Modified nano-crystalline ferrites for high-temperature WGS membrane reactor applications

In the present study, selected metal ions (M = Cr, Mn, Co, Ni, Cu, Zn, and Ce) were introduced into iron oxide (spinel lattice) and screened for effectiveness for a high-temperature water–gas shift reaction. Simultaneous precipitation of Fe(III) nitrates along with metal nitrate(s) at optimal concentrations resulted in the formation of high-surface area nanosized catalysts. A noticeable interaction between iron and the other substitutent metal was interpreted from the formation of either inverse or mixed spinels of composition A(1−δ)Bδ[AδB(2−δ)]O4. The incorporation of metal cations into the hematite crystal structure modified the magnetic hyperfine field and also influenced the reducibility of hematite particles, as observed in Mössbauer effect and temperature-programmed reduction studies. These effects strongly depend on the nature of incorporated metal cations. Mössbauer hyperfine fields, isomer shifts and transmission electron microscopy findings support nanoscale nature of the catalysts. Amongst catalysts tested, Fe/Cr and Fe/Ce are found to be the most active, with activity approaching equilibrium conversion at high temperatures.