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挥发性有机化合物(VOCs)作为PM2.5和臭氧的重要前驱体,已经对大气环境质量和人体健康造成直接和间接的危害[1-2],VOCs废气治理成为了近年来的环境热点话题之一。在VOCs废气的众多处理技术中,催化燃烧技术因处理效率高、能耗低、二次污染小而在工业上应用广泛[3]。为达到VOCs催化燃烧所需温度,工业上多采用电加热使VOCs废气达到起燃温度。由于电加热是采用热传导的加热方式,因而对大气量的VOCs废气加热时能耗巨大。另外,VOCs催化燃烧时,持续的高温环境会使催化剂活性组分烧结而影响VOCs降解效果[4]。微波加热应用于VOCs催化燃烧是一种新技术,它利用电磁波的选择性仅对催化剂进行加热,因而能耗低且催化剂受热均匀、快速[5]。而且,微波对催化剂活性组分的热点效应有利于引发VOCs的催化燃烧,同时微波的偶极极化作用还可降低VOCs的反应阈能而促进其氧化降解[6]。卜龙利等[7]、姚泽等[8]利用吸波型催化剂证实了微波催化燃烧VOCs效果优于电加热催化燃烧。
微波催化燃烧技术的关键是高效而稳定的催化剂。过渡金属氧化物催化剂种类丰富、经济性好、不易中毒,但其对于某些难降解有机物的催化活性差、低温活性以及热稳定性有待提高[9]。贵金属催化剂具有催化活性高、高温下稳定性好和适用范围广的优点,但也存在资源稀少和价格高昂的问题[10]。目前,市面上较为常见的是铜锰铈三元金属氧化物催化剂。胡旭睿[11]研究证实,铜锰铈氧化物催化剂对芳香烃类、醇类、酮类等有机物具有良好的氧化性能,但其矿化效果不佳且对芳香烃的降解效果低于醇、酮类。贵金属Pt、Pd等在低温时对芳烃类和3个碳以上的直链烷烃活化能力强[12]。已有研究证实,将贵金属与过渡金属复合可以增强催化剂活性。SHI等[13]通过还原法和离子交换法合成了Pt /Ce-USY催化剂,其对1,2-二氯乙烷的催化活性高于Pt/USY催化剂,Pt与CeO2之间的相互作用抑制了碳物质的沉积,从而增强了催化剂的耐久性。LEE等[14]将贵金属金、钯沉积在CeO2表面,证实适量Au的加入使得Pd/CeO2催化剂活性增强。CHEN等[15]合成了Pd/Fe3O4催化剂用于去除CO,当沉积适量Fe3O4时,CO氧化的起燃温度明显降低。因此,本研究在铜锰铈三元催化剂基础上复合微量贵金属Pt,以期提高催化剂对芳烃类VOCs的活化能力,进而提高总VOCs的去除效果。
本研究选取油墨印刷VOCs废气中含量最多的2种物质甲苯和乙酸乙酯作为目标污染物,以蜂窝状堇青石为载体制备Pt复合铜锰铈(CMC)负载型催化剂(Pt-CMC/堇青石),重点考察Pt复合前后催化剂对模拟VOCs废气催化燃烧效果的差异,以探究低含量贵金属添加对铜锰铈氧化物催化剂催化活性的影响程度。
Application of Pt-CuMnCeOx/Cordierite catalyst in microwave catalytic combustion of VOCs
- Received Date: 26/05/2021
- Available Online: 10/05/2022
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Key words:
- microwave /
- CuMnCeOx/Cordierite /
- Pt composition /
- catalytic combustion /
- VOCs
Abstract: Microwave catalytic combustion is an emerging technology for VOCs treatment, and preparation of the catalyst with higher catalytic activity and stability is the key to highly efficient VOCs removal. Noble metal Pt was composited with copper-manganese-cerium oxides and loaded on the surface of honeycomb cordierite carrier to prepare a Pt-CuMnCeOx/Cordierite catalyst by incipient-wetness impregnation method. Based on SEM, BET and XRD characteristics, the catalytic activity and stability of three catalysts in microwave catalytic combustion of bi-component VOCs toluene and ethyl acetate were tested in this work. The experimental results showed that Pt composition improved the dispersion of active particles on the catalyst surface, increased specific surface area and pore volume of the catalyst and lifted valence states of copper and manganese to enhance the low temperature catalytic activity of the catalyst greatly. The removal efficiencies of toluene and ethyl acetate on the surface of Pt-CuMnCeOx/Cordierite catalyst were higher 16% and 11% than CuMnCeOx/Cordierite catalyst under 40 W of microwave power. Toluene and ethyl acetate were degraded completely by Pt-CuMnCeOx/Cordierite catalyst under 70 W of microwave power, and the removal rate of total VOCs reached 97% simultaneously. Pt-CuMnCeOx/cordierite catalyst exhibited a high catalytic activity and an excellent stability during consecutive seven times test. This study can provide a reference for microwave catalytic combustion of VOCs technology.