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fbtwitterlinkedinvimeoflicker grey 14rssslideshare1
Languages: English
Types: Doctoral thesis
Subjects: QD
The selective oxidation of methanol to formaldehyde over iron molybdate catalysts has been investigated. It has been shown that when Fe2C 3 is present at the surface CO2 and H2 are observed from surface formates, while neighbouring pairs of molybdena sites leads to the production of formaldehyde and water from surface methoxys. When molybdenum sites are isolated then the surface methoxy is stabilised and a direct pathway to CO and H2 is created. On molybdena rich surfaces the production of CO is observed, but as a secondary oxidation product following the linear pathway: CH3OH → CH2O → CO → CO 2, established by varying bed lengths. Catalysts with addition of small amounts of molybdena added to the surface of Fe2O 3, are similar to those with a low bulk ratio of Mo:Fe showing increased activity over Fe2O3. Selectivity is dictated by the presence of isolated or pairs of molybdena sites, which guide the reaction to the primary products of CO and formaldehyde respectively. Structural analysis showed the phases of a-Fe2O3, (X-MoO3 and a-Fe2(MoO4)3, depending on the ratio of the cations present. Molybdenum has been shown to concentrate at the surface of iron molybdates by reactor results from low ratio catalysts, Raman spectroscopy, XP spectroscopy and STEM/EEL spectroscopy. The normal reaction of iron molybdates is via the Mars-van Krevelen mechanism, so tests were made without the presence of gaseous oxygen. The reduction of the surface layer can occur at temperatures as low as 200°C. At temperatures above 250°C diffusion of lattice oxygen to replace the lost surface oxygen can occur, leading to the production of further oxidised products. If the oxidation state of surface molybdenum drops below +6 then formaldehyde selectivity drops markedly, with direct production of CO and secondary production of CO2 observed.
  • The results below are discovered through our pilot algorithms. Let us know how we are doing!

    • 1 Introduction and Literature Review...........................................1 1.1 Catalysis ........... 2 1.2 Background ........... 3 1.2.1 Iron - Uses and Properties......................................................... ........... 3 1.2.2 Molybdenum - Uses and Properties.................................................... 4 1.2.3 Methanol - Uses and Properties ........... 6 1.2.4 Formaldehyde - Uses and Properties ........... 8 1.3 Industrial Process 10 1.3.1 Industrial Plant 11 1.3.2 Current Industrial Catalyst 13 1.4 Thermodynamics of Methanol Oxidation 14 1.5 Alternative Catalysts 16 1.5.1 Silver 16 1.5.2 Sodium Catalysts 18 1.5.3 Ag-Si0 2 -Mg0 -Al2 0 3 Catalysts 19 1.5.4 Vanadium Containing Catalysts 19 1.5.5 Supported Ruthenium Oxide Clusters 20 1.6 The Structure of Oxides Relevant to Iron Molybdate Catalysis........... 21 1 .6 . 1 M o 0 3 2 1 1.6.2 Fe2 0 3 22 1.6.3 Fe2 (M o 0 4 ) 3 23 1.6.4 FeM o04 25 1.6.5 M o 0 2 25 1.7 Reactivity ........... 26 1.7.1 Molybdena 26 1.7.2 Iron Oxide 30 1.7.3 Iron Molybdates 31 1.8 Preparations of Iron Molybdates 38 1.9 Supported Catalysts 39 1.10 Promoted Iron Molybdates 44 1.11 Reactor Designs 46 1.12 Deactivation of the Catalyst 47 1.13 Other Uses of Iron Molybdate Catalysts 51 1.14 Previous work within the Bowker Group 52 1.15 Research Objectives 56 1.16 References 57
    • 2.3.4 Methanol Peak Area
    • 2.3.5 Quadrupole Mass Spectrometry
    • 2.3.6 Vacuum Pumps 2.3.6.1 Turbo Molecular Pumps 2.3.6.2 Rotary Vane Pumps
    • 2.3.7 Pressure M easurement 2.3.7.1 Pirani Gauges 23.1.2 Ionisation Gauges
    • 2.3.8 Quantification 2.3.8.1 Blank Tube Reactivity 2.3.8.2 Reproducibility 2.3.8.3 Cracking Patterns X-Ray Diffraction
    • 2.4.1 Theory
    • 2.4.2 Experimental Raman Spectroscopy
    • 2.5.1 Theory
    • 2.5.2 Experimental X-Ray PhotoelectronSpectroscopy
    • 2.6.1 Theory
    • 2.6.2 Generation of X-rays
    • 2.6.3 Experimental BET Surface area measurement
    • 2.7.1 Theory
    • 2.7.2 Experimental Super-STEM
    • 2.8.1 Theory
    • 2.8.2 Experimental
    • 2.8.3 Electron Energy Loss Spectroscopy 2.8.3.1 Theory 2.8.3.2 Experimental References
    • 3.3.4 Flow Conditions............................................................. ........... 133
    • 3.3.5 Effect of space velocity................................................. ........... 138 3.3.5.1 Varying Catalyst Loadings.................................... ........... 138 3.3.5.2 Varying Pulse Size.................................................. ........... 147
    • 3.3.6 Varying Preparation Parameters.............................................. 148 3.3.6.1 Co-precipitation with W ashing ........... 149 3.3.6.2 Use of Different Iron Precursor ........... 149 3.3.6.3 Preparation at High pH ........... 150 3.3.6.4 Comparison ........... 151
    • 3.3.7 Temperature ProgrammedDesorption..................................... 152
    • 3.3.8 Characterisation.......................................................................... 160 3.3.8.1 XRD ........... 160 3.3.8.2 Raman Spectroscopy............................................... ........... 163 3.3.8.3 XPS........................................................................................ 165 3.3.8.4 STEM and EELS...................................................... ........... 168 Conclusions ........... 176 References ........... 177 Anaerobic Reaction of Methanoland Reaction with Reduced P h ases.............................................................................179
    • 4.1 Introduction....................................................................... ........... 180
    • 4.2 Experimental..................................................................... ........... 186 4.2.1 Calculation of Oxygen Removal.............................. ........... 187
    • 4.3 Results and Discussion.................................................... ........... 188 4.3.1 Anaerobic TPPFR....................................................... ........... 188 4.3.2 Reduction profile at 200 °C................................... ........... 193 4.3.3 Reduction profile at 250 °C................................... ........... 194 4.3.4 Reduction profile at 275 °C................................... ........... 195 4.3.5 Reduction profile at 300 °C................................... ........... 195 4.3.6 Reduction profile at 330 °C................................... ........... 196 4.3.7 Comparison with Fe2 (M o0 4 ) 3 .............................................. 200 4.3.8 Temperature Programmed Desorption.................... ........... 203 4.3.9 X-Ray Diffraction....................................................... ........... 204 4.3.10 X-Ray Photoelectron Spectroscopy......................... ........... 208
    • 4.4 Action of the Reduced Phases.................................................... 213 4.4.1 M0 O2........................................................................................ 213 4.4.1.1 Temperature Programmed Pulsed Flow Reaction ...213 4.4.1.2 Temperature Programmed Desorption ............215 4.4.1.3 X-Ray Diffraction ........... 217 4.4.1.4 X-Ray Photoelectron Spectroscopy ........... 218 4.4.2 FeM o04 ........... 219 4.4.2.1 Temperature Programmed Pulsed Flow Reaction ...219 4.4.2.2 Temperature Programmed Desorption ........... 221 4.4.2.3 X-Ray Diffraction ........... 222 4.4.2.4 X-Ray Photoelectron Spectroscopy ........... 222
    • 4.5 Conclusions.................................................................................... 224 References ........... 225
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