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Gas-phase selective oxidation of C3-C4 hydrocarbon using only molecular oxygen

Xuan, Zheng-Qian 2009. Gas-phase selective oxidation of C3-C4 hydrocarbon using only molecular oxygen. PhD Thesis, Cardiff University.

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The gas-phase epoxidation of propylene to propylene oxide (PO) has been investigated over a series of supported copper-based bimetallic (Cu-Ni, Cu-Ag and Cu-Au) or even trimetallic (Cu-Ag-Ni) alloy catalysts using only molecular oxygen as oxidant. Supported single metal (Cu, Ag and Au) catalysts have been tested for contrast. Zinc oxide and nano powder of silica have been applied as two main supports. It has been found that support has a significant effect on the catalytic performances of final catalysts. For the single metal support on zinc oxide, Cu presents better selectivity than that of Ag or Au. Cu-Ag supported on zinc oxide pre-treated in 5% F/Ar has exhibited very high selectivity to PO (ca. 81%) propylene conversion (ca. 0.011%) at comparatively low temperature, 210 &deg;C. The observation of high selectivity to PO only at low temperature correlates to the intrinsic instability of PO. However, other alloys supported on zinc oxide did not show better selectivity than Cu-Ag. Particularly for Cu-Ni catalysts, the addition of nickel poisons the catalysts so that poor selectivity is obtained. For the support of nano-SiO<sub>2</sub>, the copper catalyst can offer both better selectivity (63%) and higher conversion (0.014%) than that supported on zinc oxide (selectivity to PO, ca. 60%, at propylene conversion, ca. 0.007%). A variety of alloy catalysts have shown very good reactivity and selectivity to PO. Typically, Cu-Ni pre-treated in 5% F/Ar can give high selectivity to PO, ca. 78%, as a propylene conversion, ca. 0.018%, at low temperature, 210 &deg;C. Cu-Ag catalysts have also shown stable performance with high selectivity to PO above 70% and propylene conversion of 0.020% at low temperature. On the other hand, gold plays the similar role in Cu-Au/nano-SiO<sub> 2</sub> as nickel in Cu-Ni/ZnO catalyst. Cu-Au/nano-SiO<sub>2</sub> is even worse than copper only supported nano-SiO<sub>2</sub>. The XPS analysis of Cu-Ag catalysts implies that Cu should be active in propylene epoxidation to PO over catalysts not only on nano-SiO<sub>2</sub> but also zinc oxide. These results suggest that there is a great potential to develop copper-based materials as an inexpensive catalyst for propylene epoxidation. The gas-phase selective oxidation of w-butane to maleic anhydride has also been studied and performed in a gas-gas periodic flow reactor under aerobic and anaerobic environments. Under anaerobic conditions, the catalytic performances of VPD and phase E are worse than that in aerobic conditions. Some vanadia supported on alumina have been loaded in both aerobic and anaerobic flow. The high loading (3.5%) vanadia supported on alumina is more reactive than the lower one (1%).

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Chemistry
Subjects: Q Science > QD Chemistry
ISBN: 9781303214950
Date of First Compliant Deposit: 30 March 2016
Last Modified: 19 Mar 2016 23:31

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