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Fabrication and Characterization of Nickel-Cobalt Catalyst by One-pot Combustion Synthesis Method for Synthesis Gas Production in Dry Reforming Methane Process

Babaei, Mojtaba | 2022

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 55367 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Sadrnezhad, Khatiboleslam
  7. Abstract:
  8. Dry reforming methane is a process during which two greenhouse gases, CH4 and CO2, using Ni-based catalysts, are altered into valuable H2 and CO gases, which are very useful from an economic and environmental point of view. The main problem with Ni-based catalysts is the formation of carbon in the dry methane reforming, which leads to rapid deactivation of the catalyst. In this research, a 10Ni-5Co/Al2O3 bimetallic catalyst was prepared by one-pot microwave-assisted combustion synthesis with a stoichiometric amount of fuel (urea) and without the use of additives. The catalyst was then calcined for 12 h at 550oC. The structure, chemical composition, particle distribution, and morphology of the catalyst surface were characterized by X-ray diffraction (XRD), energy dispersive X-ray (EDX-Dot mapping), and field emission scanning electron microscopy (FESEM) analysis. The textural and reducibility properties of the catalyst were also investigated using BET-BJH and temperature programmed reduction (TPR-H2) analysis. The XRD results of the synthesized catalyst showed the formation of NiAl2O4 and CoAl2O4 spinel phases with low and wide intensity peaks, which meant strong metal-support interaction of the catalyst. FESEM and EDX-Dot mapping images showed plate-like morphology without agglomeration, with high dispersion and small particle sizes of Ni and Co. The specific surface area of the synthesized catalyst was 49 m2 g-1. The TPR-H2 profile showed very high reducibility. In order to evaluate the catalytic performance, the stability test of dry methane reforming was performed at 700 °C, atmosphere pressure, CO2/CH4 = 0.8/1, GHSV = 1.8 × 104 mL g-1 h-1 for 900 min (15 h). The results of the catalyst stability test recorded 70% CH4 conversion, 94% CO2 conversion, and a 1.3 H2/CO molar ratio, and its diagrams showed high stability. The amount of carbon deposited on the spent catalyst was determined by thermogravimetric analysis (TG-DTG). According to the results of the TG-DTG test, the carbon deposition rate was about 9.28 mg(carbon) /g(catalyst) h. The XRD pattern also showed the presence of active metal phases of Ni0, Co0 and a carbon crystal phase with a hexagonal structure (Graphite). Also, using the Scherer’ equation, the average carbon crystal size was determined to be about 20.7 nm. According to FESEM images, the carbon formed on the catalyst was filamentous (Whisker). EDX-Dot mapping images also showed the formation of small amounts of carbon. In these images, no trace of agglomeration of Ni and Co particles was observed, and fine and dispersed particles were located on the base surface of the catalyst
  9. Keywords:
  10. Catalyst Deactivation ; Nickel Aluminate Spinel ; Aqueous Combustion Synthesis ; Nickel-Cobalt Alloy ; Microwave Assisted Synthesis ; Dry Reforming ; Methane ; Coke-Resistance

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