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基于載錳沸石分子篩的臭氧催化分解特性

Catalytic decomposition of ozone in air by Mn-modified zeolite molecular sieves

  • 摘要: 臭氧作為重點防控的室內氣態污染物廣泛存在于人類生產、生活中,亟待開發高效的臭氧分解轉化器從源頭進行凈化,催化劑是其核心關鍵.本文基于金屬離子改性沸石分子篩進行臭氧催化性能研究,基于不同沸石拓撲結構、陽離子種類、改性手段及干燥方法,優選得到了采用等體積浸漬法和微波干燥法組合制備的載錳USY沸石Mn-USY-DT/WB,相較商用臭氧分解催化劑具有可逆再生的優勢. 通過系列表征,提出了可能的長效穩定催化臭氧的機制:單位時間內臭氧分子在沸石上的吸附與催化分解的相互協調,決定了沸石對臭氧的穩態催化分解,呈現宏觀所得的脫除效率隨時間變化曲線. 通過XPS表征分析優選沸石升溫可逆再生的潛在原因,再生后Mn-USY-DT/WB的平均化合態(Average oxidation state,AOS)由2.95降至2.81,經過加熱處理后部分吸附在活性位點的中間氧物種脫附,氧空位釋放,因此催化活性恢復. 將優選沸石涂敷制得整體式蜂窩沸石催化劑,在實際應用條件(170 ℃、50000 h–1空速)下可維持99%臭氧分解效率1000 h以上. 本工作為長效低阻臭氧分解催化劑的開發提供了新思路.

     

    Abstract: Ozone is a significant indoor air pollutant found in our daily lives. To effectively purify this pollutant at its source, it is essential to develop a high-efficiency ozone decomposition converter, with the catalyst being its pivotal component. This study investigates the catalytic performance of modified zeolites for ozone decomposition by adjusting their topological structure, cation form, modification, and drying methods to enhance their adsorption and catalytic properties. The Mn-USY-DT/WB zeolite catalyst demonstrated effective and stable ozone purification for more than 30 h at ?5 ℃ and 720000 h?1, outperforming commercial MnO2 catalysts in regeneration. X-ray photoelectron spectroscopy (XPS)characterization revealed that the decrease in the average oxidation state of Mn decreased from 2.95 to 2.81 after regeneration. The X-ray diffraction (XRD) results show that the cationic modification did not alter the crystal structure of the zeolite molecular sieve. The BET results indicate a slight reduction in the specific surface area of the modified samples, with Mn-USY-YX showing a significant drop to 146 m2·g?1 owing to the formation of a large number of hydrates during the liquid phase sampling, which was difficult to remove by calcination. The primary pore sizes varied among the samples, with the USY series at approximately 0.74 nm, Mn-Beta-DT zeolite at 0.58 nm, and Mn-ZSM-5-DT at 0.55 nm. The EDS images of the sample show that the content of Mn in Mn-USY-YX was low and that the Mn distribution was distinct. The Mn distribution in the Mn-USY-DT/WB sample was uniform, mostly in a linear arrangement along the crystal structure. The Mn element was obviously aggregated in the Mn-USY-DT/CG sample. Adjusting modification and drying methods helps preserve metal cationic clusters within the zeolite skeleton, preventing aggregation and enhancing catalyst activity. We propose a mechanism for long-term stable catalysis of ozone based on the coordination of ozone molecule adsorption and catalytic decomposition on zeolite, explaining the observed efficiency over time. The optimized zeolite powder was coated on a glass fiber support to obtain a low-gas-resistance monolithic honeycomb catalyst that maintains ≥99.9% efficiency for over 1000 h in practical applications.

     

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