Key Takeaways & Executive Findings
- •• • Pd@UiO-66 achieved >90% removal of 4-CP within 15 minutes, demonstrating rapid catalytic hydrodechlorination suitable for water treatment applications. • • The initial activity of Pd@UiO-66 was 2.1 times higher than that of Pd/UiO-66, and the turnover frequency was 1.2 times higher, indicating superior catalytic efficiency due to confinement effects. • • Pd@UiO-66 maintained over 90% of its initial activity after five reaction cycles, with activity change below 10%, showcasing excellent operational stability for repeated use. • • The sole degradation product was phenol, which has significantly lower predicted toxicity (ECOSAR) than 4-CP, confirming the detoxification capability of the process.
Abstract
Halophenols are highly toxic disinfection byproducts and common taste-and-odor pollutants in drinking water. In this study, a palladium catalyst confined within the pores of UiO-66 (Pd@UiO-66) was prepared via a double-solvent method and applied for the catalytic hydrodechlorination of 4-chlorophenol (4-CP). A surface-supported catalyst (Pd/UiO-66) was synthesized by deposition-precipitation as a benchmark. Comprehensive characterization using ICP-OES, XRD, TEM, EDX mapping, XPS, and in situ CO-IR revealed that Pd@UiO-66 exhibited smaller Pd particle sizes, higher Pd dispersion, and a greater proportion of cationic Pd species (Pdn+) compared to Pd/UiO-66. These features enhanced the activation and cleavage of the C–Cl bond. Catalytic tests demonstrated that Pd@UiO-66 achieved >90% removal of 4-CP within 15 minutes, with phenol as the sole degradation product, showing significantly lower predicted toxicity (ECOSAR) than the parent compound. The kinetics followed the Langmuir-Hinshelwood model. Pd@UiO-66 exhibited 2.1 times higher initial activity and 1.2 times higher turnover frequency than Pd/UiO-66. Moreover, the pore confinement effect imparted high stability, with no significant loss in initial activity (within 10%) after five reaction cycles. These results highlight the potential of confined Pd catalysts for efficient removal of halophenolic odorants from water.
1. Introduction
Halophenols, such as 4-chlorophenol (4-CP), are notorious disinfection byproducts formed during chlorination of drinking water. They not only impart unpleasant taste and odor but also pose significant health risks due to their high toxicity and persistence. Conventional water treatment methods, such as adsorption or biological degradation, often suffer from slow kinetics, incomplete mineralization, or generation of secondary pollutants. Catalytic hydrodechlorination (HDC) offers a promising alternative, enabling the selective cleavage of carbon-chlorine bonds under mild conditions. However, the effectiveness of HDC relies heavily on the design of the catalyst, particularly the dispersion and stability of noble metal nanoparticles. Traditional supported catalysts often suffer from metal sintering and leaching, leading to deactivation and loss of activity.
To address these bottlenecks, this study introduces a confinement strategy using a metal-organic framework (MOF), UiO-66, as a host to encapsulate palladium nanoparticles within its pores. The double-solvent method ensures that Pd precursors are preferentially introduced into the micropores, resulting in well-dispersed, ultrasmall Pd clusters. This confinement not only restricts particle growth but also enhances metal-support interactions, increasing the proportion of electron-deficient Pd species (Pdn+), which are known to facilitate C–Cl bond activation. Compared to conventional surface-loaded catalysts, the confined Pd@UiO-66 exhibits superior activity, stability, and selectivity, offering a robust solution for the removal of halophenolic odorants from water.
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ZHAO Jiayi, XIE Xinyi, SUN Jingya, ZHANG Yufan, FU Heyun (2026). Catalytic Hydrogenation Removal of Typical Halophenol Odorous Substances by Palladium Catalysts Confined in UiO-66. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2025040202
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Frequently Asked Questions
What is the mechanism behind the enhanced catalytic activity of Pd@UiO-66 compared to Pd/UiO-66?
The enhanced activity is attributed to the confinement effect of UiO-66 pores, which restricts Pd particle growth, leading to smaller particle sizes and higher dispersion. This increases the number of accessible active sites. Additionally, the strong metal-support interaction results in a higher proportion of cationic Pd species (Pdn+), which are more effective in activating and cleaving the C–Cl bond in 4-CP, as evidenced by XPS and in situ CO-IR analyses.
How does the catalyst perform under repeated use, and what is the deactivation rate?
Pd@UiO-66 demonstrates excellent stability. After five consecutive reaction cycles, the initial activity remained above 90% of its original value, with an activity change of less than 10%. This indicates minimal deactivation, likely due to the confinement effect preventing Pd sintering and leaching.
What are the degradation products and their toxicity compared to the parent compound?
The sole degradation product is phenol, which is significantly less toxic than 4-CP. ECOSAR predictions indicate that phenol has a much lower toxicity, confirming that the catalytic hydrodechlorination process effectively detoxifies the pollutant.
What are the optimal reaction conditions for achieving >90% removal within 15 minutes?
The study did not specify exact optimal conditions in the provided text, but it is implied that the catalyst dosage and initial pH were optimized. The results show that under the tested conditions, Pd@UiO-66 achieved >90% removal of 4-CP within 15 minutes, indicating high efficiency.
How does the catalytic performance compare to other reported catalysts for halophenol removal?
The study does not provide a direct comparison with other catalysts, but the high initial activity and turnover frequency (2.1 times and 1.2 times higher than Pd/UiO-66, respectively) suggest that Pd@UiO-66 is a highly efficient catalyst. The rapid removal rate and stability make it a promising candidate for practical water treatment applications.
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