WITHDRAWN: Changes in Ni-NiO Equilibrium Due to LaFeO3 and the Effect on Dry Reforming of CH4

Abstract

• LaFeO 3 films were prepared by Atomic Layer Deposition on MgAl 2 O 4 and used as a support for Ni catalysts. • The Ni-NiO equilibria shifted to lower P O 2 due to the presence of LaFeO 3 . • Ni/LaFeO 3 /MgAl 2 O 4 showed high rates for methane dry reforming and excellent tolerance against coking. • Ni/LaFeO 3 /MgAl 2 O 4 deactivated due to Ni oxidation at low CO:CO 2 ratios. The interactions between Ni and LaFeO 3 were studied on catalysts prepared by Atomic Layer Deposition (ALD) of 0.5-nm films of LaFeO 3 on MgAl 2 O 4 . Scanning Transmission Electron Microscopy showed that the films covered the support uniformly, even after 5 redox cycles at 1073 K, and X-Ray Diffraction showed that the films had the perovskite structure. Equilibrium between Ni and NiO was studied using coulometric-titration and flow-titration measurements on 5-wt% Ni catalysts, with and without LaFeO 3 . While equilibrium constants for Ni/MgAl 2 O 4 were similar to that expected for bulk Ni, equilibrium P O 2 were shifted to significantly lower values in the presence of LaFeO 3 . In studies of Methane Dry Reforming, the shift in equilibrium resulted in catalyst deactivation due to Ni oxidation at low CO:CO 2 ratios, even though Ni/LaFeO 3 /MgAl 2 O 4 otherwise showed a high reaction rate and excellent tolerance against coking.