Date

2016

Author

Ağca, Can

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Climate change and more efficient energy system research have directed researchers to fuel cells related fields. There is much interest in onboard fuel cell vehicles nowadays. Polymer electrolyte membrane fuel cells (PEMFC) are very widely used and commercial onboard systems are readily on sale. Rather than pressurized hydrogen, much safer liquid hydrogen feedstock such as methanol and ethanol are being used. However, fuel cell’s platinum catalyst requires low amounts of carbon monoxide in the cell feed. This study focuses on new reaction types and catalyst syntheses that can produce low amounts of CO. Formaldehyde steam reforming (FSR) is thought to be producing syngas having low amount of CO compatible with the PEMFC at low temperatures. As support materials SBA-15 synthesized by hydrothermal method and CMK-3 synthesized by nanocasting were used. 18 wt. % of metal loading to SBA-15 and CMK-3 mesoporous supports was performed by wet impregnation method. Their chemical and physical properties were investigated by XRD, N2 physisorption, XPS, ICP, SEM, TGA and FTIR. CuZn/SBA-15, Cu/SBA-15 and CuZn/CMK-3 had BET surface areas of 381 m2/g, 394 m2/g, and 548 m2/g, respectively. Pore diameters were 4.80 nm for both CuZn/SBA-15 and Cu/SBA-15, and 3.86 nm for CuZn/CMK-3. The behavior of CuZn/SBA-15 and Cu/SBA-15 catalysts resembled Type IV isotherm behavior with H1 type hysteresis loop. On the other hand, CuZn/CMK-3 showed Type IV isotherm with H2 hysteresis loop. Crystal size of copper increased after activity tests. All the synthesized catalysts had acid sites in their structure except the CuZn/CMK-3 catalyst. A commercial copper based catalyst’s (HIFUEL R120) activity was tested by a fixed-bed flow reactor system between 175-250°C. Other three synthesized catalysts were tested only at 250°C. HIFUEL R-120 converted formaldehyde 100 % at even low temperatures. Hydrogen yield increased with increasing temperature and reached to its maximum theoretical value at 250°C. Furthermore, CO was not formed, except for startups at 225 and 250°C in the presence of HIFUEL R-120 catalyst. These traits show the suitability of the catalyst and reaction for PEMFC applications. Cu/SBA-15 was also found the most active one among the synthesized catalysts. However, it lost its activity fast over time due to instability. Zn addition was found to increase stability of catalyst and dispersion of copper efficiently with less crystal size as in the CuZn/SBA-15 catalyst. Zn addition to Cu/SBA-15 was also found to increase the acidity of the catalyst. CuZn/CMK-3 had stability, but had also insufficient activity for methanol and formaldehyde steam reforming due to lack of acidic properties. The synthesized catalysts did not produce any CO. They all are also suitable for PEMFC systems. In the activity tests of FSR reactions, HIFUEL R-120 resulted in the most successful in terms of overall and methanol conversion, product selectivity and hydrogen yield amongst all the tested catalysts.

Subject Keywords

Formaldehyde., Hydrogen., Catalysts., Steam., Copper., Zinc.

URI

http://etd.lib.metu.edu.tr/upload/12620226/index.pdf
https://hdl.handle.net/11511/25880

Collections

Graduate School of Natural and Applied Sciences, Thesis