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Preparation, Evaluation and Investigation of NiO-MgO-SiO2 Catalyst Deactivation in Propane Reforming

Barzegari, Fatemeh | 2021

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 53901 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Frahadi, Fathollah; Kazemeini, Mohammad; Rezaei, Mehran; Keshavarz, Ahmad Reza
  7. Abstract:
  8. Synthesis gas (H2, CO) is widely used in chemical and petrochemical industries, utilized for methanol and ammonia production. Hydrogen is the main component of syngas which is considered as an appropriate alternative for fossil fuels. Catalytic steam reforming is one of the most common and economical pathway for syngas production. Light hydrocarbons such as propane which can easily be transported, stored and distributed, is a promising feed candidate for steam reforming. Catalyst deactivation along with low stability resulting from carbon formation and sintering is one of the main crucial problems in this process, leading to much research on the preparation of stable and coke resistant catalysts. In this study, in order to achieve an active and coke resistant catalyst, meso-structured Ni catalysts supported on MgO-SiO2 were examined. The catalysts were synthesized via co-precipitation-hydrothermal method and the effect of synthesis parameters including hydrothermal temperature, hydrothermal time, pH and calcination temperature on the specific surface area was studied and the optimum values were reported. The maximum specific surface area of 740 m2/g and average pore size of 3.6 nm was obtained by the sample synthesized under pH=9 and exposed to the hydrothermal treatment for 7h at 200ºC. Besides, increasing the calcination temperature from 500 to 800ºC decreased the catalyst reducibility, activity and the amount of deposited coke. In the next step, NiO-MgO-SiO2 catalysts with different nickel oxide loadings (5, 10, 15 and 20 wt. %) were developed and evaluated during propane steam reforming. The obtained results revealed that 15wt.% NiO loading possessed the highest activity (98% propane conversion and 46% hydrogen yield at 550°C) owning to the high surface area (619 m2/g), suitable reducibility and sufficient active sites. Furthermore, the influence of operating parameters including GHSV, S/C and reduction temperature on the catalytic performance was evaluated. Increasing the reduction temperature up to 550°C, improved the active phase dispersion (8.8%) and catalytic activity, while the higher reduction temperatures led to the agglomeration of active species with lower activity. Afterwards, the influence of MgO to SiO2 on the structural properties, reducibility and catalytic activity was investigated. The obtained results revealed that, the synergic effect of MgO and SiO2 enhanced the BET surface area and metal-support interaction. Moreover, the basic characteristic improved as the MgO content increased. The highest activity (69% propane conversion at 550°C) along with the lowest amount of coke deposition were observed over the NiO-0.5MgO-SiO2. This observation can be assigned to its high surface area (691 m2/g) as well as appropriate reducibility and basic characteristic. Furthermore, the effect of various promotes including Ce, La, Zr and Y on the catalyst resistance against coke deposition was studied. The promoted catalysts possessed lower surface area, pore volume and less reducibility, in comparison to the un-promoted one. The highest and lowest amount of deposited carbon were observed over the promoted catalyst with Zr and La, respectively. Finally, The effect of various La2O3 loading (1.5, 3, 4.5 and 6 wt. %) on the physio-chemical properties and catalytic performance was studied.1.5 wt. % La2O3 loading covered the active sites followed by decreasing the catalyst activity, while the highest dispersion (15.8%) and lowest nickel particle size () was observed over 3 wt. % La2O3 content. The optimum value for La loading was reported to be 3 wt. %, which resulted in the lowest amount of coke deposition (0.06 gcarbon/gcat) under reaction condition. In conclusion, the catalyst containing 15 wt. % NiO, 3 wt. % La2O3 supported on magnesium silicate (MgO/SiO2=0.5) defined as the superior catalyst, which yields the highest activity and lowest amount of deposited carbon
  9. Keywords:
  10. Synthesis Gas ; Solid Solution ; Steam Reforming ; Propane ; Synthesis Gas Production ; Coke Formation

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