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Selective oxidation of n-butanol using heterogeneous platinum metal nanoparticulate-based catalysts

Alghareeb, Shaimaa 2019. Selective oxidation of n-butanol using heterogeneous platinum metal nanoparticulate-based catalysts. PhD Thesis, Cardiff University.
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Abstract

The selective oxidation of alcohols plays a significant role for the manufacturing of valuable organic compounds. Currently, the chemical industry uses organic and inorganic stoichiometric oxidants to produce carbonyl compounds, it is therefore highly desirable to use a heterogeneous catalyst with oxygen as oxidant as an alternative to this. The research presented herein, utilizes n-butanol as a model substrate. The activity and selectivity of various heterogeneous catalysts towards the corresponding aldehyde is examined, to draw conclusions on how the physicochemical properties of the catalyst influences viability in this oxidative transformation. In addition, there have been recent developments for producing n-butanol via sustainable methods, providing an additional motive for its selection as a model compound. This research focusses on the base free selective oxidation of n-butanol with O2 in the aqueous phase over supported Pt nanoparticles. A sol-immobilization technique was used to synthesize different catalysts. The 1 wt.Pt/TiO2 catalyst displayed activity (30 %) and selectivity towards butyraldehyde (91 %), however Pt was observed to leach (5.2 %), even in the presence of small concentrations of butyric acid, during the reaction (100 °C, 3 bar O2). However, this catalyst was observed to deactivate after 2 h of reaction. This was evidenced by a stop in the butanol conversion after 2 h. It has been suggested that the inhibition of the reaction by the presence of a product affects the conversion of n- butanol. It was observed that exposing the catalyst to a reductive pre-treatment under 5 vol.%H2/Ar at 200 °C for 2 hours, could enhance the catalysts activity (43 %). In order to improve catalyst performance and limit the deactivation, additional experiments were conducted in aerobic and anaerobic conditions, to better understand the conditions which influence catalytic performance. Based on this observation the effect of the concentration of oxygen was studied. It was found that the best pressure, which gives the highest conversion, is 2 bar (conversion 38 %).To improve the performance of platinum catalyst, the preparation of a Pt-base bimetallic can be an effective route, the elements Al, Zn, Sn, Bi and Pb were selected and added to the Pt for the selective oxidation of n-butanol at 100 °C, 2 bar O2 for 2 h. The addition of Pb and Sn show higher activity for n-butanol. Accordingly, it was decided to carry on the work focussing on the 1 wt.%Pt-0.5 wt.%Pb/TiO2 and 1 wt.%Pt-1 wt.%Sn/TiO2 catalysts. It seems that the addition of Pb and Sn improve the catalyst performance, and suppress the poisoning, due to product formation, observed with Pt alone. The interaction between the metal and supports plays an important role in the properties of the catalyst. Generally, this electronic interaction has a positive effect towards the enhancement of catalytic v properties and stability. Based on this observation it has been decided to prepare Pt using a carbon support. Changing the support is likely to have an effect, such that with Pt/C the oxygen may assist with the removal or oxidation of inhibiting species. It was also found that the Pt leaching reduced from 3.1 % to 1.5 % under operating conditions (100 °C, 2 bar O2 for 2 h) when changing supports. In order to determine the effect of the support and promoter on the structural and electronic properties of the Pt catalysts characterisation including ICP, XRD, BET, TGA, XPS, SEM and TEM were performed.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Chemistry
Subjects: Q Science > QD Chemistry
Date of First Compliant Deposit: 30 July 2019
Last Modified: 30 Jul 2019 12:52
URI: http://orca-mwe.cf.ac.uk/id/eprint/124585

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