To design the ideal water oxidation catalyst, understanding of the catalytic mechanism and decomposition pathways is essential. The aim of the research described in this thesis is to provide... Show moreTo design the ideal water oxidation catalyst, understanding of the catalytic mechanism and decomposition pathways is essential. The aim of the research described in this thesis is to provide mechanistic insight on the water oxidation reaction catalyzed by homogeneous electrocatalysts and topostulate design criteria for the ideal water oxidation catalyst. Show less
Nitrate reduction on Sn-modified polycrystalline Pt has been investigated. NO is the main product at high Sn coverage, whereas N2O is dominant at low Sn coverage. The N2O reduction on Sn-modified... Show moreNitrate reduction on Sn-modified polycrystalline Pt has been investigated. NO is the main product at high Sn coverage, whereas N2O is dominant at low Sn coverage. The N2O reduction on Sn-modified Pt electrodes indicates electrochemical formation of N2 is related to pristine Pt sites. Moreover, homogeneous chemical reactions of intermediates products also contribute to N2O and N2 formation of in solution. The p-block metals have been studied: Cd, In and Sn show a promoting effect; Ga shows a limited enhancement; Tl shows a special promoting effect in sulfuric acid; Pb shows a weak formation of N2O. Density Functional Theory calculations show that Sn and In enhance nitrate adsorption compared with pristine Pt. Moreover, ammonia is found as the only product on Pt. After modification by Sn, hydroxylamine is specifically found with nitrite, which supports that nitrate reduction to nitrite is enhanced by Sn and Sn could steer the hydrogenation of NOads. However, solution pH is an important factor. On Pt, nitrate reduction is only observed in acidic solution. On Rh, a higher activity is observed in wide pH, which suggests a mechanism that HNO3 molecule is the active species. However, Rh additionally shows a special ability to reduce NO3- directly. Show less
This project has dealt with the mechanistic study of the electrocatalytic nitrite reduction, the selectivity-determining step of nitrate reduction. Nitrate is a polluting ion targeted by wastewater... Show moreThis project has dealt with the mechanistic study of the electrocatalytic nitrite reduction, the selectivity-determining step of nitrate reduction. Nitrate is a polluting ion targeted by wastewater remediation; electrochemistry strives to achieve selectivity to harmless products (N2). A multi-pronged approach has been followed, aimed at establishing the influence of several variables (electrocatalyst material, surface structure, pH and electrode potential) on the catalytic activity and the product distribution, which has been determined with in situ analytical techniques (mass spectrometry and infrared spectroscopy). The molecular underpinnings of nitrite reduction have thereby been unravelled for transition metals, showing that an optimal catalytic performance is achieved when metals intermediate affinities to reaction intermediates (Sabatier Principle). The all-important concept of structure sensitivity also applies to nitrite reduction at Pt electrodes, although only in alkaline media: a Pt(100) single-crystal is the sole Pt surface able to achieve the desired direct conversion of nitrite into 100% N2. Such selectivity is unparalleled for a simple monometallic surface and is an outstanding finding. Additionally, the nitrite-reducing performance of bio-inspired catalysts, (electroactive metalloporphyrins) was investigated. A further side-project of this PhD thesis has also been the electrochemical characterization of preferentially-oriented cuboid Pt nanoparticles synthesized with the innovative __cathodic corrosion__. Show less
The thesis contains work on the catalytic mechanism, and then especially on the reversibility of the reaction and the order of substrate addition and reduction of the catalytically active type-2... Show moreThe thesis contains work on the catalytic mechanism, and then especially on the reversibility of the reaction and the order of substrate addition and reduction of the catalytically active type-2 copper site. Furthermore, protein engineering of the type-1 copper site is reported and a study into the reorganizational energy of this site. Show less
Wat begonnen is als een zoektocht naar katalysatoren voor schone oxidatieprocessen is ge_indigd met de vondst van een onverwachte moleculaire magneet. Het onderzoek naar verbindingen van de metalen... Show moreWat begonnen is als een zoektocht naar katalysatoren voor schone oxidatieprocessen is ge_indigd met de vondst van een onverwachte moleculaire magneet. Het onderzoek naar verbindingen van de metalen mangaan en ijzer wordt sterk gestimuleerd door een groot scala aan mogelijke toepassingen van deze verbindingen, waaronder de toepassing als selectieve oxidatiekatalysatoren (bijvoorbeeld te gebruiken in wasmiddelen) en als moleculaire magneten. De Indiase Meenal Godbole promoveert op 12 januari 2006 bij het Leids Instituut voor Chemisch onderzoek op de resultaten van haar speurtocht naar nieuwe oxidatiekatalysatoren. De gevonden oxidatiekatalysatoren zijn weliswaar actief en veelbelovend, maar nog niet goed genoeg voor industri_le toepassing. Ook is er grote vooruitgang geboekt in het begrip van de werking van de katalysatoren. Tijdens haar onderzoek aan zulke nieuwe katalysatoren heeft mw. Godbole min of meer bij toeval ook een nieuwe cluster opgebouwd uit mangaan gemaakt die bij heel lage temperatuur magnetisch is. Grote inspanningen worden wereldwijd verricht in de ontwikkeling van nieuwe materialen die clusters van metalen bevatten. De uitkomst van dit onderzoek zal leiden tot de ontdekking van andere nieuwe moleculaire magneten, die een mogelijke toepassing kunnen vinden in bijvoorbeeld dataopslag in computers. Show less
