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Effects of precursor and support variation in the genesis of uranium oxide catalysts for CO oxidation and selective reduction of NO: synthesis and characterization

Effects of precursor and support variation in the genesis of uranium oxide catalysts for CO oxidation and selective reduction of NO: synthesis and characterization
Effects of precursor and support variation in the genesis of uranium oxide catalysts for CO oxidation and selective reduction of NO: synthesis and characterization
A range of uranium oxide-based catalysts, derived from UO2(NO3)2·6H2O and UCl4 precursors, and supported on ?-Al2O3, SiO2 and mesoporous H1SiO2, have been synthesized and then characterized using the following methods: isothermal nitrogen adsorption/desorption measurements, diffuse reflectance infrared spectroscopy (DRIFTS), gas titration of surface hydroxyl groups using Grignard reagents, U LIII extended X-ray absorption fine structure (EXAFS), powder X-ray diffraction (PXRD), and thermogravimetric and differential thermal analysis. Brij76-templated H1SiO2 mesoporous silicas are found to be essentially stable under flowing oxygen after 16 h at 1073 K. At temperatures above this, however, extensive structural collapse, together with extensive dehydroxylation, ensues. Titration of the accessible hydroxyl group concentrations shows that in these materials the density of OH groups is considerably lower than in their amorphous counterparts. The adsorption of uranyl nitrate onto these dispersants results in a supported, and partially dehydrated, phase of the parent molecule with little obvious structural distortion; however, the adsorption of UCl4 leads to a complex adstructure which may best be described as U(O)2Cl2. The subsequent formation of the uranium oxide phase, nominally active for the oxidation of CO and selective reduction of NO (generally accepted to be U3O8), is found to be a considerable function of both the precursor and support system employed. Calcination of such systems to 1073 K results in extensive extrusion of the supported uranium phase from mesoporous supports, resulting in the formation of very large orthorhombic U3O8 domains. PXRD, however, shows that on amorphous SiO2 and -Al2O3 similar treatment results in the formation of a hexagonal phase of U3O8. The formation of U3O8 is found to be promoted in mesoporous systems and by the presence of Cl in the catalyst make up. Some evidence is also found that suggests that a persistence of Cl limits the growth of U3O8 domains.
neutron-diffraction, mixed catalysts, carbon-monoxide, tetrachloride, chloride, silica
1089-5647
2885-2893
Campbell, Tom
57689594-8890-4064-b0e0-3eae0099a6b0
Newton, Mark A.
73aab2af-4641-47f3-89ad-3b7d3026164f
Boyd, Vicky
9c5d96d0-ff66-4e6d-8c69-ec85970dd6d4
Lee, Darren F.
12cd8d73-be60-49e0-b29c-dd501622e37a
Evans, John
05890433-0155-49fe-a65d-38c90ea25c69
Campbell, Tom
57689594-8890-4064-b0e0-3eae0099a6b0
Newton, Mark A.
73aab2af-4641-47f3-89ad-3b7d3026164f
Boyd, Vicky
9c5d96d0-ff66-4e6d-8c69-ec85970dd6d4
Lee, Darren F.
12cd8d73-be60-49e0-b29c-dd501622e37a
Evans, John
05890433-0155-49fe-a65d-38c90ea25c69

Campbell, Tom, Newton, Mark A., Boyd, Vicky, Lee, Darren F. and Evans, John (2005) Effects of precursor and support variation in the genesis of uranium oxide catalysts for CO oxidation and selective reduction of NO: synthesis and characterization. Journal of Physical Chemistry B, 109 (7), 2885-2893. (doi:10.1021/jp0404394).

Record type: Article

Abstract

A range of uranium oxide-based catalysts, derived from UO2(NO3)2·6H2O and UCl4 precursors, and supported on ?-Al2O3, SiO2 and mesoporous H1SiO2, have been synthesized and then characterized using the following methods: isothermal nitrogen adsorption/desorption measurements, diffuse reflectance infrared spectroscopy (DRIFTS), gas titration of surface hydroxyl groups using Grignard reagents, U LIII extended X-ray absorption fine structure (EXAFS), powder X-ray diffraction (PXRD), and thermogravimetric and differential thermal analysis. Brij76-templated H1SiO2 mesoporous silicas are found to be essentially stable under flowing oxygen after 16 h at 1073 K. At temperatures above this, however, extensive structural collapse, together with extensive dehydroxylation, ensues. Titration of the accessible hydroxyl group concentrations shows that in these materials the density of OH groups is considerably lower than in their amorphous counterparts. The adsorption of uranyl nitrate onto these dispersants results in a supported, and partially dehydrated, phase of the parent molecule with little obvious structural distortion; however, the adsorption of UCl4 leads to a complex adstructure which may best be described as U(O)2Cl2. The subsequent formation of the uranium oxide phase, nominally active for the oxidation of CO and selective reduction of NO (generally accepted to be U3O8), is found to be a considerable function of both the precursor and support system employed. Calcination of such systems to 1073 K results in extensive extrusion of the supported uranium phase from mesoporous supports, resulting in the formation of very large orthorhombic U3O8 domains. PXRD, however, shows that on amorphous SiO2 and -Al2O3 similar treatment results in the formation of a hexagonal phase of U3O8. The formation of U3O8 is found to be promoted in mesoporous systems and by the presence of Cl in the catalyst make up. Some evidence is also found that suggests that a persistence of Cl limits the growth of U3O8 domains.

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More information

Published date: 24 February 2005
Keywords: neutron-diffraction, mixed catalysts, carbon-monoxide, tetrachloride, chloride, silica

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Local EPrints ID: 20751
URI: https://eprints.soton.ac.uk/id/eprint/20751
ISSN: 1089-5647
PURE UUID: ffe84d17-51b6-4b74-bb6f-a6c90a316d5b

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Date deposited: 02 Mar 2006
Last modified: 17 Jul 2017 16:28

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