Determining Number of Active Sites and TOF for the High-Temperature Water Gas Shift Reaction by Iron Oxide-Based Catalysts

This study demonstrates, with C 16 O 2 /C 18 O 2 isotope switch and H 2 -TPR experiments, for the first time that ( i ) the high-temperature water–gas shift (HT-WGS) reaction by copper–chromium-iron oxide catalysts follows a redox mechanism dominated by the surface layer, ( ii ) the number of catalytic active sites can be quantified by the isotopic switch, and ( iii ) the turnover frequency (TOF) can be determined from knowledge of the number of sites. The quantitative TOF values reveal that chromium is only a textural promoter, whereas copper is a chemical promoter.