Kinetics Studies Of CO Oxidation Over Pt-based Catalysts

CO oxidation is a very important topic in catalysis because of its important role in fundamental and practical applications.In the fundamental research,CO oxidation widely used to understand some important questions in Catalysis, such as structure-sensitivity, active sites/phase and reaction mechanism. At present,the most commonly employed catalysts include noble metal catalysts and non-noble metal catalysts. Noble metal catalysts have advantages of high activity, stability and long service life. Therefore,noble metal catalysts are widely applied in CO oxidation.In the thesis,a series of Pt-based catalysts were prepared at tested for CO oxidation.Various techniques such as X-ray diffraction,CO chemisorption,transmission electronic microscope,hydrogen temperature-programmed reduction,Raman spectroscope, X-ray photonspectroscope and in-situ Fourier-transition infrared spectroscope were employed to determine physico-chemico properties of these catalysts.In addition, detailed kinetic investigations were conducted to deduce reaction pathway and reaction mechanism, as well as the role of the interaction between metal and support on the reaction.The main contents of the thesis are as follows:1.A series of Pt/CeO2 catalysts with different Pt contents were prepared using an incipient wetness impregnation method and tested for CO oxidation. Kinetic study on the catalysts indicated that the reaction rate was independent of the partial pressures of CO and O2 (r = kapp [CO]0[O2]0). The derived reaction pathways involved chemisorption of CO on surface Pt atoms and reacting with lattice oxygen provided by the CeO2 support at the Pt-CeO2 interface, suggesting a Mars van-Krevelen type reaction on these catalysts. Also, turnover frequencies (TOFs) calculated based on Pt dispersion and periphery Pt atoms were found to be proportional to the Pt particle size, with the large Pt particles possessing higher TOF than the small ones. Such a trend was interpreted by the important role of the oxygen vacancies via the formation of Pt-Ce-O solid solution, which could accelerate the mobility of lattice oxygen and consequently the activity.2. A series of potassium-promoted Pt/Al2O3 catalysts were tested for CO oxidation and it was found that the addition of K significantly enhanced the activity. Detailed kinetic study revealed the activation energies of the K-containing catalysts were lower than those on the K-free ones, particularly for the catalyst with high Pt content. The reaction orders of CO were much higher on the K-containing catalysts (about -0.2) than on the K-free ones (about -0.5), with the former having much lower equilibrium constants of CO adsorption than the latter. In-situ Fourier transform infrared spectroscopic results revealed easier desorption of surface CO from the 0.42K-2.0Pt/Al2O3 compared to that from the 2.0Pt/Al2O3. Therefore, the promoting effect of K-addition was due to the weakened interaction between CO and surface Pt atoms, which remarkably lowered the reaction barrier between chemisorbed CO and O2 species.