Applications of Neutron Scattering in Technical Catalysis: Characterisation of Hydrogenous Species on/in Unsupported and Supported Palladium

Recent results from inelastic neutron scattering (INS) measurements are reviewed that show the synergy between research on hydrogen adsorption/absorption on/in catalysts and chemical engineering. The proton dynamics of catalysts for large scale reactor technology are compared. The focus is the identification and quantification of hydrogenous species on, and inside, fresh, hydrogenated and dehydrogenated palladium black and supported palladium catalysts of different particle size, type of support and, therefore, morphology. INS studies of in-situ hydrogenation/ dehydrogenation of catalysts of 25–60 g size per sample are carried out in stainless steel cans as a function of varying hydrogen pressures. Differences in hysteresis effects in retaining hydrogen inside the catalyst in desorption from palladium hydrides and hydrogen bonding in adsorption sites in varying particle morphologies on different supports were evaluated. This aids the understanding of hydrogen/palladium interactions in catalytic processes with varying local hydrogen partial pressure, e.g. in loop reactors. The importance of the measured on-top Pd–H site in catalytic hydrogenation reactions is discussed together with previous INS results on the degree of deactivation of a technical catalyst by molecular blocking of the on-top site.