The Reduction Construction Of High Efficient Pd-based Catalysts For Catalytic Oxidation Of O-xylene At Low Temperature

Volatile organic compounds（VOCs）are detrimental to the environment and human body.Catalytic oxidation has been widely used in the treatment of VOCs because of its safety and high efficiency.It is necessary to develop high-efficiency noble metal catalysts at low temperature so as to meet the challenge of high cost and high energy consumption.In this study,three kinds of morphologies（nanoflake,nanorod and nanobeam）forγ-Al₂O₃ were prepared by hydrothermal method,then 1%Pdwas loaded by wet impregnation method.The catalysts were tested for catalytic oxidation of o-xylene after different reduction methods and conditions（such as adjusting reduction gas concentration,reduction temperature and reduction time）.Firstly,the catalytic performance of Pd/Al₂O₃ prepared under different pretreatment conditions were investigated at the temperature range of 70℃～150℃.The results show that Pd/NF-Al₂O₃-CO exhibited excellent catalytic performance,which can completely oxidize 50 ppm o-xylene under the condition of 90℃and 60,000 mL·g^-1·h^-1.Secondly,some characterizations were taken for Pd/Al₂O₃.The SEM pictures show the formation of three kinds of regular morphologies of Al₂O₃.XRD patterns show the formation ofγ-Al₂O₃ crystalline phase.ICP-MS results show that the Pdload were around at 1 wt%.XPS results show that metal Pdis the main form in all the catalysts after reduction pretreatment.The TEM images and CO chemical adsorption results show that the Pd（111）and Pd（100）crystal faces were exposed on the reduced catalyst,which are beneficial to adsorb reactants and activate oxygen species.The results of CO pulse chemisorption show that the Pddispersion is one of the key factors affecting the catalytic performance.Finally,o-xylene oxidation pathways were studied by In-situ DRIFTS.The o-xylene oxidation reaction pathways were mainly divided into two cases:（1）o-Xylene is adsorbed and activated on the catalyst surface to form benzyl,then benzyl is oxidized to benzaldehyde,which is further oxidized to key intermediate products such as benzoic acid and formate,and finally convert to CO₂ and H₂O.（2）Phthalates may be formed.Then,after the ring structure opened,the adsorbed phthalate species are further oxidized to carboxylate species and finally converted to CO₂.The research results show that reduced Pd,dispersion and exposed crystal face are the key factors affecting the catalytic performance.The study of reduction construction high-efficiency Pd-based catalysts and their catalytic oxidation for o-xylene at low temperature provide basic data for the development of catalytic oxidation technology.