The review of Cr-free Fe-based catalysts for high-temperature water-gas shift reactions

Since it was patented by Bosch and Wild at 1914, the Fe/Cr-based mixed oxide catalyst has been used for water-gas shift reactions (WGSRs). Until the present, this catalyst has been used as the primary catalyst for industrial high-temperature shift (HTS) reactions. However, because environmental concerns about chromium elements were raised in the early 1980s, the replacement of chromium in HTS catalysts has been intensely studied by many groups. These studies have contributed notable insights into HTS catalysis using Fe-based oxides, especially about the reaction mechanism and functions of promoter elements. In some cases, the potential of using a substituent metal previously neglected because of properties inferior to those of chromium was rediscovered after noteworthy improvements were produced by combining it with other metals in promoting the Fe-oxide catalyst. This paper reviews the recent studies of Cr-free Fe-based HTS catalysts, especially focusing on the roles and functions of the non-chromium promoters in the catalysts.