Dissertation > Excellent graduate degree dissertation topics show

Solid-State NMR Studies on Methanol Conversion over Heterogeneous Catalysts

Author: ZengDanLin
Tutor: DengFeng
School: Wuhan Institute of Physics and Institute of Mathematics
Course: Radio Physics
Keywords: solid-state NMR heterogeneous catalysis methanol NMR probe molecule solid acid
CLC: O643.32
Type: PhD thesis
Year: 2007
Downloads: 204
Quote: 0
Read: Download Dissertation

Abstract


In this dissertation, methanol-to-aromatics (MTA) reaction over silver exchanged HZSM-5 zeolites and methanol selective oxidation over supported vanadium oxide catalysts were studied by using solid-state NMR techniques including probe molecule techniques as well as quantum chemical calculation.Solid-state 13C NMR spectroscopy was used to study the conversion of methanol to aromatics over silver exchanged HZSM-5 zeolites. The experimental results show that in addition to the Br?nsted acid sites the silver oxide in the air-calcined AgZSM-5 zeolite also plays a crucial role for the aromatic selectivity in the MTA reaction. We found that the yield of aromaticson the air-calcined AgZSM-5 reaches 96.3%, while the yields of aromatics on the HZSM-5 and vacuum-calcined AgZSM-5 are only 61.8% and 53.6% at 673 K, respectively. 129Xe NMR spectroscopy was employed to characterize the state of silver species dispersed on the fresh and decayed AgZSM-5 catalysts and its function during the methanol-to-aromatics reaction. Based on our experimental results, A possible reaction mechanism is proposed as follows: the small alkanes (mainly propane and isobutane) were first produced from dimethyl ether, and then the isobutene and propane were dehydrogenated, rearranged and polymerized to form the aromatic products (mainly toluene and benzene). Deactivation of the air-calcined AgZSM-5 catalyst is mainly due to the gradual reduction of the silver oxide into the silver metal with time on stream.Methanol catalytic oxidation over VOx/Al2O3, VOx/ZrO2, and VOx/MgO catalysts has been studied by solid-state NMR spectroscopy. It was found that stronger acid sites in VOx/Al2O3 result in almost the same selectivities for DMM, paraformaldehyde and formic acid, and weaker acid sites in VOx/ZrO2 favor paraformaldehyde synthesis while the VOx/MgO catalyst with the base support shows high selectivity for formate. Supporting VOx species onĪ³-Al2O3 and ZrO2 leads to the formation of Br?nsted acid sites as revealed by the adsorption of probe molecules. The acid strength of Br?nsted acid sites on the VOx/Al2O3 catalyst is found to be stronger than that of the VOx/ZrO2 catalyst which has the similar acid strength to zeolite HZSM-5. The proposed bridging hydroxyl models accounting for the Br?nsted acid sites formation were also confirmed by quantum chemical calculation.Methanol selective oxidation over NaOH and HNO3 modified VOx/Al2O3 was studied by solid-state NMR spectroscopy. The NMR experimental results indicate that acid sites play a key role in the formation of dimethoxymethane during the methanol oxidation reaction. Comparing to the VOx/Al2O3 catalyst, stronger Br?nsted acid site on the acid-treated VOx/Al2O3 catalyst results in higher selectivity for dimethoxymethane, while the base-treated VOx/Al2O3 catalyst without Br?nsted acid site gives rise to formate instead of dimethoxymethane.

Related Dissertations

  1. Study on the Preparation of Biodiesel from Fried Oil with Supercritical Methanol,TE667
  2. Multi-walled Carbon Nanotubes Au _AT_ of Pt, Au _AT_ of Pd core-shell structure of the catalyst preparation and electrochemical properties of,O643.36
  3. Pt -based catalysts of direct methanol fuel cells,TM911.4
  4. Direct Oxidation of Primary Alcohols to Methyl Esters Catalyzed by Nano-Au/SBA-16 Catalyst,TQ225.241
  5. Effects of Methanol Application on the Growth of the Radish (Raphanus Sativus), and Host Preference and Damage by Plutella Xylosterra, Phyllotreta Striolata, Myzus Persicae, and Liriomyza Sativae to Methanol-Treated Radish,S436.31
  6. Nano Pt / SiC Preparation, Characterization and Electrochemical Catalytic Performance,TM911.4
  7. Qinghai Oilfield grid refining 300,000 tons of methanol project evaluation,F426.72
  8. Study on Influential Factor to Methane Metabolic of Methane-utilizing Bacteria and Methoanol Detection Method,Q93
  9. Synthesis and Modification of SAPO-34 Molecular Sieve Catalyst for Methanol-to-Olefin Reaction,TQ221.2
  10. Simulation and Emulation of Methanol Distillation Process in Large-scale Coal Chemical Industry,TQ223.121
  11. Simulation and Analysis of Methanol Production in Coal Chemical Industry,TQ223.121
  12. Design and Synthesis of Novel Planar Chiral N-Containing Nucleophilic Catalysts and Their Applciations in Asymmertric Reaction,O643.36
  13. Data Rectification Technical Based on SV Regression for Methanol Synthesis Unit,TP18
  14. Experimental Study on Performance and Emissions Characteristics of CI Engine Operated with Methanol/DME Dual-Fuel,TK428.9
  15. An Experimental Study on the Combustion and Exhaust Emissions of Engine Fueled with DME/Methanol Blended Fuel,TK421
  16. Instrument-to-Instrument Calibration Transfer and Standardization of Spectra,O657.33
  17. Based on the principle of suction air -breathing direct methanol fuel cell three-dimensional numerical simulation,TM911.4
  18. Using ReaxFF reactive molecular dynamics study acidic ZSM-5 type zeolite catalyzed methanol to olefins process,TQ203.2
  19. Density Functional Theory Studies of the Interaction between Gold Cluster and Organic Molecules,O561
  20. Study on Bactrial Cellulose Production Using Methanol Wastewater,X783
  21. Experimental study on Jatropha biodiesel,TE667

CLC: > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > Chemical kinetics,catalysis > Catalytic > Catalytic reaction
© 2012 www.DissertationTopic.Net  Mobile