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.

Tunable Interfacial Electronic Pd–Si Interaction Boosts Catalysis via Accelerating O2 and H2O Activation

“…It is well known that the activation of O 2 and H 2 O is a critical step in heterogeneous catalytic oxidation. For example, the activation of O 2 is closely associated with CO oxidation, while the activation of H 2 O is closely associated with the water–gas shift reaction. − For the catalytic oxidation of formaldehyde (HCHO, a typical oxygenated VOC and one of the main indoor gaseous pollutants attracting increasing attention), the catalytic ability highly depends on the activation of both O 2 and H 2 O. − Therefore, the construction of active interfaces is vital in enhancing electron delocalization and adjusting the d -band center of metal sites to form the EMSI effect, which is important for the design and development of efficient HCHO degradation catalysts.…”

“…Therefore, boosting the interfacial sites through appropriate SMSI is necessary to effectively modulate the strength of EMSI and maintain the accessibility of partial metal surface sites to reactant molecules. While successful cases of tuning EMSI on reducible oxide-supported PGM catalysts have been documented, , SMSI resulting from reducible metal oxide supports has poor water durability as the oxide overlayers tend to undergo dynamic migration during reactions in a humid atmosphere . In contrast, non-reducible oxide supports such as SiO 2 and zeolites are well-known “inert” supports or shell materials to fabricate core–shell structures, which present excellent hydrothermal stability as well as great moisture resistance .…”

Adsorption of Molecules on Defective CeO2 for Advanced Catalysis

“…generally participate in a variety of catalytic reactions under harsh reaction conditions (e.g., high temperatures, high pressures), causing unsatisfactory activity and selectivity as well as serious burdens to the environment. Therefore, the activation of small molecules under mild conditions has always been the focus of fundamental investigations and a challenging frontier topic in heterogeneous catalysis. ,− In terms of chemical essence, the key scientific principles are the controllable activation and selective transformation of H–H, C–H, C–O, and C–X (X represents heteroatom), which are generally determined by how they interact with the interfacial active sites. Nanoscale CeO 2 materials possess a rich surface chemistry, including the surface Lewis acid (Ce cation) and base (O anion), and then form classic Lewis acid–base adjuncts. , Generally, small molecules, including H 2 , CO 2 , H 2 O, etc ., are bonded with the CeO 2 surface on the top of Ce and/or O atoms, being activated via a typical Lewis acid–base interaction (Figure a). ,− Considering the coordination environments of the Ce cation (Lewis acid) and lattice oxygen (Lewis base), the activation of small molecules is generally less efficient.…”

Effects of indium doping on methanol deep oxidation over Ag/CeO2 catalysts

“…Among them, CeO 2 is widely used due to its outstanding redox performance, oxygen storage, and unique interfacial effect derived from its interaction with various metals. 7–9…”