Browsing by Author "Malatji, Peter"

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    Development of bimetallic Pd-Zn catalysts for methanol steam reforming: hydrogen production for fuel cells
    (2015) Xalabile, Philasande; Fletcher, Jack; Luchters, Niels; Malatji, Peter
    Proton exchange membrane fuel cell (PEMFC) has been reported as clean and efficient energy technology from conversion of H₂. However, one of the main challenges remains the storage and transport of hydrogen. The promising alternative is to produce H₂ on site by a reformer using a H₂-dense liquid as a fuel, a technology known as fuel processing. Methanol is an attractive source of H₂ compared to other fuels as it presents several advantages, i.e. it is obtained sulphur-free, has a high H to C ratio and therefore produces a H₂-rich reformate, can be reformed at low temperatures (200 - 300°C) and is a liquid at ambient conditions so that it can be easily handled. Typically, Cu-based catalysts are used for steam reforming of methanol due to their high activity (i.e. H₂ production) and high selectivity towards CO₂. As CO poisons anodic catalyst of PEMFC, high selectivity towards CO₂ is crucial so as to eliminate or at least minimize CO removal load downstream a fuel processor. However, Cubased catalysts are thermally unstable and suffer deactivation due to sintering at high temperatures (> 250°C). Moreover, Cu-based catalysts are pyrophoric and therefore difficult to handle. Recent studies show that PdZn catalysts are very promising as they exhibit comparable activity and selectivity to Cu-based ones. Furthermore, PdZn catalysts are thermally stable in the typically methanol steam reforming temperature range (200 - 300°C). Most literature attributes high CO₂ selectivity of PdZn catalysts to formation of PdZn alloy. It is generally agreed that PdZn alloy is formed when PdZn catalysts are reduced in H₂ at high temperatures (> 250°C). In this work, a Pd/ZnO catalyst aimed at 2.5 wt% Pd was successfully prepared via incipient wetness impregnation and the duplicate preparation of the catalyst was successful. Both impregnation catalysts were confirmed by ICP-OES to contain similar weight Pd loadings i.e. 2.8 and 2.7 wt%, respectively. The actual Pd loading (ICP-OES) was slightly higher than the target loading (2.5 wt%) due to Pd content of Pd salt underestimated during catalyst preparation. Furthermore, crystallite size distribution, i.e. PdO crystallites on ZnO support, was similar (i.e. 6.7 ± 2.4 nm and 6.3 ± 1.9 nm) for both impregnation catalysts.
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    Ferrocenyl derivatives of dithizone : photochromic properties and potential as electrochemical sensors
    (2008) Malatji, Peter; Hutton, Alan T.
    New ferrocenyl derivatives of dithizone were successfully prepared and characterised by various analytical techniques. In the first part of this project interactions between photochromic and redox properties were investigated for the new ferrocenylmercury dithizonate complexes (N,S-dithizonato )(ferrocenyl)mercury(II) (11) and (ferrocene-l, 1'- diyl)bis[(N,S-dithizonato)mercury(II)] (12). UV-Vis spectroscopy showed that these complexes exhibited similar photochromic behaviour to related compounds known in the literature, i.e., a change in colour from orange to blue upon irradiation of organic solutions with visible light. The molar extinction coefficient of compound (12) was almost double that of compound (11), indicating that there are two chromophores absorbing in compound (12) compared to one in compound (11). Cyclic voltammetry on acetonitrile solutions of these photochromic compounds showed no noticeable differences in the voltammograms for the activated blue form compared to the normal orange form when irradiated with sunlight. This suggests that the interactions between the redoxactive group and the changes in the conformation of the photochromic group were not significant enough to make any noticeable changes to the voltammetric behaviour. In the second part of this project the electrochemical recognition of various metal ions by the new ligands S-ferrocenyldithizone (13) and S-ferrocenylmethyldithizone (14) was investigated. In both compounds the transducer is the ferrocenyl substituent and the binding site is the formazan group. These receptors showed a reversible redox wave in acetonitrile assigned to the ferrocene/ferrocenium couple: for receptor (13), E1I2 = 203 mV and for receptor (14), E1I2 = 136 mV relative to ferrocene as a standard reference. Addition of Cu2 + ions to ligand solutions in acetonitrile showed contrasting behaviour: ligand (13) produced a new wave with shift in E1I2 from 203 to 387 mV (M1I2 = 184 mY). For receptor (14), titration with Cu2 + ions resulted in a continuous shift of the EI/2 of the original receptor from 136 mV up to a maximum of 180 mV (MlI2= 44 mY). It was discovered that the formazan binding site of the receptor was likely oxidised by Cu2 + ions to form a tetrazolium salt, and this was proven from the product obtained during the attempted synthesis of a receptor(13)-Cu2 + complex: the product obtained was detennined crystallographically to be 5-ferrocenylthio-2,3-diphenyltetrazolium perchlorate. On the other hand, upon addition of PhHg+ to a solution of receptor (13) a new wave with M1/2 = 177 m V was observed resulting from the formation of a receptormetal complex, while addition of this organomercury ion to a solution of receptor (14) resulted in the continuous shift of the original receptor wave up to a maximum of M1/2 = 32 mY. No binding was observed when receptor (13) was titrated wi1h Ni2 + ions; when receptor (14) was titrated with this metal ion a gradual shift of the ferrocenyl wave up to a maximum of M,1/2 = 39 mV was obtained. Large potential shifts were observed when the receptor (13) was titrated with various metal ions compared to small potential shifts which were observed during titration experiments with receptor (14). The methylene link present in receptor (14) increased the distance between the binding site and the transducer, decreasing the interaction between the binding events and the transducer. The electronic communication between the transducer and the metal ions during titration of receptor (13) with metal ions is most likely a combination of through-space and throughbond interaction, while through-space communication seems likely for receptor (14). Synthesis of several receptor-metal complexes was attempted in order to elucidate the coordination mode of the ligand with the metal ion; however, no solid compound was successfully isolated. In addition, the data obtained from cyclic voltammetry did not allow confinnation of reliable receptor : metal ratios, thus unambiguous coordination modes for the receptor-metal complexes could not be specified. The possible application in bio-electrochemistry of the new compound (13) in its oxidized form as the tetrazolium salt (5-ferrocenylthio-2,3-diphenyltetrazolium perchlorate) has also been recognized and preliminary experiments were conducted.
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    Studies towards degradable polymers new zinc (II) and palladium (II) complexes as catalysts for lactide polymerization and carbon monoxide
    (2012) Malatji, Peter
    In this study a range of new zinc and palladium complexes were synthesized, characterized and used in the production of degradable polymers. Zinc complexes were used for the production of polylactides (PLAs) functionalized with a drug candidate on a polymer tail. These functionalized polymers displayed slow drug release properties under physiological conditions. Palladium complexes were utilized for the production of a photodegradable CO/styrene copolymer (CP) which was subsequently reacted with lactide to form a new poly(lactide-co-CO/styrene) block copolymer.