Catalyst support effects on hydrogen spillover

• Published in: Nature (London) 2017-01, Vol.541 (7635), p.68-71
• Main Authors: Karim, Waiz, Spreafico, Clelia, Kleibert, Armin, Gobrecht, Jens, VandeVondele, Joost, Ekinci, Yasin, van Bokhoven, Jeroen A.
• Format: Article
• Language: English
• Subjects: 119/118; 121/135; 142/126; 639/638/77/885; 639/638/77/887; 639/925/357/354; Aluminum; Atoms & subatomic particles; Catalysis; Catalysts; Chemical properties; Humanities and Social Sciences; Hydrogen; Iron oxides; letter; Metal oxides; multidisciplinary; Nanoparticles; Observations; Platinum; Science; Spectrum analysis; Synergistic effect; Titanium
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature20782

The mechanism of hydrogen spillover is described using a precisely nanofabricated model system, explaining why it is slower on an aluminum oxide catalyst support than on a titanium oxide catalyst support. Hydrogen spillover in supported catalysts Hydrogen spillover—the surface migration of hydrogen atoms from the metal catalyst particle on which they are generated onto the catalyst support—was discovered in the early 1960s, but remains poorly understood. Waiz Karim and colleagues now use advanced nanofabrication to place multiple pairs of iron oxide and platinum nanoparticles on titanium oxide and aluminium oxide supports, with varying inter-particle distance, and observe the extent of the reduction of the iron oxide particles by hydrogen atoms generated on the platinum. The results reveal that hydrogen spillover is fast and efficient on titanium oxide, and extremely slow and short-ranged on aluminium oxide. The results should aid our understanding of hydrogen storage and catalytic hydrogenation reactions, and the approach to creating and probing model catalyst systems open up new avenues for studying fundamental processes in supported catalysts. Hydrogen spillover 1 is the surface migration of activated hydrogen atoms from a metal catalyst particle, on which they are generated, onto the catalyst support 2 . The phenomenon has been much studied 3 , 4 , 5 , 6 , 7 and its occurrence on reducible supports such as titanium oxide is established, yet questions remain about whether hydrogen spillover can take place on nonreducible supports such as aluminium oxide 8 , 9 , 10 , 11 , 12 , 13 . Here we use the enhanced precision of top-down nanofabrication 14 , 15 to prepare controlled and precisely tunable model systems that allow us to quantify the efficiency and spatial extent of hydrogen spillover on both reducible and nonreducible supports. We place multiple pairs of iron oxide and platinum nanoparticles on titanium oxide and aluminium oxide supports, varying the distance between the pairs from zero to 45 nanometres with a precision of one nanometre. We then observe the extent of the reduction of the iron oxide particles by hydrogen atoms generated on the platinum using single-particle in situ X-ray absorption spectromicroscopy 14 applied simultaneously to all particle pairs. The data, in conjunction with density functional theory calculations 16 , 17 , reveal fast hydrogen spillover on titanium oxide that reduces remote iron oxide nanoparticles via coupled prot