Discovery of new catalysts using supercritical CO2

Perea Marín, Raimon 2012. Discovery of new catalysts using supercritical CO2. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Supercritical CO2 has been revealed as a green alternative to conventional organic solvents in several chemical reactions. Supercritical CO2 technology (supercritical anti-solvent (SAS) and gas anti-solvent (GAS) precipitation) have been successfully applied to synthesize materials, such as pharmaceuticals, polymers or metal oxide precursors. The present work discusses the preparation of catalyst precursors by SAS and GAS and the thermal activation of these catalysts. Several metal acetates (Mn, Cu, Co, Fe and Ni) were precipitated by SAS. It was found that after calcination of the precipitates, the Co3O4 was the most active catalyst for low temperature propane total oxidation. It was found that acetates are exchanged with arbonate/hydroxycarbonates if water and supercritical CO2 are present. The formation of carbonate/hydroxycarbonates yielded very active nanocrystalline Co3O4, after calcination at 250 °C under static air, for low temperature propane total oxidation. This catalyst was observed to be more active than 5 wt% Pt/Al2O3 and did not deactivate under time-on-line reactions. The GAS process was used to impregnate TiO2 with cobalt acetate to obtain a catalyst precursor for the Fischer-Tropsch reaction (FT). Initially, parameters such as volumetric expansion rate, solvent nature or temperature during GAS experiments were investigated. The low expansion of cobalt acetate and TiO2 in methanol produced small and relatively stable cobalt metal particles. Further addition of ruthenium to the catalyst promoted the cobalt metal surface area and ultimately a very active and stable catalyst for FT synthesis. Cobalt-zinc catalysts were co-precipitated by SAS and tested for FT. It was found that the addition of 5 and 15 vol% of water into the starting solution produced cobalt-zinc carbonate/hydroxycarbonates, which, after thermal treatments, yielded high cobalt metal surface area and active for FT. Thermal treatments at high temperatures resulted in a decrease of metal surface area with the concomitant decrease in FT activity.

Item Type:	Thesis (PhD)
Status:	Unpublished
Schools:	Chemistry
Subjects:	Q Science > QD Chemistry
Date of First Compliant Deposit:	30 March 2016
Last Modified:	19 Mar 2016 23:06
URI:	https://orca.cardiff.ac.uk/id/eprint/38726

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