Optimised SBA-15 mesoporous silica with high surface area (794 m2/g) and very thick pore wall (~ 5.0 nm), which maintained its structural and hydrothermal stability in steam, up to 800 °C was successfully synthesised and used as support material for synthesis of Au/SBA-15 catalysts. Gold nano-particles of different sizes were anchored on SBA-15 using cationic gold precursor (Au(en2)Cl3), post or one pot functionalisation of SBA-15 with MPTMS, APTMS or phosphine ligand before gold loading via HAuCl4 gold precursor. Characterisation of the catalysts were done using the following techniques: Scanning Electron Microscopy (SEM), Energy Dispersive X-ray spectroscopy (EDX), Transmission Electron Microscopy (TEM), X-Ray Diffraction spectroscopy (XRD), Fourier – Transform Infrared Spectroscopy (FT-IR), Nitrogen Physisorption and Hiden Analytical CATLAB system. Characterisation results confirmed that gold particle size, dispersion of gold on SBA-15 and the oxidation state of gold had significant influence on the catalytic activity of Au/SBA-15 catalysts. The most active and stable Au/SBA-15 catalyst (Au-0.6Mdp/SBA-15), prepared by one pot synthesis of SBA-15 with MPTMS before gold loading, had high surface area of 726 m2/g, with the smallest gold particle size of 1.3 nm, well dispersed on SBA-15 support. Hydrogen reduced Au/SBA-15 catalysts were more active than their as-synthesised forms in complete oxidation of non-chlorinated VOCs, with the most active Au/SBA-15 catalyst (Au-0.6Mdp/SBA-15) attaining 100 % acetone conversion at 250 °C and 11% propane conversion at and 300 °C. The as-synthesised form of Au-0.6Mdp/SBA-15 catalyst attained 100 % acetone conversion at 280 °C and 1.8 % propane conversion at 300 °C. The reduced Au-0.6Mdp/SBA-15 catalyst was also more active than the as-synthesised form in complete oxidation of aromatic and olefin VOC mixture (BTEXB of 820 ppm). For chlorinated VOCs using dichloromethane (DCM) as model compound, only the as-synthesised form of Au/SBA-15 catalyst was active, attaining 100 % DCM conversion at 305 °C. The reduced form of Au/SBA-15 catalyst was inactive, probablyiidue to instant poisoning from strong attachment of chlorides with metallic gold. A novel coating technique (fine spray of catalyst, colloidal silica and methyl cellulose slurry on heated reactor at 150°C), which drastically reduced the amount of catalyst required for VOC oxidation was developed to introduce only 2.5 mg of Au-0.6Mdp/SBA-15 catalyst in the channels of a micro-reactor. Higher conversion of propane (VOC model compound) was achieved with the catalytic micro-reactor. The use of the micro-reactor has the potential to reduce the amount of expensive catalyst used and attain higher VOC conversions at lower temperatures, which could boost the commercial viability of this noble catalytic device for elimination of indoor VOCs.
|Date of Award||19 Dec 2017|
|Supervisor||Maria Olea (Supervisor)|