The Extent of Platinum-Induced Hydrogen Spillover on Cerium Dioxide

Abstract

Hydrogen spillover from metal nanoparticles to oxides is an essential process in hydrogenation catalysis and other applications such as hydrogen storage. It is important to understand how far this process is reaching over the surface of the oxide. Here, we present a combination of advanced sample fabrication of a model system and in situ X-ray photoelectron spectroscopy to disentangle local and far-reaching effects of hydrogen spillover in a platinum–ceria catalyst. At low temperatures (25–100 °C and 1 mbar H2) surface O–H formed by hydrogen spillover on the whole ceria surface extending microns away from the platinum, leading to a reduction of Ce4+ to Ce3+. This process and structures were strongly temperature dependent. At temperatures above 150 °C (at 1 mbar H2), O–H partially disappeared from the surface due to its decreasing thermodynamic stability. This resulted in a ceria reoxidation. Higher hydrogen pressures are likely to shift these transition temperatures upward due to the increasing chemical potential. The findings reveal that on a catalyst containing a structure capable to promote spillover, hydrogen can affect the whole catalyst surface and be involved in catalysis and restructuring.

How Pt Influences H2 Reactions on High Surface-Area Pt/CeO2 Powder Catalyst Surfaces

“…However, no mechanistic discussions associated with the origin of these behaviors apart from the prevalence of H-spillover were provided. 10 The agreement between specific behaviors of [OH ads − ] and [Ce 3+ ] suggests that the mechanistic details proposed here for the influence of Pt on CeO 2 surface reactions with H 2 are valid over a wide range of H 2 chemical potentials. 4 .…”

“…However, no mechanistic discussions associated with the origin of these behaviors apart from the prevalence of H-spillover were provided. 10 The agreement between specific behaviors of [OH ads − ] and [Ce 3+ ] suggests that the mechanistic details proposed here for the influence of Pt on CeO 2 surface reactions with H 2 are valid over a wide range of H 2 chemical potentials. CeO 2 was reduced in situ with H 2 at 450 °C, while Pt/CeO 2 was reduced in situ with H 2 at 400 °C to ensure complete H 2 consumption in <60 min (the time used in between EELS collection on oxidized and reduced samples).…”

“…Surface science analyses have shown that PGMs promote interactions between H 2 and CeO 2 surfaces by dissociating H 2 and spilling over H to CeO 2 . − However, the translation of this mechanistic picture to high-surface area powder catalysts is complicated by spatial heterogeneities, such as PGMs existing as single atoms (SAs) or nanoclusters (NCs), and the existence of CeO 2 –CeO 2 particle boundaries, which may affect interactions with H 2 . In addition, most reports assert that V o (and associated Ce 3+ ) species produced via H 2 interactions with PGM/CeO 2 localize around PGMs. ,− However, the influence of Pt on various elementary steps involved in V o formation across the CeO 2 surface has not been resolved, and direct measurements of Ce 3+ spatial distribution in nonmodel PGM-supported CeO 2 samples are lacking.…”

Disentangling Local Interfacial Confinement and Remote Spillover Effects in Oxide–Oxide Interactions

“…For metal−oxide interfaces, the conditions such as metal−oxide distance, gas partial pressure, and reaction temperature can be used to control the spillover process and the oxide reduction. 62,68,69 Here, we show that modulating the proximity between Co 3 O 4 and ZnO can effectively control the hydrogen spillover effect and catalytic activity (Figure 7). All the results confirm that there are remote H-spillover effects in the oxide− oxide interaction, which play an important role in the structure evolution and catalytic performance of the supported oxide catalysts.…”

Macroscopic Study on the Behavior of Spillover Hydrogen Atoms

“…Hydrogen spillover has been extensively studied not only for catalytic reactions using hydrogen but also for hydrogen storage to meet the increasing demand for hydrogen energy. − Metal nanoparticles, such as Pt, Pd, Ru, Rh, Au, and Ir nanoparticles, dissociatively adsorb H 2 molecules, and the chemisorbed H atoms on the nanoparticles spill over onto catalyst supports including metal oxides and carbon-based materials. − The mobility of spillover H atoms has been studied and revealed to depend on the types of catalyst supports onto which the H atoms spill over. − Existence of spillover H atoms can be confirmed by inelastic neutron scattering spectroscopy that differentiates H atoms from H 2 molecules. , Recent studies have enabled direct observations of spillover H atoms through low-temperature scanning tunneling microscopy, owing to the slow diffusion of H atoms at low temperatures. − Such observations reveal the behavior of H atoms but are limited to flat support surfaces and low-temperature conditions. On the other hand, the diffusion of H atoms is too fast for direct observation at room temperature; ,,,− however, the fast diffusion of spillover H atoms is advantageous for selective hydrogenation. − Therefore, there remains considerable interest in studying the behavior of spillover H atoms from room to high temperatures.…”