國立高雄大學圖資館 |

Photocatalytic Reforming of Poly-Alcohols Over Pt/TiO2 for the Production of H2 and Value-Added Chemicals /

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Photocatalytic Reforming of Poly-Alcohols Over Pt/TiO₂ for the Production of H₂ and Value-Added Chemicals /Luke M Roebuck.
作者:	Roebuck, Luke M.,
面頁冊數:	1 electronic resource (221 pages)
附註:	Source: Dissertations Abstracts International, Volume: 87-04, Section: B.
附註:	Advisors: Falkowska, Marta; Fan, Xiaolei; Hardacre, Christopher.
Contained By:	Dissertations Abstracts International87-04B.
標題:	Biodiesel fuels.
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=32293348
ISBN:	9798297674899

Photocatalytic Reforming of Poly-Alcohols Over Pt/TiO2 for the Production of H2 and Value-Added Chemicals /
Roebuck, Luke M.,

Photocatalytic Reforming of Poly-Alcohols Over Pt/TiO2 for the Production of H2 and Value-Added Chemicals /Luke M Roebuck. - 1 electronic resource (221 pages)

Source: Dissertations Abstracts International, Volume: 87-04, Section: B.

Photocatalytic reforming (photoreforming) involves the reduction of water to H2 enabled by the simultaneous oxidation of an organic hole scavenger over semiconductor photocatalysts. The feasibility and green credentials of this hydrogen production strongly depend on the nature of the organic hole scavenger. Ideally renewable feedstocks are used, and this is the primary focus of this thesis. If biomass derived substrates are used, the technology can be close to carbon-neutral as any CO2 produced originated from the atmosphere prior to photosynthesis by plants. Furthermore, if full oxidation to CO2 can be inhibited with the selective oxidation of the hole scavenger to valuable chemical products, then the technology could potentially be carbon-negative. The production of value-added chemical products could also off-set part of the selling cost of the hydrogen, further enhancing the economic viability of this technology. Photoreforming could also be used as a method for the conversion of waste materials such as polymer waste with simultaneous production of H2 .The mechanism of H2 production from ethylene glycol as a model compound for photoreforming over platinised TiO2 is presented with particular focus on the effect of the TiO2 polymorph. It was found that Pt/anatase and Pt/anatase:rutile (P25) had similar H2 production activities and both catalysts followed an indirect oxidation pathway where ethylene glycol was oxidised via hydroxyl radicals to glycolaldehyde. In contrast, Pt/rutile primarily oxidised ethylene glycol directly into formaldehyde. The formaldehyde was unable to react further, which significantly reduced the formation of hydrogen despite similar conversion of ethylene glycol compared with the other supports used. We propose that these differences are due to different adsorption behaviour and hole transfer mechanism on the different TiO2 crystalline phases. In particular, ethylene glycol complexation on Ti5c sites on the dominant (110) facet of rutile leads to a direct hole transfer and an oxidative C-C cleavage mechanism prevailing. To prove this effect, rutile nanorods were prepared with a high degree exposed (110) facets. Indeed these nanorods were found to increase C-C cleavage over a range of substrates bearing vicinal diol groups. Notably, these nanorods were found to give a two-fold increase in hydrogen production from glucose photoreforming versus non-shape specific anatase or rutile. Stereochemical effects were also found in these reactions. Using 2,3-butanediol the 2S,3R- stereoisomer was converted at a much slower rate (13%) to the glycol cleavage product acetaldehyde than the 2S,3S- and 2R,3R- isomers (both 29%). Similar effects were found with 1,2-cyclopentanediol where the trans -isomer was converted at twice the rate and selectivity to glutaraldehyde compared to the cis-isomerIt was observed that in mixed phase TiO2 that there was often an in-homogenous dispersion of Pt nanoparticles. Electron microscopy and electron energy-loss spectroscopy was used to map metal nanoparticle density on P25 and similar TiO2 materials as a function of the supporting crystal phase. It was found that metal nanoparticles typically prefer to sit on rutile crystallites, which form the minority (~15 wt.%) of the P25 mixture. Our study includes a range of platinum on titania (Pt/TiO2 ) materials synthesised by wet impregnation with 0.2 wt.% Pt and shows that the rutile preference is robust to synthesis parameters such as reduction temperature and Pt precursor solution. These results suggest that Pt/rutile segregation may be more common than suggested in the literature, with important implications for material efficiency in Pt/TiO2 catalysts.The use of waste polyethylene terephthalate as a photoreforming substrate has been previously investigated, however its insolubility in aqueous media and the resistance of the aromatic terephthalate towards conversion are major obstacles. Commonly an alkaline pretreatment step is used to initiate hydrolysis to ethylene glycol and terephthalic acid which promotes H2 evolution. However, in this work we have found that terephthalic acid has both promotional and inhibitory effects by modification of the catalyst surface that depend on the relative concentration of ethylene glycol. Terephthalic acid inhibits the oxidation reactions by scavenging hydroxyl radicals and blocking complexation sites. This leads to lower H2 evolution compared to the photoreforming of an equivalent concentration of ethylene glycol. Even in trace amounts, terephthalic acid would still inhibit the reaction unless the concentration of ethylene glycol was high enough. Surprisingly, at ethylene glycol concentrations of >1.2 M, residual terephthalic acid promoted the reaction which is thought to be due to increasing the interaction between ethylene glycol and the catalyst surface but also an increased role of water. On the basis of these results, we suggest that, if polyethylene terephthalate is to be used as a feedstock for H2 generation by photoreforming, an initial hydrolysis should be performed after which terephthalic acid is separated for re-use. The remaining hydrolysate may then be used for photoreforming. Furthermore, the ethylene glycol concentration should be maximised in order to overcome the inhibitory effects of residual terephthalic acid.Finally, the concentration dependent structure of ethylene glycol/water mixtures was investigated. Mixtures with concentrations XEG = 1, 0.9, 0.46, 0.11 were investigated by total neutron scattering. The neutron scattering data was then used to constrain molecular dynamics type simulations of the studied systems to allow for in depth analysis of the systems' structures. It was found that at low ethylene glycol concentrations (XEG = 0.11) that water structure was preserved, and ethylene glycol molecules were well hydrated. At the intermediate concentrations (XEG = 0.46) the tetrahedral ordering of water was lost and water molecules existed as interconnected string-like structures. At high concentrations (XEG = 0.9), water molecules are completely isolated mostly existing as single molecules or dimers. This behaviour is in contrast to aqueous mixtures of mono-alcohols such as methanol, isopropanol, t-butanol where water structure can be found to persist even at high alcohol concentrations. Evidence for intra-molecular hydrogen bonding was found at all concentrations, however, became much more significant in the more diluted mixtures. These structural features of the ethylene glycol/water mixtures may explain their cryoprotectant properties as well as other concentration dependent properties.

English

ISBN: 9798297674899Subjects--Topical Terms:

275339
Biodiesel fuels.
Subjects--Index Terms:

Photocatalysts

Photocatalytic Reforming of Poly-Alcohols Over Pt/TiO2 for the Production of H2 and Value-Added Chemicals /
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520 $a Photocatalytic reforming (photoreforming) involves the reduction of water to H2 enabled by the simultaneous oxidation of an organic hole scavenger over semiconductor photocatalysts. The feasibility and green credentials of this hydrogen production strongly depend on the nature of the organic hole scavenger. Ideally renewable feedstocks are used, and this is the primary focus of this thesis. If biomass derived substrates are used, the technology can be close to carbon-neutral as any CO2 produced originated from the atmosphere prior to photosynthesis by plants. Furthermore, if full oxidation to CO2 can be inhibited with the selective oxidation of the hole scavenger to valuable chemical products, then the technology could potentially be carbon-negative. The production of value-added chemical products could also off-set part of the selling cost of the hydrogen, further enhancing the economic viability of this technology. Photoreforming could also be used as a method for the conversion of waste materials such as polymer waste with simultaneous production of H2 .The mechanism of H2 production from ethylene glycol as a model compound for photoreforming over platinised TiO2 is presented with particular focus on the effect of the TiO2 polymorph. It was found that Pt/anatase and Pt/anatase:rutile (P25) had similar H2 production activities and both catalysts followed an indirect oxidation pathway where ethylene glycol was oxidised via hydroxyl radicals to glycolaldehyde. In contrast, Pt/rutile primarily oxidised ethylene glycol directly into formaldehyde. The formaldehyde was unable to react further, which significantly reduced the formation of hydrogen despite similar conversion of ethylene glycol compared with the other supports used. We propose that these differences are due to different adsorption behaviour and hole transfer mechanism on the different TiO2 crystalline phases. In particular, ethylene glycol complexation on Ti5c sites on the dominant (110) facet of rutile leads to a direct hole transfer and an oxidative C-C cleavage mechanism prevailing. To prove this effect, rutile nanorods were prepared with a high degree exposed (110) facets. Indeed these nanorods were found to increase C-C cleavage over a range of substrates bearing vicinal diol groups. Notably, these nanorods were found to give a two-fold increase in hydrogen production from glucose photoreforming versus non-shape specific anatase or rutile. Stereochemical effects were also found in these reactions. Using 2,3-butanediol the 2S,3R- stereoisomer was converted at a much slower rate (13%) to the glycol cleavage product acetaldehyde than the 2S,3S- and 2R,3R- isomers (both 29%). Similar effects were found with 1,2-cyclopentanediol where the trans -isomer was converted at twice the rate and selectivity to glutaraldehyde compared to the cis-isomerIt was observed that in mixed phase TiO2 that there was often an in-homogenous dispersion of Pt nanoparticles. Electron microscopy and electron energy-loss spectroscopy was used to map metal nanoparticle density on P25 and similar TiO2 materials as a function of the supporting crystal phase. It was found that metal nanoparticles typically prefer to sit on rutile crystallites, which form the minority (~15 wt.%) of the P25 mixture. Our study includes a range of platinum on titania (Pt/TiO2 ) materials synthesised by wet impregnation with 0.2 wt.% Pt and shows that the rutile preference is robust to synthesis parameters such as reduction temperature and Pt precursor solution. These results suggest that Pt/rutile segregation may be more common than suggested in the literature, with important implications for material efficiency in Pt/TiO2 catalysts.The use of waste polyethylene terephthalate as a photoreforming substrate has been previously investigated, however its insolubility in aqueous media and the resistance of the aromatic terephthalate towards conversion are major obstacles. Commonly an alkaline pretreatment step is used to initiate hydrolysis to ethylene glycol and terephthalic acid which promotes H2 evolution. However, in this work we have found that terephthalic acid has both promotional and inhibitory effects by modification of the catalyst surface that depend on the relative concentration of ethylene glycol. Terephthalic acid inhibits the oxidation reactions by scavenging hydroxyl radicals and blocking complexation sites. This leads to lower H2 evolution compared to the photoreforming of an equivalent concentration of ethylene glycol. Even in trace amounts, terephthalic acid would still inhibit the reaction unless the concentration of ethylene glycol was high enough. Surprisingly, at ethylene glycol concentrations of >1.2 M, residual terephthalic acid promoted the reaction which is thought to be due to increasing the interaction between ethylene glycol and the catalyst surface but also an increased role of water. On the basis of these results, we suggest that, if polyethylene terephthalate is to be used as a feedstock for H2 generation by photoreforming, an initial hydrolysis should be performed after which terephthalic acid is separated for re-use. The remaining hydrolysate may then be used for photoreforming. Furthermore, the ethylene glycol concentration should be maximised in order to overcome the inhibitory effects of residual terephthalic acid.Finally, the concentration dependent structure of ethylene glycol/water mixtures was investigated. Mixtures with concentrations XEG = 1, 0.9, 0.46, 0.11 were investigated by total neutron scattering. The neutron scattering data was then used to constrain molecular dynamics type simulations of the studied systems to allow for in depth analysis of the systems' structures. It was found that at low ethylene glycol concentrations (XEG = 0.11) that water structure was preserved, and ethylene glycol molecules were well hydrated. At the intermediate concentrations (XEG = 0.46) the tetrahedral ordering of water was lost and water molecules existed as interconnected string-like structures. At high concentrations (XEG = 0.9), water molecules are completely isolated mostly existing as single molecules or dimers. This behaviour is in contrast to aqueous mixtures of mono-alcohols such as methanol, isopropanol, t-butanol where water structure can be found to persist even at high alcohol concentrations. Evidence for intra-molecular hydrogen bonding was found at all concentrations, however, became much more significant in the more diluted mixtures. These structural features of the ethylene glycol/water mixtures may explain their cryoprotectant properties as well as other concentration dependent properties.
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650 4 $a Acids. $3 329098
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650 4 $a Neutrons. $3 267018
650 4 $a Polyethylene terephthalate. $3 661694
650 4 $a Emissions. $3 915579
650 4 $a Methane. $3 737623
650 4 $a Adsorption. $3 193126
650 4 $a Biomass. $3 328057
650 4 $a Energy resources. $3 1010477
650 4 $a Aldehydes. $3 247587
650 4 $a Oxidation. $3 188332
650 4 $a Biogas. $3 558624
650 4 $a Glucose. $3 698759
650 4 $a Alcohol. $3 333241
650 4 $a Chemicals. $3 265745
650 4 $a Alternative energy sources. $3 966898
650 4 $a Emission standards. $3 1010478
650 4 $a Chemical engineering. $3 206267
653 $a Photocatalysts
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