Alumina supported Pd catalyst (Pd/Al2O3) is active for complete oxidation of methane,while often suffers transient deactivation during the cold down process.Herein,heating and cool-ing cycle tests between 200 and 900℃ and isothermal experiments at 650℃ were conducted to investigate the influence of NOx on transient deactivation of Pd/θ-Al2O3 catalyst during the methane oxidation.It was found that the co-fed of NO alleviated transient deactivation in the cooling ramp from 800 to 500℃,which was resulted from the in situ formation of NO2 during the process of methane oxidation.Over the Pd/θ-Al2O3,thermogravimetric analysis and O2 temperature programmed oxidation measurements confirmed that transient deac-tivation was due to the decomposition of PdO particles and the hysteresis of Pd reoxidation,while the metal Pd entities were less active for methane oxidation than the PdO ones.CO pulse chemisorption and scanning transmission electron microscopy characterizations rule out the NO2 effect on Pd size change.Powder X-ray diffraction and X-ray photoelectron spec-troscopy characterizations were used to obtain palladium status of Pd/θ-Al2O3 before and after reactions,indicating that in lean conditions at 650℃,the presence of NO2 increases the content of active PdO on the catalyst surface,thus benefits methane oxidation.Homo-geneous reaction between CH4,O2,and NOx may be partially responsible for the alleviation above 650℃.The interesting research of alleviation in transient deactivation by NOx,the components co-existing in exhausts,are of great significance for the application.

State Key Joint Laboratory of Environment Simulation and Pollution Control,Research Center for Eco-Environmental Sciences,Chinese Academy of Sciences,Beijing 100085,China;University of Chinese Academy of Sciences,Beijing 100049,China;Center for Excellence in Regional Atmospheric Environment and Key Laboratory of Urban Pollutant Conversion,Institute of Urban Environment,Chinese Academy of Sciences,Xiamen 361021,China;Ningbo Research Center for Urban Environment,Chinese Academy of Sciences,Ningbo 315800,China;Ganjiang Innovation Academy,Chinese Academy of Sciences,Ganzhou 341000,China

[1]Chang Cui;Yan Zhang;Wenpo Shan;Yunbo Yu;Hong He-.Influence of NOx on the activity of Pd/θ-Al2O3 catalyst for methane oxidation:Alleviation of transient deactivation)[J].环境科学学报（英文版）,2022(02):38-47

reoxidation

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