Raman spectroscopy of NiMo catalysts supported on solid oxides. A review

The NiMo supported on alumina catalysts used by refineries in hydrotreatment reactions are characterized by different techniques that describe the properties of the NiMoS active phases. Raman Spectroscopy permits identify the degree of polymerization of the precursors of the active phases according to the vibrational modes of the different Mo species. The objective of this review is study the support effect on the Raman band shift and the molybdenum polymerization degree. The review commences with a background on catalysis and its application in hydrotreating reactions. Afterward, the characterization techniques for supported NiMo catalysts and the advantages of Raman Spectroscopy are discussed. Subsequently, the main Raman bands used in the assignment of the vibrational modes of the different Mo species in NiMo catalysts supported on alumina are reported. In the main section, the effects of partial or total replacement of the alumina support with Mg, Ti, Mn, Si, Zn, Ce oxides, and others, are discussed. Posteriorly, some studies are revised in which the activity of different catalysts is correlated with the results obtained by Raman Spectroscopy. To conclude, recent and future applications of Raman spectroscopy in the characterization of supported NiMo catalysts are also presented.