Yawen Zhang's research group in the School of Chemistry has made new progress in the regulation of the interfacial electronic structure and catalytic performance of nano-cerium oxide systems

Because of its stable interface structure and easy separation and recovery, supported catalysts are widely used in petrochemical industry, automobile exhaust treatment, new energy batteries and other fields
.
For supported catalysts, there are unavoidable interactions between metal nanoparticles and the carrier, including charge transfer between the two, changes in particle morphology and chemical composition, and the formation of an envelope structure
after carrier migration.
These interfacial interactions together affect the adsorption and transformation process of the reactants and are key factors
in determining the catalytic performance.

Among the various interfacial effects, the electronic effect has the most significant
adjustment of catalytic performance.
The interfacial electronic structure is closely related to the adsorption strength of surface species, and the adsorption of surface species directly affects the catalytic activity and selectivity
.
It is found that the catalytic activity of the reaction is usually volcanically related to the adsorption strength of species, and only moderate species adsorption intensity can reach the highest catalytic performance
.
However, how to accurately control the interfacial electronic effect through chemical means to make the adsorption strength of important intermediates reach the most suitable position is a difficult point in catalysis research.
At the same time, it is not clear
what is an important intermediate for complex reactions.
Therefore, it is urgent to develop accurate interface control strategies to analyze the structure-activity relationship of complex reactions and guide the design
of catalytic materials for key energy reactions including_CO2 conversion and hydrogen energy regeneration.

Recently, Professor Yawen Zhang's research group from the CeO_2-based supported catalytic materials developed two methods for precise control of the electronic structure of the interface, the electrochemically induced interface control strategy and the ammonia heat treatment interface control strategy, respectively, to enhance the interface electronic interaction and weaken the interface electronic interaction (Figure 1).

Figure 1: Schematic diagram
of the governance policy.
(a) Electrochemically induced interface regulation strategies; (b) Ammonia heat treatment interface control strategy

The electrochemical induction strategy is as follows: firstly, Au(OH)₃ species are loaded on the surface of_CeO2, and in the subsequent electrochemical pretreatment, the strong oxidation of Au³⁺ species can be used to induce the reduction of_CeO2 support while it is reduced, thereby increasing the interaction
between the two.
The obtained catalytic material Au-CeO2-DP is used in the_CO2 electrocatalytic reduction reaction and exhibits more than 95% CO Faraday efficiency at a wide potential of -0.
7 to -1.
0V (Figure 2).

Thanks to the control of the interfacial electronic state, the Au mass current density of -0.
7V is 5.
8 times higher than that of the traditional NaBH₄ reduction catalyst, which is also at the leading level
compared with the results reported in the literature.
Follow-up studies showed that the enhanced metal-support interaction caused the Au nanoparticles to exhibit a valence state of ^δ+ while generating abundant oxygen vacancies
at the interface.
The change of the electronic structure of the interface improves the adsorption stability of the catalytic materials for CO2, accelerates the formation of important carboxylic acid intermediates, and then improves the catalytic performance
of the_CO2 electroreduction reaction.

Figure 2: Catalytic properties
of Au-CeO2-DP.
(a) LSV curve; (b)_CO2 electrocatalytic reduction activity; (c) Au mass current density; (d) Catalytic stability

The ammonia heat treatment strategy introduces N doping in CeO2 through the_NH3 heat treatment process of_CeO2 nanostructure, thereby sealing the oxygen vacancy and weakening its interaction
with surface metal species.
The Co-CeO2 catalyst obtained by this synthesis strategy was used in the hydrogen production reaction of water gas conversion, and it was found that with the increase of NH₃ treatment temperature, the catalytic activity was gradually enhanced, and the sample Co/800N-CeO₂ was treated at 800 degrees The catalytic activity is 23.
8 times that of the untreated samples, and the comparison with the literature results shows that the weakened interfacial electron interaction greatly improves the catalytic efficiency, making it possible
for Co-based catalysts to be used in industrial production.
The improvement of activity mainly comes from two aspects: on the one hand, due to the weakening of metal-support interaction, the average valence state of Co species decreases under reaction conditions, and the increase of 0-valent Co site is conducive to stabilizing CO adsorption and accelerating the formation of important intermediate carboxylates; On the other hand, N species are unstable under reaction conditions, and the departure of N species is conducive to the formation of oxygen vacancies, thereby enhancing the activation ability
of water molecules.
The two work together to improve the catalytic performance
of the coal-water vapor shift reaction.

Fig.
3: Catalytic performance of coal-water vapor shift reaction of
Co-CeO2 catalytic materials.
(a) Curve of CO conversion as a function of temperature; (b) Reaction rate of 280 °C

A two-part study of metal-support interactions "Au³⁺ species-induced interfacial activation enhances metal?" Support Interactions for Boosting Electrocatalytic CO₂ Reduction toCO" and "Weakening the Metal? Support Interactions of M/CeO₂ (M = Co, Fe, Ni) Using a NH₃? Treated CeO₂ Support for an Enhanced Water? GasShift Reaction" was recently published at ACS Catal.
2022, 12, 923?934; ACS Catal.
2022,12, 11942?11954）
。 The first author is Sun Xiaochen, a doctoral student in Zhang Yawen's research group, and Zhang Yawen is the corresponding author
of the work.
Professor Liu Haichao's research group also made substantial contributions
to the research.
This series of work provides new ideas
for the development of stable, highly active supported catalysts.

The research was supported by the National Natural Science Foundation of China, the National Key Research and Development Program of China, and the Beijing National Research Center for Molecular Sciences, and was strongly supported
by Academician Yan Chunhua and Professor Sun Lingdong's research group.