Synthesis of 2-iodomethylene-2,3-dihydro-1,4-oxazepine derivatives

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2014
Çakal, Deniz
In this thesis, platinum nanoparticles were prepared by using PtCl4 as a starting material, sodium borohydride (Group I), hydrazine (Group II) and formaldehyde (Group III) as reducing agents and hexylamine (Group -a), N-methylhexylamine (Group -b), N,N-dimethylhexylamine (Group -c) as surfactants (the last two surfactants were used for the first time). These platinum nanoparticles were dispersed on Carbon XC-72 to be utilized as catalyst for methanol oxidation reaction which can be used in direct methanol fuel cells. The characterization, electrochemical properties and performance of catalysts were defined by using inductively coupled plasma spectroscopy (ICP), cyclic voltametry (CV), chronoamperometry (CA), X-ray diffraction (XRD), X-photoelectron Spectroscopy (XPS), transmission electron microscopy (TEM), BET surface area analysis and fourier transform infrared spectroscopy (FTIR). XRD and TEM results indicated that platinum crystallizes in face-centered cubic (fcc) structure with a size of ~5 nm. In addition to these small particles, agglomerated particles were also observed in different size, shape and density. In Group I, cubic platinum nanoparticles come together to form large particles with a size of 20 - 200 nm. In Group II, agglomerated particles were appeared to be dense, large and spherical lumps with a size of 50 - 200 nm. In Group III, the agglomerated particles were also formed in spherical shape but not as much dense and large (50 - 150 nm) as in Group II. XPS results revealed that there are two different oxidation states of platinum in each catalyst. These are Pt(0) and Pt(IV) and their percentages changes between 65 - 73 and 35 - 27, respectively. XPS data also showed the existence of two kinds of oxygen, HOads and H2Oads, with a ratio of 85:15, 90:10 and 80:20 for Group I, II and III, respectively. BET analyses indicated that the surface area of catalysts depends on reducing agent not surfactant. It was 30 - 35 m2/g, 4 - 9 m2/g and 20 - 30 m2/g for Group I, II and III, respectively. CV records demonstrated that the order of catalysts performance was Group II < Group I < Group III. Within all catalysts, Catalyst IIIb exhibited the highest performance (258 mA/mg Pt) towards methanol oxidation reaction and provided 3.5 times greater performance than the commercial E-TEK Pt catalyst. All these data indicated that the performance of these catalysts depends on: a) active surface area, b) HOads/ H2Oads ratio, and c) morphology of the catalysts.
Citation Formats
D. Çakal, “Synthesis of 2-iodomethylene-2,3-dihydro-1,4-oxazepine derivatives,” M.S. - Master of Science, Middle East Technical University, 2014.