Ni-containing catalysts are investigated under reaction conditions for two different cases, during sulfidation, with Ni-Mo based catalysts, and during ammoxidation reaction, with the Ni-Nb catalysts. It is shown how Raman spectroscopy can follow some of the transformations of these catalysts upon different treatments. For the NiMo/Al(2)O(3)-SiO(2) system it was possible to identify some of the sulfided Mo species formed during the sulfidation of the oxide precursors, while for the bulk Ni-Nb oxide catalysts the simultaneous reaction-Raman results strongly suggest that the incipient interaction between niobium and nickel oxides at low Nb/Ni atomic ratios is directly related to catalytic activity, and that a larger size well-defined NiNb(2)O(6) mixed oxide phase is not active for this reaction. Moreover, the promotion by niobium doping appears to be limited to a moderate niobium loading. It was found that in situ and operando Raman are valuable techniques that allowed the identification of active Mo-S and Ni-Nb species under reaction conditions, and that are not stable under air atmospheres.
This journal is © the Owner Societies 2011