Sensitivity is often a problem when studying catalysts with neutrons, only solids which have high surface areas can be studied. One still needs more neutron flux to widen the range of applications.

With INS, the advent of the VISION instrument at the Spallation Neutron Source (SNS) at the Oak Ridge National Laboratory (ORNL), the LAGRANGE instrument being operational at the ILL, and possible improvements on the instrument TOSCA at ISIS should allow us to tackle in the near future grafted catalysts, fuel cells, small supported metal particles (metal loading <1 %), etc. The large Q values which are inherent to these spectrometers at large energy transfers is a serious limitation. The detrimental influence of the Debye-Waller factor on the INS spectra has been known for a long time [30]. This can be partially resolved using direct geometry instruments which allow access of lower Qs [31], but different incident energies have to be selected so that various parts of the spectrum can be combined. On the other hand, the technique is particularly suited to study the different hydrogen species which are formed after dissociation of dihydrogen, during reduction or activation of the cat­alyst. The problem of characterizing active hydrogen is still a big issue in catalysis.

In the same way as ab initio methods are increasingly being used in INS, molecular simulations are now combined with QENS experiments. Since the space and time scales of the neutron techniques match closely the ones covered by molecular simulations, one expects, and usually finds, good agreement between neutrons and simulations. QENS constitute a benchmark to validate and further develop the modelling work, and the computed trajectories of the sorbate guest molecules within the host matrices are invaluable to understand QENS observables. Discrepancies between experiment and simulation do happen and require in such cases the consideration of a flexible lattice or an improved force field.

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