Preparation And Environmental Catalytic Performance Of Zeolite Supported Metal Catalysts

Catalytic oxidation of VOCs to harmless carbon dioxide and water is a highly effective and economic technology for the removal of VOCs,therefore,the design and selection of catalyst is the focus of catalytic combustion technology.In this thesis,zeolites loaded noble metals and transition metal oxides as the research object,ZSM-5 and Beta zeolites with large specific surface area and good hydrothermal stability were prepared by amino acid-assisted and traditional hydrothermal methods,and the metal/metal oxide components were impregnated on the zeolite supports to prepare zeolite supported metal catalysts.Taking the catalytic oxidation of toluene as a model reaction,the structure-activity relationship of the prepared zeolite supported metal catalysts was studied.The main research results are as follows:（1）Two nano-sized ZSM-5（MFI）zeolites(Z5-L_0.2 and Z5-L₀)were synthesized by amino acid-assisted hydrothermal methods and conventional hydrothermal methods,and the metal catalyst Mn O_x/ZSM-5 supported by zeolites was prepared.The effect of zeolite crystal size on the Mn O_x.was studied.The catalytic oxidation reaction of toluene was used as a probe reaction to evaluate its catalytic performance.The characterization test results showed that the nano-sized ZSM-5 zeolite(Z5-L_0.2)prepared by amino acid-assisted hydrothermal method has a smaller crystal size（about 155 nm）and a larger specific surface area（354 m²/g）than that of Z5-L₀ zeolite,which can improve the dispersibility and redox ability of active Mn O_x species.The activity test results showed that Mn O_x/Z5-L_0.2optimized the catalytic oxidation performance of toluene,The toluene conversion rate reached 100%at 315℃,while the highest conversion rate of Mn O_x/Z5-L₀ toluene oxidation was only 98.8%.（2）In order to reveal the effect of surface acidity of zeolite on the catalytic performance,nano-sized ZSM-5 zeolite supported Mn O_x catalysts with different concentration of acid sites（Si/Al ratio）were prepared.Characterization results show that other properties of prepared samples are comparable,except for the different amount of acid.The catalytic activity of the prepared Mn O_x/ZSM-5 samples was evaluated by the catalytic oxidation of toluene.The results showed that the conversion of toluene was positively correlated with the total acid site concentration of the Mn O_x/ZSM-5 catalysts,indicating that the concentration of zeolite acid sites is beneficial to promoting the catalytic performance of Mn O_x/ZSM-5 catalysts for toluene oxidation reactions.（3）Nanometer Beta（BEA）zeolite supported Pt Co alloy catalyst（Pt Co/nm Beta）was synthesized for catalytic combustion of toluene.XPS test shows that the transfer of Pt and Co binding energy in Pt Co/nm Beta catalyst.When the escaping electrons in Co²⁺and Co³⁺are captured by Pt²⁺,Pt²⁺is reduced to Pt⁰,and the oxygen vacancy on the catalyst surface increases.The composite metal catalyst（im Pt Co/Beta）prepared by impregnation method has higher adsorbed oxygen concentration(O_ads/O_latt=13.57)and active Pt⁰(Pt⁰/Pt²⁺=2.46),and the activity(T₉₀=227℃)was much higher than that of Pt/nm Beta and Co/nm Beta(T₉₀=280℃and 331℃).