| dc.description.abstract | Convectional hydrogen (H2) production process such as steam methane reforming process (SMR) produces massive amounts of CO2 (i.e., 13.7 kg CO2 per kg H2 production). Because of the large amount of CO2 production during the process, it is questionable whether H2 can be considered as a clean fuel. Besides, H2 is the main ingredient of ammonia production process, and ammonia is the second highest chemical all over the world based on quantity production per year. In order to solve this issue, hydrogen either needs to be produced from water electrolysis or CO2 needs to be captured without releasing to the atmosphere. Water electrolysis process requires a large amount of energy for the water splitting process and CO2 capturing could be capital intensive. However, the most promising process, thermocatalytic decomposition (TCD) of methane, provides several benefits those include but not limited to i) provide a more straightforward path for hydrogen production, ii) eliminate COx production, and iii) reduce production costs.
In the present study, six catalysts (Zeolite Socony Mobil-5 (ZSM-5), 3% Ruthenium (Ru) doped ZSM-5 (Ru-ZSM-5), activated carbon (AC) (commercial), 3% Ru doped AC (Ru-AC), and biochars (chemically activated (KOH) biochar and heat treated biochar) were used for TCD of methane at 800 oC and atmospheric pressure in a fixed bed reactor. Two different feed flow rates (0.1 and 0.4 WHSV (weight hourly space velocity: total mass flow rate of reactants divided by total mass of catalyst in the reactor)) were used to examine catalytic behavior in this thesis. XRD (Powder X-ray Diffraction) analysis, TPR (Temperature Programmed Reduction) analysis, surface area, pore volume and pore size distributions analysis, chemisorption, elemental analysis, TGA (Thermogravimetric Analysis), SEM and EDS (Scanning Electron Microscope and Energy Dispersive X-ray spectroscopy) analysis were performed to characterize these catalysts. From the reaction results, it is evident that 3% Ru enhanced the activity of ZSM-5 and AC. Pure ZSM-5 exhibited 20% and 10% conversion at 0.1 and 0.4 WHSV, respectively. These conversions increased to 40% and 26% at 0.1 and 0.4 WHSV, respectively when Ru-ZSM-5 catalyst was used. AC exhibited 51% and 35% conversion at 0.1 and 0.4 WHSV, respectively, whereas Ru-AC exhibited 73% and 61% conversion for the same flow rates. HB (heat-treated biochar) exhibited 41% and 29% conversion for 0.1 and 0.4 WHSV, respectively. On the other hand, AB (activated biochar) exhibited 69% and 59% conversion for the same flow rates. Among six different catalysts, Ru-AC and AB displayed highest conversions. Therefore, both of catalysts were tested for the catalytic stability over the long run (60 h) at 800 oC and 0.1 WHSV. Ru-AC achieved 21% conversion, whereas AB displayed 51% conversion after 60 h of reaction time. Carbon produced in reactions were analyzed using scanning and transmission electron microscope. All of the catalysts showed production of carbon nano-tubes (CNTs) except with the use of AC. From all of the results, it can be concluded that Douglas fir biomass-derived catalysts have great potentials to be used as catalysts for thermocatalytic decomposition of methane to produce COx-free hydrogen. | en_US |
