Weakening the Metal–Support Interactions of M/CeO2 (M = Co, Fe, Ni) Using a NH3-Treated CeO2 Support for an Enhanced Water–Gas Shift Reaction

Abstract

The metal–support interface plays a crucial role in heterogeneous catalysis. The modulation of the metal–support interaction (MSI) affords the possibility of promoting the catalytic efficiency per active site. Here, we report a strategy to modulate the interfacial interaction and then optimize the interfacial activity of Co/CeO2 catalysts for the water–gas shift reaction (WGSR) by a facile NH3 treatment process for the CeO2 support. The sample of Co/800N-CeO2 treated at 800 °C exhibited the highest reaction rate of 260 μmolCO/(gCo s), which was 23.8 times higher than the rate of the untreated Co/CeO2 sample. A combination of ex situ and in situ characterizations suggested that addition of the NH3 treatment process did not only weaken the metal–support interaction between the Co species and CeO2 support to strengthen CO adsorption and CO activation ability but also induced oxygen vacancy generation under reaction conditions to accelerate H2O activation. Both worked together in promoting the catalytic efficiency for the WGSR via the carboxyl pathway at a low temperature. It was worth mentioning that the N species of the CeO2 support introduced by the NH3 treatment was removed after changing the catalyst structure under reaction conditions. The interfacial structure was robust in a 60 h test at 400 °C due to the coexistence mechanism of carboxyl and formate pathways avoiding the poisoning effect of formate species on the active sites. The construction of active interfaces could be extended to Fe/CeO2 and Ni/CeO2 catalysts and could bring great promise in the design of the interfacial structure of supported catalysts in wide applications including chemical transformation reactions and industrial catalysis.