a nanoparticle to the support suggested by indirect experimental measurements of platinum nanoparticles adsorbed on alumina, 71,72 silica, 73,74 titania, 75 zirconia, 76 zeolite, 77 and carbon-based materials. 78,79 In contrast, the reverse hydrogen spillover found in this work is compatible with DFT and QM/ MM studies of supported six-atom clusters of the metals of groups 8 to 11. 80,81 The new bond-length distributions ( Figure 17) lie between that for an isolated cluster and a cluster adsorbed on a nonterminated armchair edge.…”

Accelerating the Understanding and Development of Hydrogen Storage Materials: A Review of the Five-Year Efforts of the Three DOE Hydrogen Storage Materials Centers of Excellence

“…The team of Lee and colleagues was the first to identify that barriers to migration are lowered sufficiently via structural (e.g., hopping between closely spaced surfaces) and electronic features. [143] Collaborative work from Mitchell et al [144] using inelastic neutron scattering spectroscopy observed spillover hydrogen on carbon supports. Deuterium tracer investigations demonstrated that, effectively, the spillover process is sequential with the first hydrogen adsorbed being the last desorbed.…”

Impregnation Nickel on Mesoporous ZSM-5 Templated Carbons as a Candidate Material for Hydrogen Storage

“…ZSM-5 is a porous material with a large surface area and pore volume, have a micro-meso pore size that is structured and it is affected by its synthesized condition [4][5][6][7]. With the characteristics of mesoporous ZSM-5, it is expected that it can be used as the right template in forming mesoporous carbon material.…”