Contents 摘要.............................................i Abstract .......................................ii 致謝............................................iii Contents.........................................iv List of figures.................................vii List of Tables...................................ix Chapter 1: Introduction...........................1 References of Chapter 1..........................3 Chapter 2: Literature survey......................4 2.1: Introduction to Catalysis and Model Catalysts.........................................4 2.2: Molecular Beam, Infrared Reflection Adsorption Spectroscopy (IRAS), and Temperature Programmed Desorption (TPD) Approach.........................8 2.2.1: Methane dissociative adsorption on oxygen-precovered Pt(110) (1×2)........9 2.2.2: The adsorbate-induced lifting of the Pt(100) surface reconstruction...........................12 2.2.3: Reactions of Methanol on Pt(100)......14 2.2.4: Adsorption and decomposition of methanol on supported Pd modal catalysis..................16 References of Chapter 2........................20 Chapter 3: Experiment Apparatus and Methods......21 3.1: Ultrahigh Vacuum Chambers and Vacuum Pumps............................................21 3.1.1: Introduction to Vacuum................21 3.1.2: An UHV System.........................22 3.1.3: Vacuum Chambers and Pumps of Our System...........................................22 3.2: Experiment Methods........................23 3.2.1: Sample Cleaning.......................23 3.2.2: Methanol Adsorption and Reaction......24 3.3: The Principle of Molecular Beam...........25 3.4: The Pulsed Molecular Beam and Pulsed Valve Control Instrument.......................................28 3.5 Temperature Programmed Desorption..........30 3.6: The principle of IRAS.....................33 3.7: Fourier Transform Interferometers.........36 References of Chapter 3.........................39 Chapter 4: Results and Conclusion................40 4.1: The Designs in Our Systems................40 4.1.1: The Design of the Main Chamber........40 4.1.2: The Design of QMS Chamber of Molecular Beam.............................................45 4.1.3: The Design of IRAS System.............48 4.2: The Alignment of IR Light.................53 4.3: The Real-time Catalyzed Methanol Decomposition on Pt(100)..........................................55 Chapter 5 Conclusions............................63 List of figures Figure 2-1: Energy diagram for the oxidation of CO on Pt catalysts. All energies are given in kJ mol-1. For comparison, the heavy dashed lines show a noncatalytic route.............................................5 Figure 2-2 : Structural and chemical complexity of a catalyst surface illustrated through the example of an oxide-supported metal catalyst (left side) and kinetic phenomena (right side), which are expected arise on this type of system....................................6 Figure 2-3: An example of the oxygen transient reaction after CH4 exposure at Ts= 650 K. At first, the molecular beam of O2 did not hit the sample. This showed the interaction between chamber and the oxygen beam. At time = 150 sec, the oxygen beam hit the sample. The CO and CO2 was yield by O2 beam and detected by quadrupole mass spectrometer.....................................10 Figure 2-4: (a) The true initial sticking probability s0 (solid line), and the apparent value, sc (dash line), versus Oa precoverage at Et= 188 meV, Tn=800 K, Ts=400 K. (b) The variation of s0 with oxygen adatom precoverage at Et = 90 and 500 meV..............................11 Figure 2-5: (a) IR spectra of CO adsorbed on Pt(100) (1×1) (b) on Pt(100) (hex) at 300 K shown as a function of exposure. Resolution 4 cm-1...................12 Figure 2-6: High resolution IR spectra of CO adsorbed on Pt(100)-hex at 300 K shown as a function of exposure. Resolution 1 cm-1................................13 Figure 2-7: TPD spectra for CH3OH, CO, H2O, and H2 following adsorption of methanol on the Pt(100)-hex at 100 K............................................14 Figure 2-8: The comparison of CO and H2 TPD spectra following methanol adsorption on the (1×1) hex surface of Pt(100) at 130 K…………………...15 Figure 2-9: (a) RAIR spectra of the CO stretching frequency region recorded for the methanol exposure at 100 K. (b) Comparison of TPD spectra for methanol as a function of exposure at 100 K adsorbed on Pd/Al2O3/NiAl (stabilized) (solid line) and on the pristine support (dash line)......................................17 Figure 2-10: RAIR spectra of the CH, CD, and CO stretching frequency regions displayed at different temperatures with a beam of CH3OH or CD3OD, respectively.....................................18 Figure 3-1: Schematic drawing of several pumps with their working ranges...................................23 Figure 3-2: Flow charts of our experiment process..........................................25 Figure 3-3: The schematic structure of continuum free-jet expansion........................................26 Figure 3-4: Schematic view of typical molecular beam source setup.....................................27 Figure 3-5: Diagram if the connection of each instrument and direction of signal flow.....................29 Figure 3-6: Screen shot of the pulsed valve control program..........................................29 Figure 3-7: Schematic diagram of the experimental setup used for TPD.....................................30 Figure 3-8: The diagram of a typical (a) first order and (b) second order desorption......................31 Figure 3-9: The diagram of the connection of Analog-Digital/Digital-Analog interface.................32 Figure 3-10: Electric vectors of the p- and s- components of IR radiation. Primed and umprimed vectors refer to reflected and incident beams respectively........34 Figure 3-11: The surface electric field, E⁄E_0 , and the quantity ((E⁄(E_0 )^2 ))⁄cos⁡θ for platinum at (a) ν ̃=500 〖cm〗^(-1) (ϵ=-3500-4200i) and (b) ν ̃=2100 〖cm〗^(-1) (ϵ=-375-200i) as a function of the angle incidence, θ................................................35 Figure 3-1: (a) The structure of Michelson interferometer and (b) the interferogram........................37 Figure 4-1: The top view of the main chamber. It shows each port, the corresponding technique and the distance between the center of the main chamber and the flange...........................................42 Figure 4-2: The engineering drawing with dimensions of the main chamber. Top left and right are show the angles between the port used for the molecular source chamber and the other ports. Bottom left shows the length 400 mm between the top and the bottom flanges. Bottom right is the cross section view showing the horizontal inclination of nipple........................................43 Figure 4-3: A top-view photograph for all instruments on the main chamber.................................44 Figure 4-4: The photograph of the molecular beam QMS system...........................................46 Figure 4-5: The schematic drawing of the entire molecular beam system......................................47 Figure 4-6: The setup of IRAS on an UHV system...48 Figure 4-7: The photograph of fixed mirrors at the (a) IR chamber 1 (b) IR chamber 2.......................50 Figure 4-8: The schematic drawing of IR chamber 1 with the dimensions...................................50 Figure 4-9: The schematic drawing of IR chamber 2 with the dimensions...................................51 Figure 4-10: (a) the schematic drawing and (b) the photograph for the sealed flange.................52 Figure 4-11: The schematic diagram illustrating how to seal liquid nitrogen tube........................52 Figure 4-12: The photograph of supported mirrors on the (a) IR chamber 1 (b) IR chamber 2................53 Figure 4-13: The photograph of IR light on the IR card.............................................54 Figure 4-14: The signal of IR in the computer....54 Figure 4-15: TPD spectra for (a) CO (m/z=28), H2 (m/z=2), and CH4 (m/z=16) from Pt (100) single crystal exposed to 21 L CH3OH at 300 K; (b) TPD spectra for CO (m/z=28), D2 (m/z=4), and CD4 or D2O (m/z=20) from Pt (100) single crystal exposed to 50 L CD3OD at 300 K................................................55 Figure 4-16: The spectra of real-time catalyzed methanol decomposition on Pt (100): (a) D2 (m/z=4), (b) CO (m/z=28), (c) D2O or CD4 (m/z=20). The sample was exposed continuously to CD3OD (p=7.8×10-8 Torr) at 300 K for 250 sec, then heated to 900 K with 3 K/sec...........56 Figure 4-17: The (a) D2 (m/z=4) and (b) CO (m/z=28) spectra of real-time catalyzed methanol decomposition on Pt (100) exposed continuously to CD3OD (p=4×10-7 Torr) at 300 K for 120 sec, then heat to 500 K with 3 K/sec. After that, decrease pressure from 4×10-7 to 9×10-8 Torr.............................................58 Figure 4-18: The background experiment: heating surface temperature from 300 to 500 K (3 K/sec) without any exposure.........................................58 Figure 4-19: The spectra of real-time catalyze reaction with methanol decomposition on Pt (100) for (a) D2 (m/z=4) (b) CO (m/z=28), exposed continuous CD3OD (p=4×10-7 Torr) at 300 K for 120 sec, then heat to 500 K with 3 K/sec. After that control the surface temperature between 400 K and 500 K..........................59 Figure 4-20: The difference in the integrated D2 signals at 500 and 400 K per second with the times of controlled temperature cycle................................60 Figure 4-21: The spectra of the real-time methanol reaction with O2 molecular beam; (a) the stagnation pressure of O2=55 psi, pulse width=170 μs and (b) the stagnation pressure of O2=40 psi, pulse width=1 ms. In both cases, the same repetition rate (8 Hz) and voltage (200 V) are used. The spectra include D2O or CD4 (m/z=20), CO (m/z=28), O2 (m/z=32), and CO2 (m/z=44) from Pt(100) exposed continuously to CD3OD at surface temperature= 480 K...............................60 Figure 4-22: The temporal profile of the optimized pulsed helium beam scattered specularly from the Pt (100)............................................62 List of Tables Table 3-1: The quality of vacuum and corresponding gas flow mode........................................21 Table 3-2: The vacuum pumps used in our molecular beam system...........................................23