A versatile in situ spectroscopic cell for fluorescence/transmission EXAFS and X-ray diffraction of heterogeneous catalysts in gas and liquid phase

A new spectroscopic cell suitable for the analysis of heterogeneous catalysts by fluorescence EXAFS (extended X-ray absorption fine structure), transmission EXAFS and X-ray diffraction during in situ treatments and during catalysis is described. Both gas-phase and liquid-phase reactions can be investigated combined with on-line product analysis performed either by mass spectrometry or infrared spectroscopy. The set-up allows measurements from liquid-nitrogen temperature to 973 K. The catalysts are loaded preferentially as powders, but also as self-supporting wafers. The reaction cell was tested in various case studies demonstrating its flexibility and its wide applicability from model studies at liquid-nitrogen temperature to operando studies under realistic reaction conditions. Examples include structural studies during (i) the reduction of alumina-supported noble metal particles prepared by flame-spray pyrolysis and analysis of alloying in bimetallic noble metal particles (0.1%Pt-0.1%Pd/Al₂O₃, 0.1%Pt-0.1%Ru/Al₂O₃, 0.1%Pt-0.1%Rh/Al₂O₃, 0.1%Au-0.1%Pd/Al₂O₃), (ii) reactivation of aged 0.8%Pt-16%BaO-CeO₂ NO_x storage-reduction catalysts including the NO_x storage/reduction cycle, and (iii) alcohol oxidation over gold catalysts (0.6%Au-20%CuO-CeO₂).