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KOÇ UNIVERSITY

GRADUATE SCHOOL OF SCIENCES & ENGINEERING

CHEMICAL AND BIOLOGICAL ENGINEERING

MS THESIS DEFENSE BY ÖZGE AKARÇAY

 

Title: Utilization of MOF Derived Highly Dispersed Fe-Based Catalyst in Ammonia Decomposition Reaction

 

Speaker: Özge Akarçay

 

Time: 14.09.18, 10:00

 

Place: ENG 208

Koç University

Rumeli Feneri Yolu

Sariyer, Istanbul

 

Thesis Committee Members:

Assoc. Prof. Alper Uzun (Advisor, Koç University)

Assoc. Prof. Seda Keskin (Koç University)

Assoc. Prof. Görkem Günbaş (Middle East Technical University)

 

Abstract:

Hydrogen is a clean energy supplier for fuel cell applications. The applicability of fuel cell systems is limited because of the storage and transportation problems of hydrogen. Instead of direct storage, using hydrogen containing materials which can be stored easier compared to pure H2 is a promising approach. Ammonia is one of the candidates thanks to its high volumetric and gravimetric energy density. Ru-based catalysts are best performing ones for ammonia decomposition to produce hydrogen. Their high cost and low abundance limit their commercial usage. Because they are cheap and abundant, Fe-based catalysts are good alternatives to Ru-based ones. However, synthesis of highly dispersed iron catalyst at very high metal loadings is very challenging, because iron tends to sinter quickly to form large nanoparticles. In this respect, using metal organic frameworks (MOFs) as catalyst precursors can offer broad advantages.

MOFs are highly porous materials containing high metal content connected with organic linkers. Their decomposition under controlled environment allows to synthesize various functional materials such as carbon or carbon supported metal nanoparticles with very high metal loadings as these parent materials includes a high metal content.

In this thesis, a serious of Fe-BTC (iron 1, 3, 5- benzene tricarboxylic acid) derived carbon-supported Fe catalysts were synthesized by the pyrolysis under N2 and the resulting catalysts were tested for ammonia decomposition reaction. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) characterization results show that Fe nanoparticle size increases, as the pyrolysis temperature increases. Results further illustrated that these changes in the pyrolysis temperature also modify the surface characteristics of the support. Accordingly, there is a linear relationship (R2 = 0.97) between the graphitic characteristics of the support and the pyrolysis temperature. For the ammonia decomposition reaction, catalysts with small nanoparticle size and high graphitic degree showed a high catalytic activity at 500 °C. Accordingly, at a space velocity of 3000 cm3 NH3 h-1 gcat-1, ammonia conversion was 85.5%, corresponding to a hydrogen production rate of 2.6 mmol H2/gcat/min. These results are among the best performing iron-based catalysts thanks to the high metal dispersion achieved at a relatively high metal loading, exceeding 34 wt%, and a high graphitic degree of the support. Results also illustrate the broad potential of utilizing MOFs as catalysts precursors offering opportunities for obtaining highly dispersed supported metal catalysts at very high metal loadings. Besides, being able to tune the surface characteristics of the carbon support provides additional advantages in the way of optimizing the structure of the active species for high performance.

 

 

 

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