基于载锰沸石分子筛的臭氧催化分解特性

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

臭氧作为重点防控的室内气态污染物广泛存在于人类生产、生活中,亟待开发高效的臭氧分解转化器从源头进行净化,催化剂是其核心关键.本文基于金属离子改性沸石分子筛进行臭氧催化性能研究,基于不同沸石拓扑结构、阳离子种类、改性手段及干燥方法,优选得到了采用等体积浸渍法和微波干燥法组合制备的载锰USY沸石Mn-USY-DT/WB,相较商用臭氧分解催化剂具有可逆再生的优势.通过系列表征,提出了可能的长效稳定催化臭氧的机制:单位时间内臭氧分子在沸石上的吸附与催化分解的相互协调,决定了沸石对臭氧的稳态催化分解,呈现宏观所得的脱除效率随时间变化曲线.通过XPS表征分析优选沸石升温可逆再生的潜在原因,再生后Mn-USY-DT/WB的平均化合态(Average oxidation state,AOS)由2.95降至2.81,经过加热处理后部分吸附在活性位点的中间氧物种脱附,氧空位释放,因此催化活性恢复.将优选沸石涂敷制得整体式蜂窝沸石催化剂,在实际应用条件(170℃、50000 h-1空速)下可维持99%臭氧分解效率1000 h以上.本工作为长效低阻臭氧分解催化剂的开发提供了新思路.

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 MnO_(2) 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 m^(2)·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.