Methanol oxidation on Au/TiO2 catalysts |
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Authors: | Abdullahi Nuhu Jorge Soares Monica Gonzalez-Herrera Andrew Watts Ghulam Hussein Michael Bowker |
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Affiliation: | (1) School of Chemistry, Cardiff University, Cardiff, CF10 3AT, UK;(2) Kano University of Technology, Wudil, P.M.B. 3244, Kano State, Nigeria;(3) Sargodha University, Sargodha, Pakistan;(4) Johnson Matthey Technology Centre, Sonning Common, Oxfordshire, England |
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Abstract: | We have investigated the adsorption and reaction of methanol with Au/TiO2 catalysts using a pulsed flow reactor, DRIFTS and TPD. The TiO2 (P25) surface adsorbed a full monolayer of methanol, much of it in a dissociative manner, forming methoxy groups associated
with the cationic sites, and hydroxyl groups at the anions. The methoxy is relatively stable until 250 °C, at which point
decomposition occurs, producing mainly dimethyl ether by a bimolecular surface reaction. As the concentration of methoxy on
the surface diminishes, so the mechanism reverts to a de-oxygenation pathway, producing mainly methane and water (at ~330 °C
in TPD), but also with some coincident CO and hydrogen. Au catalysts were prepared by the deposition-precipitation method
to give Au loadings between 0.5–3 wt %. The effect of low levels of Au on the reactivity is marked. The pathway which gives
methane, which is characteristic of titania, remains, but a new feature of the reaction is the evolution of CO2 and H2 at lower temperature (a peak is seen in TPD at 220 °C), and the elimination of the DME-producing state. Clearly this is associated
with the presence of Au and appears to be due to the production of a formate species on the surface of the Au component. This
formate species is mainly involved in the reaction of methanol with the Au/TiO2 catalysts which results in a combustion pathway being followed, with complete conversion occurring by ~130 °C. |
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Keywords: | Au Catalysis methanol oxidation methanol catalytic combustion TPD DRIFTS |
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