Photocatalytic behavior of tungsten hexacarbonyl, and ruthenium dodecacarbonyl supported on porous Vycor glass.
Item
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Title
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Photocatalytic behavior of tungsten hexacarbonyl, and ruthenium dodecacarbonyl supported on porous Vycor glass.
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Identifier
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AAI9510734
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identifier
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9510734
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Creator
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Xu, Shuping.
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Contributor
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Adviser: Harry D. Gafney
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Date
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1994
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Language
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English
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Publisher
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City University of New York.
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Subject
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Chemistry, Inorganic | Chemistry, Physical
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Abstract
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UV photolysis ({dollar}\lambda\sb{lcub}\rm ex{rcub} \le{dollar} 310 nm) of W(CO){dollar}\sb6{dollar} physisorbed onto Corning's code 7930 porous Vycor glass in vacuo leads to CO evolution followed by CH{dollar}\sb4{dollar} evolution. Although photoinduced CH{dollar}\sb4{dollar} evolution initially occurs with concurrent oxidation of the metal, photoactivation leads to a catalytic system where excitation of the resultant metal oxide continues CH{dollar}\sb4{dollar} evolution. Isotope labeling experiments confirm that these photoactivated hybrid systems are capable of promoting the hydrogenation of an external carbon source, i.e., {dollar}\sp{13}{dollar}CO{dollar}\sb2{dollar}. Stoichiometry and deuterium labeling experiments indicate that the metal oxide catalyzes the reaction, CO{dollar}\sb2{dollar} + 2H{dollar}\sb2{dollar}O {dollar}\to{dollar} CH{dollar}\sb4{dollar} + 2O{dollar}\sb2{dollar}, in which water acts as the source of hydrogen and the reducing equivalents. The relative rates of methane evolution suggest that methanation occurs at a site originally occupied by a carbonaceous impurity.;Diffuse reflectance FTIR and emission spectra indicate that both tetrahedral and octahedral tungsten oxide species are present on the PVG surface. Selective emission quenching and rate data suggest that the tetrahedral tungsten oxide species selectively photocatalyzes CH{dollar}\sb4{dollar} formation, while the octahedral tungsten oxide species photocatalyzes CO evolution.;UV photolysis of Ru{dollar}\sb3{dollar}(CO){dollar}\sb{12}{dollar} physisorbed onto PVG leads to oxidative addition of a surface silanol group across an Ru-Ru band and formation of the surface grafted species ({dollar}\mu{dollar}-H)Ru{dollar}\sb3{dollar}(CO){dollar}\sb{10}{dollar}({dollar}\mu{dollar}-OSi). The latter species is bound to the glass via electron deficient bonds and exposure to an alkene results in immediate reaction. UV photolysis of the 1-pentene adduct leads to cis- and trans-2-pentene, where the trans-cis ratio increases from 1.5 {dollar}\pm{dollar} 0.2 to 2.5 {dollar}\pm{dollar} 0.1 during photolysis, but remains significantly smaller than the thermodynamic ratio. Deuterating the oxidative addition product yields deuterated olefines, and the product distribution suggests an excited state similar to a pi-allyl complex. The photogenerated grafted complex shows a high selectivity for olefin isomerization with no evidence for hydrogenation even in the presence of H{dollar}\sb2{dollar}.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
