| Popis: |
This work investigated the partial oxidation reactions of styrene on Cu{110} and Cu{111} and butadiene on Cu{111}. For the first time it has been shown that it is possible to epoxidise alkenes over single crystal copper surfaces, the reaction is not confined to silver alone. The techniques used included temperature programmed reaction spectroscopy (TPRS), auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), near edge X-ray absorption fine structure (NEXAFS) and scanning tunnelling microscopy (STM). The work described in this dissertation involves the adsorption of styrene onto the Cu{111} and Cu{110} surfaces modified with oxygen and caesium. The styrene adsorbed flat on the surface and reacted with partially oxidised copper to give styrene epoxide at very high selectivity. Fully oxidised surfaces were found to be inactive to styrene epoxidation, the alkene desorbs without reacting and with no change in geometry. The change in reactivity is due to changes in the intrinsic surface properties rather than a change in the styrene bonding. The process does not appear to be desorption rate limited, there is no evidence for the long term residence of styrene epoxide on the copper surface, suggesting that the reaction is reaction rate limited. Caesium reduced the surface oxidation, reducing oxidised copper to give bare copper and caesium oxides. This was accompanied by an increase in the activity of styrene epoxidation without adversely effecting selectivity, this is directly the opposite behaviour to caesium on silver. Studies involving butadiene showed the same basic behaviour. Partially oxidised Cu{111} epoxidises butadiene to epoxybutene at high selectivity. No other side chain products were observed, unlike the case on silver. Caesium was found to increase the activity of this reaction, resulting in almost 100% conversion. Work was conducted to enhance the resistance of the surface to over oxidation, nitroxy species were found to have little effect due to the formation of surface nitrites not nitrates. |
