Abstract
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.
Highlights
Heterogeneous catalysts accelerate chemical reactions by selective binding of the reactants and subsequently formed intermediates on the surface
We demonstrate the use of inelastic neutron scattering by application on the CO2 methanation reaction catalyzed by a standard Ni-alumina/silica catalyst
In a typical Diffusive reflectance infrared Fourier transform spectroscopy (DRIFTS) experiment, after temperature equilibration of the catalyst in a pure He (H2 ) atmosphere a DRIFT spectrum is measured, after which the conditions are changed to H2 (CO2 + H2 ), while DRIFTS spectra are continuously recorded
Summary
Heterogeneous catalysts accelerate chemical reactions by selective binding of the reactants and subsequently formed intermediates on the surface. Modern catalysts are complex materials, consisting of various material classes (oxides, metals) structured on length scales from nanometers to millimeters Their characterisation is an art of its own, and a particular challenge is the in situ detection and quantification of chemical species adsorbed on them. The signals of the adsorbed as well as gaseous on the infrared(IR)-reflectivity of the catalyst [4,5,6], which is related to peculiar electronic, optical and molecules depend on the infrared(IR)-reflectivity of the catalyst [4,5,6], which is related to peculiar structural parameters sample in addition tosample the optical selection rules of IR-spectroscopy [7]. Given the much contribution from the untreated catalyst is subtracted from the spectra obtained post mortem after the higher incoherent scattering cross section of hydrogen (80.26 barn) relative to that of carbon Directlybecause compared to the DRIFTS spectra.isDespite the 20 promising advantages of INS, the method can only be used post mortem, because the measurement temperature is low (around 20 K)
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