Key Takeaways & Executive Findings
- •• • Rh/CeO2-NR outperforms Rh/CeO2-NC and Rh/CeO2-NO under all tested conditions (inert, O2-containing, and H2O-containing), achieving higher N2O conversion at lower temperatures, which is critical for energy-efficient industrial abatement. • • Rh/CeO2-NR exhibits abundant oxygen vacancies and intrinsic defect sites, facilitating O intermediate transfer and enhancing catalytic turnover, as confirmed by characterization. • • The Rh0/Rhn+ ratio on Rh/CeO2-NR is optimal, promoting redox cycling between Rh species and reactants, which is essential for sustained catalytic activity. • • The study demonstrates that support morphology engineering is a viable strategy to boost catalytic performance, potentially reducing precious metal loading requirements and operational costs in N2O emission control.
Abstract
N2O is a potent greenhouse gas, and its catalytic decomposition is of significant environmental importance. In this study, three CeO2 supports with different morphologies—nanorods (NR), nanocubes (NC), and nanooctahedra (NO)—were prepared via a hydrothermal method. Rh catalysts supported on these CeO2 materials were synthesized using a deposition-precipitation method, and their catalytic performance for N2O decomposition was evaluated. Results demonstrate that Rh/CeO2-NR exhibits superior catalytic activity compared to Rh/CeO2-NC and Rh/CeO2-NO under identical reaction conditions, including in the presence of O2 and H2O. Characterization reveals that Rh/CeO2-NR possesses abundant oxygen vacancies and a relatively high number of intrinsic defect sites, which facilitate the transfer of O intermediates. Additionally, Rh/CeO2-NR exhibits an appropriate Rh0/Rhn+ ratio, promoting the redox cycle between Rh species and reactants, thereby enhancing catalytic activity. The study underscores the critical role of CeO2 support morphology in optimizing Rh-based catalysts for N2O decomposition, offering a strategy to improve catalytic efficiency and stability for industrial applications.
1. Introduction
Nitrous oxide (N2O) is a potent greenhouse gas with a global warming potential approximately 300 times that of CO2, and it also contributes to stratospheric ozone depletion. Industrial sources such as adipic acid production and nitric acid manufacturing, along with fossil fuel combustion, release significant quantities of N2O. Existing abatement technologies, including high-temperature thermal decomposition and selective catalytic reduction, suffer from high energy costs and secondary pollution risks. Direct catalytic decomposition of N2O into N2 and O2 is a greener and more cost-effective alternative, but its industrial deployment hinges on the development of highly active and stable catalysts that operate at lower temperatures.
Rhodium-based catalysts supported on ceria (CeO2) have shown promise due to Rh's high intrinsic activity and CeO2's oxygen storage and redox properties. However, the performance of Rh/CeO2 is strongly influenced by the support's morphology, which affects metal dispersion, exposed crystal facets, and metal-support interactions. This study systematically investigates the impact of CeO2 morphology—nanorods, nanocubes, and nanooctahedra—on the catalytic decomposition of N2O over Rh/CeO2. By correlating structural and electronic properties with catalytic activity, the work identifies key descriptors for designing superior catalysts, addressing the bottleneck of low-temperature activity and stability in N2O abatement.
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WANG Haoran, BAO Shidong, ZHENG Shourong (2026). Strong Impact of Support Morphology on Catalytic Decomposition of N2O over Rh/CeO2 Catalysts. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2025012901
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Frequently Asked Questions
What is the specific advantage of Rh/CeO2-NR over other morphologies in terms of oxygen vacancy concentration and Rh oxidation state?
Rh/CeO2-NR exhibits a higher concentration of oxygen vacancies and a greater number of intrinsic defect sites compared to Rh/CeO2-NC and Rh/CeO2-NO. These defects facilitate the transfer of oxygen intermediates during N2O decomposition. Additionally, Rh/CeO2-NR possesses an optimal Rh0/Rhn+ ratio, which promotes efficient redox cycling between Rh species and reactants, enhancing catalytic activity.
How does the presence of O2 and H2O in the feed gas affect the catalytic performance of Rh/CeO2-NR?
Rh/CeO2-NR maintains superior catalytic performance even in the presence of O2 and H2O, which are common components in industrial exhaust streams. While O2 and H2O can inhibit N2O decomposition over many catalysts by competing for active sites, Rh/CeO2-NR's abundant oxygen vacancies and appropriate Rh0/Rhn+ ratio mitigate these effects, ensuring stable and high conversion rates under realistic conditions.
What is the practical significance of the Rh0/Rhn+ ratio in Rh/CeO2 catalysts for N2O decomposition?
The Rh0/Rhn+ ratio is crucial for the redox cycle between Rh species and reactants. An optimal ratio ensures that Rh can readily donate and accept electrons, facilitating the dissociation of N2O and the desorption of oxygen. Rh/CeO2-NR achieves this balance, leading to enhanced catalytic activity and stability, which is essential for long-term industrial operation.
Can the findings on support morphology be extended to other noble metal catalysts for N2O decomposition?
The principles demonstrated—that support morphology influences oxygen vacancy concentration, metal dispersion, and metal-support interactions—are likely applicable to other noble metals such as Pd, Pt, or Au supported on CeO2. However, the optimal morphology may vary depending on the metal's specific properties and the reaction mechanism. Further studies are needed to validate the generality of these findings.
What are the potential limitations of Rh/CeO2-NR catalysts for industrial N2O abatement?
While Rh/CeO2-NR shows excellent catalytic performance, potential limitations include the cost of rhodium and the scalability of the hydrothermal synthesis method for producing nanorod supports. Additionally, long-term stability under harsh industrial conditions (e.g., high temperatures, presence of poisons) needs to be thoroughly evaluated. Nevertheless, the enhanced activity may allow for lower Rh loadings, partially offsetting costs.
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