A kinetic study on the structural and functional roles of lanthana in iron-based high temperature water–gas shift catalysts

Abstract

The structural and functional roles of varying amounts of lanthana in co-precipitated high temperature Fe2O3/Cr2O3/CuO water–gas shift catalysts were studied at 1 atm and 350–425 °C temperature range.Addition of 0.5 wt% of lanthana enhanced the reducibility of the catalyst, increased its surface area and its WGS activity from 24 to 31 mmol CO/(gcat min), and reduced the deactivation rate at 400 °C from 23% to 11% relative to a similar catalyst with no lanthana. XRD results suggested that 0.5 wt% of lanthana stabilized the iron–chromium cubic spinel structure most efficiently under the operating conditions; however, further additions appeared to disrupt the spinel structure and degrade the performance of the catalysts.The power-law and Langmuir–Hinshelwood models provided much better fits to the rate data than either the redox or the Eley–Rideal models, suggesting that the reaction tends to follow an adsorptive mechanism. The CO adsorption equilibrium constant was largest for the catalyst with 0.5 wt% lanthana, indicating that the addition of lanthana might facilitate CO adsorption. Water inhibited the reaction as it strongly adsorbed on the catalyst surface.