Catalytic Oxidation Of Toluene Over CeO₂ Nanorod Loaded With Nano Noble Metal

Volatile organic compounds(VOCs)are the key precursors of O3 and PM2.5,which do harm to human health and environment.There are many ways to treat industrial VOCs,and catalytic combustion is one of the most important technologies.Pt/CeO2 catalyst with both advantages of CeO2 and noble metal is the focus of the research on catalytic combustion of VOCs.Using toluene as VOCs probe pollutants,this paper focused on the controllable synthesis of Pt particles with small size and high dispersion,selecting a specific size of Pt loaded highly active Pt/CeO2 catalyst,examining the influence of Pt size on the reaction of toluene catalytic oxidation and analyzing the essential reasons,finding the control factors that affect the rate of catalytic oxidation of toluene in the Pt/CeO2 system.The stability of the catalyst under different operating conditions and the suitable conditions of application were investigated and the parameters for the industrial application of the catalyst were provided.In chapter 3,a series of Pt-x nanoparticles with different sizes(x= 1.41?1.57?1.79?1.95?2.12?2.32 nm)had been successfully synthesized by polyol reduction method and loaded onto CeO2-rod.These Pt-x/CeO2-rod samples were tested in the catalytic oxidation of toluene.The results indicated that the catalysts activity exhibited a volcano-shaped curve with respect to Pt particle size and Pt-1.79/CeO2-rod showed the highest catalytic activity with T90=133 ?.The UV Raman,XRD and XPS results showed a higher surface oxygen vacancies concentration accompanied with the larger the Pt particles.The increasing of surface oxygen vacancies was found to accelerate the lattice oxygen transfer effectively,promote the adsorption and activation process of oxygen.Therefore,it could be conclude that the catalytic oxidation of toluene activity on Pt/CeO2 catalysts was found to be led by the coefficient of Pt dispersion and CeO2 surface oxygen vacancies concentration.In chapter 4,The OSC test found that the Pt-2.32/CeO2-rod(147.2?mol O g-1)had higher surface oxygen vacancy concentration than other samples.TOFPt was positively correlated with Pt particle size,TOFOV was negatively correlated with Pt particle size and TOFPt·OV did not vary with the size of the Pt particle.The above showed that the concentration of oxygen vacancy in the catalyst surface and the dispersion degree of Pt control the reaction of the catalyst.In conjunction with other researchers' findings,we believe that the reaction path of the Pt/CeO2 catalyzed toluene reaction may be based on the Mars-van Krevelen mechanism.In chapter 5,Further tests on the performance of the catalyst was taken.The catalyst had excellent activation regeneration ability,a long service life and maintained good activity in the fluctuation of toluene concentration and water vapor added.The influence of the external diffusion on the catalytic oxidation of toluene was largely eliminated when the airflow velocity was larger than 4.14 cm·s-1.When the catalyst size was reduced to 40 to 60 size mesh(0.25 ~ 0.38 mm),the effect of internal diffusion on the catalytic oxidation of toluene was eliminated.In addition,Reducing the quality of catalyst to enhance the space velocity could obviously reduce the conversion rate of toluene,especially in low temperature.But,under the condition of high space velocity(120000 ml·g-1·h-1),the pollutants toluene conversion rate can still be to 100% at relatively low temperature(165 ?).