Copper promotion of chromium-doped iron oxide prepared via co-precipitation for high-temperature water–gas shift (WGS) catalysis is investigated. Low-temperature Mössbauer spectra demonstrate that copper doping delays hematite (?-Fe2O3) formation in the fresh catalyst, favoring small crystallites ferrihydrite (Fe5HO8?4 H2O). Catalysts are treated under industrial WGS conditions at 360 °C (activ...