Volatile Hydrogen Intermediates of CO2 Methanation by Inelastic Neutron Scattering

Despite vast research efforts, the detection of volatile intermediates of catalytic reactions remains a challenge: in addition to the compatibility of the technique to the harsh reaction conditions, a molecular understanding is hampered by the difficulty of extracting meaningful information from operando techniques applied on complex materials. Diffusive reflectance infrared Fourier transform spectroscopy (DRIFTS) is a powerful method, but it is restricted by optical selection rules particularly affecting the detection of hydrogen. This gap can be filled by inelastic neutron scattering (INS). However, INS cannot be used on hydrogenated systems at temperatures higher than 20 K. We demonstrate how its use as a post-mortem method gives insights into the crucial intermediates during CO2 methanation on Ni/alumina-silica catalysts. We detect a variety of H-, O-, and C-based intermediates. A striking outcome is that hydrogen and oxygen are concurrently chemisorbed on the catalysts, a result that needs the combined effort of DRIFTS and INS.