Resolving the Reaction Mechanism for H2 Formation from High-Temperature Water–Gas Shift by Chromium–Iron Oxide Catalysts

The reaction mechanism of the high-temperature water–gas shift (HT-WGS) reaction catalyzed by chromium–iron oxide catalysts for H2 production has been studied for 100 years with two reaction mechanisms proposed: redox and associative (involving surface HCOO*). Direct experimental support for either mechanism, however, is still lacking, which hinders a thorough understanding of catalytic roles of each elements and the rational design of Cr-free catalysts. The current study demonstrates, with temperature-programmed surface reaction (TPSR) spectroscopy (CO-TPSR, CO+H2O-TPSR, and HCOOH-TPSR), for the first time that the HT-WGS reaction follows the redox mechanism and that the associative mechanism does not take place.