Observation of adsorbed hydrogen species on supported metal catalysts by inelastic neutron scattering
H Yoshida, A. Yamamoto, S. Hosokawa, S. Yamazoe, S. Kikkawa, K. Hara, M. Nakamura, K. Kamazawa, T. Tanaka, Top. Catal., accepted.

Adsorbed hydrogen (H) species on catalyst surfaces are important active intermediates in many catalytic reactions and detailed analyses of them are necessary to understand the catalyses. Inelastic neutron scattering (INS) enables direct and selective observation of H species due to the extremely large incoherent neutron scattering cross section of a hydrogen atom. In the present study, the adsorbed H species on some heterogeneous precious metal catalysts supported by alumina and carbon black were investigated by in situ INS spectroscopy with a newly designed sample cell. The newly designed double-walled long cell gave clear INS spectra with less elastic scattering. Three alumina-supported metal catalysts having Pt, Pd, and Rh metal nanoparticles with different particle sizes exhibited different INS spectra in intensities and band distribution. Observation of the H species on the metal nanoparticles and the alumina surface revealed their properties. In addition, the H atoms stored in Pd nanoparticles were observed as palladium hydride. In contrast, the H species on a Pt catalyst supported by carbon black were found to be strongly adsorbed on the carbon support. The properties of these H species were dependent on both the properties of the precious metals and those of the support materials.