Operando Raman Spectroscopic Analysis of Silica Supported V-Nb Catalysts for Tuning Redox Properties

We report that the redox properties of traditional silica supported vanadia catalysts can be tuned through the addition of niobia. Heterogeneous catalysis has widespread use in industry for numerous processes. Vanadium over silica is a traditional precursor metal oxide catalyst usually employed in the reduction of alkanes to form terminal olefins. In order to improve the conversion rate to olefins, it is desirable to balance the reductive and oxidative properties of the catalyst so that the processes of catalytic action (alkane reduction) and active site regeneration (vanadium oxidation) occur closer to the same rate.

Inclusion of a secondary component in the catalyst alters dispersion and monolayer coverage of vanadium, altering the reaction kinetics of oxidation and reduction for the catalyst. However, not much is known about how a second metal in ternary systems like this influences the physical and chemical properties of the vanadium oxide active site. For a series of vanadia catalysts with different amounts of a secondary component, niobia, a state of the art methodology was utilized to perform Operando Raman spectroscopy to monitor the rate of change of the catalyst state at the surface. This was followed by mass spectroscopy using pulses of gaseous reagent in separate experiments to analyze the bulk of the catalyst. Thus, the redox properties of the surface and the bulk of the catalyst were analyzed simultaneously, providing new insight into the complete redox behavior. From this, the most effective catalyst composition of those tested was determined.