Key Takeaways & Executive Findings
- •• • The 2Pd-1Ru/S-1 catalyst achieved T50 and T90 of approximately 339 °C and 380 °C, respectively, with a stable 94% methane conversion over 48 h at 375 °C, demonstrating superior low-temperature activity and long-term stability compared to monometallic Pd/S-1. • • Ru doping significantly enhanced water resistance: the bimetallic catalyst maintained high activity under humid conditions, attributed to the Pd-Ru electronic synergy that strengthens PdO-support interaction and reduces competitive adsorption of H2O on active sites. • • Mechanistic analysis confirmed that PdO is the primary active phase and the reaction proceeds via the Eley-Rideal (E-R) mechanism, where gaseous oxygen is activated on the catalyst surface before reacting with gas-phase methane. • • The hydrophobic Silicalite-1 support preserved its MFI framework and pore structure during reaction, ensuring efficient mass transfer and providing structural stability for the active phase, which is critical for industrial application under demanding conditions.
Abstract
Complete catalytic oxidation of methane requires catalysts with high low-temperature activity, long-term thermal stability, and excellent water resistance for industrial application. This study constructed supported Pd-Ru/S-1 bimetallic catalysts using hydrophobic all-silica zeolite Silicalite-1 as support. Systematic catalytic performance tests evaluated methane oxidation activity, thermal stability, and water resistance, while multiple physicochemical characterizations revealed the reaction mechanism. Results showed that the catalyst with Pd/Ru ratio of 2:1 (2Pd-1Ru/S-1) exhibited optimal comprehensive performance, achieving T90 of 380 °C, maintaining 94% methane conversion at 375 °C for 48 h, and demonstrating excellent water resistance. Mechanistic studies indicated that PdO is the main active phase, and the reaction follows the Eley-Rideal (E-R) mechanism. The electronic synergy between Pd and Ru enhances the interaction between PdO and the support, effectively inhibiting sintering and water poisoning of active components. This study aims to provide a new strategy for industrial catalyst design to advance the industrialization of low-concentration methane catalytic technology, addressing its climate and pollution impacts.
1. Introduction
Methane, as the second-largest greenhouse gas after CO2, has a global warming potential 23–25 times that of CO2. Its atmospheric concentration has risen from pre-industrial levels of ~700 μg·kg−1 to 1,934±2 μg·kg−1 in 2023, significantly contributing to climate change and extreme weather events. Catalytic oxidation offers a low-temperature, high-efficiency route for methane removal, but conventional noble metal catalysts, particularly Pd-based systems, face critical bottlenecks: sintering of active components at high temperatures and deactivation by water vapor present in industrial exhaust. For instance, PdO/Al2O3 catalysts lose over 50% activity above 1000 °C due to support collapse, and Pd/SiO2 catalysts nearly completely deactivate upon introduction of 10% water vapor. These limitations hinder the industrialization of methane catalytic combustion technology.
This study addresses these bottlenecks by constructing Pd-Ru bimetallic catalysts supported on hydrophobic Silicalite-1 zeolite. The choice of Silicalite-1 provides a well-defined pore structure, high thermal stability, and hydrophobicity, which mitigates water poisoning. The addition of Ru, a noble metal with 4d orbital electrons, induces electronic interactions with Pd, modulating its surface electronic state and redox behavior. By systematically varying the Pd/Ru ratio, the research identifies an optimal composition (2:1) that achieves high low-temperature activity, long-term stability, and water resistance. This work not only demonstrates a practical catalyst formulation but also elucidates the synergistic mechanism, offering a strategic pathway for designing efficient methane oxidation catalysts for industrial application.
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WEI Yuwei, LYU Xuanzheng, MA Chunyan, XU Yan, SONG Maoyong (2026). Construction of Pd-Ru/Silicalite-1 Bimetallic Catalysts and Their Performance and Mechanism for Complete Methane Oxidation. Chinese Journal of Environmental Engineering. https://doi.org/10.12030/j.cjee.202511010
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Frequently Asked Questions
What is the optimal Pd/Ru ratio for maximizing methane oxidation activity and stability, and what are the corresponding T50 and T90 values?
The optimal Pd/Ru ratio is 2:1 (2Pd-1Ru/S-1), which achieves T50 and T90 of approximately 339 °C and 380 °C, respectively. This catalyst maintains 94% methane conversion at 375 °C for 48 h, demonstrating superior stability compared to other ratios and monometallic Pd/S-1.
How does the addition of Ru improve the water resistance of the Pd-based catalyst under humid feed conditions?
Ru doping enhances water resistance by promoting electronic synergy between Pd and Ru, which strengthens the interaction between PdO and the Silicalite-1 support. This interaction inhibits the decomposition of PdO and reduces the competitive adsorption of water molecules on active sites, thereby maintaining catalytic activity in the presence of water vapor.
What is the proposed reaction mechanism for complete methane oxidation over the 2Pd-1Ru/S-1 catalyst?
The reaction follows the Eley-Rideal (E-R) mechanism, where gaseous oxygen is first adsorbed and activated on the catalyst surface, then reacts with gas-phase methane to produce CO2 and H2O. PdO is identified as the primary active phase, and the Silicalite-1 support maintains its MFI structure, ensuring efficient mass transfer and structural integrity.
What are the key factors contributing to the long-term stability of the catalyst at high temperatures?
The long-term stability is attributed to the synergistic effect of Pd and Ru, which enhances the interaction between PdO and the Silicalite-1 support, preventing sintering and decomposition of the active phase. Additionally, the hydrophobic nature of Silicalite-1 mitigates water-induced deactivation, and the well-defined pore structure preserves the dispersion of active sites.
How does the performance of the Pd-Ru/S-1 catalyst compare to conventional Pd-based catalysts in terms of industrial applicability?
The 2Pd-1Ru/S-1 catalyst demonstrates superior low-temperature activity (T90 = 380 °C) and long-term stability (94% conversion after 48 h) compared to conventional Pd/Al2O3 or Pd/SiO2 catalysts, which suffer from severe deactivation under high temperatures and humid conditions. The enhanced water resistance and thermal stability make it a promising candidate for industrial methane emission control.
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