High temperature water gas shift catalysts (WGS) were synthesized by co-precipitation with typical industrial formulations containing iron oxides, chromia, and copper, but augmented by small additions (0.5 to 5 wt%) of rare earth oxides, such as ceria or lanthana, at the expense of the active iron phase. The catalysts were characterized by standard techniques and kinetically evaluated under WGS conditions. Despite containing less of the active iron phase, the rare earth oxide modified catalysts produced up to 29% higher WGS rates. Operando UV-visible spectroscopy was used to correlate reaction rate with absorption response and calibrated extent of reduction measurements. Traditional analyses using the Kubelka-Munk function to determine edge energies for the catalysts at various stages of reduction and oxidation conditions were performed. Although the catalysts look black, the absorption spectra respond sensitively to WGS reaction conditions and provide useful information on the extent of reduction. Figure 1 shows the result of these experiments on a catalyst with a fully oxidized composition of 1 wt% La2O3, 87 wt% Fe2O3, 8 wt% Cr2O3, and 4 wt% CuO (1 La). The changes in absorption were correlated to oxidation state using operando XANES experiments. Figure 2 shows the average Fe oxidation state in this 1La catalyst was ~+2.31 during reaction and less than one without lanthana (0La).

Operando UV-visible spectroscopy of high temperature water gas shift catalysts

256th National Meeting (2018)

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