In situ Raman spectroscopy - a valuable tool to understand operating catalysts

Laser Raman spectroscopy (LRS) is one of the most powerful tools for the in situ study of catalytic materials and surfaces under working conditions. Raman characterizations can be carried out at temperatures as high as 1000 K and in controlled atmospheres. Modern high light-throughput spectrometers permit the recording of the whole spectral range from 100 to 4000 cm-1 at once and time resolutions in the sub-second regime for materials with high Raman cross sections. Transient temperature or pressure response studies, e.g. pulse experiments with isotope labels, are thus possible, and kinetic and spectroscopic characteristics can be related. Modern quartz fiber optics render possible easy spectroscopic access to catalytic reactors of defined and well characterized operation conditions. Quantitative relation of real catalytic steady state operation, e.g. catalytic activity and selectivity, to changes in the catalyst structure is thus made possible. Several in situ LRS studies are discussed including the characterization of supported and unsupported Mo-based catalysts, confocal Raman microspectroscopy of mixed MoVW oxide catalysts, oxygen exchange in Sb2O3/MoO3 oxide physical mixtures elucidating the catalytic synergy effects, and active surface intermediates during oxidative coupling of methane, and NO and N2O decomposition over Ba/MgO catalysts related to the catalytic reaction via transient pressure step experiments