Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.583388
Title: Partial oxidation of methane to methanol using modified mixed metal oxides
Author: Hammond, Charles Rhodri
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2004
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Abstract:
The current steam reforming process for the production of CH3OH is complicated and difficult, and therefore the direct partial oxidation of CH4 to CH3OH would be economically desirable. In previous work a design approach for a selective partial oxidation catalyst has been investigated, which comprises the combination of components with a desired reactivity, producing a successful selective partial oxidation catalyst. In this approach, it is considered a successful partial oxidation catalyst must activate methane, activate oxygen and not destroy the desired product, methanol. All these properties could not be found in a single catalyst, so it was proposed that two synergistic components could be combined, one responsible for methane activation and the other for oxygen activation/insertion. Previous work has studied the CH4/D2 exchange reaction as an indication of the ability of a metal oxide surface to activate CH4. Two metal oxides demonstrated appreciable activity for the activation of CH4, these being Ga2C3 and ZnO. These oxides were then doped with different metals in order to try and increase the activity of the catalyst. The doping of Ga2O3 with Zn or Mg did not improve the methane oxidation properties of Ga2C3, and the doping of ZnO with Ga significantly lowered the light off temperature, the temperature at which CH4 was first detected, and increased its oxidative capacity. The addition of precious metals significantly affected the catalysts ability to activate CH4. The addition of Au to the Ga and Zn catalysts dramatically reduced the light off temperature, and increased its rate of oxidation at lower temperatures, with the optimum loading 2% for both catalysts. For GaO(OH) and ZnO, the addition of 1%Au and l%Pt by coprecipitation produced a synergistic effect, producing lower light offs and higher CH4 conversion than the singly doped catalysts with Au and Pt separately. When the methane activation catalysts were combined with MoO3 in a physical mixture, a number of the mixtures produced higher methanol per pass percentage yields than its constituent parts. It is concluded that the increased methane activation properties beneficially interact with the oxygen activation and insertion properties of MoO3. However, none of the yields reported were significantly higher. A dual bed system, with the lower layer comprising the methane activation catalysts, and the upper layer consisting of MoO 3 was tested. The results for this system were promising, with the low temperature activation of CH4, combined with the oxygen insertion ability of MoO3, producing high selectivities of CH3OH at much lower temperatures. The best results were obtained when the ratio of the two layers was 50:50 with respect to 2%Au ZnO and MoO3. In previous work a design approach for a selective partial oxidation catalyst has been investigated, by combining components with a desired reactivity to produce a successful selective partial oxidation catalyst, which must activate methane and oxygen, and not destroy methanol. All these properties could not be found in a single catalyst, so it was proposed that two synergistic components could be combined, one responsible for methane activation and the other for oxygen activation/insertion. The doping of ZnO with Ga significantly lowered the light off temperature, and increased its oxidative capacity, an effect which was not seen with the doping of Ga2O3 with Zn or Mg. The addition of Au to the Ga and Zn catalysts dramatically reduced the light off temperature, and increased its rate of oxidation at lower temperatures, both with optimum loading of 2%. The addition of l%Au and l%Pt produced a synergistic effect, producing lower light offs and higher CH4 conversion than the singly doped catalysts with Au and Pt separately. When the methane activation catalysts were combined with MoO3 in a physical mixture, a number of the mixtures produced higher methanol per pass percentage yields than its constituent parts. It is concluded that the increased methane activation properties beneficially interact with the oxygen activation and insertion properties of MoO3. The dual bed system, with the lower layer comprising the methane activation catalysts, and the upper layer consisting of MoO 3 produced promising results, with the low temperature activation of CH4, combined with the oxygen insertion ability of MoO3, producing high selectivities of CH3OH at much lower temperatures. The best results were obtained when the ratio of the two layers was 50:50 with respect to 2%Au ZnO and MoO3. (Abstract shortened by UMI.).
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.583388  DOI: Not available
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