Control And Optimization Of Industrial Waste Gas Of Volatile Organic Compounds By Supported Pd-Based Catalysts

With the social progress and the era development,it is urgent to dispose volatile organic compounds（VOCs）in industrial flue gas,which not only directly harm human health,but also cause secondary pollution problems such as photochemical smog.At present,catalytic combustion technology is widely used in the VOCs treatment due to its many merits.As the pivotal technology of catalytic combustion,the development and optimization of loaded noble metal catalysts have become a hot research topic in academia.However,the high cost of catalyst preparation limits its application because of the high loading of precious metals.Therefore,in this thesis,the Pd-based catalysts with low loadings and excellent catalytic oxidation activitywere obtained by optimizing the preparation technology,introducing transition metal additives and adjusting their components.Furthermore,the catalytic mechanism of the active centers on the loaded Pd-based catalysts was intensively studied.The main research contents and results are as follows:（1）Hydrogen reduction method was employed to regulate the relative content of Pd⁰and PdO on the catalyst.The effect of the chemical state of the active center Pd on the catalytic activity was investigated.The Pd/Si O₂-H₂catalyst exhibited better catalytic activity for toluene and n-hexane.It is revealed that the catalytic activity of active center Pd⁰was superior to that of active center PdO,which is more conducive to the adsorption of VOCs molecules by the catalyst.Furthermore,it is observed that Pd⁰and PdO could interconvert during the catalytic reaction until reaching dynamic equilibrium.（2）The effect of the loading process of the promoter CeO₂and active component Pd on the catalytic activity was examined.In comparison to one-step method,a two-step approach was developed to prepare high-loaded Pd systems.The results indicated that the catalysts produced by two-step method had higher catalytic oxidation activity,which may be attributed to the higher surface active oxygen O_Vand relative content of Pd⁰on 0.5%Pd-2.5%CeO₂/Si O₂-T.The catalyst also possesses stronger adsorption activation ability towards n-hexane.However,0.1%Pd-2.5%CeO₂/Si O₂-O prepared by the one-step method exhibits higher catalytic oxidation activity towards n-hexane in low-loaded Pd systems,resulting from the higher surface active oxygen O_Vand relative content of Pd⁰on 0.1%Pd-2.5%CeO₂/Si O₂-O catalyst.（3）The effect of plasma discharge process on the catalytic activity was explored.And the performance of VOCs catalytic oxidation was studied by regulating the active component.Pd-CMC/Si O₂-P and Pd-CMC/Si O₂catalysts were prepared by plasma discharge method and equal volume impregnation method,respectively.The results showed that Pd-CMC/Si O₂-P delivers higher catalytic oxidation activity towards n-hexane due to its higher O_V/O_Lratio and stronger adsorption activation ability towards n-hexane.After adjusting the Pd loading amount,it is found that0.02%Pd-15%CMC/Si O₂-P could achieve complete oxidation of n-hexane at 260℃,and its catalytic performance is superior to that of 0.1%Pd-15%CMC/Si O₂-P.Moreover,considering the complex working conditions of industrial VOCs emissions,a machine learning model was established to fit and predict the catalytic oxidation process of VOCs by 0.02%Pd-15%CMC/Si O₂-P catalyst,enabling refinement of the activity evaluation results and obtaining more information on the catalytic oxidation of VOCs under various conditions.The model can forecast the industrial application prospects of the catalyst as well.