The design of new catalysts for the partial oxidation of methane to methanol.

Hamilton. Taylor, Stuart (1994) The design of new catalysts for the partial oxidation of methane to methanol. PhD thesis, University of Liverpool.

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Abstract

The direct partial oxidation of CH4 to CH30H would offer considerable economic advantages over the current two stage process. It would also facilitate the utilisation of natural gas reserves in remote locations. To date, the catalytic partial oxidation of CH4 to CH30H has been extensively studied, however, it has proved to be an extremely demanding reaction which has met with little success. This study has adopted a design approach for the identification of new catalysts by considering the efficacy of single oxides for CH4 activation, CH30H oxidation and 02 isotope exchange activity. On the basis of CH30H stability Sb203 was the best oxide, showing only 3 % CH30H conversion at 500°C. The majority of oxides totally combusted CH30H below 400°C. Mo03, Nb20S, Ta20S and W03 showed high selectivity to HCHO and (CH3hO with low levels of COx throughout the range of conversion. These oxides were not considered unsuitable from the perspective of CH30H stability as the products HCHO and (CH3hO are not considered undesirable by products from a CH4 partial oxidation process. A weak but significant correlation was observed between the combustion activity of the oxides and the oxygen exchange rate. Using CH4/D2 exchange as an indication of CH4 activation it has been shown that Ga203 was a particularly good catalyst, followed by ZnO and Cr203. A relationship between exchange activity and oxide basicity was established for the rare earth sesquioxides, MgO and CaO. This relationship indicak:d that CH4 activation took place by H+ abstraction to form a surface CH3- species. From these results and literature studies of oxygen isotope exchange, dual component oxides have been formulated as catalysts for CH4 partial oxidation. The best catalysts was Ga203/Mo03, prepared by a physical mixing process. This catalyst showed an increased yield of CH30H over the homogeneous gas phase oxidation of CH4 in a quartz chips packed reactor. This increased yield has been attributed to the development of a cooperative effect between the two component oxides. Comparison of the catalytic data with the homogeneous reaction in the empty reactor tube showed that the presence of a catalyst had a detrimental effect on the CH30H yield.

Item Type:	Thesis (PhD)
Depositing User:	Symplectic Admin
Date Deposited:	23 Oct 2023 11:00
Last Modified:	23 Oct 2023 11:00
DOI:	10.17638/03176199
Copyright Statement:	Copyright © and Moral Rights for this thesis and any accompanying data (where applicable) are retained by the author and/or other copyright owners. A copy can be downloaded for personal non-commercial research or study, without prior permission or charge.
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3176199